Underappreciated contributions of biogenic volatile organic compounds from urban green spaces to ozone pollution

Abstract. The use of urban green spaces (UGSs), such as parks and gardens, is widely promoted as a strategy to improve the urban atmospheric environment. However, this study reveals that it can exacerbate urban ozone (O3) levels under certain conditions, as demonstrated by a September 2017 study in Guangzhou, China. Using the Weather Research and Forecasting model with the Model of Emissions of Gases and Aerosols from Nature (WRF-MEGAN) and the Community Multiscale Air Quality (CMAQ) model, we assessed the impact of UGS-related biogenic volatile organic compound (BVOC) emissions (hereafter referred to as UGS-BVOC emissions) on urban O3. Our findings indicate that the UGS-BVOC emissions in Guangzhou amounted to 666 Gg (∼90Mgkm-2), with isoprene (ISOP) and monoterpene (TERP) contributing remarkably to the total UGS-BVOC emissions. Compared to anthropogenic VOC (AVOC) and BVOC emissions, UGS-BVOC emissions account for ∼33.45 % in the city center, and their inclusion in the model reduces ISOP underestimation. The study shows improved simulation mean biases for MDA8 (maximum daily 8 h average) O3, from −3.63 to −0.75 ppb in the city center. Integrating UGS-BVOC emissions and UGS-LUCC emissions (where LUCC denotes land use cover change) enhances surface monthly mean O3 by 1.7–3.7 ppb (+3.8%-8.5%) and adds up to 8.9 ppb (+10.0 %) to MDA8 O3 during pollution episodes. UGS-BVOC emissions alone increase monthly mean O3 by 1.0–1.4 ppb (+2.3%-3.2%) in urban areas and contribute up to 2.9 ppb (+3.3 %) to MDA8 O3 during pollution episodes. These impacts can extend to surrounding suburban and rural areas through regional transport, highlighting the need to accurately account for UGS-BVOC emissions to better manage air quality.