Significant but Overlooked: The Role of Anthropogenic Monoterpenes in Ozone Formation in a Chinese Megacity

Recent observations have revealed unexpectedly high concentrations of monoterpenes (MT) in urban areas, frequently surpassing those in forested regions. These findings suggest significant anthropogenic contributions (MT ANT ), challenging the traditional view that MT emissions are predominantly natural (MT NAT ) in current inventories. This oversight likely results in a substantial underestimation of MT’s role in urban ozone (O 3 ) production. Therefore, we developed a novel approach to generate a gridded emission inventory (EI) of MT ANT, integrating flux measurements of MT and carbon monoxide (CO). Results show that MT ANT emission rate in Beijing core areas exceeds MT NAT by a factor of 1.83, with household volatile chemical products (VCPs) contributing 56% of total MT ANT emissions. Incorporating MT ANT emissions into the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem) model significantly improved the simulation of diurnal MT variations (correlation coefficient, r = 0.985) and reduced the normalized mean bias ( NMB ) in surface MT concentration predictions by 53%. Notably, the combined effects of anthropogenic and biogenic MT emissions increased summertime maximum daily 8-h average (MDA8) O 3 levels by 12.8 ppb in Beijing core areas, with MT from household VCPs (MT VCP ) accounting for 62% of the MT ANT -driven O 3 increase. This study provides a robust quantitative foundation for assessing the impact of anthropogenic MT emissions on urban air quality and highlights the urgent need for targeted regulatory measures to mitigate their growing contribution to O 3 pollution.