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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]

Visibility can be used as a highly relevant visual indicator of the air pollution level. Published data on the correlations between visibility and health outcomes are very limited in China, and the health effects of slight haze on the human body have not been clarified. A semi-parametric generalized additive model (GAM) was used to assess the acute health effects of visibility on respiratory–cardiovascular mortality in Beijing, China. The correlation between visibility and PM 2.5 as well as the contributions of PM 2.5 to the health effects of visibility were analysed. Stratification model was employed to investigate the health effects of slight haze. The mortality risk of impaired visibility on the current exposure day peaked and was statistically significant for all the mortality outcomes. Every 1 km decrease in visibility corresponded to a 0.78% (95% CI: 0.62–0.95%) increase in total respiratory mortality and 0.54% (95% CI: 0.45–0.61%) increase in total cardiovascular mortality. Older people (age ≥65) were at a higher risk than the younger age group under impaired visibility. PM 2.5 had a negative logarithmic relationship relative to visibility. After adjustment for PM 2.5 , the risk estimates for both respiratory and cardiovascular mortality reduced. Short-term exposure to low visibility was significantly associated with increased respiratory and cardiovascular mortality in Beijing. The health risk of impaired visibility was particularly high, even in slight haze. The hazardous effects of visibility can be partially attributed to the effects of PM 2.5. These results can provide useful reference for relevant agencies to determine whether an adjustment to the haze warning level is warranted. Our findings indicate that visibility can be used as an alternative indicator for air quality assessments if air pollution data are insufficient or not available, particularly in developing countries. Image 1 • Studies on association between visibility and health outcomes are rare in China. • Exposure to impaired visibility is significantly related to increased mortality. • Health effects of impaired visibility can be partially explained by PM 2.5. • Health risk of impaired visibility is intense, even in slight haze. [ABSTRACT FROM AUTHOR]

Black carbon (BC) and its mixing state were measured with a ground-based single particle soot photometer in urban Beijing during the extremely polluted winter of 2013. Up to 70 ± 14% of the BC-containing particles were thickly-coated during periods of haze, compared to 37 ± 9% on non-hazy days. The thickly-coated number fraction (NF BC-thick ) increased with increasing BC, reaching a plateau at ∼80–90% when BC concentrations were ≥15 μg m −3 and visibility was ≤2 km. Regional inflows brought more aged, highly thickly-coated BC to Beijing during haze. The absorption coefficient showed a distinct linear correlation with BC concentration; the mass absorption efficiency (MAE) of BC was acquired, with an overall mean of 4.2 ± 0.01 m 2 g −1 at 870 nm. The MAE of BC amplified with increasing ambient relative humidity. This was largely explained by the increase in NF BC-thick , which was likely due to the enhanced production of secondary aerosol under humid conditions. [ABSTRACT FROM AUTHOR]