Estimating emissions of biogenic volatile organic compounds from urban green spaces and their contributions to secondary pollution†

Abstract

The role of biogenic emissions in forming ozone (O₃) and secondary organic aerosol (SOA) is increasingly important with decreasing anthropogenic emissions in China. However, biogenic volatile organic compounds (BVOCs) from urban green spaces are often neglected mainly because available land cover datasets do not reflect the distribution and density of vegetation in urban areas. In this study, urban BVOC emissions in Beijing at 1 km spatial resolution are estimated based on Google Earth Engine and a high-resolution land cover dataset and then used for air quality simulation in the summer of 2017. The updated urban BVOC emissions show better agreement with observed isoprene emission fluxes than other inventories. Air quality simulation shows that the contribution of urban BVOCs to the maximum daily averaged 8 h O₃ in Beijing typically exceeds 5 ppb with the maximum value of 8 ppb. Although BVOC emissions are higher in rural areas than urban areas, their contributions to O₃ concentrations are lower in rural regions. In contrast, the mean concentrations of biogenic SOA (BSOA) in urban areas (1.44 μg m⁻³) are 17% lower than in rural areas. Compared to other inventories, the average difference in BSOA concentrations in urban areas reached 0.18 μg m⁻³, and the relative changes in ISOA, MSOA, and SSOA were 14.3%, 17.7%, and 32.6%, respectively. This study emphasizes the importance of considering BVOC emissions from urban green spaces in understanding urban atmospheric chemistry. The methodology used to update urban green spaces in this study is equally applicable to other cities.