Impacts of global biogenic isoprene emissions on surface ozone during 2000–2019

Abstract

Biogenic isoprene is an important precursor of tropospheric ozone (O₃). Here, a coupled chemistry–vegetation model was used to quantify the contributions of isoprene emissions to surface O₃ pollution on the global scale during 2000–2019. The biogenic isoprene emissions showed high values in mid–low latitudes and seasonal peaks in the summer hemispheres. They promote global surface O₃ concentrations by 1.75 ppbv annually with regional hotspots of 4.39 ppbv (8.8%) in China and 5.36 ppbv (11.1%) in the U.S. in boreal summer. In the past two decades, isoprene emissions increased by 1.32 TgC yr⁻¹ (0.67% yr⁻¹) in the Northern Hemisphere but decreased by 0.71 TgC yr⁻¹ (0.44% yr⁻¹) in the Southern Hemisphere. Such changes of isoprene made opposite contributions to the surface O₃ trend, with 0.26 ppbv yr⁻¹ in eastern China but −0.32 ppbv yr⁻¹ in the southeastern U.S. due to the changes in the background regime of chemical reactions. The impact of anthropogenic changes on the O₃ trend is consistent with that of biogenic isoprene, but two to four times stronger in magnitude. This study revealed that the effective control of anthropogenic NO_x emissions could mitigate regional O₃ pollution even with the increased isoprene emissions under global warming.