Chuen-Meei Gan

Historical Trends in PM2.5-Related Premature Mortality during 1990-2010 across the Northern Hemisphere.

Background: Air quality across the northern hemisphere over the past two decades has witnessed dramatic changes, with continuous improvement in developed countries in North America and Europe, but a contrasting sharp deterioration in developing regions of Asia. Objective: This study investigates the historical trend in the long-term exposure to PM2.5 and PM2.5-related premature mortality (PM2.5-mortality) and its response to changes in emission that occurred during 1990–2010 across the northern hemisphere. Implications for future trends in human exposure to air pollution in both developed and developing regions of the world are discussed. Methods: We employed the integrated exposure–response model developed by Health Effects Institute to estimate the PM2.5-mortality. The 1990–2010 annual average PM2.5 concentrations were obtained from the simulations using the WRF-CMAQ model. Emission mitigation efficiencies of sulfur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3), and primary PM are estimated from the PM2.5-mortality responses to the emission variations. Results: Estimated PM2.5-mortalities in East Asia and South Asia increased by 21% and 85% respectively, from 866,000 and 578,000 in 1990, to 1,048,000 and 1,068,000 in 2010. PM2.5-mortalities in developed regions (i.e., Europe and high-income North America) decreased substantially by 67% and 58% respectively. Conclusions: Over the past two decades, correlations between population and PM2.5 have become weaker in Europe and North America due to air pollution controls but stronger in East Asia due to deteriorating air quality. Mitigation of primary PM appears to be the most efficient way for increasing health benefits (i.e., providing the largest mortality reduction per unit emissions). However, reductions in emissions of NH3 are needed to maximize the effectiveness of NOx emission controls. Citation: Wang J, Xing J, Mathur R, Pleim JE, Wang S, Hogrefe C, Gan CM, Wong DC, Hao J. 2017. Historical trends in PM2.5-related premature mortality during 1990–2010 across the northern hemisphere. Environ Health Perspect 125:400–408; http://dx.doi.org/10.1289/EHP298

Air pollution and climate response to aerosol direct radiative effects: A modeling study of decadal trends across the northern hemisphere

Decadal hemispheric Weather Research and Forecast-Community Multiscale Air Quality simulations from 1990 to 2010 were conducted to examine the meteorology and air quality responses to the aerosol direct radiative effects. The models performance for the simulation of hourly surface temperature, relative humidity, wind speed, and direction was evaluated through comparison with observations from NOAAs National Climatic Data Center Integrated Surface Data. The inclusion of aerosol direct radiative effects improves the models ability to reproduce the trend in daytime temperature range which over the past two decades was increasing in eastern China but decreasing in eastern U.S. and Europe. Trends and spatial and diurnal variations of the surface-level gaseous and particle concentrations to the aerosol direct effect were analyzed. The inclusion of aerosol direct radiative effects was found to increase the surface-level concentrations of SO2, NO2, O3, SO42−, NO3−, and particulate matter 2.5 in eastern China, eastern U.S., and Europe by 1.5–2.1%, 1–1.5%, 0.1–0.3%, 1.6–2.3%, 3.5–10.0%, and 2.2–3.2%, respectively, on average over the entire 21 year period. However, greater impacts are noted during polluted days with increases of 7.6–10.6%, 6.2–6.7%, 2.0–3.0%, 7.8–9.5%, 11.1–18.6%, and 7.2–10.1%, respectively. Due to the aerosol direct radiative effects, stabilizing of the atmosphere associated with reduced planetary boundary layer height and ventilation leads to an enhancement of pollution. Consequently, the continual increase of aerosol optical depth (AOD) in eastern China leads to an increasing trend in the air quality feedback which exacerbates air pollution, while emission reductions in eastern U.S. and Europe result in a declining trend in both AODs and feedback which make the air pollution control strategies more effective.

Unexpected Benefits of Reducing Aerosol Cooling Effects

Impacts of aerosol cooling are not limited to changes in surface temperature since modulation of atmospheric dynamics resulting from the increased stability can deteriorate local air quality and impact human health. Health impacts from two manifestations of the aerosol direct effects (ADE) are estimated in this study: (1) the effect on surface temperature and (2) the effect on air quality through atmospheric dynamics. Average mortalities arising from the enhancement of surface PM2.5 concentration due to ADE in East Asia, North America and Europe are estimated to be 3-6 times higher than reduced mortality from decreases of temperature due to ADE. Our results suggest that mitigating aerosol pollution is beneficial in decreasing the impacts of climate change arising from these two manifestations of ADE health impacts. Thus, decreasing aerosol pollution gets direct benefits on health, and indirect benefits on health through changes in local climate and not offsetting changes associated only with temperature modulations as traditionally thought. The modulation of air pollution due to ADE also translates into an additional human health dividend in regions (e.g., U.S. Europe) with air pollution control measures but a penalty for regions (e.g., Asia) witnessing rapid deterioration in air quality.

Investigation of Trends in Aerosol Direct Radiative Effects over North America Using a Coupled Meteorology-Chemistry Model

A comprehensive investigation of the processes regulating tropospheric aerosol distributions, their optical properties, and their radiative effects in conjunction with verification of their simulated radiative effects for past conditions relative to measurements is needed in order to build confidence in their estimates of the projected impacts on future climate. This study aims at addressing this issue through a systematic investigation of changes in anthropogenic emissions of SO2 and NOx over the past two decades in the United States, the consequent changes in anthropogenic aerosol loading in the North American troposphere, and subsequent impact on regional radiation budgets.

Long-term trends in the ambient PM 2.5 - and O 3 -related mortality burdens in the United States under emission reductions from 1990 to 2010

Concentrations of both fine particulate matter (PM2.5) and ozone (O3) in the United States (US) have decreased significantly since 1990, mainly because of air quality regulations. Exposure to these air pollutants is associated with premature death. Here we quantify the annual mortality burdens from PM2.5 and O3 in the US from 1990 to 2010, estimate trends and inter-annual variability, and evaluate the contributions to those trends from changes in pollutant concentrations, population, and baseline mortality rates. We use a fine-resolution (36 km) self-consistent 21-year simulation of air pollutant concentrations in the US from 1990 to 2010, a health impact function, and annual county-level population and baseline mortality rate estimates. From 1990 to 2010, the modeled population-weighted annual PM2.5 decreased by 39 %, and summertime (April to September) 1 h average daily maximum O3 decreased by 9 % from 1990 to 2010. The PM2.5-related mortality burden from ischemic heart disease, chronic obstructive pulmonary disease, lung cancer, and stroke steadily decreased by 54% from 123 700 deaths year-1 (95% confidence interval, 70 800-178 100) in 1990 to 58 600 deaths year-1 (24 900-98 500) in 2010. The PM2.5-related mortality burden would have decreased by only 24% from 1990 to 2010 if the PM2.5 concentrations had stayed at the 1990 level, due to decreases in baseline mortality rates for major diseases affected by PM2.5. The mortality burden associated with O3 from chronic respiratory disease increased by 13% from 10 900 deaths year-1 (3700-17 500) in 1990 to 12 300 deaths year-1 (4100-19 800) in 2010, mainly caused by increases in the baseline mortality rates and population, despite decreases in O3 concentration. The O3-related mortality burden would have increased by 55% from 1990 to 2010 if the O3 concentrations had stayed at the 1990 level. The detrended annual O3 mortality burden has larger inter-annual variability (coefficient of variation of 12%) than the PM2.5-related burden (4%), mainly from the inter-annual variation of O3 concentration. We conclude that air quality improvements have significantly decreased the mortality burden, avoiding roughly 35 800 (38%) PM2.5-related deaths and 4600 (27%) O3-related deaths in 2010, compared to the case if air quality had stayed at 1990 levels (at 2010 baseline mortality rates and population).

Multiscale Modeling of Multi-decadal Trends in Ozone and Precursor Species Across the Northern Hemisphere and the United States

Multi-decadal model calculations for the 1990–2010 period are performed with the coupled WRF-CMAQ modeling system over a domain encompassing the northern hemisphere and a nested domain over the continental U.S. Simulated trends in ozone and precursor species concentrations across the U.S. over the past two decades are compared with those inferred from available measurements during this period. The model results suggest large and contrasting changes in tropospheric composition over the northern hemisphere with significant reductions in air pollution over North America and Western Europe and increase in large portions of Asia. The model is able to capture the changing seasonal distributions in surface O3 in the U.S. during 1990–2010 arising from changing emissions and long-range transport.