Robustness of the aerosol weekly cycle over Southeastern China

Abstract

A 7-day cycle is a special time-scale that corresponds with the weekly working schedule. However, there is no consensus on the existence of the weekly cycle of aerosol loading, which is closely related to human activities. In the present study, we analyzed the surface concentration of PM10 (Particulate Matter with a diameter of less than 10 μm) and other physically linked variables over Southeastern China under calm weather conditions to detect signs of the aerosol loading weekly cycle. Results show that the weekly cycle of PM10 is distinct; the maximum occurs on Thursday and the minimum occurs on Saturday and Sunday. The range of this cycle is over 8 μg m -3, approximately 8% of the daily average. The existence of the PM10 weekly cycle was supported by the pronounced amplitude of the 7-day cycle compared with those of 6-day and 8-day cycles and by significant results from the Monte-Carlo test. There are also distinct weekly cycles in the directly linked variables of adjusted horizontal visibility, sulfur dioxide (SO 2) and nitrogen dioxide (NO 2); the patterns of these cycles are corresponding with that of PM10. The changes of total cloud cover and relative humidity on the weekly time-scale were analyzed, and the relationship with PM10 was discussed. It is likely that the cloud cover weekly cycle is conducted by the change of PM10 through the semi-direct aerosol effect. We also found that precipitation and wind might weaken the PM10 weekly cycle by scavenging the heavy aerosol loading. © 2012 Elsevier Ltd.