Abstract: The most pollution time over Pudong region,Shanghai,China is during the transition season in late autumn and early winter. It is known that air pollution is not only closely related to the emission,but also the meteorological conditions. Based on the hourly mass concentration of PM_2.5,minimum temperature,precipitation,average air pressure,and maximum wind speed data during 2007-2014 in late autumn and early winter,the variation characteristics of PM_2.5 before and after different intensity cold air processes,and the impacts of precipitation and wind on PM_2.5 were discussed statistically by the correlation analysis and percentile method. Results show that mass concentration of PM_2.5 over Pudong region was much higher in late autumn and early winter with a mean annual concentration of 55.9 μg·m^-3,and the pollution days accounted for 23.4% of the total days. The cold air had great influences on PM_2.5 concentration,which caused the PM_2.5 concentration increased obviously in the day before cold air with a mean value of 13.7%,declined during the day of cold air with a mean value of 7.4%, and then increased again in the next two days. In addition,different intensity of cold air had different effects on PM_2.5 concentration. The stronger the cold air was,the more obviously the PM_2.5 concentration changed. Cold air impacted PM_2.5 concentration through the wind and precipitation,and there existed close correlation between wind speed and PM_2.5 concentration;the PM_2.5 mass concentration decreased 7.8 μg·m^-3 as the wind speed increased 1 m·s^-1. Precipitation had less clearance effect on PM_2.5 compared with the wind speed caused by cold air, since the precipitation was very less in this season. Typical case suggested that PM_2.5 was also closely related with the peak value of 24 h changed pressure and its alternating time of positive and negative value. Results in this paper are important for PM_2.5 concentration forecasting and meteorological disaster prevention and control in late autumn and early winter. But it still needs further discussion since the PM_2.5 concentration could also be influenced by the emission and transportation of regional pollution.

Key words: cold air, precipitation, wind speed, PM_2.5, air quality, winter