Search

Abstract: Measurements of aerosol scattering coefficient (σsp) and PM2.5 concentration obtained during June 2008 to May 2009 at urban, suburban, and rural sites in Beijing area. The mean value of σsp during measurement period was 301±307, 263±263, 182±201Mm−1 at Baolian (BL: urban site), Changping (CP: suburban site) and Shangdianzi (SDZ: rural site), respectively. The seasonal and diurnal patterns of σsp were analyzed with the measurement data. The σsp showed different seasonal and diurnal patterns at these three sites. The seasonal fluctuations inσsp in urban area were mostly influenced by seasonal variability in both emissions and meteorological conditions, while the seasonal wind patterns seemed to dominate the σsp in the suburban and rural areas. The diurnal activity of σsp generally showed a bimodal, trimodal and a unimodal pattern at BL, CP and SDZ sites, respectively. The diurnal variation of boundary layer height companying with source activity was mainly dominated the diurnal variation of σsp at urban and suburban sites. The mountain-valley breeze and boundary layer growth in SDZ region mostly dominated the diurnal variation of σsp. The mass scattering efficiency of PM2.5 was estimated at BL and SDZ, which showed a decreasing trend from urban to rural site with different seasonal variation at two sites. During fog and haze episodes, the lower northeasterly winds could result in significant spatial difference in σsp, while the σsp was spatially uniform under the influence of stronger southerly winds. [Copyright &y& Elsevier]

Three years of measurement of PM2.5 with 5-min time resolution was conducted from 2005 to 2007 in urban and rural environments in Beijing to study the seasonal and diurnal variations in PM2.5 concentration. Pronounced seasonal variation was observed in the urban area, with the highest concentrations typically observed in the winter and the lowest concentrations generally found in the summer. In the rural area, the maximum in PM2.5 concentration usually appeared during the spring, followed by a second maximum in the summer, while the minimum generally occurred in the winter. Significant diurnal variations in PM2.5 concentration were observed in both urban and rural areas. In the urban area, the PM2.5 concentration displays a bimodal pattern, with peaks between 7:00 and 8:00 a.m. and between 7:00 and 11:00 p.m. The minimum generally appears around noon. The morning peak is attributed to enhanced anthropogenic activity during rush hours. The decreases of boundary layer height and wind speed in the afternoon companying with increased source activity during the afternoon rush hour result in the highest PM2.5 concentration during evening hours. In the rural area, the PM2.5 concentration shows a unimodal pattern with a significant peak between 5:00 and 11:00 p.m. The seasonal and diurnal variations in PM2.5 concentration in the urban area are mostly dominated by the seasonal and diurnal variability of boundary layer and source emissions. The year-to-year variability of rainfall also has an important influence on the seasonal variation of PM2.5 in the urban area. The seasonal and diurnal wind patterns are more important factors for PM2.5 variation in the rural area. Southerly winds carry pollutants emitted in southern urban areas northward and significantly enhance the PM2.5 concentration level in the rural area. [Copyright &y& Elsevier]