Historical Trend in PM2.5 Long-term Exposure and its Health Impacts Associated with Emission Mitigations during 1990-2010 Across the Northern Hemisphere

Air quality across the northern hemisphere over the past two decades has witnessed dramatic changes, with continuous improvements in developed countries in North America and Europe, but a contrasting sharp deterioration in developing regions of Asia. Estimates of health impacts depend on the product of air pollution and population density. Thus, more serious health impacts from air pollution are expected in developing countries due to the rapid urbanization and rising population densities. This study investigates the historical trend in the PM2.5 exposure and its health impacts during 1990-2010 across the northern hemisphere. We employed the integrated exposure-response model developed by Health Effects Institute (HEI) to estimate the PM2.5-related mortality. The 1990-2010 surface annual PM2.5 concentrations are obtained from the simulation of a hemispheric regional climate model, i.e., WRF-CMAQ developed by US EPA. The gridded population datasets are derived from the 2000-2010 LandScan data developed by Oak Ridge National Laboratory, and 1990, 1995 Gridded Population of the World, Version 3 (GPWv3) developed by Columbia University. Estimated mortalities in East Asia and South Asia increased by 76% and 134% respectively, from 438786 and 190260 in 1990, to 771229 and 444724 in 2010. Mortalities in developed regions, i.e., high-income North America and Europe remarkably decreased by 46% and 76% respectively, from 4.5, 26.8 thousands in 1990 to 2.4, 6.4 thousands in 2010. The correlation between population and PM2.5 is quantified by a factor named “population scaled factor” (PSF), defined as the ratio of population-weighted average PM2.5 to regional average PM2.5. Large PSF values (~2.06) are noted in East Asia and Europe, suggesting strong positive correlation between population and PM2.5. The simultaneous growth of population and PM2.5 concentration in Asia leads to an increase of PSF, suggesting more serious health impacts from air pollution. In contrast, Europe and high-income North America exhibit decreasing trends of PSF, suggesting more health benefits from air pollution controls. Emission mitigation efficiencies (EME) of SO2, NOx, NH3 and primary PM are estimated from the mortality responses to the emission variations. In East Asia, about 84% of the growth of mortality during past two decades is associated with the increase of SO2, NOx and NH3 emissions. In high-income North America and Europe, the mitigation of primary PM shows largest EME values, suggesting the most effective health benefits. In high-income North America, the mitigation of NOx emissions presents no or even negative health benefits due to the offset by the increase in aerosol nitrate associated with the growth of NH3 emissions. However, the reduction of NOx emissions becomes more effective in Europe when NH3 emissions are simultaneously controlled.