Post Date: 15 August 2022

Volatile organic compounds in subtropical Hong Kong: characteristics, sources and impacts

Abstract

As ubiquitous components in the atmosphere, volatile organic compounds (VOCs) adversely affect human health and air quality, playing crucial roles on the formation of ozone (O3) and secondary aerosols. Comprehensive characterization of various VOCs in the atmosphere and their roles in secondary air pollution formation has been emerging as an urgent issue in urban regions around the world. Though plenty of effort has been made into the VOCs analysis in the atmosphere, the distributions and roles of VOCs, especially oxygenated VOCs (OVOCs) in the atmosphere are still not well understood. This study performed continuous ambient measurements of VOCs using a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a suburban coastal site in Hong Kong. A total of 83 species with noticeable concentrations were observed during November to December in 2020, with the total average concentration of 36.75 ± 20.65 ppb, in which OVOCs contributed to 77.4% of the total measured species. Methanol was the most abundant species (6.51 ppb), followed by acetaldehyde (4.07 ppb), acetic acid (4.04 ppb), and acetone (3.28 ppb). Two distinct periods were observed during the campaign: Period 1 was associated with high daytime concentrations of O3, OVOCs and biogenic isoprene, while Period 2 was characterized with high primary emissions of aromatics. OVOCs contributed the most to the total OH reactivity and O3 formation potential (OFP), in which acetaldehyde and acetic acid accounted for largest proportions during both periods. Potential source contribution function (PSCF) results indicated that air mass transport from the junction of Guangdong and Jiangxi province influenced VOC pollution on Period 1, while air mass transport from Guangdong province and local sources both contributed significantly on Period 2. Six sources were identified by positive matrix factorization (PMF) analysis, including biogenic source, vehicle emission, solid fuel combustion (SFC), secondary formation, solvent usage, and mixed regional emissions. Vehicle emission was identified as the important primary source for short-term high and intense VOC pollution episodes. This study highlights the important contribution of OVOCs to atmospheric chemistry and provides further insights for formulating VOCs and O3 control strategies in Hong Kong.