中文摘要：

近年来，北京地区霉霾污染事件频发，大气PM2.5污染引起国内外强烈关注．利用北京市35个PM2.5监测站自2012年10月开始发布数据至2013年9月的小时观测数据，对其时空变化特征进行了分析．结果表明：（1）35个站点的平均PM2.5浓度为88．6μg/m^3；（2）PM2.5浓度与风速等气象要素关系密切，低浓度通常出现在大风天或者大风过后的紧邻时段，重污染天通常风速小，相邻天的PM2.5浓度可相差几倍甚至十倍以上；（3）PM2.5浓度随季节变化较大，1月和6月份较高，4月、8月和11月相对较低；（4）PM2.5浓度随站点类型变化明显，交通环境站点的平均浓度高于城市环境评价站点（可超过10％）；（5）北部PM2.5浓度低于东部和南部，而与河北交界的南部和西南地区浓度为全区最高；（6）PM2.5浓度由北到南整体上呈线性增加趋势，每向南10km，PM2.5平均浓度升高4．6μg/m^3（R^2=0．89），南部PM2.5平均浓度接近北部2倍；（7）PM2.5平均浓度存在一定的局部变化，但相邻站点变化幅度一般在20％以内．

英文摘要：

PM2.5 pollution in sive attention in recent years, Beijing has attracted extensive attention in recent years, but research on the detailed spatiotemporal characteristics of PM2.5 is critically lacking for effective pollution control. In our study, hourly PM2.5 concentration data of 35 fixed monitoring sites in Beijing were collected continuously from October 2012 to September 2013, for exploring the diurnal and seasonal characteristics of PM2.5 at traffic, urban, and background environments. Spatial trend and regional contribution of PM2.5 under different pollution levels were also investigated. Results show that the average PM2.5 concentration of all the 35 sites （including 5 traffic sites） was 88.6 μg/m^3. Although PM2.5 varied largely with the site location and seasons, a clear spatial trend could be observed with the PM2.5 concentration decreasing linearly from south to north, with a gradient of -0.46 μg/m^3/km for average days, -0.83 μg/m^3/km for heavily-severely polluted days, -0.52μg/m^3/km at lightly-moderately polluted days, and -0.26 μg/m^3/km for excellent-good days. PM2.5 at traffic sites was varied, but was generally over 10 % higher than at the nearby urban assessment sites.