Impact of Aerosol Direct Effect on Wintertime PM2.5 Simulated by an Online Coupled Meteorology-Air Quality Model over East Asia

Ami Sekiguchi,Akira Kondo,Hikari Shimadera

doi:10.4209/aaqr.2016.06.0282

Abstract

This study aims to evaluate the impacts of the aerosol direct effect on simulated concentrations of fine particulate matter (PM2.5) over East Asia, which is controlled by heavy local air pollution and long-range transport. The online coupled Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) modeling system was applied to one-way and two-way simulations (without and with the aerosol direct effect) of a period from January till March of 2014. The differences between the two simulations showed that there were particularly large impacts of the aerosol direct effect on the eastern Asian continent with high aerosol loading. The temporal mean contributions of the direct effect averaged over the regions from Northeast to Central China were a 15% decrease in the surface shortwave radiation, a 9.0% decrease in the planetary boundary layer (PBL) height, and an 8.6% increase in the ground-level PM2.5 concentration. In addition, there were negative contributions of the direct effect to the PM2.5 concentration over the ocean from the Sea of Japan to the East China Sea (a 1.0% decrease on average throughout the period). The PM2.5 decrease over the ocean was likely attributable to a reduction in the secondary PM2.5 outflow from the continent to the downwind region, which was caused by the increased dry deposition of PM2.5 precursors from the increased ground-level concentrations within a more stable PBL over the continent. Overall, the substantial decrease in the surface shortwave radiation due to the aerosol direct effect led to enhanced atmospheric stability and therefore increased the ground-level PM2.5 in the heavily polluted region.

Highlights

Aerosol particles can be generated naturally or anthropogenically from various sources including direct emissions into the atmosphere and secondary formations through gas-to-particle conversion
This study aims to evaluate the impacts of the aerosol direct effect on simulated concentrations of fine particulate matter (PM2.5) over East Asia, which is controlled by heavy local air pollution and long-range transport
The temporal mean contributions of the direct effect averaged over the regions from Northeast to Central China were a 15% decrease in the surface shortwave radiation, a 9.0% decrease in the planetary boundary layer (PBL) height, and an 8.6% increase in the ground-level PM2.5 concentration

Summary

Introduction

Aerosol particles can be generated naturally or anthropogenically from various sources including direct emissions into the atmosphere (e.g., biomass burning, dust and sea salt) and secondary formations through gas-to-particle conversion (e.g., oxidations of sulfur dioxide, nitrogen oxides and volatile organic compounds). The presence of aerosol particles affects the solar radiation by scattering and absorption in the atmosphere, which is called the aerosol direct effect. The direct effect can cause changes in photolysis rates for photochemistry and surface temperature that affects atmosphere stability controlling vertical dispersion of air pollutants (Wong et al, 2012; Xing et al, 2015). In Asia, the rapid growth in economic activities and energy consumption in recent decades has caused tremendous increases in anthropogenic emissions of air pollutions (Ohara et al, 2007; Kurokawa et al, 2013). In Asia with substantial aerosol loading, aerosol particles are likely to have important influence on meteorology, and in turn, on the atmospheric

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