Four-year long-path monitoring of ambient aerosol extinction at a central European urban site: dependence on relative humidity
Four-year long-path monitoring of ambient aerosol extinction at a central European urban site: dependence on relative humidity
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DOI：
10.5194/acp-16-1863-2016
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发表时间：
2015-04
影响因子：
6.3
通讯作者：
A. Skupin;A. Ansmann;R. Engelmann;P. Seifert;T. Müller
中科院分区：
文献类型：
--
作者：
A. Skupin;A. Ansmann;R. Engelmann;P. Seifert;T. Müller
抽象的。自2009年以来，在德国莱比锡（51.3° N，12.4° E）的城市环境中，使用光谱气溶胶消光监测系统（SAEMS）沿着2.84 km的水平路径在离地面30-50 m的高度测量环境气溶胶粒子消光系数。粒子消光系数（波长范围从300至1000 nm）的相对湿度高达几乎100%的依赖性进行了研究。主要结果。对于550 nm波长，相对湿度从40%增加到80%时，平均消光增强因子为1.75 ± 0.4。当相对湿度从40%增加到95%时，相应的4年平均灭绝增强因子为2.8 ± 0.6。提出了一种城市粒子消光系数对相对湿度依赖性的参数化方法。确定2009-2012年期间的平均吸湿指数为0.46。基于后向轨迹聚类分析，研究了8种气流状态下气溶胶光学特性的相关性。结果表明，城市上空的气溶胶状况受本地污染源的控制。SAEMS消光系数统计数据与AERONET太阳光度计观测数据的比较结果吻合较好。此外，粒子消光系数的时间序列计算从原位测量的干颗粒尺寸分布和湿度校正的SAEMS消光值（40%相对湿度）被发现在良好的整体一致性，这验证了开发的湿度参数化方案的适用性。对粒子消光的光谱依赖性（埃指数）的分析表明，在4年的时间内，390-881 nm埃指数平均从0.3（在30%相对湿度下）增加到1.3（在95%相对湿度下）。
Abstract. The ambient aerosol particle extinction coefficient is measured with the Spectral Aerosol Extinction Monitoring System (SAEMS) along a 2.84 km horizontal path at 30–50 m height above ground in the urban environment of Leipzig (51.3° N, 12.4° E), Germany, since 2009. The dependence of the particle extinction coefficient (wavelength range from 300 to 1000 nm) on relative humidity up to almost 100 % was investigated. The main results are presented. For the wavelength of 550 nm, the mean extinction enhancement factor was found to be 1.75 ± 0.4 for an increase of relative humidity from 40 to 80 %. The respective 4-year mean extinction enhancement factor is 2.8 ± 0.6 for a relative-humidity increase from 40 to 95 %. A parameterization of the dependency of the urban particle extinction coefficient on relative humidity is presented. A mean hygroscopic exponent of 0.46 for the 2009–2012 period was determined. Based on a backward trajectory cluster analysis, the dependence of several aerosol optical properties for eight air flow regimes was investigated. Large differences were not found, indicating that local pollution sources widely control the aerosol conditions over the urban site. The comparison of the SAEMS extinction coefficient statistics with respective statistics from ambient AERONET sun photometer observations yields good agreement. Also, time series of the particle extinction coefficient computed from in situ-measured dry particle size distributions and humidity-corrected SAEMS extinction values (for 40 % relative humidity) were found in good overall consistency, which verifies the applicability of the developed humidity parameterization scheme. The analysis of the spectral dependence of particle extinction (Angstrom exponent) revealed an increase of the 390–881 nm Angstrom exponent from, on average, 0.3 (at 30 % relative humidity) to 1.3 (at 95 % relative humidity) for the 4-year period.