西安大气细粒子(PM_(2.5))质量浓度变化特征及其影响因素

Characterization of Ambient Fine Particles(PM_(2.5)) Concentration and Its Influential Factors in Xi'an

分析了西安站点从2003年9月至2007年7月连续观测的PM2.5日质量浓度以及气象因子和能见度、API数据变化特征.获得4年的PM2.5日质量浓度为183.8±104.2μg/m3,而且质量浓度有增加的趋势.每日PM2.5质量浓度变化受排放源和气象因素变化明显;一周内日平均质量浓度成周二和周六的双峰分布;季节质量浓度分布成冬季>秋季>春季>夏季规律.降水对大气中PM2.5具有明显的湿清除作用,而风速大于2.25m/s对大气颗粒物具有扩散作用,小于2.25m/s具有一定的积累作用.PM2.5质量浓度和能见度、API之间有较明显的相关性.

Daily PM2.5(particle size smaller than 2.5 μm) samples were collected in Xi'an from September,2003 to July,2007,synchronously during that period,meteorological data(temperature,wind speed,rainfall and visibility) and air pollution index(API) were obtained.The average PM2.5 mass concentration in 4 years was 183.8±104.2 μg/m3 with an increasing trend.Weekly variation of PM2.5 concentrations showed two peaks corresponding to the busy traffic hours.Seasonal variations of PM2.5,which were circulative in annual scale,exhibited a same decreasing order as follows:winter>autumn>spring>summer.The temporal series of PM2.5,meteorological parameters,visibility,and air pollution index,API,indicated that wet deposition efficiently removed aerosols resulting in low PM2.5 level.The wind speed could lead to dilute PM levels when it was above 2.25 m/s.In contrast,lower wind speed most likely contributed to high PM levels.PM2.5 had a moderate positive relationship with API and a moderate negative relationship with visibility.