Particulate matter and gaseous pollutions in three megacities over China: Situation and implication

Lately released particular matter (PM) and gaseous pollutants (SO2, NO2, CO, and O3) data observed in three mega cities (Beijing, Shanghai, and Guangzhou) over China from April 2014 to March 2015 are employed to analyze the current situation of air pollutions. Meteorological data during the same time period are also used to explain the variations of air pollutants. Annual averaged PM2.5 and PM10 mass concentrations shows that the highest magnitude and strongest seasonal variations occurring in Beijing and lowest magnitude and weakest seasonal variations in Guangzhou. During the study period, 37%, 21% and 7% of the PM2.5, and 20%, 6% and 1% of the PM10 mass concentration exceeded the National Ambient Air Quality Standard (NAAQS) Grade II. Large differences in the ratios of PM2.5 to PM10 between the episode and non-episodes days are found in Beijing (0.22), which is almost twice as in Shanghai (0.12) due to less episode days in the latter. Compared to Beijing and Shanghai, no episode days were found in spring and summer in Guangzhou, the episode days occur only from mid-fall to winter. NO2 concentrations shows a marked increase during the late fall to wintertime over all three cities, which is consistent with the seasonal variations of PM concentrations. SO2 concentrations show a slight increase during the wintertime and CO also shows an increase in winter due to emissions by vehicle cold start. SO2 and CO concentrations during the study period are below the Grade-II standards but NO2 concentrations exceed the Grade-II standards from late to winter. Compared to the concentrations of decade ago, SO2 decreases around 70%, NO2 decreases around 25%, and CO decreases around 45%. O3 shows a strong seasonal variation, with relatively high magnitude in summer and low in winter, which is quite distinct from the seasonal variations of other gases pollutant and PM pollutions. The impact of meteorological conditions, such as precipitation, wind speed, relative humidity, and temperature, on PM and gaseous concentrations are also examined.