Aerosol optical properties and related chemical apportionment at Xinken in Pearl River Delta of China

Aerosol optical properties (AOPs) of sub-10μm particles under dry conditions (relative humidity (RH) <20%<20%) were investigated at Xinken in Pearl River Delta of China from 4 October to 5 November 2004. Severe aerosol optical pollution has been found characterized by strongly light-absorbing particles. At 550 nm, the magnitude of the light scattering (333±138Mm-1) and absorption (70±42Mm-1), limited visual range (5.3±2.5km), and low single scattering albedo (0.83±0.050.83±0.05) show Xinken to be comparable to the most polluted urban cores rather than even a polluted rural site. Other presented AOPs include hemispheric backscattering fraction (11±1%11±1%) and asymmetry parameter (0.67±0.010.67±0.01) at 550 nm, and Ångström exponent (a˚450/700=1.6±0.15). Systematic relationships exist among the various AOPs. Their diurnal variations cannot be solely explained with the development of atmospheric boundary layer, but also obviously influenced by local wind patterns, variation of sources, photochemistry and nighttime heterogeneous chemistry. The fractional contributions to extinction, scattering and absorption (fep;sp;apfep;sp;ap) due to sub-aerosol-populations and individual chemical compounds are derived by the Mie simulations. The sub-1μm particles contribute more than 90% of the particle extinction (σep,550nm). Under dry conditions, fepfep of non-sea-salt sulfate, particulate organic matter, elemental carbon (EC) and residual are about 44%, 17%, 17% and 15%, respectively. However, the water uptake of particles can contribute 50–60% to σep,550nm at RH 90%. So in the ambient atmosphere, sulfate, carbonaceous material and water all play very important roles, concerning the visibility impairment at Xinken. The respective mass extinction, scattering and absorption efficiencies (αep;sp;apαep;sp;ap) are mostly consistent with previously reported values for the polluted area. αap,EC,550nm for sub-1μm and sub-10μm ranges are 9.3±1.49.3±1.4 and 7.2±1.0m2g-1, respectively. Our results imply a higher αap,ECαap,EC for more internally mixed EC under the atmospheric conditions present at Xinken.