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Current day concentrations of ambient air pollution have been associated with a range of adverse health effects, particularly mortality and morbidity due to cardiovascular and respiratory diseases. In this review, we summarize the evidence from epidemiological studies on long-term exposure to fine and coarse particles, nitrogen dioxide (NO 2 ) and elemental carbon on mortality from all-causes, cardiovascular disease and respiratory disease. We also summarize the findings on potentially susceptible subgroups across studies. We identified studies through a search in the databases Medline and Scopus and previous reviews until January 2013 and performed a meta-analysis if more than five studies were available for the same exposure metric. There is a significant number of new studies on long-term air pollution exposure, covering a wider geographic area, including Asia. These recent studies support associations found in previous cohort studies on PM 2.5 . The pooled effect estimate expressed as excess risk per 10 μg/m 3 increase in PM 2.5 exposure was 6% (95% CI 4, 8%) for all-cause and 11% (95% CI 5, 16%) for cardiovascular mortality. Long-term exposure to PM 2.5 was more associated with mortality from cardiovascular disease (particularly ischemic heart disease) than from non-malignant respiratory diseases (pooled estimate 3% (95% CI −6, 13%)). Significant heterogeneity in PM 2.5 effect estimates was found across studies, likely related to differences in particle composition, infiltration of particles indoors, population characteristics and methodological differences in exposure assessment and confounder control. All-cause mortality was significantly associated with elemental carbon (pooled estimate per 1 μg/m 3 6% (95% CI 5, 7%)) and NO 2 (pooled estimate per 10 μg/m 3 5% (95% CI 3, 8%)), both markers of combustion sources. There was little evidence for an association between long term coarse particulate matter exposure and mortality, possibly due to the small number of studies and limitations in exposure assessment. Across studies, there was little evidence for a stronger association among women compared to men. In subjects with lower education and obese subjects a larger effect estimate for mortality related to fine PM was found, though the evidence for differences related to education has been weakened in more recent studies.

Several studies have linked long-term exposure to particulate air pollution with increased cardiopulmonary mortality; only two have also examined incident circulatory disease. To examine associations of individualized long-term exposures to particulate and gaseous air pollution with incident myocardial infarction and stroke, as well as all-cause and cause specific mortality. We estimated long-term residential air pollution exposure for more than 100,000 participants in the California Teachers Study, a prospective cohort of female public school professionals.We linked geocoded residential addresses with inverse distance-weighted monthly pollutant surfaces for two measures of particulate matter and for several gaseous pollutants. We examined associations between exposure to these pollutants and risks of incident myocardial infarction and stroke, and of all-cause and cause-specific mortality, using Cox proportional hazards models. We found elevated hazard ratios linking long-term exposure to particulate matter less than 2.5 μm in aerodynamic diameter (PM2.5), scaled to an increment of 10 μg/m3 with mortality from ischemic heart disease (IHD) (1.20; 95% confidence interval [CI], 1.02-1.41) and, particularly among postmenopausal women, incident stroke (1.19; 95% CI, 1.02-1.38). Long-term exposure to particulate matter less than 10 μm in aerodynamic diameter (PM10) was associated with elevated risks for IHD mortality (1.06; 95% CI, 0.99-1.14) and incident stroke (1.06; 95% CI, 1.00-1.13), while exposure to nitrogen oxides was associated with elevated risks for IHD and all cardiovascular mortality. This study provides evidence linking long-term exposure to PM2.5 and PM10 with increased risks of incident stroke as well as IHD mortality; exposure to nitrogen oxides was also related to death from cardiovascular diseases.

Objectives. We quantified health benefits of transportation strategies to reduce greenhouse gas emissions (GHGE). Methods. Statistics on travel patterns and injuries, physical activity, fine particulate matter, and GHGE in the San Francisco Bay Area, California, were input to a model that calculated the health impacts of walking and bicycling short distances usually traveled by car or driving low-emission automobiles. We measured the change in disease burden in disability-adjusted life years (DALYs) based on dose–response relationships and the distributions of physical activity, particulate matter, and traffic injuries. Results: Increasing median daily walking and bicycling from 4 to 22 minutes reduced the burden of cardiovascular disease and diabetes by 14% (32 466 DALYs), increased the traffic injury burden by 39% (5907 DALYS), and decreased GHGE by 14%. Low-carbon driving reduced GHGE by 33.5% and cardiorespiratory disease burden by less than 1%. Conclusions: Increased physical activity associated with active transport could generate a large net improvement in population health. Measures would be needed to minimize pedestrian and bicyclist injuries. Together, active transport and low-carbon driving could achieve GHGE reductions sufficient for California to meet legislative mandates.

Background: Epidemiologic studies have demonstrated an association between acute exposure to ambient fine particles and both mortality and morbidity. Less is known about the relative impacts of the specific chemical constituents of particulate matter < 2.5 μm in aerodynamic diameter$({\\rm PM}_{2.5})$on hospital admissions. Objective: This study was designed to estimate the risks of exposure to${\\rm PM}_{2.5}$and several species on hospital admissions for respiratory diseases among children. Data and methods: We obtained data on daily counts of hospitalizations for children < 19 and < 5 years of age for total respiratory diseases and several subcategories including pneumonia, acute bronchitis, and asthma for six California counties from 2000 through 2003, as well as ambient concentrations of${\\rm PM}_{2.5}$and its constituents, including elemental carbon (EC), organic carbon (OC), and nitrates (NO₃). We used Poisson regression to estimate risks while controlling for important covariates. Results: We observed associations between several components of${\\rm PM}_{2.5}$and hospitalization for all of the respiratory outcomes examined. For example, for total respiratory admissions for children < 19 years of age, the interquartile range for a 3-day lag of${\\rm PM}_{2.5}$, EC, OC, NO₃, and sulfates was associated with an excess risk of 4.1% [95% confidence interval (CI), 1.8-6.4], 5.4% (95% CI, 0.8-10.3), 3.4% (95% CI, 1.1-5.7), 3.3% (95% CI, 1.1-5.5), and 3.0% (95% CI, 0.4-5.7), respectively. We also observed associations for several metals. Additional associations with several of the species, including potassium, were observed in the cool season. Conclusion: Components of${\\rm PM}_{2.5}$were associated with hospitalization for several childhood respiratory diseases including pneumonia, bronchitis, and asthma. Because exposure to components (e.g., EC, OC, NO₃, and K) and their related sources, including diesel and gasoline exhaust, wood smoke, and other combustion sources, are ubiquitous in the urban environment, it likely represents an identifiable and preventable risk factor for hospitalization for children.

Background Indonesian peatlands have been drained for agricultural development for several decades. This development has made a major contribution to economic development. At the same time, peatland drainage is causing significant air pollution resulting from peatland fires. Peatland fires occur every year, even though their extent is much larger in dry (El Niño) years. We examine the health effects of long-term exposure to fine particles (PM 2.5 ) from all types of peatland fires (including the burning of above and below ground biomass) in Sumatra and Kalimantan, where most peatland fires in Indonesia take place. Methods We derive PM 2.5 concentrations from satellite imagery calibrated and validated with Indonesian Government data on air pollution, and link increases in these concentrations to peatland fires, as observed in satellite imagery. Subsequently, we apply available epidemiological studies to relate PM 2.5 exposure to a range of health outcomes. The model utilizes the age distribution and disease prevalence of the impacted population. Results We find that PM 2.5 air pollution from peatland fires, causes, on average, around 33,100 adults and 2900 infants to die prematurely each year from air pollution. In addition, peatland fires cause on average around 4390 additional hospitalizations related to respiratory diseases, 635,000 severe cases of asthma in children, and 8.9 million lost workdays. The majority of these impacts occur in Sumatra because of its much higher population density compared to Kalimantan. A main source of uncertainty is in the Concentration Response Functions (CRFs) that we use, with different CRFs leading to annual premature adult mortality ranging from 19,900 to 64,800 deaths. Currently, the population of both regions is relatively young. With aging of the population over time, vulnerabilities to air pollution and health effects from peatland fires will increase. Conclusions Peatland fire health impacts provide a further argument to combat fires in peatlands, and gradually transition to peatland management models that do not require drainage and are therefore not prone to fire risks.

Background: Several studies have reported associations between long-term exposure to ambient fine particulate matter (PM) and cardiovascular mortality. However, the health impacts of long-term exposure to specific constituents of ${\\rm PM}_{2.5}$ (PM with aerodynamic diameter ≤ 2.5 μm) have not been explored. Methods: We used data from the California Teachers Study, a prospective cohort of active and former female public school professionals. We developed estimates of long-term exposures to ${\\rm PM}_{2.5}$ and several of its constituents, including elemental carbon, organic carbon (OC), sulfates, nitrates, iron, potassium, silicon, and zinc. Monthly averages of exposure were created using pollution data from June 2002 through July 2007. We included participants whose residential addresses were within 8 and 30 km of a monitor collecting ${\\rm PM}_{2.5}$ constituent data. Hazard ratios (HRs) were estimated for long-term exposure for mortality from all nontraumatic causes, cardiopulmonary disease, ischemic heart disease (IHD), and pulmonary disease. Results: Approximately 45,000 women with 2,600 deaths lived within 30 km of a monitor. We observed associations of all-cause, cardiopulmonary, and IHD mortality with ${\\rm PM}_{2.5}$ mass and each of its measured constituents, and between pulmonary mortality and several constituents. For example, for cardiopulmonary mortality, HRs for interquartile ranges of ${\\rm PM}_{2.5}$, OC, and sulfates were 1.55 [95% confidence interval (CI), 1.43-1.69], 1.80 (95% CI, 1.68-1.93), and 1.79 (95% CI, 1.58-2.03), respectively. Subsequent analyses indicated that, of the constituents analyzed, OC and sulfates had the strongest associations with all four outcomes. Conclusions: Long-term exposures to ${\\rm PM}_{2.5}$ and several of its constituents were associated with increased risks of all-cause and cardiopulmonary mortality in this cohort. Constituents derived from combustion of fossil fuel (including diesel), as well as those of crustal origin, were associated with some of the greatest risks. These results provide additional evidence that reduction of ambient ${\\rm PM}_{2.5}$ may provide significant public health benefits.

Background: Elevated temperature has been associated with increased mortality. Few epidemiologic studies, however, have considered air pollutants as potential confounders or effect modifiers. None has focused on California, where the climate is generally mild and pollution levels tend to be high--an ideal setting to examine the independent effect of temperature from air pollution. Methods: We examined the association between mean daily apparent temperature and nonaccidental mortality in 9 counties throughout California from May to September 1999-2003. Data were obtained from the National Climatic Data Center (temperature and relative humidity), the California Department of Health Services (mortality), and the California Air Resources Board (particulate matter, ozone, carbon monoxide, and nitrogen dioxide). We conducted a time-stratified case-crossover study, with a time-series analysis as a sensitivity analysis, adjusting for day of the week using both methods and adjusting for time trend in the time-series analysis. We first obtained county-specific estimates and then combined them using meta-analytic methods. Results: A total of 248,019 deaths were included. Each 10° (Fahrenheit) increase in same-day mean apparent temperature corresponded to a 2.3% increase in mortality (95% confidence interval = 1.0%-3.6%) in the case-crossover analysis for all 9 counties combined, with nearly identical results produced from the time-series analysis. No air pollutant examined was found to be a significant confounder or effect modifier. Conclusions: Even without extremes in apparent temperature, we observed an association between temperature and mortality in California that was independent of air pollution.

Background: Green spaces are reported to improve health status, including beneficial effects on pregnancy outcomes. Despite the suggestions of air pollution-related health benefits of green spaces, there is no available evidence on the impact of greenness on personal exposure to air pollution. Objectives: We investigated the association between surrounding greenness and personal exposure to air pollution among pregnant women and to explore the potential mechanisms, if any, behind this association. Methods: In total, 65 rounds of sampling were carried out for 54 pregnant women who resided in Barcelona during 2008-2009. Each round consisted of a 2-day measurement of particulate matter with aerodynamic diameter ≤ 2.5 μm (PM₂.₅) and a 1-week measurement of nitric oxides collected simultaneously at both the personal and microenvironmental levels. The study participants were also asked to fill out a time-microenvironment-activity diary during the sampling period. We used satellite retrievals to determine the surrounding greenness as the average of Normalized Difference Vegetation Index (NDVI) in a buffer of 100 m around each maternal residential address. We estimated the impact of surrounding greenness on personal exposure levels, home-outdoor and homeindoor pollutant levels, and maternal time-activity. Results: Higher residential surrounding greenness was associated with lower personal, homeindoor, and home-outdoor PM₂.₅ levels, and more time spent at home-outdoor. Conclusions: We found lower levels of personal exposure to air pollution among pregnant women residing in greener areas. This finding may be partly explained by lower home-indoor pollutant levels and more time spent in less polluted home-outdoor environment by pregnant women in greener areas.

Objective: Several epidemiologic studies provide evidence of an association between daily mortality and particulate matter$< 2.5 \\mu m$in diameter (PM2.5). Little is known, however, about the relative effects of PM2.5constituents. We examined associations between 19 PM2.5components and daily mortality in six California counties. Design: We obtained daily data from 2000 to 2003 on mortality and PM2.5mass and components, including elemental and organic carbon (EC and OC), nitrates, sulfates, and various metals. We examined associations of PM2.5and its constituents with daily counts of several mortality categories: all-cause, cardiovascular, respiratory, and mortality age > 65 years. Poisson regressions incorporating natural splines were used to control for time-varying covariates. Effect estimates were determined for each component in each county and then combined using a random-effects model. Results: PM2.5mass and several constituents were associated with multiple mortality categories, especially cardiovascular deaths. For example, for a 3-day lag, the latter increased by 1.6, 2.1, 1.6, and 1.5% for PM2.5, EC, OC, and nitrates based on interquartile ranges of 14.6, 0.8, 4.6, and$5.5 \\mu g/m^3$, respectively. Stronger associations were observed between mortality and additional pollutants, including sulfates and several metals, during the cool season. Conclusion: This multicounty analysis adds to the growing body of evidence linking PM2.5with mortality and indicates that excess risks may vary among specific PM2.5components. Therefore, the use of regression coefficients based on PM2.5mass may underestimate associations with some PM2.5components. Also, our findings support the hypothesis that combustion-associated pollutants are particularly important in California.

Objective Quantitative estimates of air pollution health impacts have become an increasingly critical input to policy decisions. The WHO project “Health risks of air pollution in Europe—HRAPIE” was implemented to provide the evidence-based concentration–response functions for quantifying air pollution health impacts to support the 2013 revision of the air quality policy for the European Union (EU). Methods A group of experts convened by WHO Regional Office for Europe reviewed the accumulated primary research evidence together with some commissioned reviews and recommended concentration–response functions for air pollutant–health outcome pairs for which there was sufficient evidence for a causal association. Results The concentration–response functions link several indicators of mortality and morbidity with short- and long-term exposure to particulate matter, ozone and nitrogen dioxide. The project also provides guidance on the use of these functions and associated baseline health information in the cost–benefit analysis. Conclusions The project results provide the scientific basis for formulating policy actions to improve air quality and thereby reduce the burden of disease associated with air pollution in Europe.