06 Dec 2022
 | 06 Dec 2022

Rethinking the role of transport and photochemistry in regional ozone pollution: Insights from ozone concentration and mass budgets

Kun Qu, Xuesong Wang, Xuhui Cai, Yu Yan, Xipeng Jin, Mihalis Vrekoussis, Jin Shen, Teng Xiao, Limin Zeng, and Yuanhang Zhang

Abstract. Understanding the role of transport and photochemistry is essential to alleviate ambient ozone pollution. However, ozone budget and source apportionment studies often report conflicting conclusions — Local photochemistry is the main cause of ozone pollution based on the analyses of the former, while contrary, non-local ozone transported to the region accounts for the majority in the latter results. In order to explore its potential causes, we calculated the contributions of both processes to the variations of mean ozone concentration and total ozone mass (the corresponding budgets are noted as ozone concentration and mass budget, respectively) within the atmospheric boundary layer (ABL) of the Pearl River Delta (PRD), China, based on the modelling results of WRF-CMAQ. Quantified results show that photochemistry drives the rapid increase of ozone concentrations in the daytime, whereas transport, especially the vertical exchange near the ABL top, controls the ozone mass budget. The changes in transport contributions in ozone budgets indicate the influences of the ABL diurnal cycle and regional wind fields, including prevailing winds and local circulations (sea breezes), on regional ozone pollution. Though transport in our simulations had a relatively limited effect on ozone concentration, its high contribution to ozone mass increase in the morning determined that most ozone in the PRD emanated from the outer regions. Consequently, the role of transport and photochemistry in ozone pollution may differ, depending on which of the two budgets is concerned. For future studies targeting ozone and other pollutants with moderately long atmospheric lifetimes, we suggest that attention should be paid to budget-type selections.

Kun Qu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1271', Anonymous Referee #1, 19 Jan 2023
  • RC2: 'Comment on egusphere-2022-1271', Anonymous Referee #2, 28 Jan 2023

Kun Qu et al.


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Short summary
Basic understandings of ozone processes, especially transport and chemistry, are essential to reduce ozone pollution, but studies often have different views on their relative importance. To explore the causes, we developed a tool based on the WRF-CMAQ modelling results to quantify their contributions in the ozone mass and concentration budgets, and found that the difference between two budgets well explains these distinct views. Future studies should be careful with budget-type selections.