Significant Biogenic Source of Oxygenated Volatile Organic Compounds and the Impacts on Photochemistry at a Regional Background Site in South China

Oxygenated volatile organic compounds (OVOCs) significantly modulate atmospheric chemistry, but the sources and air quality impacts of OVOCs in aged urban outflows remain to be elucidated. At a background site in South China, the ozone formation potential of six nonformaldehyde OVOCs studied was equivalent to that of 3.56 ppbv of formaldehyde, more than half of which was contributed by acetaldehyde. Source apportionment incorporating photochemical age revealed that considerable fractions (52.7%-62.6%) of the OVOCs were of biogenic origin, except for ethanol, which was primarily derived from anthropogenic emissions. The oxidation of cis-/trans-2-butene explained 71.1% of the in situ acetaldehyde formation. In contrast, alpha/beta-pinenes and isoprene contributed 73.8% and 28.4% to acetone and methylglyoxal formation, respectively. An average of 12.4% of net in situ ozone (O3) production rate was attributed to the OVOCs studied, where the biogenic fractions accounted for 59%. The changes in the O3 production rate and hydroxyl radical (OH) concentration caused by OVOCs were mainly affected by ozone formation sensitivity. The effects of primary acetaldehyde and acetaldehyde-led O3 on secondary acetaldehyde formation were weak at this background site; however, they cannot be ignored in polluted areas. This study provides a scientific basis for mitigating O3 pollution driven by biogenic emissions and OVOCs.