安徽省大气污染物浓度的周循环特征评估

Evaluation of Weekly Cycle of Air Pollution in Anhui Province

大气质量的周循环特征反映了人类周期性的活动规律对大气环境的影响。基于安徽省16个城市PM2.5、PM10、CO、NO2、SO2和O3这6种污染物的监测结果,对安徽省大气污染的周循环特征进行了评估。首先基于原始逐小时污染物浓度时间序列在日和周窗口时间宽度上的滑动平均序列,定义了周循环距平百分率序列的计算方法,排除了日循环和长期低频变化的影响。以此为基础,基于合成分析以及贝叶斯统计分析,发现这6种大气污染物中,PM2.5、PM10、CO和NO2有着较为明显的周循环变化特征,其周循环距平百分率有着较大的变幅;而O3的周循环特征相对不明显。主成分分析获得的周循环,第1模态发现除O3以外的其他5种污染物的周循环有着同样的演进模式,即从周三开始持续到周五的累积和周六之后的衰减;O3的周循环峰值与谷值与其他污染物存在着大于12 h的滞后,反映了在周循环尺度上O3距平变化对其光化学反应前体距平变化的滞后响应特征。

The weekly cycle of air quality in a given location reflects the impact of human activity there.In the present study,the characteristic of weekly cycle of air pollution in Anhui Province,China,is assessed based on hourly time series of six air pollutants:PM2.5,PM10,CO,NO2,SO2 and O3.In order to better understand the weekly cycle,a new definition of the weekly cycle departure percentage(WCDP)series is proposed,based on the sliding average series of the original hourly data.Specifically,the WCDP of a given time is the percentage deviation of the average value of the corresponding 24-hour window from the averaged value of the corresponding 168-hour window.The advantage of the WCDP series is that the daily cycle component and low-frequency component are filtered out,while the weekly cycle component is retained.Based on the composite analysis and Bayes statistics analysis performed on the WCDP,it is found that that PM2.5,PM10,CO and NO2 have much stronger weekly cycles,while O3 shows the weakest weekly cycle.Among the four seasons,the weekly cycle in summer is weaker than the other seasons,which results from the superior diffusion capacity in summer.Based on the first principal component,it can be found that all variables except O3 have almost the same cycle pattern,i.e.an accumulative process began on Wednesday,and a decreasing process after Saturday.However,the weekly cycle of O3 has a lag of over 12 hours more than the other five variables,indicating a lag relationship between O3 and its photochemical precursors at the weekly cycle scale.The results of the present paper indicate that it is preferable to explore the weekly cycle process,but not only the weekend/weekday ratio;in addition,the WCDP defined in this study is a useful tool for exploring the weekly cycle of air pollution or other meteorological variables.