NOx-Induced Changes in Upper Tropospheric O3 During the Asian Summer Monsoon in Present-Day and Future Climate

Abstract

The upper tropospheric ozone (O3) strongly influences the atmosphere's radiative budget. Using the Aerosol and Chemistry Model Intercomparison Project simulations, we study the influence of present-day and future anthropogenic nitrogen oxides (NOx) emissions on the upper tropospheric O3 concentrations over India during the Asian summer monsoon (ASM). We observe that the upper tropospheric O3 concentrations increased 1.5 times over the ASM anticyclone region during the ASM due to higher NOx emissions in 2014 compared to 1850, and their transport due to convection. These NOx-induced O3 changes exert a regional positive radiative forcing of 0.6 Wm−2 at the top of the atmosphere. The upper tropospheric O3 increases in the future with increasing NOx emissions. However, air quality policies to reduce surface NOx emissions also reduce the upper tropospheric O3 over India during the ASM.