Spatial and temporal variations of aerosols around Beijing in summer2006: Model evaluation and source apportionment

摘要

Regional aerosol model calculations were made using the Weather Research andForecasting (WRF)-Community Multiscale Air Quality (CMAQ) and WRF-chemmodels to study spatial and temporal variations of aerosols around Beijing, China, inthe summer of 2006, when the Campaigns of Air Quality Research in Beijing andSurrounding Region 2006 (CAREBeijing) intensive campaign was conducted. Modelcalculations captured temporal variations of primary (such as elemental carbon (EC))and secondary (such as sulfate) aerosols observed in and around Beijing. The spatialdistributions of aerosol optical depth observed by the MODIS satellite sensors were alsoreproduced over northeast China. Model calculations showed distinct differences inspatial distributions between primary and secondary aerosols in association withsynoptic-scale meteorology. Secondary aerosols increased in air around Beijing on ascale of about 1000 x 1000 km~2under an anticyclonic pressure system. This air masswas transported northward from the high anthropogenic emission area extending south ofBeijing with continuous photochemical production. Subsequent cold front passagebrought clean air from the north, and polluted air around Beijing was swept to the south ofBeijing. This cycle was repeated about once a week and was found to be responsible forobserved enhancements/reductions of aerosols at the intensive measurement sites. Incontrast to secondary aerosols, the spatial distributions of primary aerosols (EC) reflectedthose of emissions, resulting in only slight variability despite the changes in synoptic-scale meteorology. In accordance with these results, source apportionment simulationsrevealed that primary aerosols around Beijing were controlled by emissions within100 km around Beijing within the preceding 24 h, while emissions as far as 500 kmand within the preceding 3 days were found to affect secondary aerosols.