Sensitivity of upper tropospheric ozone to anthopogenic emissions during the Asian summer monsoon

Ozone in the upper troposphere (UT) is critical for maintaining radiative balance at the top of the atmosphere (TOA). This study utilizes CMIP6 simulations to investigate photochemical pathways influencing ozone production in the UT during the Asian summer monsoon (ASM). We analyze the impact of convectively transported ozone precursors like nitrogen oxides (NO_x), non-methane volatile organic compounds (NMVOCs), and carbon monoxide (CO) on the sensitivity of ozone formation over the Asian region in the UT. Our results show an increase of ozone in the UT by ~70% in the present-day compared to the pre-industrial era. This excess ozone is photochemically produced due to the elevated levels of NO_x and CO in the UT, along with its direct convective transport from the boundary layer. Changes in formaldehyde (HCHO), a proxy for VOCs, are negligible in the UT. Analysis of ozone in relation to its precursors (HCHO, CO, and NO₂) suggests that the UT is primarily NO_x-limited, and ozone production follows the NO_x-CO-O₃ pathway. The UT ozone changes due to increasing ozone precursor emissions affect the radiative balance by exerting a positive ozone radiative effect at the TOA over the ASM anticyclone region. These findings indicate that suitable emission control strategies must be formulated to reduce NO_x and CO emissions for limiting ozone enhancement in the UT