Dao-Yi Gong, Chang-Hoi Ho, Deliang Chen, Yun Qian, Yong-Sang Choi, and Jinwon Kim

Weekly cycles of the concentration of anthropogenic aerosols have been observed in many regions around the world. The phase and magnitude of these cycles, however, vary greatly depending on region and seasons. In the present study authors investigated the features of the weekly cycles of aerosol concentration and their interactions with the meteorological conditions in major urban regions over east China, one of the most polluted areas in the world, in summer time during the period 2001-2006. The PM10 (aerosol particulate matters of diameter < 10mm) concentration from 29 pollution stations shows a significant weekly cycle with the largest values around midweek and smallest values in weekend. The weekly cycle of PM10 is found being tightly related to and interacting with the atmospheric circulations. The weekly cycle begins with the accumulation of anthropogenic aerosols in the lower troposphere during the early part of a week. Around midweek, the accumulated aerosols induce radiative heating, thereby destabilizing the mid- to lower troposphere and generating anomalously stronger winds. The resulting circulation promotes ventilation to reduce aerosol concentrations in the boundary layer during the later part of the week. This aerosol-meteorology feedback suggests a self-modulation mechanism for low-level aerosol concentrations cycle at a weekly timescale in China. Corresponding to this cycle in anthropogenic aerosols the frequency of precipitation, particularly the light rain events, tends to be suppressed around mid-weekdays through indirect aerosol effects. This is well consistent with the observed anthropogenic weather cycles, i.e., more (less) solar radiation near surface, higher (lower) maximum temperature, larger (smaller) diurnal temperature range, less (more) precipitation events in mid-weekday (weekend).