A modeling analysis of a heavy air pollution episode occurred in Beijing

[摘要] The concentrations of fine particulate matter (PM) and ozone in Beijingoften exceed healthful levels in recent years, therefore China is to takingsteps to improve Beijing's air quality for the 2008 Olympic Games. In thispaper, the Models-3 Community Multiscale Air Quality (CMAQ) Modeling Systemwas used to investigate a heavy air pollution episode in Beijing during3–7 April 2005 to obtain the basic information of how heavy air pollutionformed and the contributions of local sources and surround emissions. Themodeling domain covered from East Asia with four nested grids with 81 to 3 kmhorizontal resolution focusing on urban Beijing. This was coupled with aregional emissions inventory with a 10 km resolution and a local 1 kmBeijing emissions database. The trend of predicted concentrations of variouspollutants agreed reasonably well with the observations and captured themain features of this heavy pollution episode. The simulated columnconcentration distribution of PM was correlated well with the MODIS remotesensing products. Control runs with and without Beijing emissions wereconducted to quantify the contributions of non-Beijing sources (NBS) to theBeijing local air pollution. The contributions of NBS to each speciesdiffered spatially and temporally with the order of PM_2.5>PM₁₀>SO₂> soil for this episode. The percentage contribution of NBSto fine particle (PM_2.5) in Beijing was averaged about 39%, up to53% at the northwest of urban Beijing and only 15% at southwest. Thespatial distribution of NBS contributions for PM₁₀ was similar to thatfor PM_2.5, with a slightly less average percentage of about 30%. Theaverage NBS contributions for SO₂ and soil (diameter between 2.5 μm and 10 μm) were 18% and 10%. In addition, the pollutanttransport flux was calculated and compared at different levels toinvestigate transport pathway and magnitude. It was found that the NBScontribution correlated with the transport flux, contributing 60% ofPM₁₀ concentration in Beijing at the time of transport flux peak duringa strong episode with a transport path from southwest to northeast.

[学科分类] 大气科学