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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]

Abstract: In China, visibility condition has become an important issue that concerns both society and the scientific community. In order to study visibility condition trends and characteristics for the BTH (Beijing, Tianjin, and Hebei) area, meteorological data (1980–2008) were collected from over 100 ground stations. The 29-year average visibilities were 21.7, 13.6, and 18.0km for Beijing, Tianjin, and Hebei, respectively, and the long-term visibility of BTH exhibited decreasing trend before 1998, slight fluctuations between 1998 and 2006, and increasing trend between 2006 and 2008. Most of the visibility trend lines depicted the same fluctuations and converged to a very narrow range for the urban stations in each area. Average visibility at non-urban stations was apparently higher than that at urban stations, with 29-year average of 19.4 and 14.4km respectively. Visibility was higher in the spring and autumn for Tianjin and Hebei, but best in the winter for Beijing probably due to higher wind speed and lower relative humidity. The visibility spatial distribution showed lower visibility that primarily occurred in the urban areas of Beijing, Tianjin, and Shijiazhuang. The trends regarding days with haze, good visibility, and fog for the urban and non-urban areas of the BTH region were also discussed. There was an increasing trend for days with haze but no apparent trend for days with good visibility. On average, there were no more than nine foggy days per year in the BTH area. Visibility and PM2.5 were observed to negatively correlate at two stations in Beijing, where PM2.5 data are available, and aerosols could cause a greater degree of visibility impairment in the summer months according to the correlations between visibility and PM2.5 concentration. [Copyright &y& Elsevier]