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https://doi.org/10.5194/egusphere-2024-1889
https://doi.org/10.5194/egusphere-2024-1889
31 Jul 2024
 | 31 Jul 2024

Anthropogenic emission controls reduce summertime ozone-temperature sensitivity in the United States

Shuai Li, Xiao Lu, and Haolin Wang

Abstract. The ozone-temperature sensitivity is widely used to predict the impact of future climate warming on ozone. However, trends in ozone-temperature sensitivity and possible drivers remained unclear. Here, we show that the observed summertime surface ozone-temperature sensitivity, defined as the slope of the best-fit line of daily anomaly in ozone versus maximum temperature (mΔO3-ΔTmax), has decreased by 50 % during 1990–2021 in the continental United States (CONUS), with a mean decreasing rate of −0.57 ppbv/K/decade (p < 0.01) across 608 monitoring sites. We conduct high-resolution GEOS-Chem simulations in 1995–2017 to interpret the mΔO3-ΔTmax trends and underlying mechanisms in the CONUS. The simulations identify the dominant role of anthropogenic nitrogen oxides (NOx) emission reduction in the observed mΔO3-ΔTmax decrease. We find that approximately 76 % of the simulated decline in mΔO3-ΔTmax can be attributed to the temperature-indirect effects arising from the shared collinearity of other meteorological effects (such as humidity, ventilation, and transport) on ozone. The remaining portion (24 %) is mostly due to the temperature-direct effects, in particular four explicit temperature-dependent processes, including the biogenic volatile organic compounds (BVOCs) emissions, soil NOx emissions, dry deposition, and the thermal decomposition of peroxyacetyl nitrate (PAN). With reduced anthropogenic NOx emissions, the expected ozone enhancement from temperature-driven BVOCs emissions, dry deposition, and PAN decomposition decreases, contributing to the decline in mΔO3-ΔTmax. However, soil NOx emissions increase mΔO3-ΔTmax with anthropogenic NOx emission reduction, indicating an increasing role of soil NOx emissions in shaping the ozone-temperature sensitivity. As indicated by the decreased mΔO3-ΔTmax, model simulations estimate that reduced anthropogenic NOx emissions from 1995 to 2017 have lowered ozone enhancement from low to high temperatures by 6.8 ppbv averaged over the CONUS, significantly reducing the risk of extreme ozone pollution events under high temperatures. Our study illustrates the dependency of ozone-temperature sensitivity on anthropogenic emission levels that should be considered in the future ozone mitigation in a warmer climate.

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Shuai Li, Xiao Lu, and Haolin Wang

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2024-1889', Russell Dickerson, 04 Aug 2024
    • AC4: 'Reply on CC1', Shuai Li, 22 Oct 2024
  • RC1: 'Comment on egusphere-2024-1889', Anonymous Referee #1, 06 Aug 2024
  • RC2: 'Comment on egusphere-2024-1889', Anonymous Referee #2, 23 Aug 2024
  • RC3: 'Comment on egusphere-2024-1889', Anonymous Referee #3, 26 Aug 2024
Shuai Li, Xiao Lu, and Haolin Wang
Shuai Li, Xiao Lu, and Haolin Wang

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Short summary
We report that the summertime ozone-temperature sensitivity decreased by 50 % from 3.0 ppbv/K in 1990 to 1.5 ppb/K in 2021 in the US. GEOS-Chem simulations show that anthropogenic NOx emission reduction is the dominant driver of the ozone-temperature sensitivity decline, through influencing both the temperature-direct and temperature-indirect processes. Reduced ozone-temperature sensitivity has decreased the ozone enhancement from low to high temperatures by an average of 6.8 ppbv across the US.