Abstract
We report the results of year-long PM2.5 (particulate matter less than 2.5 µm in diameter) simulations over Northeast Asia for the base year of 2013 under the framework of the Long-range Transboundary Air Pollutants in Northeast Asia (LTP) project. LTP is a tripartite project launched by China, Japan, and Korea for cooperative monitoring and modeling of the long-range transport (LRT) of air pollutants. In the modeling aspect in the LTP project, each country’s modeling group employs its own original air quality model and options. The three regional air quality models employed by the modeling groups are WRF-CAMx, NHM-RAQM2, and WRF-CMAQ. PM2.5 concentrations were simulated in remote exit-and-entrance areas associated with the LRT process over China, Japan, and Korea. The results showed apparent bias that remains unexplored due to a series of uncertainties from emission estimates and inherent model limitations. The simulated PM10 levels at seven remote exit-and-entrance sites were underestimated with the normalized mean bias of 0.4 ± 0.2. Among the four chemical components of PM2.5 (SO42−, NO3−, organic carbon (OC), and elemental carbon (EC)), the largest inter-model variability was in OC, with the second largest discrepancy in NO3−. Our simulation results also indicated that under considerable SO42− levels, favorable environments for ammonium nitrate formation were found in exit-and-entrance areas between China and Korea, and gas-aerosol partitioning for semi-volatile species of ammonium nitrate could be fully achieved prior to arrival at the entrance areas. Other chemical characteristics, including NO3−/SO42− and OC/EC ratios, are discussed to diagnose the LRT characteristics of PM2.5 in exit-and-entrance areas associated with transboundary transport over China, Japan, and Korea.
Highlights
PM2.5 (ultrafine particulate matter (PM) with a diameter of less than 2.5 μm) has adverse effects on both climate radiative forcing and the human body, leading to numerous respiratory diseases
The wind fields exhibited close resemblance in all three models, showing that northwest air currents prevailed over northeast China, Korea, and Japan in spring (April) and winter (January), whereas southerlies prevailed over southern China, Korea, and Japan in summer (July) due to the East Asia summer monsoon over the Pacific Ocean, and the pattern in autumn (October) was similar to that in the winter, but with much lower wind speeds
The transboundary transport of PM in Northeast Asia has become a serious concern in recent years
Summary
PM2.5 (ultrafine particulate matter (PM) with a diameter of less than 2.5 μm) has adverse effects on both climate radiative forcing and the human body, leading to numerous respiratory diseases. PM2.5 formation processes, especially secondary formation, during LRT are highly complicated Gaseous precursors such as SO2 , NO2 , and volatile organic compounds (VOCs) may be converted through photo-oxidation during LRT, and in turn, semi-volatile condensable vapors can be formed via the secondary aerosol formation process during (as well as before or after) the LRT process [6,7]. Such secondary aerosol formation can occur in two manners: homogeneous and heterogeneous formation. Over Northeast Asia, PM2.5 over major metropolitan areas has been frequently studied, remote and near-border areas (referred to as “exit-andentrance” areas in this study) over Northeast Asia are lacking in data, as the monitoring of both inflow and outflow areas requires international cooperation
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