Abstract
The recent proliferation of cohort studies of long-term exposure to outdoor fine particulate air pollution and mortality has led to a significant increase in knowledge about this important global health risk factor. As scientific knowledge has grown, mortality relative risk estimators for fine particulate matter have evolved from simple risk models based on a single study to complex, computationally intensive, integration of multiple independent particulate sources based on nearly one hundred studies. Since its introduction nearly 10 years ago, the integrated exposure-response (IER) model has become the state-of-the art model for such estimates, now used by the Global Burden of Disease Study (GBD), the World Health Organization, the World Bank, the United States Environmental Protection Agency’s benefits assessment software, and scientists worldwide to estimate the burden of disease and examine strategies to improve air quality at global, national, and sub-national scales for outdoor fine particulate air pollution, secondhand smoke, and household pollution from heating and cooking. With each yearly update of the GBD, estimates of the IER continue to evolve, changing with the incorporation of new data and fitting methods. As the number of outdoor fine particulate air pollution cohort studies has grown, including recent estimates of high levels of fine particulate pollution in China, new estimators based solely on outdoor fine particulate air pollution evidence have been proposed which require fewer assumptions than the IER and yield larger relative risk estimates. This paper will discuss the scientific and technical issues analysts should consider regarding the use of these methods to estimate the burden of disease attributable to outdoor fine particulate pollution in their own settings.
Highlights
Exposure to outdoor fine particulate matter (PM2.5 ) was the eighth leading risk factor for global mortality in 2017, contributing to 2.9 (95% confidence interval: 2.5, 3.4) million deaths, largely from non-communicable cardiovascular and respiratory diseases [1]
The preponderance of global excess deaths attributable to past exposure to outdoor PM2.5 has occurred in low- and middle-income countries (LMICs) in East Asia, South Asia, Africa, and the Middle East, with 52% occurring in China and India alone
Levels of outdoor PM2.5 increased over the past several decades while, over the same period, levels markedly declined in high-income countries of Europe and North America, reaching current levels that are as much as an order of magnitude lower than in some of the most polluted LMICs [1,2,3] (Figure 1)
Summary
Exposure to outdoor fine particulate matter (PM2.5 ) was the eighth leading risk factor for global mortality in 2017, contributing to 2.9 (95% confidence interval: 2.5, 3.4) million deaths, largely from non-communicable cardiovascular and respiratory diseases [1]. Extrapolating log-linear model coefficients derived from studies in low-exposure, high-income, Western countries to much greater levels of outdoor PM2.5 results in implausibly large estimates of relative risk and attributable deaths in LMICs. GBD 2004 was the first time the GBD included outdoor PM2.5 as a risk factor [23]. Exposures considered by Pope and colleagues, the GBD added a fourth type: household pollution from heating and cooking sources [17] This enabled the GBD to estimate attributable mortality from three combustion-derived risk factors, outdoor fine particulate air pollution, secondhand smoking, and household burning of solid fuels, using a single risk function. A comprehensive assessment of the influence of these updates is provided in the Methods Appendices of the GBD capstone papers [1]
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