Citation:

Sahu, S., L. Chen, S. Liu, J. Xing, AND R. Mathur. Effect of Future Climate Change on Stratosphere-to-Troposphere-Exchange Driven Ozone in the Northern Hemisphere. AEROSOL AND AIR QUALITY RESEARCH . Chinese Association for Aerosol Research in Taiwan, , Taiwan, Province Of China, 23(12):220141, (2023). https://doi.org/10.4209/aaqr.220414

Impact/Purpose:

Stratosphere-Troposphere Exchange (STE) modulates the amount of ozone of natural origin throughout the troposphere and is important to quantify as the role of "background" ozone becomes more prominent in air quality management. Changes in atmospheric dynamics resulting from changing climate is likely to alter the frequency and strength of STE events thereby modulating the amount of ozone of stratospheric origin that is transported downwards to the troposphere and eventually the ground level. Using the Hemispheric CMAQ modeling system, this study investigates the impacts of these possible changes in STE processes on tropospheric ozone distributions across the Northern Hemisphere under two Representative Concentration Pathways (RCP): RCP4.5 and RCP8.5. The results highlight the need for improved quantification of STE processes and their incorporation in assessments of climate change on tropospheric air pollution.

Description:

Future estimates of atmospheric pollutant concentrations serve as critical information for policy makers to formulate current policy indicators to achieve future targets. Tropospheric burden of O3 is modulated not only by anthropogenic and natural precursor emissions, but also by the downward transport of O3 associated with stratosphere to troposphere exchange (STE). Hence changes in the estimates of STE and its contributions are key to understand the nature and intensity of future ground level O3 concentrations. The difference in simulated O3 mixing ratios with and without the O3-Potential Vorticity (PV) parameterization scheme is used to represent the model estimated influence of STE on tropospheric O3 distributions. Though STE contributions remain constant in Northern hemisphere as a whole, regional differences exist with Europe (EUR) registering increased STE contribution in both spring and winter while Eastern China (ECH) reporting increased contribution in spring in 2050 (RCP8.5) as compared to 2015. Importance of climate change can be deduced from the fact that ECH and EUR recorded increased STE contribution to O3 in RCP8.5 compared to RCP4.5. Comparison of STE and non-STE meteorological process contributions to O3 due to climate change revealed that contributions of non-STE processes were highest in summer while STE contributions were highest in winter. EUR reported highest STE contribution while ECH reported highest non-STE contribution. None of the 3 regions show consistent low STE contribution due to future climate change (< 50%) in all seasons indicating the significance of STE to ground level O3.

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