Spatiotemporal Distributions of Ambient Volatile Organic Compounds in China: Characteristics and Sources

Ambient volatile organic compounds (VOCs) play a critical role in air quality as important precursors for the formation of ozone and secondary organic aerosols. The characteristics of ambient VOCs vary among different regions. In this study, characteristics and sources of VOCs from 33 sites in 32 major cities across China were compiled from field measurements and literature. The annual average VOC concentrations ranged from 6.7 to 75.0 ppbv and featured spatial variations, with a high value in northwestern China (62.7 +/- 17.5 ppbv) but no significant difference among northern, central, southern, and southwestern China (32.0-36.0 ppbv). The VOC concentrations in Qingdao and Fuzhou were consistent with the background values for the region (7.6 +/- 1.2 ppbv). VOC concentrations exhibited different seasonal variations across China. High concentrations occurred in winter and autumn, especially in cities in northern China, attributed to the combined contributions from weather and heating activities. The annual average chemical compositions of ambient VOCs across China were dominated by alkanes (36.5%-69.3%), followed by aromatics (7.7%-47.8%), alkenes (6.9%-53.4%), and alkynes (0.7%-15.0%). Chemical compositions also exhibited different seasonal variations across China, depending on the emission and consumption of VOCs. Vehicle exhaust, natural gas/liquefied petroleum gas, fuel combustion, and solvent usage were the dominant VOC contributors, followed by industrial, fuel evaporation, and biogenic sources. Listing VOCs as a mandatory monitoring pollutant for environmental monitoring stations in China and developing accurate source apportionment methods are critical to guide policy making and for understanding of the spatiotemporal distribution of ambient VOCs.