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Bibliometric Analysis for the U.S. Environmental Protection Agency/Office of Research and Developments Air (Particulate Matter, Ozone, Air Toxics, and Indoor Air) Research Program

September 21, 2007

This is a bibliometric analysis of the papers prepared by intramural and extramural researchers of the U.S. Environmental Protection Agency’s (EPA) Air Research Program. For this analysis, 2,064 papers were reviewed, and they were published from 1998 to 2007. These publications were cited 34,562 times in the journals covered by Thomson Scientific’s Web of Science1 and Elsevier’s Scopus2. Of these 2,064 publications, 1,827 (88.5%) have been cited at least once in a journal.

Searches of Web of Science and Scopus were conducted to obtain times cited data for the Air Research Program journal publications. The analysis was completed using Thomson’s Essential Science Indicators (ESI) and Journal Citation Reports (JCR) as benchmarks. ESI provides access to a unique and comprehensive compilation of essential science performance statistics and science trends data derived from Thomson’s databases. For this analysis, the ESI highly cited papers thresholds as well as the hot papers thresholds were used to assess the influence and impact of the air papers. JCR is a recognized authority for evaluating journals. It presents quantifiable statistical data that provide a systematic, objective way to evaluate the world’s leading journals and their impact and influence in the global research community. The two key measures used in this analysis to assess the journals in which the EPA air papers are published are the Impact Factor and Immediacy Index. The Impact Factor is a measure of the frequency with which the “average article” in a journal has been cited in a particular year. The Impact Factor helps evaluate a journal’s relative importance, especially when compared to other journals in the same field. The Immediacy Index is a measure of how quickly the “average article” in a journal is cited. This index indicates how often articles published in a journal are cited within the same year and it is useful in comparing how quickly journals are cited.

The report includes a summary of the results of the bibliometric analysis, an analysis of the 2,064 air research papers analyzed by ESI field (e.g., Clinical Medicine, Environment/Ecology, and Geosciences), an analysis of the journals in which the air papers were published, a table of the highly cited researchers in the Air Research Program, a list of patents that have resulted from the program, and other parameters reported by ESI.

Summary of Results

  1. One-third of the air publications are highly cited papers. 679 (32.9%) of the air papers qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. This is 3.3 times the 10% of papers expected to be highly cited. 107 (5.2%) of the air papers qualify as highly cited when using the ESI criteria for the top 1%, which is 5.2 times the number expected. 14 (0.7%) of these papers qualify as very highly cited when using the criteria for the top 0.1%, which is 7 times the number anticipated. None of the papers actually meets the 0.01% threshold for the most highly cited papers, which is not surprising given that the expected number for this program is 0.2 papers.
  2. The air papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, in 15 of the 19 fields in which the 2,064 EPA air papers were published, the ratio of actual to expected cites is greater than 1, indicating that the air papers are more highly cited than the average papers in those fields. For all 19 fields combined, the ratio of total number of cites to the total number of expected cites (34,562 to 15,305.25) is 2.2, indicating that the air papers are more highly cited than the average paper.
  3. More than one-third of the air papers are published in high impact journals. 696 of the 2,064 papers were published in the top 10% of journals ranked by JCR Impact Factor, representing 33.7% of EPA’s air papers. This number is 3.4 times higher than the expected 206 papers. 966 of the 2,064 papers appear in the top 10% of journals ranked by JCR Immediacy Index, representing 46.8% of EPA’s air papers. This number is 4.7 times higher than the expected 206 papers.
  4. Fifty-two of the air papers qualify as hot papers. Using the hot paper thresholds established by ESI as a benchmark, 52 hot papers, representing 2.5% of the air papers, were identified in the analysis. Hot papers are papers that were highly cited shortly after they were published. The number of air hot papers identified is 25 times higher than the expected 2 hot papers.
  5. The authors of the air papers cite themselves much less than the average author. 1,605 of the 34,562 cites are author self-cites. This 4.6% author self-citation rate is well below the accepted range of 10-30% author self-citation rate.
  6. Fifty-nine of the 3,452 authors of the air papers are included in ISIHighlyCited.com,which is a database of the world’s most influential researchers who have made key contributions to science and technology during the period from 1981 to 1999.
  7. There were 6 patents issued to investigators from 1998 to 2007 for research that was conducted under EPA’s Air Research Program. Two of these patents were cited by a total of 9 other patents.
  8. EPA’s Air Research Program includes 4 of the top 20 air pollution papers (published from January 2003 to April 2005) and 18 of the top 20 air pollution authors (from 1995 to 2005) authored papers for EPA’s Air Research Program.
  9. The United States ranks first among the top 20 countries publishing on air pollution.
  10. More than one-half of the EPA air papers are published in ESI’s top 20 journals in air pollution.
  11. Harvard University (one of EPA’s grantees) ranks number one and EPA ranks number two on ESI’s top 20 institutions publishing on air pollution.
  12. The number of air pollution papers published in journals covered by ESI from 2001 to 2005 has declined compared to the number published from 2000 to 2004. The number of cites and cites/paper for papers published from 2001 to 2005 also have declined. The number of EPA Air Research Program publications, however, has increased slightly from 2001 to 2005 (1,257 publications) when compared to the number published from 2000 to 2004 (1,240 publications). Like the overall air pollution paper trends identified by ESI, the number of cites and the cites per paper have declined.

Highly Cited Air Publications

All of the journals covered by ESI are assigned a field, and to compensate for varying citation rates across scientific fields, different thresholds are applied to each field. Thresholds are set to select highly cited papers to be listed in ESI. Different thresholds are set for both field and year of publication. Setting different thresholds for each year allows comparable representation for older and younger papers for each field.

The 2,064 air research papers reviewed for this analysis were published in journals that were assigned to 19 of the 22 ESI fields. The distribution of the papers among these 19 fields and the number of citations by field are presented in Table 1.

Table 1. Air Papers by ESI Fields

ESI Field

No. of Citations

No. of Air Papers

Average Cites/Paper

Biology & Biochemistry

546

41

13.3

Chemistry

2,375

150

15.8

Clinical Medicine

6,479

260

24.9

Computer Science

15

4

3.8

Economics & Business

25

3

8.3

Engineering

4,259

360

11.8

Environment/Ecology

7,910

435

18.2

Geosciences

8,477

490

17.3

Immunology

377

14

26.9

Materials Science

1

2

0.5

Mathematics

35

7

5.0

Microbiology

22

1

22.0

Molecular Biology & Genetics

62

8

7.8

Multidisciplinary

421

10

42.1

Neuroscience & Behavior

227

20

11.4

Pharmacology & Toxicology

2,951

220

13.4

Physics

194

15

12.9

Plant & Animal Science

124

11

11.3

Social Sciences, general

62

13

4.8

 

Total = 34,562

Total = 2,064

16.7

There are 679 (32.9% of the papers analyzed) highly cited EPA air papers in 14 of the 19 fields—Biology & Biochemistry, Chemistry, Clinical Medicine, Economics & Business, Engineering, Environment/Ecology, Geosciences, Immunology, Mathematics, Multidisciplinary, Pharmacology & Toxicology, Physics, Plant & Animal Science, and Social Sciences—when using the ESI criteria for the top 10% of papers. Table 2 shows the number of EPA air papers in those 14 fields that meet the top 10% threshold in ESI. One hundred-seven (5.2%) of the papers analyzed qualify as highly cited when using the ESI criteria for the top 1% of papers. These papers cover 9 fields—Biology & Biochemistry, Chemistry, Clinical Medicine, Economics & Business, Engineering, Environment/ Ecology, Geosciences, Multidisciplinary, and Pharmacology & Toxicology. Table 3 shows the 107 (5.2% of the papers analyzed) papers by field that meet the top 1% threshold in ESI. The citations for these 107 papers are provided in Tables 4 through 12. Table 13 shows the 14 (0.7%) papers by field that meet the top 0.1% threshold in ESI. These 14 very highly cited air papers in the fields of Chemistry, Clinical Medicine, Economics & Business, Engineering, Environment/Ecology, and Geosciences are listed in Table 14. None of the air papers meet the top 0.01% threshold in ESI, which is not surprising because the expected number of papers that should meet this threshold for this analysis is 0.2. The highly cited papers in Tables 4 through 13 are presented in order of year of publication with the oldest papers appearing first. Within the year of publication, the papers are ordered by increasing number of times cited.

Table 2. Number of Highly Cited Air Papers by Field (top 10%)

ESI Field

No. of Citations

No. of Papers

Average Cites/Paper

% of Papers in Field

Biology & Biochemistry

216

6

36.0

14.6%

Chemistry

1,156

34

34.0

22.7%

Clinical Medicine

4,970

91

54.6

35.0%

Economics & Business

7

1

7.0

33.3%

Engineering

3,525

144

24.5

40.0%

Environment/Ecology

5,655

170

33.3

39.1%

Geosciences

5,737

164

35.0

33.5%

Immunology

303

5

60.6

35.7%

Mathematics

25

2

12.5

28.6%

Multidisciplinary

398

6

66.3

60.0%

Pharmacology & Toxicology

1,692

47

36.0

21.4%

Physics

117

3

39.0

20.0%

Plant & Animal Science

64

2

32.0

18.2%

Social Sciences, general

20

4

5.0

30.8%

 

Total = 23,885

Total = 679

35.2

32.9%

Table 3. Number of Highly Cited Air Papers by Field (top 1%)

ESI Field

No. of Citations

No. of Papers

Average Cites/Paper

% of Air Papers in Field

Biology & Biochemistry

37

1

37.0

2.4%

Chemistry

62

2

31.0

1.3%

Clinical Medicine

1,513

8

189.1

3.1%

Economics & Business

7

1

7.0

33.3%

Engineering

1,768

32

55.2

8.9%

Environment/Ecology

1,549

31

50.0

7.1%

Geosciences

2,255

28

80.5

5.7%

Multidisciplinary

272

2

136.0

20.0%

Pharmacology & Toxicology

259

2

129.5

0.9%

 

Total = 7,722

Total = 107

72.2

5.2%

Table 4. Highly Cited Air Papers in the Field of Biology & Biochemistry (top 1%)

No. of Cites

ESI Threshold

First Author

Paper

37

33

Kadiiska MB

Biomarkers of Oxidative Stress Study II: are oxidation products of lipids, proteins, and DNA markers of CCl4 poisoning? Free Radical Biology & Medicine 2005;38(6):698-710.

Table 5. Highly Cited Air Papers in the Field of Chemistry (top 1%)

No. of Cites

ESI Threshold

First Author

Paper

59

43

Gao S

Low-molecular-weight and oligomeric components in secondary organic aerosol from the ozonolysis of cycloalkenes and alpha-pinene. Journal of Physical Chemistry A 2004;108(46):10147-10164.

3

2

Rudich Y

Aging of organic aerosol: bridging the gap between laboratory and field studies. Annual Review of Physical Chemistry 2007;58:321-352.

Table 6. Highly Cited Air Papers in the Field of Clinical Medicine (top 1%)

No. of Cites

ESI Threshold

First Author

Paper

187

144

Abbey DE

Long-term inhalable particles and other air pollutants related to mortality in nonsmokers. American Journal of Respiratory and Critical Care Medicine 1999;159(2):373-382.

216

133

Gold DR

Ambient pollution and heart rate variability. Circulation 2000;101(11):1267-1273.

249

115

Peters A

Increased particulate air pollution and the triggering of myocardial infarction. Circulation 2001;103(23):2810-2815.

634

99

Pope CA

Lung cancer, cardiopulmonary mortality and long-term exposure to fine particulate air pollution. Journal of the American Medical Association 2002;287(9):1132-1141.

89

54

Peters A

Exposure to traffic and the onset of myocardial infarction. New England Journal of Medicine 2004;351(17):1721-1730.

131

54

Pope CA

Cardiovascular mortality and long-term exposure to particulate air pollution: epidemiological evidence of general pathophysiological pathways of disease. Circulation 2004;109(1):71-77.

2

2

Baccarelli A

Effects of exposure to air pollution on blood coagulation. Journal of Thrombosis and Haemostasis 2007;5(2):252-260.

5

2

Miller KA

Long-term exposure to air pollution and incidence of cardiovascular events in women. New England Journal of Medicine 2007;356(5):447-458.

Table 7. Highly Cited Air Papers in the Field of Economics & Business (top 1%)

No. of Cites

ESI Threshold

First Author

Paper

7

4

Peng RD

Model choice in time series studies of air pollution and mortality. Journal of the Royal Statistical Society: Series A (Statistics in Society) 2006;169(2):179-203.

Table 8. Highly Cited Air Papers in the Field of Engineering (top 1%)

No. of Cites

ESI Threshold

First Author

Paper

54

46

Zhang Y

Simulation of aerosol dynamics: a comparative review of algorithms used in air quality models. Aerosol Science and Technology 1999;31(6):487-514.

45

44

Wilson WE

Estimating separately personal exposure to ambient and non-ambient particulate matter for epidemiology and risk assessment; why and how. Journal of the Air & Waste Management Association 2000;50(7):1167-1183.

52

44

Tobias HJ

Real-time chemical analysis of organic aerosols using a thermal desorption particle beam mass spectrometer. Aerosol Science and Technology 2000;33(1-2):170-190.

75

44

Sarnat JA

Assessing the relationship between personal particulate and gaseous exposures of senior citizens living in Baltimore. Journal of the Air & Waste Management Association 2000;50(7):1184-1198.

78

44

Long CM

Characterization of indoor particle sources using continuous mass and size monitors. Journal of the Air & Waste Management Association 2000;50(7):1236-1250.

207

44

Jayne JT

Development of an aerosol mass spectrometer for size and composition analysis of submicron particles. Aerosol Science and Technology 2000;33(1-2):49-70.

209

44

Richter H

Formation of polycyclic aromatic hydrocarbons and their growth to soot –
a review of chemical reaction pathways. Progress in Energy and Combustion Science 2000;26(4-6):565-608.

38

37

Vette AF

Characterization of indoor-outdoor aerosol concentration relationships during the Fresno PM exposure studies. Aerosol Science and Technology 2001;34(1):118-126.

42

37

Lewtas J

Comparison of sampling methods for semi-volatile organic carbon associated with PM2.5. Aerosol Science and Technology 2001;34(1):9-22.

57

37

Tolocka MP

East versus West in the US: chemical characteristics of PM2.5 during the winter of 1999. Aerosol Science and Technology 2001;34(1):88-96.

92

37

Woo KS

Measurement of Atlanta aerosol size distributions: Observations of ultrafine particle events. Aerosol Science and Technology 2001;34(1):75-87.

105

37

Weber RJ

A particle-into-liquid collector for rapid measurement of aerosol bulk chemical composition. Aerosol Science and Technology 2001;35(3):718-727.

31

31

Cabada JC

Sources of atmospheric carbonaceous particulate matter in Pittsburgh, Pennsylvania. Journal of the Air & Waste Management Association 2002;52(6):732-741.

34

31

Zhang Z

Cyclic micron-size particle inhalation and deposition in a triple bifurcation lung airway model. Aerosol Science and Technology 2002;33(2):257-281.

37

31

Kim S

Size distribution and diurnal and seasonal trends of ultrafine particles in source and receptor sites of the Los Angeles basin. Journal of the Air & Waste Management Association 2002;52(3):297-307.

40

31

Zhang X

A numerical characterization of particle beam collimation by an aerodynamic lens-nozzle system: Part I. an individual lens or nozzle. Aerosol Science and Technology 2002;36(5):617-631.

63

31

McMurray PH

The relationship between mass and mobility for atmospheric particles: A new technique for measuring particle density. Aerosol Science and Technology 2002;36(2):227-238.

130

31

Zhu YF

Concentration and size distribution of ultrafine particles near a major highway. Journal of the Air & Waste Management Association 2002;52(9):1032-1042.

31

25

Lewis CW

Source apportionment of Phoenix PM2.5 aerosol with the Unmix receptor model. Journal of the Air & Waste Management Association 2003;53(3):325-338.

22

18

Lemieux PM

Emissions of organic air toxics from open burning: a comprehensive review. Progress in Energy and Combustion Science 2004;30(1):1-32.

23

18

Zhang XF

Numerical characterization of particle beam collimation: Part II integrated aerodynamic-lens-nozzle system. Aerosol Science and Technology 2004;38(6):619-638.

23

18

Zhu Y

Seasonal trends of concentration and size distribution of ultrafine particles near major highways in Los Angeles. Aerosol Science and Technology 2004;38(S1):5-13.

24

18

Cabada JC

Estimating the secondary organic aerosol contribution to PM2.5 using the EC tracer method. Aerosol Science and Technology 2004;38(S1):140-155.

25

18

Drewnick F

Measurement of ambient aerosol composition during the PMTACS-NY 2001 campaign using an aerosol mass spectrometer. Part II: Chemically speciated mass distribution. Aerosol Science and Technology 2004;38(S1):104-117.

26

18

Cho A

Determination of four quinones in diesel exhaust particles, SRM 1649a and atmospheric PM2.5. Aerosol Science and Technology 2004;38(S1):68-81.

33

18

Stanier CO

Nucleation events during the Pittsburgh Air Quality Study: description and relation to key meteorological, gas phase, and aerosol parameters. Aerosol Science and Technology 2004;38(S1):253-264.

34

18

Drewnick F

Measurement of ambient aerosol composition during the PMTACS-NY 2001 campaign using an aerosol mass spectrometer. Part I: Mass concentrations. Aerosol Science and Technology 2004;38(S1):92-103.

39

18

Subramanian R

Positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations. Aerosol Science and Technology 2004;38(S1):27-48.

55

18

Canagaratna M

Chase studies of particulate emissions from in-use New York City vehicles. Aerosol Science and Technology 2004;38(6):555-573.

13

10

Kim E

Estimation of organic carbon blank values and error structures of the speciation trends network data for source apportionment. Journal of the Air & Waste Management Association 2005;55(8):1190-1199.

14

4

Byun D

Review of the governing equations, computational algorithms, and other components of the Models-3 Community Multiscale Air Quality (CMAQ) modeling system. Applied Mechanics Reviews 2006;59:51-77.

17

4

Bond TC

Light absorption by carbonaceous particles: an investigative review. Aerosol Science and Technology 2006;40(1):27-67.

Table 9. Highly Cited Air Papers in the Field of Environment/Ecology (top 1%)

No. of Cites

ESI Threshold

First Author

Paper

175

103

Liao D

Daily variation of particulate air pollution and poor cardiac autonomic control in the elderly. Environmental Health Perspectives 1999;107(7):521-525.

208

88

Laden F

Association of fine particulate matter from different sources with daily mortality in six U.S. cities. Environmental Health Perspectives 2000;108(10):941-947.

83

77

Fine PM

Chemical characterization of fine particle emissions from the fireplace combustion of woods grown in the northeastern United States. Environmental Science & Technology 2001;35(13):2665-2675.

83

77

Jang M

Atmospheric secondary aerosol formation by heterogeneous reactions of aldehydes in the presence of a sulfuric acid aerosol catalyst. Environmental Science & Technology 2001;35(24):4758-4766.

94

77

Dockery DW

Epidemiologic evidence of cardiovascular effects of particulate air pollution. Environmental Health Perspectives 2001;109(S4):483-486.

67

48

Park K

Relationship between particle mass and mobility for diesel exhaust particles. Environmental Science & Technology 2003;37(3):577-583.

144

48

Li N

Ultrafine particulate pollutants induce oxidative stress and mitochondrial damage. Environmental Health Perspectives 2003;111(4):455-460.

34

34

Landrigan PJ

Health and environmental consequences of the World Trade Center disaster. Environmental Health Perspectives 2004;112(6):731-739.

40

34

Chow JC

Equivalence of elemental carbon by thermal/optical reflectance and transmittance with different temperature protocols. Environmental Science & Technology 2004;38(16):4414-4422.

44

34

Xia T

Quinones and aromatic chemical compounds in particulate matter induce mitochondrial dysfunction: implications for ultrafine particle toxicity. Environmental Health Perspectives 2004;112(14):1347-1358.

45

34

Zhang Q

Insights into the chemistry of new particle formation and growth events in Pittsburgh based on aerosol mass spectrometry. Environmental Science & Technology 2004;38(18):4797-4809.

58

34

Pope CA

Ambient particulate air pollution, heart rate variability, and blood markers of inflammation in a panel of elderly subjects. Environmental Health Perspectives 2004;112(3):339-345.

59

34

Gao S

Particle phase acidity and oligomer formation in secondary organic aerosol. Environmental Science & Technology 2004;38(24):6582-6589.

17

17

Reisen F

Atmospheric reactions influence seasonal PAH and nitro-PAH concentrations in the Los Angeles Basin. Environmental Science & Technology 2005;39(1):64-73.

18

17

Delfino RJ

Potential role of ultrafine particles in associations between airborne particle mass and cardiovascular health. Environmental Health Perspectives 2005;113(8):934-946.

19

17

Dockery DW

Association of air pollution with increased incidence of ventricular tachyarrhythmias recorded by implanted cardioverter defibrillators. Environmental Health Perspectives 2005;113(6):670-674.

22

17

Zanobetti A

The effect of particulate air pollution on emergency admissions for myocardial infarction: a multicity case-crossover analysis. Environmental Health Perspectives 2005;113(8):978-982.

23

17

Lim H

Isoprene forms secondary organic aerosol through cloud processing: model simulations. Environmental Science & Technology 2005;39(12):4441-4446.

25

17

Park SK

Effects of Air Pollution on Heart Rate Variability: The VA Normative Aging Study. Environmental Health Perspectives 2005;113(3):304-309.

26

17

Bahreini R

Measurements of secondary organic aerosol from oxidation of cycloalkenes, terpenes, and m-xylene using an Aerodyne aerosol mass spectrometer. Environmental Science & Technology 2005;39(15):5674-5688.

27

17

Lough GC

Emissions of metals associated with motor vehicle roadways. Environmental Science & Technology 2005;39(3):826-836.

40

17

Zhang Q

Deconvolution and quantification of hydrocarbon-like and oxygenated organic aerosols based on aerosol mass spectrometry. Environmental Science & Technology 2005;39(13):4938-4952.

133

17

Oberdorster G

Nanotoxicology: an emerging discipline evolving from studies of ultrafine particles. Environmental Health Perspectives 2005;113(7):823-839.

6

6

Selgrade MK

Induction of asthma and the environment: what we know and need to know. Environmental Health Perspectives 2006;114(4):615-619.

7

6

Dubowsky SD

Diabetes, obesity, and hypertension may enhance associations between air pollution and markers of systematic inflammation. Environmental Health Perspectives 2006;114(7):992-998.

7

6

Elder A

Translocation of inhaled ultrafine manganese oxide particles to the central nervous system. Environmental Health Perspectives 2006;114(8):1172-1178.

7

6

Okin GS

Multi-scale controls on and consequences of aeolian processes in landscape change in arid and semi-arid environments. Journal of Arid Environments 2006;65(2):253-275.

8

6

Shrivastava MK

Modeling semivolatile organic aerosol mass emissions from combustion systems. Environmental Science & Technology 2006;40(8):2671-2677.

8

6

Donahue NM

Coupled partitioning, dilution, and chemical aging of semivolatile organics. Environmental Science & Technology 2006;40(8):2635-2643.

9

6

Presto AA

Investigation of α-pinene + ozone secondary organic aerosol formation at low total aerosol mass. Environmental Science & Technology 2006;40(11):3536-3543.

13

6

McConnell R

Traffic, susceptibility, and childhood asthma. Environmental Health Perspectives 2006;114(5):766-772.

Table 10. Highly Cited Air Papers in the Field of Geosciences (top 1%)

No. of Cites

ESI Threshold

First Author

Paper

116

114

Wang YH

Global simulation of tropospheric O3-NOx-hydrocarbon chemistry, 2. Model evaluation. Journal of Geophysical Research–Atmospheres 1998;103(D9):10727-10756.

148

114

Wang YH

Global simulation of tropospheric O3-NOx-hydrocarbon chemistry, 1. Model formulation. Journal of Geophysical Research–Atmospheres 1998;103(D9):10713-10726.

149

114

Nenes A

ISORROPIA: a new thermodynamic equilibrium model for multiphase multicomponent inorganic aerosols. Aquatic Geochemistry 1998;4:123-152.

121

98

Simpson D

Inventorying emissions from nature in Europe. Journal of Geophysical Research–Atmospheres 1999;104(D7):8113-8152.

166

98

Griffin RJ

Organic aerosol formation from the oxidation of biogenic hydrocarbons. Journal of Geophysical Research–Atmospheres 1999;104(D3):3555-3567.

170

98

Yu J

Gas-Phase ozone oxidation of monoterpenes: gaseous and particulate products. Journal of Atmospheric Chemistry 1999;34(2):207-258.

188

98

Simoneit BRT

Levoglucosan, a tracer for cellulose in biomass burning and atmospheric particles. Atmospheric Environment 1999;33(2):173-182.

112

85

Russell A

NARSTO critical review of photochemical models and modeling. Atmospheric Environment 2000;34(12-14):2283-2324.

130

85

Fuentes JD

Biogenic hydrocarbons in the atmospheric boundary layer: a review. Bulletin of the American Meteorological Society 2000;81(7):1537-1575.

174

85

Guenther A

Natural emissions of non-methane volatile organic compounds, carbon monoxide, and oxides of nitrogen from North America. Atmospheric Environment 2000;34(12-14):2205-2230.

92

69

Sokolik IN

Introduction to special section: outstanding problems in quantifying the radiative impact of mineral dust. Journal of Geophysical Research–Atmospheres 2001;106(D16):18015-18027.

178

69

Huser RB

Asian dust events of April 1998. Journal of Geophysical Research– Atmospheres 2001;106(D16):18317-18330.

121

54

Zhu Y

Study of ultrafine particles near a major highway with heavy-duty diesel traffic. Atmospheric Environment 2002;36(27):4323-4335.

42

41

Binkowski FS

Models-3 Community Multiscale Air Quality (CMAQ) model aerosol component. 1. Model description. Journal of Geophysical Research– Atmospheres 2003;108(D6):4183.

53

41

Orsini DA

Refinements to the particle-into-liquid sampler (PILS) for ground and airborne measurements of water soluble aerosol composition. Atmospheric Environment 2003;37(9-10):243-1259.

85

41

Jiminez JL

Ambient aerosol sampling using the Aerodyne Aerosol Mass Spectrometer. Journal of Geophysical Research–Atmospheres 2003;108(D7):8425.

29

29

Zhang KM

Evolution of particle number distribution near roadways: Part II: The “road-to-ambient” process. Atmospheric Environment 2004;38(38):6655-6665.

31

29

Wittig AE

Pittsburgh Air Quality Study overview. Atmospheric Environment 2004;38(20):3107-3125.

31

29

Kim E

Improving source identification of Atlanta aerosol using temperature resolved carbon fractions in positive matrix factorization. Atmospheric Environment 2004;38(20):3349-3362.

18

18

McKeen S

Assessment of an ensemble of seven real-time ozone forecasts over eastern North America during the summer of 2004. Journal of Geophysical Research–Atmospheres 2005;110(D21307).

27

18

Edney EO

Formation of 2-methyl tetrols and 2-methylglyceric acid in secondary organic aerosol from laboratory irradiated isoprene/NOx/SO2/air mixtures and their detection in ambient PM2.5 samples collected in the eastern United States. Atmospheric Environment 2005;39(29):5281-5289.

32

18

Zhang Q

Hydrocarbon-like and oxygenated organic aerosols in Pittsburgh: insights into sources and processes or organic aerosols. Atmospheric Chemistry and Physics 2005;5(12):3289-3311.

8

7

Hallock-Waters KA

Carbon monoxide in the U. S. Mid-Atlantic troposphere: evidence for a decreasing trend. Geophysical Research Letters 2006;26(18):2861-2864.

8

7

Offenberg JH

Thermal properties of secondary organic aerosols. Geophysical Research Letters 2006;33(3):L03816.

8

7

Takegawa N

Seasonal and diurnal variations of submicron organic aerosol in Tokyo observed using the Aerodyne aerosol mass spectrometer. Journal of Geophysical Research–Atmospheres 2006;111(D11206).

12

7

Guenther A

Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature). Journal of Geophysical Research–Atmospheres 2006;6:3181-3210.

3

3

Kondo Y

Oxygenated and water-soluble organic aerosols in Tokyo. Journal of Geophysical Research–Atmospheres 2007;112(D1):D01203.

3

3

Pathak RK

Ozonolysis of a-pinene at atmospherically relevant concentrations: Temperature dependence of aerosol mass fractions (yields). Journal of Geophysical Research–Atmospheres 2007;112(D3):D03201.

Table 11. Highly Cited Air Papers in the Field of Multidisciplinary (top 1%)

No. of Cites

ESI Threshold

First Author

Paper

117

55

Gard EE

Direct Observation of Heterogeneous Chemistry in the Atmosphere. Science 1998;279(5354):1184-1187.

155

93

Jang M

Heterogeneous Atmospheric Aerosol Production by Acid-Catalyzed Particle-Phase Reactions. Science 2002;298(5594):814-817.

Table 12. Highly Cited Air Papers in the Field of Pharmacology & Toxicology (top 1%)

No. of Cites

ESI Threshold

First Author

Paper

157

99

Oberdorster G

Pulmonary effects of inhaled ultrafine particles. International Archives of Occupational and Environmental Health 2001;74(1):1-8.

102

44

Oberdorster G

Translocation of inhaled ultrafine particles to the brain. Inhalation Toxicology 2004;16(6-7):437-445.

Table 13. Number of Very Highly Cited Papers by Field (Top 0.1%)

ESI Field

No. of Citations

No. of Papers

Average Cites/Paper

% of Air Papers in Field

Chemistry

3

1

3.0

0.7%

Clinical Medicine

639

2

319.5

0.8%

Economics & Business

7

1

7.0

33.3%

Engineering

671

7

95.8

1.9%

Environment/Ecology

277

2

138.5

0.5%

Geosciences

178

1

178.0

0.2%

 

Total = 1,775

Total = 14

126.8

0.7%

Table 14. Very Highly Cited Air Papers (top 0.1%)

ESI Field

ESI Threshold

No. of Cites

First Author

Paper

Chemistry

3

3

Rudich Y

Aging of organic aerosol: bridging the gap between laboratory and field studies. Annual Review of Physical Chemistry 2007;58:321-352.

Clinical Medicine

288

634

Pope CA

Lung cancer, cardiopulmonary mortality and long-term exposure to fine particulate air pollution. Journal of the American Medical Association 2002;287(9):1132-1141.

 

4

5

Miller KA

Long-term exposure to air pollution and incidence of cardiovascular events in women. New England Journal of Medicine 2007;356(5):447-458.

Economics & Business

7

7

Peng RD

Model choice in time series studies of air pollution and mortality. Journal of the Royal Statistical Society: Series A (Statistics in Society) 2006;169(2):179-203.

Engineering

116

207

Jayne JT

Development of an aerosol mass spectrometer for size and composition analysis of submicron particles. Aerosol Science and Technology 2000;33(1-2):49-70.

 

116

209

Richter H

Formation of polycyclic aromatic hydrocarbons and their growth to soot – a review of chemical reaction pathways. Progress in Energy and Combustion Science 2000;26(4-6):565-608.

 

76

130

Zhu YF

Concentration and size distribution of ultrafine particles near a major highway. Journal of the Air & Waste Management Association 2002;52(9):1032-1042.

 

39

39

Subramanian R

Positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations. Aerosol Science and Technology 2004;38(S1):27-48.

 

39

55

Canagaratna M

Chase studies of particulate emissions from in-use New York City vehicles. Aerosol Science and Technology 2004;38(6):555-573.

 

9

14

Byun D

Review of the governing equations, computational algorithms, and other components of the Models-3 Community Multiscale Air Quality (CMAQ) modeling system. Applied Mechanics Reviews 2006;59:51-77.

 

9

17

Bond TC

Light absorption by carbonaceous particles: an investigative review. Aerosol Science and Technology 2006;40(1):27-67.

Environment/ Ecology

116

144

Li N

Ultrafine particulate pollutants induce oxidative stress and mitochondrial damage. Environmental Health Perspectives 2003;111(4):455-460.

 

43

133

Oberdorster G

Nanotoxicology: an emerging discipline evolving from studies of ultrafine particles. Environmental Health Perspectives 2005;113(7):823-839.

Geosciences

176

178

Huser RB

Asian dust events of April 1998. Journal of Geophysical Research–Atmospheres 2001;106(D16):18317-18330.

Ratio of Actual Cites to Expected Citation Rates

The expected citation rate is the average number of cites that a paper published in the same journal in the same year and of the same document type (article, review, editorial, etc.) has received from the year of publication to the present. Using the ESI average citation rates for papers published by field as the benchmark, in 15 of the 19 fields in which the EPA air papers were published, the ratio of actual to expected cites is greater than 1, indicating that the air papers are more highly cited than the average papers in those fields (see Table 15). For one field, the ratio is equal to 1, indicating that the papers in that ESI field are cited the same as the average paper. For all 19 fields combined, the ratio of total number of cites to the total number of expected cites (34,562 to 15,305.25) is 2.2, indicating that the air papers are more highly cited than the average paper.

Table 15. Ratio of Actual Cites to Expected Cites for Air Papers by Field

ESI Field

Total Cites

Expected Cite Rate

Ratio

Biology & Biochemistry

546

570.96

1.0

Chemistry

2,375

1,476.02

1.6

Clinical Medicine

6,479

2,404.04

2.7

Computer Science

15

14.06

1.1

Economics & Business

25

7.29

3.4

Engineering

4,259

1,178.88

3.6

Environment/Ecology

7,910

3,299.45

2.4

Geosciences

8,477

3,378.05

2.5

Immunology

377

225.52

1.7

Materials Science

1

9.72

0.1

Mathematics

35

15.00

2.3

Microbiology

22

20.07

1.1

Molecular Biology & Genetics

62

202.11

0.3

Multidisciplinary

421

42.32

9.9

Neuroscience & Behavior

227

330.78

0.7

Pharmacology & Toxicology

2,951

1,868.21

1.6

Physics

194

138.43

1.4

Plant & Animal Science

124

88.47

1.4

Social Sciences, general

62

35.87

1.7

TOTAL

34,562

15,305.25

2.2

JCR Benchmarks

Impact Factor. The JCR Impact Factor is a well known metric in citation analysis. It is a measure of the frequency with which the “average article” in a journal has been cited in a particular year. The Impact Factor helps evaluate a journal’s relative importance, especially when compared to others in the same field. The Impact Factor is calculated by dividing the number of citations in the current year to articles published in the 2 previous years by the total number of articles published in the 2 previous years.

Table 16 indicates the number of air papers published in the top 10% of journals, based on the JCR Impact Factor. Six hundred ninety-six (696) of 2,064 papers were published in the top 10% of journals, representing 33.7% of EPA’s air papers. This indicates that more than one-third of the air papers are published in the highest quality journals as determined by the JCR Impact Factor, which is 3.4 times higher than the expected percentage.

Table 16. Air Papers in Top 10% of Journals by JCR Impact Factor

EPA Air Papers in that Journal

Journal

Impact Factor
(IF)

JCR IF Rank

2

New England Journal of Medicine

51.296

2

7

Science

30.028

9

3

Lancet

25.800

18

5

JAMA—Journal of the American Medical Association

23.175

23

1

Journal of Clinical Investigation

15.754

42

1

Annual Review of Physical Chemistry

11.250

83

10

Circulation

10.940

88

1

Nano Letters

9.960

110

2

Proceedings of the National Academy of Sciences of the United States of America

9.643

116

27

American Journal of Respiratory and Critical Care Medicine

9.091

131

7

Journal of Allergy and Clinical Immunology

8.829

136

1

Neuroscience & Biobehavioral Reviews

8.293

149

1

Advanced Drug Delivery Reviews

7.977

156

1

Journal of the American Chemical Society

7.696

168

2

Cancer Research

7.656

172

1

Mutation Research–Reviews in Mutation Research

7.579

175

1

Journal of Neuroscience

7.453

177

1

FASEB Journal

6.721

206

1

Critical Care Medicine

6.599

211

5

Journal of Immunology

6.293

223

1

Plant Physiology

6.125

232

5

Thorax

6.064

237

1

American Journal of Pathology

5.917

249

130

Environmental Health Perspectives

5.861

255

4

Journal of Biological Chemistry

5.808

260

14

Analytical Chemistry

5.646

276

6

Free Radical Biology & Medicine

5.440

289

1

Stroke

5.391

293

12

American Journal of Epidemiology

5.241

308

1

Journal of Thrombosis and Haemostasis

5.138

325

4

European Respiratory Journal

5.076

335

2

TrAC - Trends in Analytical Chemistry

5.068

337

1

Cellular Signaling

4.887

363

1

Faraday Discussions

4.731

393

27

Toxicology and Applied Pharmacology

4.722

397

1

Environmental Microbiology

4.630

406

18

American Journal of Respiratory Cell and Molecular Biology

4.593

412

1

Journal of Leukocyte Biology

4.572

415

5

Journal of Catalysis

4.533

418

1

International Journal of Epidemiology

4.517

424

1

Antioxidants & Redox Signaling

4.491

431

2

Atmospheric Chemistry and Physics

4.362

449

24

Epidemiology

4.339

452

2

American Journal of Physiology - Cell Physiology

4.334

455

3

Progress in Energy and Combustion Science

4.333

456

1

Cancer Epidemiology Biomarkers & Prevention

4.289

463

36

American Journal of Physiology - Lung Cellular and Molecular Physiology

4.250

472

4

Journal of Physical Chemistry B

4.115

501

2

Mutation Research–Fundamental and Molecular Mechanisms of Mutagenesis

4.111

505

167

Environmental Science & Technology

4.040

518

1

Journal of Pharmacology and Experimental Therapeutics

3.956

545

2

Applied Catalysis B: Environmental

3.942

548

3

Chest

3.924

552

1

Carbon

3.884

562

1

Experimental Cell Research

3.777

596

1

Human Reproduction

3.769

599

5

Bulletin of the American Meteorological Society

3.728

614

1

American Journal of Physiology - Heart and Circulatory Physiology

3.724

616

1

American Journal of Public Health

3.698

626

1

Journal of Cellular Physiology

3.638

646

3

Clinical Immunology

3.606

659

1

Optics Letters

3.598

662

41

Toxicological Sciences

3.598

662

1

Biochemical Pharmacology

3.581

667

1

Genomics

3.558

676

4

Journal of Chromatography A

3.554

678

3

Journal of Neuroscience Research

3.476

704

1

Ecological Applications

3.470

708

1

Cancer Letters

3.277

777

15

Journal of Applied Physiology

3.178

807

2

Journal of Chemical Physics

3.166

814

8

Chemical Research in Toxicology

3.162

818

1

Remote Sensing of Environment

3.064

855

38

Journal of Physical Chemistry A

3.047

863

1

American Journal of Cardiology

3.015

876

Total = 696

 

 

 

Immediacy Index. The JCR Immediacy Index is a measure of how quickly the average article in a journal is cited. It indicates how often articles published in a journal are cited within the year they are published. The Immediacy Index is calculated by dividing the number of citations to articles published in a given year by the number of articles published in that year.

Table 17 indicates the number of air papers published in the top 10% of journals, based on the JCR Immediacy Index. Nine hundred sixty-six (966) of the 2,064 papers appear in the top 10% of journals, representing 46.8% of the air papers. This indicates that nearly one-half of the air papers are published in the highest quality journals as determined by the JCR Immediacy Index, which is 4.7 times higher than the expected percentage.

Table 17. Air Papers in Top 10% of Journals by JCR Immediacy Index

EPA Air Papers in that Journal

Journal

Immediacy Index
(II)

JCR II Rank

2

New England Journal of Medicine

12.743

2

5

JAMA - Journal of the American Medical Association

7.781

4

3

Lancet

7.419

6

7

Science

5.555

16

1

Journal of Clinical Investigation

3.911

29

1

Faraday Discussions

2.766

59

10

Circulation

2.674

63

1

International Journal of Epidemiology

2.200

84

27

American Journal of Respiratory and Critical Care Medicine

2.006

98

7

Journal of Allergy and Clinical Immunology

1.790

118

1

Annual Review of Physical Chemistry

1.762

124

2

Proceedings of the National Academy of Sciences of the United States of America

1.758

126

1

Critical Care Medicine

1.641

146

4

Philosophical Transactions of the Royal Society of London Series A: Mathematical and Physical Sciences

1.534

166

1

Journal of the American Chemical Society

1.510

168

1

Nano Letters

1.485

177

5

Thorax

1.460

184

24

Epidemiology

1.437

187

1

Journal of Thrombosis and Haemostasis

1.397

194

1

Journal of Neuroscience

1.319

216

1

Stroke

1.242

237

1

FASEB Journal

1.241

238

1

Neuroscience & Biobehavioral Reviews

1.222

243

2

Cancer Research

1.220

246

1

Cellular Signaling

1.213

249

1

Antioxidants & Redox Signaling

1.131

281

4

Journal of Biological Chemistry

1.110

291

3

Chest

1.110

291

4

European Respiratory Journal

1.108

294

12

American Journal of Epidemiology

1.091

306

1

Mutation Research–Reviews in Mutation Research

1.050

331

15

Journal of Applied Physiology

1.026

343

2

Atmospheric Chemistry and Physics

1.015

350

130

Environmental Health Perspectives

0.994

373

1

Environmental Science and Pollution Research

0.982

376

18

American Journal of Respiratory Cell and Molecular Biology

0.925

404

2

American Journal of Physiology - Cell Physiology

0.906

417

1

Plant Physiology

0.900

423

5

Journal of Immunology

0.886

435

1

Journal of Cellular Physiology

0.867

453

1

Physical Chemistry Chemical Physics

0.866

454

1

Environmental Microbiology

0.850

469

1

Computer Physics Communications

0.845

478

1

American Journal of Pathology

0.833

487

36

American Journal of Physiology - Lung Cellular and Molecular Physiology

0.832

493

2

Annals of Occupational Hygiene

0.808

513

14

Analytical Chemistry

0.795

524

2

Journal of Pharmacology and Experimental Therapeutics

0.791

531

1

Optics Letters

0.778

543

1

American Journal of Physiology - Heart and Circulatory Physiology

0.777

547

2

TrAC - Trends in Analytical Chemistry

0.752

578

6

Free Radical Biology & Medicine

0.751

580

5

Journal of Catalysis

0.751

580

1

American Journal of Public Health

0.740

588

1

Human Reproduction

0.734

597

41

Toxicological Sciences

0.734

597

38

Journal of Physical Chemistry A

0.730

602

2

Journal of Chemical Physics

0.721

616

4

Journal of the Atmospheric Sciences

0.712

631

1

Biochemical Pharmacology

0.705

641

1

Carbon

0.690

664

145

Journal of Geophysical Research

0.684

673

1

Agricultural and Forest Meteorology

0.669

690

1

Journal of Leukocyte Biology

0.668

691

8

Chemical Research in Toxicology

0.663

703

1

Genomics

0.659

706

1

Cancer Letters

0.658

707

1

Monthly Weather Review

0.654

716

167

Environmental Science & Technology

0.646

729

5

Bulletin of the American Meteorological Society

0.646

729

1

Journal of Environmental Pathology, Toxicology and Oncology

0.639

742

4

Journal of Physical Chemistry B

0.637

746

5

Boundary-Layer Meteorology

0.629

758

1

American Journal of Cardiology

0.615

781

1

Equine Veterinary Journal

0.611

790

3

Clinical Immunology

0.604

804

6

Journal of Exposure Science and Environmental Epidemiology

0.596

821

7

Environmental Research

0.583

844

135

Aerosol Science and Technology

0.571

872

Total = 966

 

 

 

Hot Papers

ESI establishes citation thresholds for hot papers, which are selected from the highly cited papers in different fields, but the time frame for citing and cited papers is much shorter—papers must be cited within 2 years of publication and the citations must occur in a 2-month time period. Papers are assigned to 2-month periods and thresholds are set for each period and field to select 0.1% of papers. There were no hot papers identified for the current 2-month period (i.e., March-April 2007), but there were a number of hot papers identified from previous periods.

Using the hot paper thresholds established by ESI as a benchmark, 52 hot papers, representing 2.5% of the air papers, were identified in six fields—Clinical Medicine, Engineering, Environment/Ecology, Geosciences, Multidisciplinary, and Pharmacology & Toxicology. The number of air hot papers is 25 times higher than expected. The hot papers are listed in Table 18.

Table 18. Hot Papers Identified Using ESI Thresholds

Field

ESI Hot Papers Threshold

No. of Cites in 2-Month Period

Paper

Clinical Medicine

7

7 cites in March-April 2002

Peters A, et al. Increased particulate air pollution and the triggering of myocardial infarction. Circulation 2001;103(23):2810-2815.

 

12

21 cites in August-September 2003

Pope CA, et al. Lung cancer, cardiopulmonary mortality and long-term exposure to fine particulate air pollution. Journal of the American Medical Association 2002;287(9):1132-1141.

 

10

11 cites in November-December 2005

Peters A, et al. Exposure to traffic and the onset of myocardial infarction. New England Journal of Medicine 2004;351(17):1721-1730.

 

13

19 cites in November- December 2005

Pope CA, et al. Cardiovascular mortality and long-term exposure to particulate air pollution: epidemiological evidence of general pathophysiological pathways of disease. Circulation 2004;109(1):71-77.

 

3

3 cites in July 2005

Ito K, et al. Associations between ozone and daily mortality: analysis and meta-analysis. Epidemiology 2005;16(4):446-457.

Engineering

4

4 cites in October-November 2001

Christoforou CS, et al. Trends in fine particle concentration and chemical composition in southern California. Journal of the Air & Waste Management Association 2000;50(1):43-53.

 

4

4 cites in July 2001

Richter H, Howard JB. Formation of polycyclic aromatic hydrocarbons and their growth to soot - a review of chemical reaction pathways. Progress in Energy and Combustion Science 2000;26(4-6):565-608.

 

3

3 cites in May 2001

Vanderpool RW, et al. Evaluation of the loading characteristics of the EPA WINSPM 2.5 separator. Aerosol Science and Technology 2001;34(5):444-456.

 

3

5 cites in May 2001

Peters TM, et al. Design and calibration of the EPA PM2.5 well impactor ninety-six (WINS). Aerosol Science and Technology 2001;34(5):389-397.

 

5

5 cites in March- April 2003

Weber RJ, et al. A particle-into-liquid collector for rapid measurement of aerosol bulk chemical composition. Aerosol Science and Technology 2001;35(3):718-727.

 

4

4 cites in November- December 2005

McMurry PH, et al. The relationship between mass and mobility for atmospheric particles: A new technique for measuring particle density. Aerosol Science and Technology 2002;36(2):227-238.

Engineering

2

3 cites in March- April 2003

Weber R, et al. Short-term temporal variation in PM2.5 mass and chemical composition during the Atlanta Supersite Experiment, 1999. Journal of the Air & Waste Management Association 2003;53(1):84-91.

 

3

4 cites in July 2003

Fujita, et al. Diurnal and weekday variations in source contributions of ozone precursors in California's South Coast Air Basin. Journal of the Air & Waste Management Association 2003;53(7):844-863.

 

3

3 cites in November- December 2003

Lewis CW, et al. Source apportionment of Phoenix PM2.5 aerosol with the Unmix receptor model. Journal of the Air & Waste Management Association 2003;53(3):325-338.

 

3

3 cites in February 2004

Vette A, et al. Environmental research in response to 9/11 and homeland security. EM: Air & Waste Management Association’s Magazine for Environmental Managers 2004;Feb:14-22.

 

4

4 cites in March-April 2005

Russell M, et al. Daily, seasonal, and spatial trends in PM2.5 mass and composition in Southeast Texas. Aerosol Science and Technology 2004;38(S1):14-26.

 

4

4 cites in March-April 2005

Zhu YF, et al. Seasonal trends of concentration and size distribution of ultrafine particles near major highways in Los Angeles. Aerosol Science and Technology 2004;38(S1):5-13.

 

3

3 cites in September- October 2004

Cho AK, et al. Determination of four quinones in diesel exhaust particles, SRM 1649a and atmospheric PM2.5. Aerosol Science and Technology 2004;38(S1):68-81.

 

4

4 cites in November- December 2004

Drewnick F, et al. Measurement of ambient aerosol composition during the PMTACS-NY 2001 campaign using an aerosol mass spectrometer. Part I: Mass concentrations. Aerosol Science and Technology 2004;38(S1):92-103.

 

3

4 cites in November- December 2005

Canagaratna MR, et al. Chase studies of particulate emissions from in-use New York City vehicles. Aerosol Science and Technology 2004;38(6):555-573.

Environment/ Ecology

3

3 cites in March-April 2001

Lumley T, Levy D. Bias in the case-crossover design: implications for studies of air pollution. Environmetrics 2000;11(6):689-704.

 

3

3 cites in August 2000

Stolzenburg MR, Hering SV. Method for the automated measurement of fine particle nitrate in the atmosphere. Environmental Science & Technology 2000;34(5):907-914.

Environment/ Ecology

6

6 cites in September-October 2001

Schwartz J. Assessing Confounding, Effect modification, and thresholds in the association between ambient particles and daily deaths. Environmental Health Perspectives 2000;108(6):563-568.

 

5

5 cites in August 2001

Seila RL, et al. Atmospheric volatile organic compound measurements during the 1996 Paso Del Norte Ozone Study. Science of the Total Environment 2001;276(1-3):153-169.

 

5

6 cites in August 2001

Fujita EM. Hydrocarbon source apportionment for the 1996 Paso del Norte Ozone Study. Science of the Total Environment 2001;276(1-3):171-184.

 

6

6 cites in September-October 2003

Jang MS, et al. Atmospheric secondary aerosol formation by heterogeneous reactions of aldehydes in the presence of a sulfuric acid aerosol catalyst. Environmental Science & Technology 2001;35(24):4758-4766.

 

5

5 cites in November-December 2004

Jang MS, et al. Particle growth by acid-catalyzed heterogeneous reactions of organic carbonyls on pre-existing aerosols. Environmental Science & Technology 2003;37(17):3828-3837.

 

5

7 cites in May-June 2004

Li N, et al. Ultrafine particulate pollutants induce oxidative stress and mitochondrial damage. Environmental Health Perspectives 2003;111(4):455-460.

 

3

3 cites in April-May 2004

Sexton K, et al. Comparison of personal, indoor, and outdoor exposures to hazardous air pollutants in three urban communities. Environmental Science & Technology 2004;38(2):423-430.

 

2

2 cites in August 2004

Landrigan PJ, et al. Health and environmental consequences of the World Trade Center Disaster. Environmental Health Perspectives 2004;112(6):731-739.

 

5

9 cites in June-July 2006

Gao S, et al. Particle Phase Acidity and Oligomer Formation in Secondary Organic Aerosol. Environmental Science & Technology 2004;38(24):6582-6589.

 

3

4 cites in May-June 2006

Thurston GD, et al. Workgroup report: workshop on source apportionment of particulate matter health effects—intercomparison of results and implications. Environmental Health Perspectives 2005;113(12):1768-1774.

 

3

3 cites in September 2005

Koenig JQ, et al. Pulmonary effects of indoor- and outdoor-generated particles in children with asthma. Environmental Health Perspectives 2005;113(4):499-503.

Environment/ Ecology

3

4 cites in March-April 2006

Presto AA, et al. Secondary organic aerosol production from terpene ozonolysis. 1. Effect of UV radiation. Environmental Science & Technology 2005;39(18):7036-7045.

 

6

6 cites in August-September 2006

Dockery DW, et al. Association of air pollution with increased incidence of ventricular tachyarrhythmias recorded by implanted cardioverter defibrillators. Environmental Health Perspectives 2005;113(6):670-674.

 

6

7 cites in December 2005-January 2006

Zanobetti A, Schwartz J. The effect of particulate air pollution on emergency admissions for myocardial infarction: a multicity case-crossover analysis. Environmental Health Perspectives 2005;113(8):978-982.

 

6

6 cites in July-August 2006

Park SK, et al. Effects of air pollution on heart rate variability: The VA Normative Aging Study. Environmental Health Perspectives 2005;113(3):304-309.

 

4

6 cites in March-April 2006

Bahreini R, et al. Measurements of secondary organic aerosol from oxidation of cycloalkenes, terpenes, and m-xylene using an Aerodyne Aerosol Mass Spectrometer. Environmental Science & Technology 2005;39(15):5674-5688.

 

5

5 cites in March-April 2006

Lough GC, et al. Emissions of metals associated with motor vehicle roadways. Environmental Science & Technology 2005;39(3):826-836.

 

6

12 cites in December-2006-January 2007

Zhang Q, et al. Deconvolution and quantification of hydrocarbon-like and oxygenated organic aerosols based on aerosol mass spectrometry. Environmental Science & Technology 2005;39(13):4938-4952.

 

10

24 cites in March-April 2007

Oberdorster G, et al. Nanotoxicology: an emerging discipline evolving from studies of ultrafine particles. Environmental Health Perspectives 2005;113(7):823-839.

 

4

4 cites in February-March 2007

Elder A. Translocation of inhaled ultrafine manganese oxide particles to the central nervous system. Environmental Health Perspectives 2006;114(8):1172-1178.

Geosciences

5

5 cites in June-July 2003

Huser RB, et al. Asian dust events of April 1998. Journal of Geophysical Research-Atmospheres 2001;106(D16):18317-18330.

 

10

10 cites in June-July 2004

Orsini DA, et al. Refinements to the particle-into-liquid sampler (PILS) for ground and airborne measurements of water soluble aerosol composition. Atmospheric Environment 2003;37(9-10):1243-1259.

Geosciences

4

4 cites in June-July 2006

Grell GA, et al. Fully coupled “online” chemistry within the WRF model. Atmospheric Environment 2005;39(37):6957-6975.

 

6

6 cites in November-December 2006

McKeen S, et al. Assessment of an ensemble of seven real-time ozone forecasts over eastern North America during the summer of 2004. Journal of Geophysical Research–Atmospheres 2005;110(D21):Art. No. D21307.

 

5

5 cites in February-March 2007

Guenther A. Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature). Atmospheric Chemistry and Physics 2006;6:3181-3210.

Multidisciplinary

6

10 cites in May-June 2004

Jang MS, et al. Heterogeneous atmospheric aerosol production by acid-catalyzed particle-phase reactions. Science 2002;298(5594):814-817.

Pharmacology & Toxicology

5

6 cites in April 2005

Lippmann M, et al. Effects of subchronic exposures to concentrated ambient particles (CAPs) in mice: I. Introduction, objectives, and experimental plan. Inhalation Toxicology 2005;17(4-5):177-187.

 

5

7 cites in April 2005

Maciejczyk P, et al. Effects of subchronic exposures to concentrated ambient particles (CAPs) in mice: II. The design of a CAPs exposure system for biometric telemetry monitoring. Inhalation Toxicology 2005;17(4-5):189-197.

 

2

2 cites in September-October 2006

Costa DL, et al. Comparative pulmonary toxicological assessment of oil combustion particles following inhalation or instillation exposure. Toxicological Sciences 2006;91(1):237-246.

 

2

2 cites in July 2003

Kodavanti UP, et al. Inhaled environmental combustion particles cause myocardial injury in the Wistar Kyoto rat. Toxicological Sciences 2003;71(2):237-245.

Author Self-Citation

Self-citations are journal article references to articles from that same author (i.e., the first author). Because higher author self-citation rates can inflate the number of citations, the author self-citation rate was calculated for the air papers. Of the 34,562 total cites, 1,605 are author self-cites—a 4.6% author self-citation rate. Garfield and Sher3 found that authors working in research-based disciplines tend to cite themselves on the average of 20% of the time. MacRoberts and MacRoberts4 claim that approximately 10% to 30% of all the citations listed fall into the category of author self-citation. Kovacic and Misak5 recently reported a 20% author self-citation rate for medical literature. Therefore, the 4.6% self-cite rate for the air papers is well below the range for author self-citation.

Highly Cited Researchers

A search of Thomson’s ISIHighlyCited.com revealed that 59 (1.7%) of the 3,452 authors of the air papers are highly cited researchers. ISIHighlyCited.com is a database of the world’s most influential researchers who have made key contributions to science and technology during the period from 1981 to 1999. The highly cited researchers identified during this analysis of the air publications are presented in Table 19.

Table 19. Highly Cited Researchers Authoring Air Publications

Highly Cited Researcher

Affiliation

ESI Field

Ames, Bruce N.

Children’s Hospital Oakland Research Institute

Biology & Biochemistry
Molecular Biology & Genetics

Andersen, Melvin E.

CIIT Centers for Health Research

Pharmacology

Anderson, James G.

Harvard University

Geosciences

Arey, Janet

University of California–Riverside

Environment/Ecology

Atkinson, Roger

University of California–Riverside

Environment/Ecology

Calvert, Jack G.

National Center for Atmospheric Research

Geosciences

Carter, William P.L.

University of California–Riverside

Environment/Ecology

Cass, Glen R.

Georgia Institute of Technology

Environment/Ecology

Corey, Lawrence

University of Washington

Clinical Medicine

Dickey, David A.

North Carolina State University

Mathematics
Economics & Business

Dockery, Douglas W.

Harvard University

Environment/Ecology

Driscoll, Charles T.

Syracuse University

Environment/Ecology

Fehsenfeld, Fred C.

National Oceanic and Atmospheric Administration

Geosciences

Folsom, Aaron R.

University of Minnesota

Clinical Medicine

Fuster, Valentin

Mount Sinai Medical Center

Clinical Medicine

Garcia, Rolando R.

National Center for Atmospheric Research

Geosciences

Giorgi, Filippo

Abdus Salam International Centre for Theoretical Physics (Trieste, Italy)

Geosciences

Hites, Ronald A.

Indiana University School of Public and Environmental Affairs

Environment/Ecology

Holben, Brent N.

National Air and Space Administration Goddard Space Flight Center

Geosciences

Houk, Kendall N.

University of California–Los Angeles

Chemistry

Hubler, Gerhard F.

National Oceanic and Atmospheric Administration

Geosciences

Jacob, Daniel J.

Harvard University

Geosciences

Karl, Thomas R.

National Oceanic and Atmospheric Administration

Geosciences

Kaufman, Yoram J.

National Air and Space Administration Goddard Space Flight Center

Geosciences

Kawachi, Ichiro

Harvard School of Public Health

Social Sciences, general

Khalil, Mohammed A.K.

Portland State University

Environment/Ecology

Kloner, Robert A.

Good Samaritan Hospital

Clinical Medicine

Koutrakis, Petros

Harvard School of Public Health

Environment/Ecology

Lay, Thorne

University of California–Santa Cruz

Geosciences

Likens, Gene E.

Institute of Ecosystem Studies

Environment/Ecology

Lindberg, Steven E.

Oak Ridge National Laboratory

Environment/Ecology

Liotta, Lance A.

National Cancer Institute

Clinical Medicine

Lioy, Paul J.

University of Medicine & Dentistry of New Jersey

Environment/Ecology

Lippmann, Morton

New York University School of Medicine

Environment/Ecology

Logan, Jennifer A.

Harvard University

Geosciences

Madronich, Sasha

National Center for Atmospheric Research

Geosciences

Mannucci, Pier M.

Università degli Studi di Milano

Clinical Medicine

Mazurek, Monica A.

Rutgers University

Environment/Ecology

Pankow, James F.

Oregon Health and Science University

Environment/Ecology

Parker, John (Jack) C.

University of Tennessee

Environment/Ecology
Engineering

Rasmussen, Reinhold A.

Oregon Health and Science University

Environment/Ecology
Geosciences

Richards, James H.

University of California–Davis

Environment/Ecology

Rogge, Wolfgang F.

Florida International University

Environment/Ecology

Salawitch, Ross J.

California Institute of Technology

Geosciences

Schwartz, Joel D.

Harvard School of Public Health

Environment/Ecology
Pharmacology

Schwartz, Stephen E.

Brookhaven National Laboratory

Geosciences

Seinfeld, John H.

California Institute of Technology

Geosciences
Environment/Ecology
Engineering

Simoneit, Bernd R.T.

Oregon State University

Environment/Ecology
Engineering

Speizer, Frank E.

Harvard Medical School

Clinical Medicine

Spengler, John D.

Harvard University

Environment/Ecology

Trainer, Michael

National Oceanic and Atmospheric Administration

Geosciences

Turco, Richard P.

University of California–Los Angeles

Geosciences

Van Thiel, David H.

Loyola University Medical Center

Clinical Medicine

Wang, J.

National Centers for Environmental Prediction

Geosciences

Watson, John G.

Desert Research Institute

Environment/Ecology

Winer, Arthur M.

University of California–Los Angeles

Environment/Ecology

Wofsy, Steven C.

Harvard University

Geosciences

Wolff, George T.

General Motors Corporation

Environment/Ecology

Zeger, Scott L.

Johns Hopkins University

Mathematics

Total = 59

 

 

Patents

There were 6 patents issued by investigators from 1998 to 2007 for research that was conducted under EPA’s air research program. The patents are listed in Table 20. Two of the 6 patents (33.3%) were referenced by a total of 9 other patents.

Table 20. Patents from the Air Research Program (1998-2007)

Patent or Patent Application No.

Inventor(s)

Title

Patent/Patent Application Date

Patents that Referenced This Patent

U.S. Patent No. 6,890,372

Dasgupta PK Morris KJ
Li J

Denuder assembly for collection and removal of soluble atmospheric gases

May 2005

None

U.S. Patent No. 5,763,360

Gundel L Daisey JM Stevens RK

Quantitative organic vapor-particle sampler

June 1998

Referenced by 6 patents:
(1) 7,122,065 Adapter for low volume air sampler
(2) 6,604,406 Human portable preconcentrator system
(3) 6,523,393 Human portable preconcentrator system
(4) 6,502,450 Single detector differential particulate mass monitor with intrinsic correction for volatilization losses
(5) 6,403,384 Device and method for analyzing a biologic sample
(6) 6,035,701 Method and system to locate leaks in subsurface containment structures using tracer gases

U.S. Patent No. 6,226,852

Gundel L Daisey JM Stevens RK

Method for fabricating a quantitative integrated diffusion vapor-particle sampler for sampling, detection and quantitation of semi-volatile organic gases, vapors and particulate components

May 2001

Referenced by 3 patents:
(1) 7,159,475 Apparatus and method of sampling semivolatile compounds
(2) 7,122,065 Adapter for low volume air sampler
(3) 7,089,747 Pressure reduction apparatus and method

U.S. Patent No. 6,780,818

Gundel L Daisey JM Stevens RK

Quantitative organic vapor-particle sampler

August 2004

None

U.S. Patent No. 7,168,292

Gundel LA Apte MG Hansen AD Black DR

Apparatus for particulate matter analysis

January 2007

None

U.S. Patent No. 7,168,292

Gundel LA Apte MG Hansen AD Black DR

Apparatus for particulate matter analysis

January 2007

None

Additional ESI Parameters for Air Pollution Publications

Since the last bibliometric analysis for the Particulate Matter/Ozone Research Program, which was conducted in 2005, ESI has begun analyzing special topics and reporting information such as the top 20 papers, top 20 authors, top 20 institutions, and top 20 countries for these special topics. One of the of ESI special topics is Air Pollution. The parameters reported by ESI for the special topic of Air Pollution are compared with the results of the analysis of the EPA Air Research Program publications below.

Top 20 Papers in Air Pollution—A review of ESI’s top 20 papers on the topic of air pollution (published from January 1, 2003 to April 30, 2005), indicates that 4 (20.0% of the top 20 papers) are papers from EPA’s Air Research Program. These papers are listed in Table 21.

Top 20 Authors in Air Pollution—Eighteen of ESI’s top 20 authors (90.0% of the top 20 authors) in air pollution (ranked by total cites from 1995-2005) authored papers for EPA’s Air Research Program. These authors are listed in Table 22.

Table 21. EPA Air Papers in ESI’s Top 20 Air Pollution Papers Overall
(Published from January 1, 2003 to April 30, 2005)

ESI Rank

EPA Air Program Publication

3

Pope CA, et al. Cardiovascular mortality and long-term exposure to particulate air pollution—epidemiological evidence of general pathophysiological pathways of disease. Circulation 2004;109(1):71-77.

4

Binkowski FS, Roselle SJ. Models-3 Community Multiscale Air Quality (CMAQ) model aerosol component. 1. Model description. Journal of Geophysical Research–Atmospheres 2003;108(D6):4183.

9

Becker S, et al. Response of human alveolar macrophages to ultrafine, fine, and coarse urban air pollution particles. Experimental Lung Research 2003;29(1):29-44.

13

McConnell R, et al. Prospective Study of Air Pollution and Bronchitic Symptoms in Children with Asthma. American Journal of Respiratory and Critical Care Medicine 2003;168(7):790-797.

Table 22. ESI’s Top 20 Overall Authors in Air Pollution (Ranked by Total Cites, 1995-2005)

ESI Rank

Author

Total Cites

Number of Papers

Cites Per Paper

EPA Air Research Paper Author

1

Schwartz, J.

2,537

93

27.28

Yes

2

Dockery, DW

2,473

35

70.66

Yes

3

Pope, CA

1,973

29

68.03

Yes

4

Samet, JM

1,255

28

44.82

Yes

5

Speizer, FE

1,193

11

108.45

Yes

6

Brunkekreef, B

967

55

17.58

Yes

7

Thun, MJ

952

4

238.00

Yes

8

Anderson, HR

906

31

29.23

No

9

Cass, GR

869

27

32.19

Yes

10

Peters, A

770

39

19.74

Yes

11

Burnett, RT

668

39

17.13

Yes

12

Zeger, SL

653

15

43.53

Yes

13

Katsouyanni, K

640

35

18.29

Yes

14

Wichmann HE

606

27

22.44

Yes

15

Donaldson, K

598

7

85.43

Yes

16

Macnee, W

598

7

85.43

Yes

17

Ghio, AJ

577

12

48.08

Yes

18

Dominici, F

556

16

34.75

Yes

19

Spix, C

546

13

42.00

No

20

Touloumi, G

539

18

29.94

Yes

Top 20 Countries Publishing in Air Pollution—The United States ranks number one among the top 20 countries publishing on air pollution. From 1995-2005, the United States published 1,608 papers that were cited 16,899 times. The second ranking country, England, published 421 papers that were cited 3,295 times.

Top 20 Journals in Air Pollution—1,038 (50.2%) of the EPA Air Research Program papers were published in ESI’s top 20 journals in air pollution (ranked by total cites from 1995-2005). The top 20 journals and the number of EPA air papers published in these journals are provided in Table 23.

Table 23. ESI’s Top 20 Journals in Air Pollution (Ranked by Total Cites, 1995-2005)

ESI Rank

Journal

Total Cites

Number of Papers

Cites Per Paper

Number of EPA Air Papers in Journal

1

Atmospheric Environment

2,869

344

8.34

266

2

Environmental Health Perspectives

2,735

148

18.48

130

3

American Journal of Respiratory and Critical Care Medicine

2,486

66

37.67

27

4

Epidemiology

1,715

544

3.15

24

5

Environmental Science & Technology

1,122

93

12.06

167

6

Lancet

995

28

35.54

3

7

American Journal of Epidemiology

986

55

17.93

12

8

Inhalation Toxicology

907

56

16.20

103

9

European Respiratory Journal

809

52

15.56

4

10

Journal of the Air & Waste Management Association

800

110

7.27

120

11

Thorax

702

25

28.08

5

12

Science

697

27

25.81

7

13

Occupational and Environmental Medicine

632

54

11.70

7

14

Journal of Geophysical Research–Atmospheres

612

74

8.27

143

15

Journal of Epidemiology and Community Health

576

38

15.16

1

16

Archives of Environmental Health

538

48

11.21

4

17

Environmental Pollution

492

71

6.93

6

18

Water, Air, and Soil Pollution

412

75

5.49

2

19

Indoor Air

356

48

7.42

2

20

JAMA-Journal of the American Medical Association

342

11

31.09

5

Total

 

 

 

 

1,038

Top 20 Institutions Publishing on Air Pollution—Harvard University ranks number one on ESI’s top 20 overall institutions publishing on air pollution with 192 papers (published from 1995-2005) that were cited 4,771 times. Harvard University is one of the recipients of EPA grants that publishes under the Air Research Program. The U.S. Environmental Protection Agency ranks number two with 175 publications that were cited 2,543 times. The top 20 institutions are listed in Table 24.

Table 24. ESI’s Top 20 Institutions Publishing on Air Pollution
(Ranked by Total Cites, 1995-2005)

ESI Rank

Institution

Total Cites

Number of Papers

Cites Per Paper

1

Harvard University

4,771

192

24.85

2

U.S. EPA

2,543

175

14.53

3

University of North Carolina

1,316

72

14.53

4

Brigham Young University

1,311

2

46.82

5

GSF Forschungszentrum Umwelt & Gesundheit

1,268

62

20.45

6

Johns Hopkins University

1,227

45

27.27

7

Health Canada

1,067

57

18.72

8

American Cancer Society

952

4

238.00

9

Wageningen University

830

38

21.84

10

Caltech

821

36

22.81

11

University of Athens

777

58

13.40

12

University of Groningen

633

19

33.32

13

St. George’s Hospital

621

24

25.88

14

University of California–Berkeley

615

72

8.54

15

University of British Columbia

604

51

11.84

16

University of California–Irvine

603

24

25.13

17

University of Rochester

599

13

46.08

18

Napier University

591

8

73.88

19

Municipal Institute of Medical Research (IMIM–Barcelona)

584

18

32.44

20

University of Maryland

564

19

29.68

Air Pollution Publication Trends—According to ESI, the number of air pollution papers rose slightly each year from 2000 to 2004; however, the number of cites and the number of cites/paper have been declining since 1999. The number of air pollution papers published from 2001 to 2005 has declined from the number published from 2000 to 2004, and the number of cites and cites/paper from 2001 to 2005 have declined as well. These trends are depicted in Figure 1. The number of EPA Air Research Program publications, however, has increased slightly from 2001 to 2005 (1,257 publications) when compared to the number published from 2000 to 2004 (1,240 publications). Like the overall air pollution paper trends identified by ESI, the number of cites and the cites per paper have declined.

Figure 1. Comparison of ESI Air Pollution Publication Trends with EPA Air Research Program Publication Trends

Figure 1. Comparison of ESI Air Pollution Publication Trends with EPA Air Research Program Publication Trends

Figure 1. Comparison of ESI Air Pollution Publication Trends with EPA Air Research Program Publication Trends

Figure 1. Comparison of ESI Air Pollution Publication Trends with EPA Air Research Program Publication Trends

ESI Field Distribution of Air Pollution Papers—The majority of air pollution papers from 1995 to 2005 were published in journals that fall within the ESI field of Clinical Medicine, followed by the fields of Environment/Ecology, Geosciences, Engineering, and Chemistry. For the EPA air papers included in this analysis, the majority of the papers were published in the ESI field of Geosciences, followed by Environment/Ecology, Engineering, Clinical Medicine, and Pharmacology & Toxicology. The distribution of air pollution papers among the 22 ESI fields and the distribution of the EPA air papers for comparison are presented in Table 25.

Table 25. Comparison of Field Distribution of Air Pollution Papers (Ranked by Number of Papers, 1995-2005) to Field Distribution of EPA Air Research Program Papers (Published from 1998-2007)

ESI Rank

ESI Field

Air Pollution Papers Overall

EPA Air Papers

Total Cites

Number of Papers

Cites Per Paper

% of Papers

Total Cites

Number of Papers

Cites Per Paper

% of Papers

1

Clinical Medicine

12,689

1,376

9.22

27.6%

6,479

260

24.9

12.6%

2

Environment/ Ecology

7,534

1,196

6.30

24.0%

7,910

435

18.2

21.1%

3

Geosciences

4,144

594

6.98

11.9%

8,478

490

17.3

23.7%

4

Engineering

1,921

566

3.39

11.3%

4,259

360

11.8

17.4%

5

Chemistry

450

301

1.50

6.0%

2,375

150

15.8

7.3%

6

Social Sciences

598

224

2.67

4.5%

62

13

4.8

0.6%

7

Pharmacology & Toxicology

1,572

139

11.31

2.8%

2,951

220

13.4

10.7%

8

Plant & Animal Science

433

116

3.73

2.3%

124

11

11.3

0.5%

9

Economics & Business

440

80

5.50

1.6%

25

3

8.3

0.1%

10

Immunology

357

75

4.76

1.5%

377

14

26.9

0.7%

11

Computer Science

91

66

1.38

1.3%

15

4

3.8

0.2%

12

Multidisciplinary

829

60

13.82

1.2%

421

10

42.1

0.5%

13

Materials Science

48

44

1.09

0.9%

1

2

0.5

0.1%

14

Biology & Biochemistry

74

41

1.8

0.8%

546

41

13.3

2.0%

15

Physics

126

34

3.71

0.7%

194

15

12.9

0.7%

16

Molecular Biology & Genetics

279

27

10.33

0.5%

62

8

7.8

0.4%

17

Agricultural Sciences

72

24

3

0.5%

18

Mathematics

60

15

4

0.3%

35

7

5.0

0.3%

19

Microbiology

23

4

5.75

0.1%

22

1

22.0

0.05%

20

Neuroscience & Behavior

8

4

2.00

0.1%

227

20

11.4

1.0%

21

Psychiatry/Psychology

3

4

0.75

0.1%

22

Space Science

1

4

0.25

0.1%

Total

 

32,422

4,994

6.49

 

34,562

2,064

16.7

 

1 Thomson Scientific’s Web of Science provides access to current and retrospective multidisciplinary information from approximately 8,830 of the most prestigious, high impact research journals in the world. Web of Science also provides cited reference searching.

2 Scopus is a large abstract and citation database of research literature and quality Web sources designed to support the literature research process. Scopus offers access to 15,000 titles from 4,000 different publishers, more than 12,850 academic journals (including coverage of 535 Open Access journals, 750 conference proceedings, and 600 trade publications), 27 million abstracts, 245 million references, 200 million scientific Web pages, and 13 million patent records.

3 Garfield E, Sher IH. New factors in the evaluation of scientific literature through citation indexing. American Documentation 1963;18(July):195-210.

4 MacRoberts MH, MacRoberts BR. Problems of citation analysis: a critical review. Journal of the American Society of Information Science 1989;40(5):342-349.

5 Kavaci N, Misak A. Author self-citation in medical literature. Canadian Medical Association Journal 2004;170(13):1929-1930.

This bibliometric analysis was prepared by
Beverly Campbell, The Scientific Consulting Group, Inc.
under EPA Contract No. EP-C-05-015

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