Characteristics of Major Air Pollutants in China.

Following the rapid development of China's economy, air pollution has become more and more serious. Air pollution in China presents complex pollution characterized by high PM2.5 and O3 concentration. This study presents an overview of the status of air quality and emission in China and discusses the temporal and spatial distribution of major pollutants (PM10, PM2.5, SO2, NOX, and O3). The results show that the reduced emissions have improved the air quality in China. However, the Chinese National Ambient Air Quality Standard (CNAAQS) for PM10 and PM2.5 still be exceeded in many cities of China in 2015. A total of 77.5% (for PM2.5) and 65.4% (for PM10) of the monitoring cities were found to be exceeded CNAAQS. The average annual O3 concentration was increasing during 2013-2015, and 16% of the total cities in 2015 did not meet the CNAAQS, indicating that O3 pollution should be paid more attention. For NO2 and SO2, the exceedances of CNAAQS are rare. PM2.5, PM10, and SO2 concentrations are higher in northern than in southern regions. High NO2 occurred in Beijing-Tianjin-Hebei and Yangtze River delta region. Secondary particles formation and motor vehicle exhaust were the main sources of PM2.5 in megacities. Dust was the main source for PM10. The formation of O3 is VOC-limited in urban areas of China and NOX-limited in nonurban areas.