Acute Effects of Ambient Particulate Matter on Mortality: APHENA Study
Acute Effects of Ambient Particulate Matter on Mortality: APHENA Study
Background: The APHENA (Air Pollution and Health: A Combined European and North American Approach) study is a collaborative analysis of multicity time-series data on the effect of air pollution on population health, bringing together data from the European APHEA (Air Pollution and Health: A European Approach) and U.S. NMMAPS (National Morbidity, Mortality and Air Pollution Study) projects, along with Canadian data.
Objectives: The main objective of APHENA was to assess the coherence of the findings of the multicity studies carried out in Europe and North America, when analyzed with a common protocol, and to explore sources of possible heterogeneity. We present APHENA results on the effects of particulate matter (PM) ≤ 10 µm in aerodynamic diameter (PM10) on the daily number of deaths for all ages and for those < 75 and ≥ 75 years of age. We explored the impact of potential environmental and socioeconomic factors that may modify this association.
Methods: In the first stage of a two-stage analysis, we used Poisson regression models, with natural and penalized splines, to adjust for seasonality, with various degrees of freedom. In the second stage, we used meta-regression approaches to combine time-series results across cites and to assess effect modification by selected ecologic covariates.
Results: Air pollution risk estimates were relatively robust to different modeling approaches. Risk estimates from Europe and United States were similar, but those from Canada were substantially higher. The combined effect of PM10 on all-cause mortality across all ages for cities with daily air pollution data ranged from 0.2% to 0.6% for a 10-µg/m increase in ambient PM10 concentration. Effect modification by other pollutants and climatic variables differed in Europe and the United States. In both of these regions, a higher proportion of older people and higher unemployment were associated with increased air pollution risk.
Conclusions: Estimates of the increased mortality associated with PM air pollution based on the APHENA study were generally comparable with results of previous reports. Overall, risk estimates were similar in Europe and in the United States but higher in Canada. However, PM10 effect modification patterns were somewhat different in Europe and the United States.
Hundreds of time-series studies worldwide provide compelling evidence of the health effects of short-term exposure to air pollution. These studies also pose problems of interpretation due to variation in analytic methods and reporting, and the possibility of publication and analytic bias. Meta-analyses of published results can provide information about patterns in the relative rates of mortality and morbidity and evidence as to the causes of their spatial variation, but they inherit many of the same limitations of the individual studies. Coordinated multicity studies, designed partly to address these issues, have now been conducted in Europe and North America (Atkinson et al. 2001; Bell et al. 2004; Burnett and Goldberg 2003; Burnett et al. 1998, 2000; Gryparis et al. 2004; Katsouyanni et al. 1997, 2001; Samet et al. 2000a, 2000b, 2000c) and currently provide the most valid epidemiologic evidence of the effects of short-term exposure. The results of these studies appear broadly similar, but their methods and data characteristics differ, precluding definitive conclusions about their quantitative consistency and about the extent of and reasons for differences in the magnitude of the effects of short-term exposure among regions of the world.
APHENA (Air Pollution and Health: A Combined European and North American Approach) is a collaborative study among investigators involved in the European APHEA (Air Pollution and Health: A European Approach) study (Atkinson et al. 2001; Gryparis et al. 2004; Katsouyanni et al. 1997, 2001) and the U.S. NMMAPS (National Morbidity, Mortality and Air Pollution Study) study (Bell et al. 2004; Samet et al. 2000a, 2000b, 2000c), as well as Canadian studies (Burnett and Goldberg 2003; Burnett et al. 1998, 2000). APHENA addresses the short-term health effects of particulate matter (PM) ≤ 10 µm in aerodynamic diameter (PM10) and ozone on daily mortality and hospital admissions. The project originated at a time when the results of the multicity analyses, including APHEA and NMMAPS, were being reported and considered in the development of ambient air quality standards for PM (European Commission 1999; World Health Organization 2004, 2006). The main objective of the project was to assess the coherence of the findings of the multicity studies carried out in Europe and North America, when analyzed with a common protocol, and to explore reasons for any observed differences in the size of the air pollution relative rates.
In this article, we present the APHENA findings on the association between daily measurements of PM10 and mortality. The results, spanning two continents with a wide range of sources of ambient air pollution, are relevant to one of the key uncertainties in our current understanding of the health effects of PM: the identification of those characteristics of PM that are associated with toxicity (National Research Council 2004). Current regulatory standards are based on overall indicators of airborne PM mass as concentration metrics, in the face of uncertainty as to the specific physical and chemical characteristics that determine toxicity. The present study permits exploration of heterogeneity in the effect of PM10 on mortality across the broad range of atmospheres included in the APHENA cities.
Any assessment of heterogeneity needs to address the potential consequences of using differing analytic strategies to estimate air pollution health risks, and the extent to which apparent heterogeneity across studies reflects the consequences of different analytical methods. Based on past work by the APHENA investigators and extensive sensitivity analysis, we developed uniform approaches for first-stage (within-city) analyses of the time-series data used in previous reports. We then used the regression estimates in second-stage analyses directed at characterizing heterogeneity of the effect of PM10 across the APHENA cities and identifying factors contributing to heterogeneity.
Abstract and Introduction
Abstract
Background: The APHENA (Air Pollution and Health: A Combined European and North American Approach) study is a collaborative analysis of multicity time-series data on the effect of air pollution on population health, bringing together data from the European APHEA (Air Pollution and Health: A European Approach) and U.S. NMMAPS (National Morbidity, Mortality and Air Pollution Study) projects, along with Canadian data.
Objectives: The main objective of APHENA was to assess the coherence of the findings of the multicity studies carried out in Europe and North America, when analyzed with a common protocol, and to explore sources of possible heterogeneity. We present APHENA results on the effects of particulate matter (PM) ≤ 10 µm in aerodynamic diameter (PM10) on the daily number of deaths for all ages and for those < 75 and ≥ 75 years of age. We explored the impact of potential environmental and socioeconomic factors that may modify this association.
Methods: In the first stage of a two-stage analysis, we used Poisson regression models, with natural and penalized splines, to adjust for seasonality, with various degrees of freedom. In the second stage, we used meta-regression approaches to combine time-series results across cites and to assess effect modification by selected ecologic covariates.
Results: Air pollution risk estimates were relatively robust to different modeling approaches. Risk estimates from Europe and United States were similar, but those from Canada were substantially higher. The combined effect of PM10 on all-cause mortality across all ages for cities with daily air pollution data ranged from 0.2% to 0.6% for a 10-µg/m increase in ambient PM10 concentration. Effect modification by other pollutants and climatic variables differed in Europe and the United States. In both of these regions, a higher proportion of older people and higher unemployment were associated with increased air pollution risk.
Conclusions: Estimates of the increased mortality associated with PM air pollution based on the APHENA study were generally comparable with results of previous reports. Overall, risk estimates were similar in Europe and in the United States but higher in Canada. However, PM10 effect modification patterns were somewhat different in Europe and the United States.
Introduction
Hundreds of time-series studies worldwide provide compelling evidence of the health effects of short-term exposure to air pollution. These studies also pose problems of interpretation due to variation in analytic methods and reporting, and the possibility of publication and analytic bias. Meta-analyses of published results can provide information about patterns in the relative rates of mortality and morbidity and evidence as to the causes of their spatial variation, but they inherit many of the same limitations of the individual studies. Coordinated multicity studies, designed partly to address these issues, have now been conducted in Europe and North America (Atkinson et al. 2001; Bell et al. 2004; Burnett and Goldberg 2003; Burnett et al. 1998, 2000; Gryparis et al. 2004; Katsouyanni et al. 1997, 2001; Samet et al. 2000a, 2000b, 2000c) and currently provide the most valid epidemiologic evidence of the effects of short-term exposure. The results of these studies appear broadly similar, but their methods and data characteristics differ, precluding definitive conclusions about their quantitative consistency and about the extent of and reasons for differences in the magnitude of the effects of short-term exposure among regions of the world.
APHENA (Air Pollution and Health: A Combined European and North American Approach) is a collaborative study among investigators involved in the European APHEA (Air Pollution and Health: A European Approach) study (Atkinson et al. 2001; Gryparis et al. 2004; Katsouyanni et al. 1997, 2001) and the U.S. NMMAPS (National Morbidity, Mortality and Air Pollution Study) study (Bell et al. 2004; Samet et al. 2000a, 2000b, 2000c), as well as Canadian studies (Burnett and Goldberg 2003; Burnett et al. 1998, 2000). APHENA addresses the short-term health effects of particulate matter (PM) ≤ 10 µm in aerodynamic diameter (PM10) and ozone on daily mortality and hospital admissions. The project originated at a time when the results of the multicity analyses, including APHEA and NMMAPS, were being reported and considered in the development of ambient air quality standards for PM (European Commission 1999; World Health Organization 2004, 2006). The main objective of the project was to assess the coherence of the findings of the multicity studies carried out in Europe and North America, when analyzed with a common protocol, and to explore reasons for any observed differences in the size of the air pollution relative rates.
In this article, we present the APHENA findings on the association between daily measurements of PM10 and mortality. The results, spanning two continents with a wide range of sources of ambient air pollution, are relevant to one of the key uncertainties in our current understanding of the health effects of PM: the identification of those characteristics of PM that are associated with toxicity (National Research Council 2004). Current regulatory standards are based on overall indicators of airborne PM mass as concentration metrics, in the face of uncertainty as to the specific physical and chemical characteristics that determine toxicity. The present study permits exploration of heterogeneity in the effect of PM10 on mortality across the broad range of atmospheres included in the APHENA cities.
Any assessment of heterogeneity needs to address the potential consequences of using differing analytic strategies to estimate air pollution health risks, and the extent to which apparent heterogeneity across studies reflects the consequences of different analytical methods. Based on past work by the APHENA investigators and extensive sensitivity analysis, we developed uniform approaches for first-stage (within-city) analyses of the time-series data used in previous reports. We then used the regression estimates in second-stage analyses directed at characterizing heterogeneity of the effect of PM10 across the APHENA cities and identifying factors contributing to heterogeneity.