Impacts of Synoptic Weather Patterns and their Persistency on Free Tropospheric Carbon Monoxide Concentrations and Outflow in Eastern China
The relationship between synoptic weather patterns (SWPs) and variability of air pollution has not been fully understood. In this study, we assess the sensitivity of carbon monoxide (CO) concentrations and outflow in the free troposphere over eastern China to SWPs and their persistency, using daily CO data from the spaceborne Atmospheric Infrared Sounder (AIRS) instrument from 2003 to 2015. The SWPs over eastern China are classified into eight patterns following the Kirchhofer approach. On a regional average over the 13 years, distinct differences are observed in CO distributions and outflows among the eight SWPs. CO concentrations tend to increase under three SWPs that are characterized with anticyclonic circulations and downdrafts in all or part of eastern China. In contrast, three SWPs related to the East Asian summer monsoon (EASM) tend to reduce CO concentrations. The remaining two SWPs, dominant in winter and autumn, respectively, tend to bring more clean episodes. CO outflow from eastern China is sensitive to the influence of the SWPs on zonal winds. CO outflow is enhanced under two SWPs that prevail in winter and spring. Under the other SWPs, CO outflow decreases or changes only slightly. CO concentrations either increase or decrease by 5–15% under the persistent control of a SWP for two to seven days. In most cases, the anomalies of CO concentrations and CO outflow tend to be amplified if a SWP persists for several days. This study statistically illustrates the synoptic influences on the regional distribution and transport of air pollutants.