Methodological issues in studies of air pollution and reproductive health

In the past decade there have been an increasing number of scientific studies describing possible effects of air pollution on perinatal health. These papers have mostly focused on commonly monitored air pollutants, primarily ozone (O₃), particulate matter (PM), sulfur dioxide (SO₂), carbon monoxide (CO), and nitrogen dioxide (NO₂), and various indices of perinatal health, including fetal growth, pregnancy duration, and infant mortality. While most published studies have found some marker of air pollution related to some types of perinatal outcomes, variability exists in the nature of the pollutants and outcomes associated. Synthesis of the findings has been difficult for various reasons, including differences in study design and analysis. A workshop was held in September 2007 to discuss methodological differences in the published studies as a basis for understanding differences in study findings and to identify priorities for future research, including novel approaches for existing data. Four broad topic areas were considered: confounding and effect modification, spatial and temporal exposure variations, vulnerable windows of exposure, and multiple pollutants. Here we present a synopsis of the methodological issues and challenges in each area and make recommendations for future study. Two key recommendations include: (1) parallel analyses of existing data sets using a standardized methodological approach to disentangle true differences in associations from methodological differences among studies; and (2) identification of animal studies to inform important mechanistic research gaps. This work is of critical public health importance because of widespread exposure and because perinatal outcomes are important markers of future child and adult health.     

Indoor air quality in urban and rural kindergartens: short-term studies in Silesia,Poland

More than 80% of people living in urban areas who monitor air pollution are exposed to air quality levels that exceed limits defined by the World Health Organization (WHO). Although all regions of the world are affected, populations in low-income cities are the most impacted. According to average annual levels of fine particulate matter (PM2.5, ambient particles with aerodynamic diameter of 2.5 μm or less) presented in the urban air quality database issued by WHO in 2016, as many as 33 Polish cities are among the 50 most polluted cities in the European Union (EU), with Silesian cities topping the list. The aim of this study was to characterize the indoor air quality in Silesian kindergartens based on the concentrations of gaseous compounds (SO₂, NO₂), PM2.5, and the sum of 15 PM2.5-bound polycyclic aromatic hydrocarbons (PAHs), including PM2.5-bound benzo(a)pyrene (BaP), as well as the mutagenic activity of PM2.5 organic extracts in Salmonella assay (strains: TA98, YG1024). The assessment of the indoor air quality was performed taking into consideration the pollution of the atmospheric air (outdoor). I/O ratios (indoor/outdoor concentration) for each investigated parameter were also calculated. Twenty-four-hour samples of PM2.5, SO₂, and NO₂ were collected during spring in two sites in southern Poland (Silesia), representing urban and rural areas. Indoor samples were taken in naturally ventilated kindergartens. At the same time, in the vicinity of the kindergarten buildings, the collection of outdoor samples of PM2.5, SO₂, and NO₂ was carried out. The content of BaP and the sum of 15 studied PAHs was determined in each 24-h sample of PM2.5 (indoor and outdoor). In the urban site, statistically lower concentrations of SO₂ and NO₂ were detected indoors compared to outdoors, whereas in the rural site, such a relationship was observed only for NO₂. No statistically significant differences in the concentrations of PM2.5, PM2.5-bound BaP, and Σ15 PAHs in kindergartens (indoor) versus atmospheric (outdoor) air in the two studied areas were identified. Mutagenic effect of indoor PM2.5 samples was twice as low as in outdoor samples. The I/O ratios indicated that all studied air pollutants in the urban kindergarten originated from the ambient air. In the rural site concentrations of SO₂, PM2.5 and BaP in the kindergarten were influenced by internal sources (gas and coal stoves).     

New Jersey: a case study of the reduction in urban and suburban air pollution from the 1950s to 2010

Background: Air pollution has been a topic of intense concern and study for hundreds of years. During the second half of the 20th century, the United States implemented regulations and controls to reduce the levels of criteria air pollutants and achieve the National Ambient Air Quality Standards (NAAQS) for the protection of human health, while concurrently reducing the levels of toxic air pollutants.Objective: In this commentary we trace the changes in air pollution in New Jersey as a case study, demonstrating the impact of local, state, and federal strategies to control emissions of pollutants and pollutant precursors from the 1950s until today.Discussion: The original NAAQS (1970–1995) have been achieved, and significant progress has been made to achieve revised standards for ozone and particulate matter (PM) < 2.5 µm in aerodynamic diameter (PM_2.5) in New Jersey, which in the past was considered a highly polluted industrial state.Conclusions: Assuming no reversals on current regulations because of some major event or energy infrastructure disruption, outdoor air pollution reductions will continue to address health risks among specific segments of the general population affected by ozone/PM and pollution caused by neighborhood, local, and regional point and mobile sources.     

A novel method to construct an air quality index based on air pollution profiles

Background

Air quality indices based on the maximum of sub-indices of pollutants are easy to produce and help quantify the degree of air pollution. However, they discount the additive effects of multiple pollutants and are only sensitive to changes in highest sub-index.

Study on ambient air quality in Beijing for the summer 2008 Olympic Games

With the coming/approaching of the Olympic Games in 2008, air pollution in Beijing attracts the attention of government and people. The objective of this study is to define the air quality during the Olympic Games; we conducted the observation of SO₂, NO, CO, NO₂, O₃, and PM₁₀ from August 7 to September 30 in 2007 in Beijing. The results showed that the average daily concentrations of SO₂, NO₂, CO, and PM₁₀ during observation were 0.024, 0.072, 2.25, and 0.19 mg m⁻³, respectively. Compared with the National Ambient Air Quality Standard II, the concentrations of SO₂ and CO in the observation were low, the concentration of NO₂ basically satisfied the National Ambient Air Quality Standard II, and the concentrations of O₃ and PM₁₀ were much higher than the values of the standard. The characteristics of diurnal variation of NO, NO₂, CO, and PM₁₀ were similar, and the lower concentrations of these pollutants were observed by day and the higher concentrations at night. The concentration of SO₂ in the daytime was a little higher than that at night. The highest 1-h concentration of O₃ occurred at 14:00 local time.     

Respiratory Disease in Relation to Outdoor Air Pollution in Kanpur,India

ABSTRACT

This paper examines the effect of outdoor air pollution on respiratory disease in Kanpur, India, based on data from 2006. Exposure to air pollution is represented by annual emissions of sulfur dioxide (SO₂), particulate matter (PM), and nitrogen oxides (NO_x) from 11 source categories, established as a geographic information system (GIS)-based emission inventory in 2 km × 2 km grid. Respiratory disease is represented by number of patients who visited specialist pulmonary hospital with symptoms of respiratory disease. The results showed that (1) the main sources of air pollution are industries, domestic fuel burning, and vehicles; (2) the emissions of PM per grid are strongly correlated to the emissions of SO₂ and NO_x; and (3) there is a strong correlation between visits to a hospital due to respiratory disease and emission strength in the area of residence. These results clearly indicate that appropriate health and environmental monitoring, actions to reduce emissions to air, and further studies that would allow assessing the development in health status are necessary.

[Supplementary materials are available for this article. Go to the publisher's online edition of Archives of Environmental & Occupational Health for material on emission of SO₂, PM, NO_x from various sources, and total number of inhabitants, total number of patients in grid squares covering the Kanpur city.]     

Airborne particulate matter and premature deaths in urban Europe: the new WHO guidelines and the challenge ahead as illustrated by Spain

Twenty first century epidemiological publications on urban air pollution are confirming that inhalation of fine, airborne particulate matter (PM) has serious chronic human health effects and is a major cause of premature death worldwide. Recently updated recommendations by WHO identify three “Interim Targets” for the stepped reduction in PM levels within world cities in the quest to achieve an annual mean Air Quality Guideline (AQG) concentration of 20 μg/m³ for particles less than 10 microns in size (PM₁₀). In this paper we offer a perspective from Spain, a country with the longest record of reporting pollution data from large numbers of urban traffic sites to a central European database (AIRBASE). We can demonstrate that average annual PM concentrations at urban traffic monitoring stations in many European cities continue to be 50–100% above the WHO AQG, a situation exacerbated by high urban PM_2.5/10 ratios which indicate a dominance of finer, more deeply inhalable particles potentially more detrimental to health. Given that WHO has estimated in 2000 there were well over 250,000 premature deaths in Europe attributable to PM inhalation, such continuing high urban pollution levels are placing a huge burden on European medical resources.     

Characteristics of atmospheric trace gases, particulate matter, and heavy metal pollution in Dhaka, Bangladesh

Aerosol particulate matter (PM₁₀ and PM_2.5) and trace gases (SO₂, NO₂, CO and O₃) were sampled at five locations in greater Dhaka, Bangladesh, between January and April 2006. Particulate matter was collected on micro-fiber filters with a low-volume sampler, and trace gases (SO₂, NO₂, and O₃) were collected with an impinger equipped with PM samplers. Carbon monoxide was determined using the Indicator Tube method. The total average concentrations of SO₂, NO₂, CO, and O₃ were 48.3, 21.0, 166.0 and 28 μg m^–3, respectively. The total average concentrations of SO₂ and NO₂ were much lower than the annual average guideline values of the World Health Organization (WHO). The total average O₃ concentration was also much lower than the daily maximum values established by WHO (average of 100 μg m^–3 for an 8-h sample). The total average concentrations of five sites were 263, 75.5 and 66.2 μg m^–3 for SPM, PM₁₀ and PM_2.5, respectively. The mass of PM_2.5 is approximately 88% of the PM₁₀ mass, indicating that fossil fuel is the main source of PM in Dhaka. An atomic absorption spectrophotometer was used to determine the heavy metal concentrations in the PM_2.5 size fraction. The total average concentrations of As, Cd, Cu, Fe, Pb, and Zn in PM_2.5 were 6.3, 13, 94, 433, 204, and 381 ng m^–3, respectively. The Pb concentration in Dhaka shows a decreasing tendency, presumably due to the ban on the use of leaded fuel. The overall trace metal concentrations in Dhaka are higher than those in European (e.g., Spain, Norway) and East Asian (e.g., Taiwan) locations, but lower than those measured in Southeast Asian (Kanpur, Delhi, Mumbai, India; Lahore, Pakistan) cities.     

Physical Activity- and Alcohol-dependent Association Between Air Pollution Exposure and Elevated Liver Enzyme Levels: An Elderly Panel Study

Objectives:

The deleterious effects of air pollution on various health outcomes have been demonstrated. However, few studies have examined the effects of air pollution on liver enzyme levels.

Methods:

Blood samples were drawn up to three times between 2008 and 2010 from 545 elderly individuals who regularly visited a community welfare center in Seoul, Korea. Data regarding ambient air pollutants (particulate matter ≤2.5 μm [PM_2.5], nitrogen dioxide [NO₂], ozone [O₃], carbon monoxide, and sulfur dioxide) from monitoring stations were used to estimate air pollution exposure. The effects of the air pollutants on the concentrations of three liver enzymes (aspartate aminotransferase [AST], alanine aminotransferase [ALT], and γ-glutamyltranspeptidase [γ-GTP)]) were evaluated using generalized additive and linear mixed models.

Results:

Interquartile range increases in the concentrations of the pollutants showed significant associations of PM_2.5 with AST (3.0% increase, p=0.0052), ALT (3.2% increase, p=0.0313), and γ-GTP (5.0% increase, p=0.0051) levels; NO₂ with AST (3.5% increase, p=0.0060) and ALT (3.8% increase, p=0.0179) levels; and O₃ with γ-GTP (5.3% increase, p=0.0324) levels. Significant modification of these effects by exercise and alcohol consumption was found (p for interaction <0.05). The effects of air pollutants were greater in non-exercisers and heavy drinkers.

Conclusions:

Short-term exposure to air pollutants such as PM_2.5, NO₂, and O₃ is associated with increased liver enzyme levels in the elderly. These adverse effects can be reduced by exercising regularly and abstinence from alcohol.     

An assessment of air pollution and its attributable mortality in Ulaanbaatar, Mongolia

Epidemiologic studies have consistently reported associations between outdoor fine particulate matter (PM_2.5) air pollution and adverse health effects. Although Asia bears the majority of the public health burden from air pollution, few epidemiologic studies have been conducted outside of North America and Europe due in part to challenges in population exposure assessment. We assessed the feasibility of two current exposure assessment techniques, land use regression (LUR) modeling and mobile monitoring, and estimated the mortality attributable to air pollution in Ulaanbaatar, Mongolia. We developed LUR models for predicting wintertime spatial patterns of NO₂ and SO₂ based on 2-week passive Ogawa measurements at 37 locations and freely available geographic predictors. The models explained 74% and 78% of the variance in NO₂ and SO₂, respectively. Land cover characteristics derived from satellite images were useful predictors of both pollutants. Mobile PM_2.5 monitoring with an integrating nephelometer also showed promise, capturing substantial spatial variation in PM_2.5 concentrations. The spatial patterns in SO₂ and PM, seasonal and diurnal patterns in PM_2.5, and high wintertime PM_2.5/PM₁₀ ratios were consistent with a major impact from coal and wood combustion in the city’s low-income traditional housing (ger) areas. The annual average concentration of PM_2.5 measured at a centrally located government monitoring site was 75 μg/m³ or more than seven times the World Health Organization’s PM_2.5 air quality guideline, driven by a wintertime average concentration of 148 μg/m³. PM_2.5 concentrations measured in a traditional housing area were higher, with a wintertime mean PM_2.5 concentration of 250 μg/m³. We conservatively estimated that 29% (95% CI, 12–43%) of cardiopulmonary deaths and 40% (95% CI, 17–56%) of lung cancer deaths in the city are attributable to outdoor air pollution. These deaths correspond to nearly 10% of the city’s total mortality, with estimates ranging to more than 13% of mortality under less conservative model assumptions. LUR models and mobile monitoring can be successfully implemented in developing country cities, thus cost-effectively improving exposure assessment for epidemiology and risk assessment. Air pollution represents a major threat to public health in Ulaanbaatar, Mongolia, and reducing home heating emissions in traditional housing areas should be the primary focus of air pollution control efforts.     

Global review of national ambient air quality standards for PM10 and SO2 (24?h)

Literature comparing national ambient air quality standards (AAQSs) globally is scattered and sparse. Twenty-four hour AAQSs for particulate matter <10???m in aerodynamic diameter (PM₁₀) and sulfur dioxide (SO₂) in 96 countries were identified through literature review, an international survey, and querying an international legal database. Eighty three percent, of the 96 countries with information on the presence or absence of AAQSs, have 24-h AAQSs for either PM₁₀ or SO₂. Slightly more countries have 24-h AAQSs for SO₂ (76 countries) than PM₁₀ (69 countries). The average 24-h AAQSs for PM₁₀ and SO₂ are 95???g/m³ (95% confidence interval [CI], 82?C108???g/m³, n?=?68) and 182???g/m³ (95% CI, 158?C205???g/m³, n?=?73). The population-weighted average AAQS for PM₁₀ is 98 and 155???g/m³ for SO₂. The average AAQS for both PM₁₀ and SO₂ are substantially higher than the recommended World Health Organization Air Quality Guideline (WHO AQG) value. Several countries have promulgated AAQSs at the WHO AQG value for PM₁₀, but none for SO₂. Further examination in selected countries found that air quality monitoring data, existing AAQSs in other countries, environmental epidemiology studies, and the WHO AQGs are considered the most often in establishing or revising AAQSs.     

Air quality assessment in Algiers city

Very few studies related with the assessment and research of air pollutants have been initiated in Algiers, which is the political and economic capital of Algeria. This lack of studies is mainly due to the non-access and insufficiency of data, and also the failure of the air quality monitoring stations during the last years. For those reasons, the use of modeling tools can be useful to assess the air pollution levels and compare different control options. The main aim of this paper is to identify anthropogenic emission sources (road traffic, industrial, residential, and waste) which are considered key sources of air pollution in the greater Algiers, and to estimate the concentration levels of suspended particles with diameter ? 10 μm (PM10) and nitrogen dioxide (NO₂) over the studied area during 2012. For this purpose, The Air Pollution Model (TAPM) was used. The results indicate that meteorology statistical measures present a perfect agreement between measured and predicted values. The index of agreement (IOA) for wind speed and its components is above 0.65, for temperature is 0.99, while for the air pollution, the comparison of predicted concentrations with measured ones shows similar results. The maximum concentration levels for PM10 (122 μg/m³) and for NO₂ (91 μg/m³) are higher than the values established by national and international legislation, and the industrial districts are more affected by air pollution than the urban areas.     

Short-term association between sulfur dioxide and daily mortality: The Public Health and Air Pollution in Asia (PAPA) study

Sulfur dioxide (SO₂) has been associated with increased mortality and morbidity, but only few studies were conducted in Asian countries. Previous studies suggest that SO₂ may have adverse health effects independent of other pollutants. In the Public Health and Air Pollution in Asia (PAPA) project, the short-term associations between ambient sulfur dioxide (SO₂) and daily mortality were examined in Bangkok, Thailand, and three Chinese cities: Hong Kong, Shanghai, and Wuhan. Poisson regression models incorporating natural spline smoothing functions were used to adjust for seasonality and other time-varying covariates. Effect estimates were obtained for each city and then for the cities combined. The impact of alternative model specifications, such as lag structure of pollutants and degree of freedom (df) for time trend, on the estimated effects of SO₂ were also examined. In both individual-city and combined analysis, significant effects of SO₂ on total non-accidental and cardiopulmonary mortality were observed. An increase of 10 μg/m³ of 2-day moving average concentrations of SO₂ corresponded to 1.00% [95% confidence interval (CI), 0.75-1.24], 1.09% (95% CI, 0.71-1.47), and 1.47% (95% CI, 0.85-2.08) increase of total, cardiovascular and respiratory mortality, respectively, in the combined analysis. Sensitivity analyzes suggested that these findings were generally insensitive to alternative model specifications. After adjustment for PM₁₀ or O₃, the effect of SO₂ remained significant in three Chinese cities. However, adjustment for NO₂ diminished the associations and rendered them statistically insignificant in all four cities. In conclusion, ambient SO₂ concentration was associated with daily mortality in these four Asian cities. These associations may be attributable to SO₂ serving as a surrogate of other substances. Our findings suggest that the role of outdoor exposure to SO₂ should be investigated further in this region.     

“Air pollution in Delhi: Its Magnitude and Effects on Health”

Air pollution is responsible for many health problems in the urban areas. Of late, the air pollution status in Delhi has undergone many changes in terms of the levels of pollutants and the control measures taken to reduce them. This paper provides an evidence-based insight into the status of air pollution in Delhi and its effects on health and control measures instituted. The urban air database released by the World Health Organization in September 2011 reported that Delhi has exceeded the maximum PM10 limit by almost 10-times at 198 μg/m3. Vehicular emissions and industrial activities were found to be associated with indoor as well as outdoor air pollution in Delhi. Studies on air pollution and mortality from Delhi found that all-natural-cause mortality and morbidity increased with increased air pollution. Delhi has taken several steps to reduce the level of air pollution in the city during the last 10 years. However, more still needs to be done to further reduce the levels of air pollution.     

The University of Akron Study on Air Pollution and Human Health Effects I. Methodology,Baseline Data,and Aerometrics

This study determined the health effects of ambient air pollutants in two grade school populations in Akron, Ohio. One school is adjacent to industry and has elevated levels of sulfur dioxide (SO₂) and moderate levels of nitrogen dioxide (NO₂), while the other school is 4 km east and unpolluted. This study was designed in this manner for two purposes: (1) to identify and monitor ambient levels of air pollutants in an area proximal to the grade school so that the levels could be accurately assessed, and (2) to determine baseline pulmonary function values and questionnaire responses from the parents indicating any acute and/or chronic respiratory problem in the child. Ninety-five percent of the children enrolled in this study lived within 2 km of the schools and aerometric stations, thus providing for careful control in the study design.

The results of this study indicate that SO₂ and NO₂ levels are significantly higher in the school adjacent to industry. Although pulmonary function data were not significantly different between schools, the frequency of questionnaire responses to acute and chronic pulmonary problems was greater in the children at the school adjacent to industry. The data tend to indicate early pulmonary effects of air pollution in children living adjacent to industry and exposed to elevated levels of SO₂ and NO₂. We suggest that additional longitudinal work that carefully monitors total suspended particulates, NO₂, SO₂, and health data should be conducted to confirm these results.     

深圳市空气污染与居民心血管疾病发病相关性的研究

目的探讨空气污染物〔可吸入颗粒物（PM10）、二氧化硫（SO2）、二氧化氮（NO2）、臭氧（O3）〕对心血管疾病门诊病人量和住院病人量的影响。方法收集深圳市中心区两大型综合医院的门诊量和住院病人量资料及同时期空气污染物浓度、气象监测资料,运用时间序列法进行回归分析,研究深圳中心城区2006年1月1日至12月31日空气污染物与居民心血管疾病发病的关系。结果空气污染物PM10、SO2、O3与医院住院病人量有一定相关性,随着污染物浓度的增加,医院的心血管内科住院病人量增加,并且有统计学意义。其中在空气污染严重的11、12月份心血管疾病的住院病人量最高。结论空气中PM10、SO2和O3是心血管疾病发病的环境病因,其中以O3影响最大。     

Associations between daily mortalities from respiratory and cardiovascular diseases and air pollution in Hong Kong, China

Objective: To investigate the association between ambient concentrations of air pollutants and respiratory and cardiovascular mortalities in Hong Kong.

Methods: Retrospective ecological study. A Poisson regression of concentrations of daily air pollutants on daily mortalities for respiratory and cardiovascular diseases in Hong Kong from 1995 to the end of 1998 was performed using the air pollution and health: the European approach (APHEA) protocol. The effects of time trend, seasonal variations, temperature, and humidity were adjusted. Autocorrelation and overdispersion were corrected. Daily concentrations of nitrogen dioxide (NO₂), sulphur dioxide (SO₂), ozone (O₃), and particulate matter <10 µm in aerodynamic diameter (PM₁₀) were averaged from eight monitoring stations in Hong Kong. Relative risks (RRs) of respiratory and cardiovascular mortalities (per 10 µg/m³ increase in air pollutant concentration) were calculated.

Results: Significant associations were found between mortalities for all respiratory diseases and ischaemic heart diseases (IHD) and the concentrations of all pollutants when analysed singly. The RRs for all respiratory mortalities (for a 10 µg/m³ increase in the concentration of a pollutant) ranged from 1.008 (for PM₁₀) to 1.015 (for SO₂) and were higher for chronic obstructive pulmonary diseases (COPD) with all pollutants except SO₂, ranging from 1.017 (for PM₁₀) to 1.034 (for O₃). RRs for IHD ranged from 1.009 (for O₃) to 1.028 (for SO₂). In a multipollutant model, O₃ and SO₂ were significantly associated with all respiratory mortalities, whereas NO₂ was associated with mortality from IHD. No interactions were detected between any of the pollutants or with the winter season. A dose-response effect was evident for all air pollutants. Harvesting was not found in the short term.

Conclusions: Mortality risks were detected at current ambient concentrations of air pollutants. The associations with the particulates and some gaseous pollutants when analysed singly were consistent with many reported in temperate countries. PM₁₀ was not associated with respiratory or cardiovascular mortalities in multipollutant analyses.

     

Air pollution and associated respiratory morbidity in Delhi

As a rapidly expanding centre of government, trade, commerce and industry, Delhi, the Indian capital, presents an instructive location for studying the possible association between air pollution and adverse health effects. This study tries to determine the association, if any, between the air pollutants—sulphur dioxide, nitrogen dioxide, carbon monoxide, ozone, suspended particulate matter and respiratory suspended particulate matter—and daily variations in respiratory morbidity in Delhi during the years 2004–2005. Data analysis was based on the Generalized Additive Poisson regression model including a Lowess smoothing function for the entire patient population and subgroups defined by season. The best fitting lag period for each pollutant was found by testing its concentration at varying lags. The model demonstrated associations between daily visits and some of the pollutants (O₃, NO₂ and RSPM) but their strongest components were observed at varying lags. A single pollutant model showed that a 10 μg m⁻³ rise in pollutant level led to statistically significant relative risks (RR): 1.033 for O₃, 1.004 for NO₂, 1.006 for RSPM. The effect of particulate was relatively low, presumably because unlike other pollutants, particulate matter is not a single pollutant but rather a class of pollutants. This study, continued on a long term basis, can provide guidelines for anticipation/preparedness in the management of health care and hospital admissions.     

Socioeconomic disparities in air pollution-associated mortality

This study aimed to determine whether individuals with lower socioeconomic status (SES) were more susceptible to the acute effects of ambient air pollution than those with higher SES. We included 24,357 Hong Kong Chinese aged 30 or above who died of natural causes in 1998. Information on individual socioeconomic characteristics was obtained by interviewing proxy informants with a standardized questionnaire in all four death registries. Individual SES was indicated by three measures: type of housing, occupational group and education attainment. Poisson regression was performed to assess the short-term effects of ambient air pollution measured by PM₁₀, NO₂, SO₂ and O₃ on mortality for each SES group. The differences in the effects between SES groups were estimated by the interaction between air pollution and SES. We found that PM₁₀ and NO₂ were associated with greater risk of mortality on people living in public rental housing than in private housing. The effects of all four pollutants were significantly greater in blue-collar workers than the never-employed and white-collar groups (p<0.05). However, we found no compelling evidence of effect modification by education attainment. Our results provide new evidence on the role of individual's SES as effect modifiers of the short-term effects of air pollution on mortality. The reduction of risks associated with air pollution for socially disadvantaged populations should be a high priority in public health and environmental policies.     

Social disadvantage, air pollution, and asthma physician visits in Toronto, Canada

Background

Previous research demonstrates that ambient air pollution exacerbates asthma. Asthma morbidity also varies with socioeconomic position (SEP). Few studies have examined if ambient air pollution has a differential impact on income subgroups of the population. This paper investigates socioeconomic variation in ambulatory physician consultations for asthma and assesses possible effect modification of SEP on the association between physician visits and air pollution for children aged 1-17 and adults aged 18-64 in Toronto, Canada, between 1992 and 2001.

Methods

Generalized additive models and generalized linear models were used to estimate the adjusted risk of asthma physician visits associated with an interquartile range increase in sulfur dioxide (SO₂), nitrogen dioxide (NO₂), particulate matter (PM_2.5), and ozone (O₃).

Results

A socioeconomic gradient in the number of physician visits was observed among children and adults and both sexes. SO₂, NO₂, and PM_2.5 had positive associations with physician visits. The risk ratios for the low socioeconomic group were significantly greater than those for the high socioeconomic group in several of the models of SO₂ and PM_2.5.

Conclusions

These findings suggest increased ambulatory physician visits represent another component of the public health impact of urban air pollution. The burden of this impact may be borne disproportionately by those with lower SEP. Clarifying the role of SEP in altering susceptibility to the effects of air pollution is essential not only to inform revisions of ambient air quality standards, but also to design public health interventions to reduce health impacts on sensitive subgroups of the population.