Impact of Aerosol Direct Effect on East Asian Air Quality During the EAST-AIRE Campaign

Abstract:

Three WRF-Chem simulations were conducted for East Asia region during March 2005 East Asian Studies of Tropospheric Aerosols: an International Regional Experiment (EAST-AIRE) Intensive Observation Campaign (IOC) period to investigate the direct effects of aerosols on surface radiation and air quality. WRF-Chem captured the temporal and spatial variations of meteorological fields, trace gases, and aerosol loadings. Surface shortwave radiation changes due to the aerosol direct effect (ADE) were calculated and compared with data from six World Radiation Data Center (WRDC) stations. The comparison indicated that WRF-Chem can simulate the surface short wave radiation moderately well, with temporal correlations between 0.4 and 0.7, and high biases between 9 to 120 W/m². Domain-wide, WRF-Chem showed a decrease of 22 W/m² in surface SW radiation due to the aerosol direct effect, consistent with observational studies. The ADE demonstrates diverse influences on air quality in East Asian. For example, the surface concentration of PM_2.5 increases in eastern China (~11.1%) due to ADE, but decreases in central China (-7.3%), western China (-8.8%), and Sichuan Basin (-4%). Surface 1-hour maximum ozone is reduced by 2.3%, owing to less radiation reaching the surface due to the ADE. Since PM_2.5 pollution raises serious public concern in China, regulations that control the emissions of PM_2.5 and its precursors have been implemented. We investigate the impact of reducing two different types of aerosols, sulfate (scattering) and black carbon (absorbing), by cutting 80% of SO₂ and black carbon (BC) emissions in two sensitivity simulations. We found that reducing SO₂ emissions results in the decline of PM_2.5 as much as 16mg/m³ in eastern China, and 20mg/m³ in the Sichuan Basin. Reducing the BC emissions by the same percentage causes the PM_2.5 to decrease as much as 40mg/m³ in eastern China, and 25mg/m³ in the Sichuan Basin. The monthly averaged surface 1-hour maximum ozone increases 3.1ppb in eastern China, and 4.3ppb in the Sichuan Basin with reduced BC emissions. However, there is minimal reduction of ozone with less SO₂ emission.