Air pollution may be considered an environmental health risk having been associated with a number of acute (e.g., respiratory and cardiovascular events, hospital and emergency room admissions) and chronic (e.g., chronic bronchitis, lung cancer, mortality) effects . In many cases it is difficult to determine direct causality with one particular constituent of air pollution (PM, sulfur dioxide, carbon monoxide, VOCs, etc.) due to its complexity and multiple sources, the inability to assign area exposure values to individuals, as well as the unavoidable confounding inherent to large scale environmental epidemiology studies. While more than 98% of air pollution in urban settings are gases or vapor-phase compounds, more recent inhalation and atmospheric pollution studies have focused on particulate matter due to some correlations with mortality and adverse respiratory health effects . It has been suggested that up to 8% of premature mortalities globally are related to both indoor and outdoor concentrations of particulate matter, though these findings are difficult to interpret given the uncertainties present in the respective study designs . A number of studies have suggested associations between long-term exposure to PM and various health effects including accelerated cardiovascular and respiratory mortality, compromised lung function and relative increase of lung cancer risk . Inhalable particulate matter (PM10), specifically, has been associated with increases in daily mortality and hospital admissions for respiratory distress (pneumonia, asthma and decreased lung function in children) . Though the multi-factorial nature of these outcomes and the inability to disentangle confounding factors make it impossible to know if PM is the causative agent behind morbidities and mortalities the findings warrant investigating potential risks from exposure to this type of air pollution.
Many factors contribute to the chemical composition of PM, including combustion sources, climate, season, and type of urban and/or industrial pollution . Particulate matter can be emitted from both natural and anthropogenic sources with both primary (directly emitted) and secondary (atmospherically derived) components . Primary sources include wildfires, sea spray, organic matter and the combustion of both fossil fuels and biofuels. Secondary sources of PM include wood smoke, gaseous vegetative emissions and vehicular emissions and other condensates from atmospheric chemistry. The major components of PM consist of inert compounds, semivolatile organic compounds, metals, carbonaceous material mainly from combustion and vehicle exhaust, biological material, and minerals. The density, concentration, and composition of particulate matter can vary widely among geographic locations.
Refinery operations have been associated with atmospheric emissions of a wide variety of criteria air pollutants, including particulate matter. The type and quality of the crude oil, refinery process and refined products all influence the variability, composition and amount of emissions from one refinery to another. One of the largest and oldest refineries in the Wider Caribbean Region is Isla Refineriá, which opened in 1918 and is located within the densely populated capital of Willemstad, Curaçao on the shores of Schottegat Bay. Although, the refinery was considered obsolete in the mid-1980s, it is still in use today processing ~335,000 barrels per day yet it has not been able or required to comply with environmental standards and permit requirements .
The objectives of this study were to analyze hourly, daily, and monthly PM10 measurements over a four year period (2010-2014) to determine if any temporal trends exist and to compare levels with public health guidelines in order to assess potential public health risks in Curaçao.
2. Materials and Methods
2.1. Site Selection
Curaçao is an island in the southern Caribbean, ~40 miles off the Venezuelan coast. It is currently considered a constituent country of the Kingdom of the Netherlands since its dissolution in 2010 from the Netherland Antilles. Curaçao is located in the Southern Caribbean Dry Zone approximately 12˚ north of the equator, which is characterized by a semi-arid to arid climate, with a distinguishable dry (March-September) and rainy season (October-February), and sustained easterlies. Curacao is typically warm and sunny with an average temperature of 27˚C and an average annual rainfall of approximately 570 mm. The island is approximately 59 kilometers in length, 4 - 11 kilometers wide and a total land mass area of ~443 km2. The population of ~152,000 consists of greater than 50 nationalities with Dutch and Papiamento as the official languages. The majority of the population (>130,000) resides in Willemstad which is home to the Isla Refineriá.
2.2. Local Monitoring Station Descriptions
Since mid-2010, two air monitoring stations, Beth Chaim and Kas Chikitu, located in Willemstad, Curaçao have been collecting validated and continuous measurements of air quality parameters (SO2, PM10, TSP, H2S). The Beth Chaim station is located at the western edge, downwind of the Schottegat industrial area of the refinery and only measures SO2 and TSP. Kas Chikitu is located approximately 2 - 3 km downwind in the Marchena/Wishi residential area and is primarily used to monitor the residential load of SO2, hydrogen sulfide (H2S) and PM10. Available hourly and daily measurements of PM10 were downloaded from June 1, 2010 through December 31, 2014 for analysis from the Kas Chikitu station. Twenty-four hour PM10 daily means (n = 1603) measured at the Kas Chikitu station were analyzed. Monitoring stations operate in accordance with the ISO/IEC 17025 accreditation (certificate number L 426) of GGD Amsterdam using tapered element oscillating balance (TEOM 50C) methodology to measure PM10.
2.3. Data Analysis
All PM10 data is expressed in μg/m3. All data analysis was performed using Statistica Version 6.1 (Stat Soft, Inc., Tulsa, OK). If data did not meet the assumptions of normality, nonparametric hypothesis tests were performed. If a potential explanatory variable was categorical (e.g. year), the nonparametric Kruskal-Wallis ANOVA was run using α = 0.05. If the Kruskal-Wallis ANOVA was found to be significant multiple comparisons revealed significant differences between categorical factors. Concentrations of PM10 were compared daily and annually and correlations were also evaluated against environmental factors (e.g. temperature, humidity and wind speed).
3. Results and Discussion
3.1. Ambient Concentrations of Inhalable Particulate Matter
Daily PM10 concentrations were downloaded from the Kas Chikitu station (n = 1603) from June 1, 2010 through December 31, 2014. The 24-hour daily mean concentrations ranged from 0.37 - 341 μg/m3 (Figure 1). Mean annual PM10 concentrations at the Kas Chikitu station ranged from 31 μg/m3 in 2010 to 122 μg/m3 in 2014 (Figure 2). There were statistically significant temporal trends
Figure 1. Daily 24-hour mean PM10 concentrations (μg/m3) collected at the Kas Chikitu air monitoring station in Curaçao from June 1, 2010 through December 31, 2014. Current 24 hour guidelines recommended by NAAQS (150 μg/m3) and the European Commission (50 μg/m3) are depicted with dashed lines, respectively.
Figure 2. Annual mean concentrations of PM10 (μg/m3) measured at the Kas Chikitu air monitoring station in Curaçao for the years 2010 through 2014. The current European Commission’s annual (40 μg/m3) recommendation is depicted with a dashed line.
observed with a strong increasing trend (R2 = 0.94) over time. In general, the 2014 mean annual PM10 concentrations were significantly (p > 0.00001) higher than the previous four years.
3.2. Global Comparisons of Ambient PM10 Concentrations
The annual average PM10 concentrations have increased 74% since 2010. Excluding 2010, since measurements are only for a seven month period, the annual average increased 61% since 2011. In contrast, PM10 concentrations in the US have shown a 34% decrease in the 24-hour average concentrations since 1999 and a 31% decrease in annual average ambient concentrations since 1990 (http://www.epa.gov/airtrends). The 2014 annual mean concentrations for PM10 in Curaçao (121.5 μg/m3) is among some of the highest concentrations reported globally, measuring approximately 13 times higher than those reported in Iceland (9 μg/m3), yet were two times lower than levels recorded in Pakistan (282 μg/m3).
3.3. PM10 Compliance with Public Health Guidelines
The maximum annual mean concentrations for PM10 that are currently recommended by Curaçao and the European Commission are 75 and 40 μg/m3, respectively. The annual mean concentrations for the years 2011 through 2014 exceeded the current PM10 guidelines recommended by the European Commission (40 μg/m3). Additionally, mean annual PM10 concentrations for 2013 (95.9 μg/m3) and 2014 (121.5 μg/m3) both exceeded the island’s guidelines for PM10 (75 μg/m3). Mean 24-hour maximum concentrations of PM10 have also been recommended by NAAQS (150 μg/m3), the European Commission (50 μg/m3) and Curaçao (150 μg/m3). The number of days that have exceeded the 24-hour daily maximum concentrations of PM10 has demonstrated strong increasing trends in this study (Figure 3). The majority of 2010 (82%), 2011 (64%), and 2012 (60%) were compliant with recommended guidelines for measured PM10 concentrations (Figure 4). Conversely, a total of 77% of 2013 and 85% of 2014 exceeded all recommended 24-hour guidelines for PM10 concentrations. Curaçao allows 5% of the calendar days to exceed 150 μg/m3; however, 10%, 22%, and 35% of 2012, 2013, 2014, respectively, exceeded this value .
3.4. Potential Risks of PM10 Inhalation
There are a number of epidemiologic studies reporting the associations of PM10 with various health outcomes, including mortality, morbidity and increased emergency room visits and hospitalization, though these results are difficult to interpret due to the inability of these studies to adequately control for confounding and the potential for exposure misclassification (Figures 5-7) - . This study primarily focused on literature published after 2010 since there are several meta-analyses and reviews covering literature published prior to 2010.
Figure 3. Number of days per year PM10 concentrations exceeded recommended guidelines. Strong increasing trends were observed for the number of days exceeding the European Commission’s recommended guidelines (R2 = 0.85) as well as recommendations by Curaçao and the NAAQS (R2 = 0.87). The current 24-hour maximum concentrations recommended by the European Commission, NAAQS and Curaçao are 50 µg/m3, 150 µg/m3 and 150 µg/m3, respectively.
Figure 4. Percentages of each year that were either in compliance or exceeded current maximum 24-hour guidelines for PM10 concentrations. Strong decreasing trend was observed in annual compliance.
The relative risk reported for various mortality demonstrate positive associations with PM10, however the data is somewhat inconsistent (Figure 5). For instance, two studies reported positive associations for respiratory mortality,
Figure 5. Relative risk estimates (95% CI) for PM10 associated mortality from published literature.
Figure 6. Relative risk estimates (95% CI) for PM10 associated morbidity and hospital admissions from published literature.
Figure 7. Hazard ratios (95% CI) for PM10 associated mortality and morbidity from published literature.
where only one was statistically significant . Liang et al. reported positive associations, with respiratory mortality (RR: 1.347, 95% CI: 0.990 - 1.833) during the winter months in Taiwan with a mean PM10 concentration of 66.7 μg/m3. However this association was not significant since the RR included unity and had a wide confidence interval range suggesting greater uncertainty. In contrast, a meta-analysis consisting of 26 studies in China with annual PM10 concentrations ranging from 44 - 156 μg/m3, reported positive associations between short-term PM10 exposure and respiratory mortality (RR: 1.0057, 95% CI: 1.004 - 1.0075), though the de minimis magnitude of effect makes this finding difficult to interpret .
Similarly, relative risks for cardio related mortality also demonstrated both significant and non-significant results with PM10 . For each 10 μg/m3 of PM10, some significant positive associations were reported for cardiovascular disease mortality (RR: 1.23, 95% CI: 1.19 - 1.26), ischemic heart disease mortality (RR: 1.37, 95% CI: 1.28 - 1.47) and heart failure mortality (RR: 1.11, 95% CI: 1.05 - 1.17) within a retrospective cohort, containing over 39,000 subjects from northern China , but these findings are unique. Liang et al. used a time-series regression model to analyze mortality among central Taiwan residents and reported non-significant positive associations during the winter months (mean PM10 of 66.7 μg/m3) between PM10 and cardiovascular mortality for residents less than 65 years of age (RR: 1.12, 95% CI: 0.998 - 1.258) and borderline, yet significant for residents greater than 65 years old (RR: 1.194; 95% CI: 1.0025 - 1.425). A meta-analysis in China also reported associations with short-term exposures to PM10 (annual means ranging from 44 - 156 μg/m3) and cardiopulmonary (RR: 1.0034; 95% CI: 1.0023 - 1.0046) and cardiovascular mortality (RR: 1.0049; 95% CI: 1.0034 - 1.0063) . Positive associations were also reported for all-cause and non-accidental mortality . All were significant with the exception of the study by Liang et al. which found a positive yet non-significant association between PM10 and all-cause mortality in Taiwan (RR: 1.059; 95% CI: 0.999 - 1.122). In addition, positive associations between lung cancer mortality and long-term PM10 exposures (RR: 1.05; 95% CI: 1.03 - 1.07) were found in a meta-analysis of 19 studies conducted globally . However, none of these measures of association achieved a magnitude of effect that clearly demonstrates a direct impact of PM on mortality in exclusion of other factors.
The relative risks reported for various morbidity and hospitalizations is much less convincing of positive associations with PM10 since many of the studies report near or include unity (Figure 6) . Significant positive associations were found in a number of studies between respiratory diseases, respiratory related hospital admissions and lung obstruction and PM10 (annual PM10 ranged 31 - 270 μg/m3). However, a study in the highly polluted industrial city of Lanzhou, China (PM10 daily mean: 197 μg/m3) reported positive, non-significant associations between PM10 and respiratory diseases (RR: 2.4, 95% CI: 0.5 - 4.2) and significant positive associations with pneumonia (RR: 5.3, 95% CI: 1.3 - 9.5) and upper respiratory tract infections in people less than 65 years of age (RR: 13.7, 95% CI: 2.5 - 26.2) . However, the confidence intervals are relatively wide suggesting increased uncertainty. Relative risks reported for incidences of lung cancer among two meta-analyses were also positive yet were not statistically significant since both included unity . The meta-analysis consisting of 60 studies from 1966-2014 by Wang et al. reported evidence of inconsistent, nonsignificant associations between short-term changes in PM10 and hemorrhagic stroke (RR: 1.009; 95% CI: 0.976 - 1.043), ischemic stroke (RR: 1.0; 95% CI: 0.976 - 1.024) and cerebrovascular disease (RR: 1.003; 95% CI: 0.999 - 1.008). A study in Scotland reported positive, nonsignificant associations between PM10 (20 - 22 μg/m3 mean annual PM10) and cardiovascular hospital admissions . In contrast, a study in China (44 - 156 μg/m3 mean annual PM10) and Iran (111.3 μg/m3 mean annual PM10) both reported significant positive associations with cardiovascular related hospital admissions .
Hazard ratios were also reported in a number of studies for various mortality and risks associated with PM10 - (Figure 7). In 2008, Puett et al. reported significant positive associations between PM10 and all-cause mortality (HR: 1.11; 95% CI: 1.01 - 1.23) and cardiovascular disease mortality (HR: 1.35; 95% CI: 1.03 - 1.77) in the Nurses’ Health Study consisting of 66,250 women with a mean age of 62 years. In 2009, Puett et al. reported nonsignificant results between PM10-2.5 and all-cause mortality (HR: 1.03; 95% CI: 0.89-1.18) and cardiovascular disease mortality (HR: 1.14; 95% CI: 0.73 - 1.77) also for the Nurses’ Health Study. It is important to note in the latter study PM2.5 was subtracted from PM10 concentrations suggesting the associations found with PM10 in the earlier study were potentially influenced by PM2.5. Nonsignificant results (HR: 1.22, 95% CI: 0.91 - 1.63) were found between long-term PM10 (13.5 - 48.1 μg/m3 annual PM10) exposure and cardiovascular disease mortality in twenty cohorts across 13 countries in Europe (ESCAPE Project) . In contrast, several studies found significant positive associations with cardio-related events. A prospective cohort consisting of 4800 women (mean age 55 years old) in Germany found significant positive associations between long-term PM10 (34.8 - 52.5 μg/m3 annual mean PM10) exposure and cardiopulmonary mortality (HR: 1.39, 95% CI: 1.17 - 1.64) . In addition, a study of 11 cohorts in the ESCAPE project reported a positive association (HR: 1.12, 95% CI: 1.01 - 1.25) with long-term PM10 (14 - 48 μg/m3 annual mean) exposure and coronary events .
A large cohort study in England consisting of over 800,000 patients, aged 40 - 89 years, reported associations (HR: 1.16, 95% CI: 1.12 - 1.21) between PM10 (19.7 μg/m3 annual mean) and respiratory mortality . Associations (HR: 1.023, 95% CI: 1.005 - 1.042) were also reported for a cohort of 71,000 middle aged Chinese men exposed to much higher concentrations of PM10 (104 μg/m3 annual mean) than those measured in the English cohort study . In contrast, the prospective cohort study in Germany reported nonsignificant associations (HR: 0.96, 95% CI: 0.6 - 1.53) with respiratory mortality in middle aged women .
A number of cohort studies in the USA, Germany, England, Norway and China have also reported inconsistent associations (HRs) between PM10 and lung cancer mortality . Associations were found between PM10 and lung cancer mortality in Norwegian women between the ages of 51 and 70 (HR: 1.22; 95% CI: 1.1 - 1.37) and between 71 and 90 (HR: 1.18; 95% CI: 1.04 - 1.33) . A German cohort study also reported associations (HR: 1.84; 95% CI: 1.23 - 2.74) in women with a mean age of 55, however the confidence interval range is large . In contrast, the USA, Norwegian and Chinese cohorts reported nonsignificant positive associations of PM10 and lung cancer mortality in men .
In summary, the epidemiological studies presented demonstrate some associations between health effects and PM10 although results are mixed, often presented with large amounts of uncertainty, and effect sizes on the level of minutiae. Cardiovascular and respiratory effects and mortality were observed in locations with annual mean concentrations ranging from 7.7 - 270 µg/m3. Potential inconsistencies between studies and results could be due to different PM10 constituents between geographical regions as well as various study designs and methodology, though there is an inherent inability of the cited studies to adequately control confounding and reliably assign area exposure estimates to individuals. The USEPA concluded that the evidence provided in the literature and the biological plausibility was suggestive of a causal relationship between short-term exposures to PM10-2.5 and cardiovascular effects, respiratory effects, mortality, yet there was inadequate evidence to suggest causative relationships with long-term exposures .
3.5. Environmental Factors and PM10 Concentrations
Daily temperature, humidity, precipitation and wind speeds were analyzed for trends and correlations with PM10 concentrations (Figure 8). The mean temperature (±standard deviation) from 2010 through 2014 was 27.9˚C (±1.2) and although Kruskal-Wallis multiple comparisons revealed annual differences (p < 0.000001) there were no observable trends (R2 = 0.0007). The mean humidity (77.7% ± 4.1%; R2 = 0.73) and precipitation (1.70 ± 6.9 mm; R2 = 0.75) from 2010 through 2014 both demonstrated moderately strong decreasing trends. Mean annual wind speeds (19.6 ± 4.7 km/h) demonstrated a strong increasing trend over time (R2 = 0.91). This is consistent with increasing global trends in wind speed . There was a weak to moderately strong correlation between PM10 concentrations and wind speed (Figure 9). There were no correlations found between PM10 and temperature (r = 0.04) and only a weak, negative correlation with humidity (r = −0.22).
Figure 8. Annual environmental parameters measured in Curaçao, 2010-2014. Trends are denoted with dash lines.
Figure 9. Regression analysis between daily PM10 (μg/m3) and wind speed measurements in Curaçao, 2010-2014. Regression bands represent 95% confidence limits.
The objectives of this investigation were to analyze levels of PM10 in ambient air surrounding Willemstad, Curaçao in order to determine if any temporal trends exist in the measured concentrations, verify if measured levels exceed current public health guidelines and to identify potential health risks. In conclusion, concentrations of PM10 in Curaçao are among the highest reported globally and demonstrate an increasing trend over time. Levels of PM10 exceeded the annual and 24-hour guidelines recommended by Curaçao, the European Commission, World Health Organization and the USEPA. Furthermore, both the 24-hour and annual mean concentrations of PM10 measured in Curaçao were within the ranges speculated by the USEPA to impact cardiovascular and respiratory outcomes and mortality as a result of short-term exposures. In addition, increasing wind speeds were correlated with increasing PM10 concentrations over time potentially impacting residents within the plume trajectory. However, as the epidemiological evidence is inadequate to infer causality between health effects and chronic, long-term exposures to PM10, the strongest conclusion that can be drawn from this analysis is that local emissions controls are inadequate to meet international PM10 public health standards.
Future research needs in Curaçao include expanding the air monitoring efforts to include areas upwind of the refinery as well as additional petrochemical emissions, including but not limited to sulfur dioxide, particulate matter (PM10 and PM2.5), benzene, as well as both the vapor and particulate phases of ambient PAHs. Additional environmental studies are encouraged to evaluate the extent of contamination in a variety of biota and matrices (i.e. water, sediment, and fish).
 Gotschi, T., Heinrich, J., Sunyer, J. and Künzli, N. (2008) Long-Term Effects of Ambient Air Pollution on Lung Function: A review. Epidemiology, 19, 690-701.
 Brook, R.D., et al. (2010) Particulate Matter Air Pollution and Cardiovascular Disease: An Update to the Scientific Statement from the American Heart Association. Circulation, 121, 2331-2378.
 Valavanidis, A., Fiotakis, K. and Vlachogianni, T. (2008) Airborne Particulate Matter and Human Health: Toxicological Assessment and Importance of Size and Composition of Particles for Oxidative Damage and Carcinogenic Mechanisms. Journal of Environmental Science and Health, Part C, 26, 339-362.
 Ravindra, K., Mittal, A.K. and Van Grieken, R. (2001) Health Risk Assessment of Urban Suspended Suspended Particulate Matter with Special Reference to Polycyclic Aromatic Hydrocarbons: A Review. Review on Environmental Health, 16, 169-189.
 WHO (2014) Mortality from Ambient Air Pollution.
 Burnett, R.T., et al. (2014) An Integrated Risk Function for Estimating the Global Burden of Disease Attributable to Ambient Fine Particulate Matter Exposure. Environmental Health Perspectives, 122, 397-403.
 DCLP (2014) SEI a Helping Hand for Environmental Requirements Smoc.
 Yang, Y., et al. (2013) The Association between Ambient Air Pollution and Daily Mortality in Beijing after the 2008 Olympics: A Time Series Study. PloS ONE, 8, e76759.
 Wang, Y., Eliot, M.N. and Wellenius, G.A. (2014) Short-Term Changes in Ambient Particulate Matter and Risk of Stroke: A Systematic Review and Meta-Analysis. Journal of the American Heart Association, 3, e000983.
 Hamra, G.B., et al. (2014) Outdoor Particulate Matter Exposure and Lung Cancer: A Systematic Review and Meta-Analysis. Environmental Health Perspectives, 122, 906-911.
 Lai, H.-K., Tsang, H. and Wong, C.-M. (2013) Meta-Analysis of Adverse Health Effects Due to Air Pollution in Chinese Populations. BMC Public Health, 13, 360.
 Park, H.Y., Bae, S. and Hong, Y.-C. (2013) PM10 Exposure and Non-Accidental Mortality in Asian Populations: A Meta-Analysis of Time-Series and Case-Crossover Studies. Journal of Preventive Medicine and Public Health, 46, 10-18.
 Mustafic, H., et al. (2012) Main Air Pollutants and Myocardial Infarction a Systematic Review and Meta-Analysis. Journal of the American Medical Association, 307, 713-721.
 Adamkiewicz, L., Gayer, A., Mucha, D., Badyda, A.J., Dabrowiecki, P. and Grabski, P. (2015) Relative Risk of Lung Obstruction in Relation to PM10 Concentration as Assessed by Pulmonary Function Tests. Advances in Experimental Medicine and Biology, 849, 83-91.
 An, X., Tao, Y., Mi, S., Hou, Q. and Sun, Z. (2015) Association between PK10 and Respiratory Hospital Admissions in Different Seasons in Heavily Polluted Lanzhou City. Journal of Environmental Health, 77, 64-71.
 Gharehchahi, E., et al. (2013) Health Impact Assessment of Air Pollution in Shiraz, Iran: A Two-Part Study. Journal of Environmental Health Science and Engineering, 11, 11.
 Zhang, L.-W., et al. (2014) Long-Term Exposure to High Particulate Matter Pollution and Cardiovascular Mortality: A 12-Year Cohort Study in Four Cities in Northern China. Environment International, 62, 41-47.
 Willocks, L.J., et al. (2012) Cardiovascular Disease and Air Pollution in Scotland: No Association or Insufficient Data and Study Design? BMC Public Health, 12, 227.
 Liang, W.-M., Wei, H.-Y. and Kuo, H.-W. (2009) Association between Daily Mortality from Respiratory and Cardiovascular Diseases and Air Pollution in Taiwan. Environmental Research, 109, 51-58.
 Heinrich, J., et al. (2013) Long-Term Exposure to NO2 and PM10 and All-Cause and Cause-Specific Mortality in a Prospective Cohort of Women. Occupational and Environmental Medicine, 70, 179-186.
 Puett, R.C., et al. (2009) Chronic Fine and Coarse Particulate Exposure, Mortality, and Coronary Heart Disease in the Nurses’ Health Study. Environmental Health Perspectives, 117, 1697-1701.
 Puett, R.C., et al. (2008) Chronic Particulate Exposure, Mortality, and Coronary Heart Disease in the Nurses’ Health Study. American Journal of Epidemiology, 168, 1161-1168.
 Puett, R.C., et al. (2014) Particulate Matter Air Pollution Exposure, Distance to Road, and Incident Lung Cancer in the Nurses’ Health Study Cohort. Environmental Health Perspectives, 122, 926-932.
 Beelen, R., et al. (2014) Effects of Long-Term Exposure to Air Pollution on Natural-Cause Mortality: An Analysis of 22 European Cohorts within the Multicentre ESCAPE Project. The Lancet, 383, 785-795.
 Beelen, R., et al. (2014) Long-Term Exposure to Air Pollution and Cardiovascular Mortality: An Analysis of 22 European Cohorts. Epidemiology, 25, 368-378.
 Zhou, M., Liu, Y., Wang, L., Kuang, X., Xu, X. and Kan, H. (2014) Particulate Air Pollution and Mortality in a Cohort of Chinese Men. Environmental Pollution, 186, 1-6.
 Atkinson, R.W., Carey, I.M., Kent, A.J., van Staa, T.P., Anderson, H.R. and Cook, D.G. (2013) Long-Term Exposure to Outdoor Air Pollution and Incidence of Cardiovascular Diseases. Epidemiology, 24, 44-53.
 Cesaroni, G., et al. (2014) Long Term Exposure to Ambient Air Pollution and Incidence of Acute Coronary Events: Prospective Cohort Study and Meta-Analysis in 11 European Cohorts from the ESCAPE Project. British Medical Journal, 348, f7412.
 Carey, I.M., Atkinson, R.W., Kent, A.J., van Staa, T., Cook, D.G. and Anderson, H.R. (2013) Mortality Associations with Long-Term Exposure to Outdoor Air Pollution in a National English Cohort. American Journal of Respiratory and Critical Care Medicine, 187, 1226-1233.
 Raaschou-Nielsen, O., et al. (2013) Air Pollution and Lung Cancer Incidence in 17 European Cohorts: Prospective Analyses from the European Study of Cohorts for Air Pollution Effects (ESCAPE). The Lancet Oncology, 14, 813-822.
 Naess, O., Nafstad, P., Aamodt, G., Claussen, B. and Rosland, P. (2007) Relation between Concentration of Air Pollution and Cause-Specific Mortality: Four-Year Exposures to Nitrogen Dioxide and Particulate Matter Pollutants in 470 Neighborhoods in Oslo, Norway. American Journal of Epidemiology, 165, 435-443.
 McDonnell, W.F., Nishino-Ishikawa, N., Petersen, F.F., Chen, L.H. and Abbey, D.E. (2000) Relationships of Mortality with the Fine and Coarse Fractions of Long-Term Ambient PM10 Concentrations in Nonsmokers. Journal of Exposure Analysis and Environmental Epidemiology, 10, 427-436.
 Beeson, W.L., Abbey, D.E. and Knutsen, S.F. (1998) Long-Term Concentrations of Ambient Air Pollutants and Incident Lung Cancer in California Adults: Results from the AHSMOG Study. Environmental Health Perspectives, 106, 813-822.