The spatial-temporal distribution characteristics of atmospheric chloromethane according to data from the CARE-China network.

The spatial and temporal distribution of atmospheric chloromethane (CH 3 Cl) in China was investigated between 2012 and 2014, and the sources of CH 3 Cl were evaluated by positive matrix factorization (PMF) according to PMF 5.0 (USEPA). Various concentrations of CH 3 Cl were found throughout China, ranging from 506.4 ± 110.5 to 1132.1 ± 523.3 pptv, showing the characteristics of high in the southeast and low in the northwest. The correlation between CH 3 Cl and chlorofluorocarbon-12 (CFC-12) at most sites was greater than 0.5 and presented regional characteristics. The distribution of CH 3 Cl in China is related to the degree of economic development, the high-concentration sites were located in the economically developed eastern region. The CH 3 Cl concentrations at western sites were similar to the global average and increased with latitude and altitude, indicating that this region was least affected by anthropogenic activities. The annual average concentrations of atmospheric CH 3 Cl in the northeastern region were below 730 pptv but had strong seasonal fluctuations. Chemical production was the main CH 3 Cl source in the northeast background areas (46%), while industrial combustion contributed 42% of the CH 3 Cl in the northeast urban areas. Large seasonal variations combined with a high relative standard deviation were observed in the southern region. Relative to the southwest, in the southeast, the onset of lower concentrations was delayed until September–October, and higher concentrations persisted for longer. Chemical production and biomass burning were the main sources in the southwest, while Chemical production and solvent use were the main contributors in the southeast. The Beijing area is discussed separately as a super megacity. No obvious seasonal fluctuations were observed in the Beijing area. According to the source analysis, chemical production contributed approximately 60% of the atmospheric CH 3 Cl in the Beijing area, while 15–24% was from solvent release. • High concentrations of CH 3 Cl are concentrated in the central and eastern regions in China. • Chemical production is the main source of atmospheric CH 3 Cl in China. • Industrial combustion is the second source of the CH 3 Cl in the northeast. • Biomass burning and solvent use are important CH 3 Cl contributors in the southern region. [ABSTRACT FROM AUTHOR]