基于太阳光度计地基观测的徐州气溶胶光学特性变化分析

Analysis to Xuzhou aerosol optical characteristics with ground-based measurements by sun photometer

利用CE-318太阳光度计,于2013年7月~2015年4月对中国南北过渡地带淮海经济区中心城市徐州的气溶胶光学特性进行了地基观测,并结合气象条件对观测数据进行分析.研究揭示：（1）徐州2014年气溶胶光学厚度（AOD）年均值高达0.92;（2）徐州AOD四季变化分明,夏秋高、春冬低;（3）徐州气溶胶体积谱四季均呈双峰结构,冬夏两季积聚模态粒子与粗模态粒子的体积浓度接近,秋季积聚模态粒子占主导,春季粗模态粒子占主导;（4）徐州气溶胶可分为3个聚类,一类为粒径较大的干粒子,AOD较小,主要出现于5,12月,二类为粒径较小的强吸光粒子,主要出现于秋末和冬春,AOD最小,以12月为主,三类为体积浓度最大的湿粒子,AOD较大,各月均有,但以8月为最多.徐州AOD的四季变化特征不同于邻近的苏鲁豫皖省会城市,却相同于苏南太湖北岸、相似于环渤海湾地区.污染排放强度大、风速低、湿度较大,并受东南季风环流及秸秆燃烧影响,是徐州AOD年均值偏高的根本原因.

Atmospheric aerosols are fine particulate matters suspended in atmosphere, and vary in size distribution, geometrical shape, total column content, and chemical composition. The Aerosol Robotic Network（AERONET） comprised of hundreds of ground-based monitoring stations all over the world aims to measure regularly and continuously the aerosol optical properties, such as aerosol optical depth（AOD） and Angstrom exponent. AERONET has supported the international researches on global, regional and local atmospheric environment issues including aerosol pollution and haze episodes. However, the past researches on China aerosol issues were mainly related with Beijing-Tianjin-Hebei region, Yangtze River delta, and Cheng-Yu plain. It had been much ignored in the Huaihai economic zone, which is also densely populated and economically developed, locates in the north-to-south geographical transition zone of China. An AERONET station was established in 2013 in the Nahu campus of China University of Mining and Technology（CUMT）, supported by the China MAESTRO（Mining Area Environment Synergic Observation Proving Ground） program, and a CE318 sun photometer was installed in this station to monitor continuously the characteristics of atmospheric aerosol variations in Xuzhou. The CE318 provides ground measurements on aerosol optical depth（AOD）, Angstrom exponent, complex refractive index, single scatter albedo, and some other important aerosol parameters. In this paper, the AERONET CE318 measurements from July 2013 to April 2015 were systematically analyzed to reveal the daily, monthly, and yearly variations of atmospheric aerosols in Xuzhou. Referring to meteorological data including wind speed, relative humidity and total rainy days, the aerosol properties were analyzed with mathematical statistics and K-means cluster methods. We discovered that：（1） the yearly mean of AOD in Xuzhou in 2104 is much high as 0.92;（2） the seasonal variation of AOD in Xuzhou is distinguished with high values in summer and fall, and relatively low values in spring and winter;（3） the volume-size distribution spectrums of Xuzhou aerosols in all four seasons are two-peaks shaped; and the particle volume density at accumulation mode is approximate to that at coarse mode in winter and summer, while that at accumulation mode dominates in fall and that at coarse mode dominates in spring;（4） the aerosols in Xuzhou fall into three clusters with K-means classification： Cluster 1 is large sized dry particles with small AOD, which appears mainly in May and December; Cluster 2 is small sized light-absorbing strongly particles with the smallest AOD, which appears mainly in December; Cluster 3 is damp particles with maximal volume density and large AOD, which appears in all months but mainly in August. The seasonal variation characteristics of AOD in Xuzhou are abnormally different from that in the four neighboring province-capital cities, but the same as that at the north bank of Taihu Lake in south Jiangsu province or similar to that in the cities around Bohai Bay in North China. We proposed that the high value of yearly mean AOD in Xuzhou is mainly resulted from massive pollutant emissions from lots of local coal mines, coal-fired power plants, heavy factories and chemical companies, as well as large amount of vehicles and seasonally biomass burning. Both the negative meteorological conditions such as low surface wind speed and high relative humidity, and the transported-in aerosols by the circle current of southeast monsoon in summer, have facilitated the local concentration of aerosols in Xuzhou. This study is to fill the gap of researches on aerosol property in Huaihai economic zone, and to provide scientific basis and guidance for decision-making on local pollutant emission reduction and air quality improvement. It will also be meaningful for regional collaboration on the battle between economy development and haze episodes.