Aircraft measurements of SO2 and aerosols over northeastern China: Vertical profiles and the influence of weather on air quality

Aircraft measurements of SO2 and aerosol scattering coefficients (bsp) were made over Shenyang, an industrialized city in northeastern China in April 2005. Weather conditions were found to have strong impact on the areaʹs air quality. Between two flights on April 10 and 11, the SO2 loading increased by an order of magnitude within 24 h, from ∼0.1 DU (Dobson Unit) to ∼1 DU. Meteorological observations and back trajectory analyses suggest that anthropogenic pollutants emitted from the area accumulated under stagnant conditions induced by a mid-latitude cyclone approaching from the west. The observed rapid buildup demonstrates that strong local emissions can expose the populace to high pollutant levels under unfavorable weather conditions. Ångström exponents determined from the aircraft and ground-based sun photometers are significantly smaller over China than over the U.S., suggesting the prevalence of dust particles in northern China, particularly in spring. The coarse mode became more pronounced with altitude, indicating dust-dominant aerosol layers in the lower free troposphere, which should be accounted for in the satellite remote sensing of surface pollution over the region. Information on the vertical distribution of aerosols and precursor gases over China will also help better understand their transport as well as effects on weather and climate.