| In the past20years, with the rapid development of urbanization, the increasing of building materials, energy consumption, and road facilities. A doubling of the gross national product, the rapid expansion of urban population, motor vehicle ownership expanded several times. Comprehensive prosperity was one of the negative effects of serious atmospheric haze pollution in cities. And the most immediate external objective of urban heavy haze pollution incidents was the weather conditions in addition to the internal reason of emission sources.Therefore, it was very necessary to carry on air pollutants monitoring and studies of the relationship between environmental and the meteorological conditions in Beijing, in order to work out the scientific and effective urban pollution prevention and control measures to improve urban air quality in Beijing and promote the healthy development of Beijing and surrounding areas.In this paper, in the base of the concentration data ofparticulate matter(PM) acquired from the twelve monitor sites and325m meteorological tower in recent years in Beijing and the meteorological data, we study the characteristics of particulate matter’temporal and spatial distribution and spatial differences,as well as based on horizonal and vertical particulate matter data, conventional and encryption automatic meterological station data, and Wind profiler data, the analysis of the influence of changes of different scales circulation patterns and boundary layer structure on the formation, accumulation, and dissipation of heavy pollutions of PM2.5in Beijing during21-28February2013was presented.The results showed that,(1) The overall situation. From2010to2013, the concentration of PM2.5showed a trend of slowly increased year by year in Beijing. The growth rate was14.3μg at observation period per year, the average growth rate was12.5%. The concentration of PM2.5focused primarily on20～100μg/m3in Beijing, the frequency of exceed standard in winter was highest, the highest concentration was600μ/m3, summer and autumn taked second place, spring was relatively low.(2)Heavy pollution incident. The long time pollution incident had become more frequent,2-3days pollution incident happened18times,4-5days pollution incident happened10times, more than5days pollution incident happened13times, the pollutions days up to120days.(3) Seasonal change. The concentration of PM2.5was highest in winter which was92.3μg/m3, higher in autumn and summer which were78.6μg/m3and66.9μg/m3, then lowest in spring which was63.8μg/m3.It was lack of rain and serious of dust pollution in spring, it had the highest percentage of secongdary paticles and strong photochemical pollution in summer. In autumn, combined radiation fog and straw burning, fog and haze caused atmospheric horizontal visibility to poor.In winter, heating additional added fossil fuels and biomass burning, coupled with the low atmospheric mixed layer height,it was very easy to form heavy pollution incident.(4) Daily variation. There were double peaks in spring and summer, which appeared at09:00and21:00respectively, peak were83.5μg/m3and93.8μg/m3. Single peak in autumn and winter which appeared at21:00, peak was105.7μg/m3, diurnal range as high as37.9μg/m3.(5) Spatial distribution. The concentration of PM2.5in horizontal spatial distribution presents high in south and low in north in Beijing, and urban daily variation of PM2.5was significantly higher than suburban. The average concentration of PM2.5was50-60μg/m3in north,30%lower than the average level. The average concentration of PM2.5was110-120μg/m3in south,30%higher than the average level. The order of the concentration of PM2.5in vertical distribution was8m>80m>240m. On the whole, when the mixing layer height was less than1000m, generally occurred a slight haze pollution.When it was more than a moderate pollution, the mixing layer height was from500to800m. At severe haze pollution process, the mixing layer height was only from200to300m.(6) Meteorological factors. Under the control of low or high weak pressure, the gathering of the southwest local wind, southeast transport wind, and north mountain wind, with clockwise wind shears in boundary layer, tended to bring on growth spurts of fine PM. Otherwise, the main cause of long time and steady growth of pollutions was the control of uniform pressure and near-surface south transport wind with high-level steady northwest wind. In addition, the key meteorlogical factor was near-surface low wind, high humidity, and maintaining a temperature inversion to promote and sustain the growth of regional haze pollution. A northwest wind in front of high pressure was a direct external power to disperse pollutions. |
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