Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 4 2006 10.5194/acpd-6-8215-2006 http://www.atmos-chem-phys-discuss.net/6/8215/2006/ http://www.atmos-chem-phys-discuss.net/6/8215/2006/acpd-6-8215-2006.html http://www.atmos-chem-phys-discuss.net/6/8215/2006/acpd-6-8215-2006.pdf 8215 8240 2006-08-29 A modeling analysis of a heavy air pollution episode occurred in Beijing X. An T. Zhu Z. Wang C. Li Y. Wang State Key Joint Laboratory of Environmental Simulation and Pollution Control, Center for Environmental Sciences, Peking University, Beijing 100871, China LAPC, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China Because concentrations of fine particulate matter (PM) and ozone in Beijing often exceed healthful levels, China is to taking steps to improve Beijing's air quality for the 2008 Olympic Games. In this paper the Models-3 Community Multiscale Air Quality (CMAQ) Modeling System was used to investigate a heavy air pollution episode in Beijing during 3–7 April 2005. The modeling domain covered from East Asia with four nested grids with 81 to 3 km horizontal resolution focusing on urban Beijing. This was coupled with a regional emissions inventory with a 10 km resolution and a local 1km Beijing emissions database. The trend of predicted concentrations of various pollutants agreed reasonably well with the observations and captured the main features of this heavy pollution episode. The simulated column concentration distribution of PM was correlated reasonably with the MODIS remote sensing products. Control runs with and without Beijing emissions were conducted to quantify the contributions of non-Beijing sources (NBS) to the Beijing local air pollution. The contributions of NBS to each species differed spatially and temporally with the order of PM₂₅>PM₁₀>SO₂>SOIL for this episode. The percentage contribution of NBS to fine particle (PM_2.5) in Beijing was averaged about 40%, up to 80% at the northwest of urban Beijing and only 10–20% at southwest. The spatial distribution of NBS contributions for PM₁₀ was similar to that for PM_2.5, with a slightly less average percentage of about 30%. The NBS contributions for SO₂ and SOIL (diameter between 2.5 μm and 10 μm) were only 10–20% and 5–10%. In addition, the pollutant transport flux was calculated and compared at different levels to investigate transport pathway and magnitude. It was found that the NBS contribution correlated with the transport flux, contributing 70% of PM₁₀ concentration in Beijing at the time of transport flux peak during a strong episode with a transport path from southwest to northeast.