城市生态系统露水凝结与雾霾的相互作用研究

As a crucial input of water balance in urban ecosystem, dew can reflect the air pollution status in urban environment, and it is of great importance to monitor the chemistry characters of dew. The frequent haze events lead to the changes of meteorological factors, type and concentration of atmospheric particulate matters in the underlying surface. This phenomenon may affect the condensation and chemical characters of dew in the different function areas. Dew is the indicator of the automobile exhaust, coal combustion or industrial pollution in the urban. The effect of precipitation in atmospheric particulates removal is obvious and sufficiently studied, however, the study on dew condensation is urgent to reveal its effects on scavenging of the PM2.5 particles. In current study, the dew amount, dew chemical characters, atmospheric particulate mass concentration and the meteorological factors were monitored and analyzed in uptown, downtown, industrial region and green area in the urban ecosystem during the haze events and normal days, in order to identify the main factors influencing the city dew intensity and analysis the dew amount and composition of each functional areas effect in haze, and further to determine the main types and sources of dew condensation nuclei in different functional areas of the city. The contribution of dew condensation in particle deposition was estimated by comparing the particle concentration and type in the dew experienced the haze and regular period . The study is aimed to reveal the relationship between dew and haze, further, evaluate the removal effects of dew condensation. The achievements of the study can provide scientific foundation on the monitoring of air quality in different regions of urban environment, the landscape planning and city development. The study also provides the theoretical basis for the air quality control and urban haze prevention.

露水是城市生态系统重要的水分输入项，其水质可直接反应近地表空气质量。城市频发的雾霾事件导致下垫面气象因素、大气颗粒物的类型和浓度等发生变化，很可能对不同功能区露水凝结强度及水质产生影响。降水对大气颗粒物去除效果明显，露水凝结对人类活动范围PM2.5等颗粒物的清除作用急需研究。本项目以长春市住宅区、工业区、商业区和绿地区雾霾天气和同时段的露水凝结量、露水水质、大气颗粒物质量浓度及相关气象因子为监测指标，确定影响城市露水凝结的主要因子，分析各功能区雾霾前后气象条件及大气颗粒物质量浓度改变对露水凝结强度和露水水质的影响，辨析城市不同功能区露水凝结核的主要类型和来源，结合露水中不同粒径及类型颗粒物的化学组成和浓度水平，评价凝露过程对近地表大气颗粒物的去除作用及贡献。研究结果可为城市空间结构的合理布局和合理的景观规划提供技术支撑，为雾霾防治及城市空气质量改善提供理论基础。

露水是城市生态系统重要的水分输入项，其水质可直接反应近地表空气质量。城市频发的雾霾事件导致下垫面气象要素、大气颗粒物类型和浓度等发生变化，很可能对露水凝结强度及水质产生影响。降水对大气颗粒物去除效果明显，露水凝结过程对人类活动范围PM2.5等颗粒物的清除作用急需研究。本研究以长春市雾霾天气和同时段的露水凝结量、露水水质、大气颗粒物质量浓度及相关气象因子为监测指标，确定影响城市露水凝结的主要因子，分析雾霾前后气象条件及大气颗粒物质量浓度改变对露水凝结强度和露水水质的影响，辨析城市露水凝结核的主要类型和来源，结合露水中不同粒径及类型颗粒物的化学组成和浓度水平，评价凝露过程对近地表大气颗粒物的去除作用及贡献。研究结果可为城市空间结构的合理布局和合理的景观规划提供技术支撑，为雾霾防治及城市空气质量改善提供理论基础。主要研究结论如下：.1）东北城市年露日数为132—136天，占无霜期的62.5%左右。绿地区是城市生态系统水汽凝结的主要区域，绿地区占市区面积的比例是城市年露水量的决定因子，长春市年露水凝结量约为23—35mm。在露水凝结的过程中，始终对近地表的颗粒物起到去除作用，在水汽凝结初始阶段，对颗粒物去除作用明显，随着露水凝结达到趋于饱和状态，净化空气能力逐渐减弱。.2）雾霾气象条件下延迟了露水凝结的时间段，有利于近地表下垫面水汽不断积聚、凝结和增长。在雾霾期间持续有露水形成，不受固有露水凝结时间段的影响，证明雾霾条件下，始终存在污染物自然凝结沉降过程。.3）雾霾天气条件下，露水中溶解气溶胶含量增加。露水以沉降PM10以上的颗粒物为主，在雾霾天气露水清除可吸入颗粒物比例增高，特别是对PM2.5的去除能力大幅度提高。在雾霾天气中，来自地壳源的Na+、Mg2+和Ca2+增加了3.01—3.67倍；来自于人为源排放酸性气体二次衍生物的NH4+、SO42-和NO3-均增长5倍以上；特别是来自于生物质燃烧的K+增长倍数最高，达到了9.32倍，判断长春市雾霾主要是由周边地区的秸秆燃烧及燃煤等因素造成的。