Ambient volatile organic compounds and their impact on ozone pollution regulation: insights from multi-platform observations and model representations from the 2021-2022 HKEPD-HKUST field campaign in Hong Kong

Volatile organic compounds (VOCs) are crucial for atmospheric radical recycling and ozone formation. Despite significant reductions in other air pollutants in China since 2013, ozone and VOC levels remain persistently high, shifting air quality management toward VOC control. However, limited and short-term speciated VOC measurements hinder our understanding of regional VOC characteristics and effective emission reduction strategies for ozone mitigation in many Chinese cities. Therefore, in this study, we leveraged year-round routine VOC measurements in Hong Kong, together with field campaign and spaceborne TROPOMI data, to explore regional VOC characteristics and their relationships with ozone in the CMAQ chemical transport model. Results show that non-methane hydrocarbons (NMHCs) had higher concentrations in colder months and lower levels in warmer months, while oxygenated VOCs (OVOCs) peaked in September, coinciding with the annual ozone maximum and indicating strong photochemical activity in late summer. Notably, HCHO demonstrated a strong temporal correlation with total measured VOCs (R = 0.72–0.85) and ozone (R = 0.7). Among all measured VOC species, many are unaccounted for in the model, resulting in the model capturing only 30% of the total observed concentrations for NMHCs and 26% for OVOCs, as well as 14% of the ozone formation potential for NMHCs and 25% for OVOCs. This underrepresentation led to an overestimation of VOC sensitivity in ozone formation, classifying more areas as VOC-limited in the model. The findings provide valuable insights into regional VOC characteristics, aiding VOC-related model development and informing ozone air quality management strategies in VOC-limited urban environments.