Characterizing oxygenated volatile organic compounds and their sources in rural atmospheres in China.

Oxygenated volatile organic compounds (OVOCs) are important precursors and products of atmospheric secondary pollution. The sources of OVOCs, however, are still quite uncertain, especially in the atmosphere with much pollution in China. To study the sources of OVOCs in rural atmospheres, a proton transfer reaction mass spectrometry (PTR-MS) was deployed at a northern rural site (WD) and a southern rural site (YMK) in China during the summer of 2014 and 2016, respectively. The continuous observation showed that the mean concentration of TVOCs (totally 17 VOCs) measured at WD (52.4 ppbv) was far higher than that at YMK (11.1 ppbv), and the OVOCs were the most abundant at both the two sites. The diurnal variations showed that local sources of OVOCs were still prominent at WD, while regional transport influenced YMK much. The photochemical age-based parameterization method was then used to quantitatively apportion the sources of ambient OVOCs. The anthropogenic primary sources at WD and YMK contributed less (2%-16%) to each OVOC species. At both the sites, the atmospheric background had a dominant contribution (~50%) to acetone and formic acid, while the anthropogenic secondary formation was the main source (~40%) of methanol and MEK. For acetaldehyde and acetic acid, the biogenic sources were their largest source (~40%) at WD, while the background (39%) and anthropogenic secondary formation (42%) were their largest sources at YMK, respectively. This study reveals the complexity of sources of OVOCs in China, which urgently needs explored further.