Potential Sources and Formations of the PM2.5 Pollution in Urban Hangzhou

Continuous measurements of meteorological parameters, gaseous pollutants, particulate matters, and the major chemical species in PM2.5 were conducted in urban Hangzhou from 1 September to 30 November 2013 to study the potential sources and formations of PM2.5 pollution. The average PM2.5 concentration was 69 μg ̈m ́3, ~97% higher than the annual concentration limit in the national ambient air quality standards (NAAQS) of China. Relative humidity (RH) and wind speed (WS) were two important factors responsible for the increase of PM2.5 concentration, with the highest value observed under RH of 70%–90%. PM2.5 was in good correlation with both NO2 and CO, but not with SO2, and the potential source contribution function (PSCF) results displayed that local emissions were important potential sources contributing to the elevated PM2.5 and NO2 in Hangzhou. Thus, local vehicle emission was suggested as a major contribution to the PM2.5 pollution. Concentrations of NO2 and CO significantly increased in pollution episodes, while the SO2 concentration even decreased, implying local emission rather than region transport was the major source contributing to the formation of pollution episodes. The sum of SO42 ́, NO3 ́, and NH4 accounted for ~50% of PM2.5 in mass in pollution episodes and the NO3 ́/EC ratios were significantly elevated, revealing that the formation of secondary inorganic species, particularly NO3 ́, was an important contributor to the PM2.5 pollution in Hangzhou. This study highlights that controlling local pollution emissions was essential to reduce the PM2.5 pollution in Hangzhou, and the control of vehicle emission in particular should be further promoted in the future.