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Abstract. Tropospheric ozone results from in situ chemical formation and stratosphere–troposphere exchange (STE), with the latter being more important in the middle and upper troposphere than in the lower troposphere. Ozone photochemical formation is nonlinear and results from the oxidation of methane and non-methane hydrocarbons (NMHCs) in the presence of nitrogen oxide (NOx=NO+NO2). Previous studies showed that O3 short- and long-term trends are nonlinearly controlled by near-surface anthropogenic emissions of carbon monoxide (CO), volatile organic compounds (VOCs), and nitrogen oxides, which may also be impacted by the long-range transport (LRT) of O3 and its precursors. In addition, several studies have demonstrated the important role of STE in enhancing ozone levels, especially in the midlatitudes. In this article, we investigate tropospheric ozone spatial variability and trends from 2005 to 2019 and relate those to ozone precursors on global and regional scales. We also investigate the spatiotemporal characteristics of the ozone formation regime in relation to ozone chemical sources and sinks. Our analysis is based on remote sensing products of the tropospheric column of ozone (TrC-O3) and its precursors, nitrogen dioxide (TrC-NO2), formaldehyde (TrC-HCHO), and total column CO (TC-CO), as well as ozonesonde data and model simulations. Our results indicate a complex relationship between tropospheric ozone column levels, surface ozone levels, and ozone precursors. While the increasing trends of near-surface ozone concentrations can largely be explained by variations in VOC and NOx concentration under different regimes, TrC-O3 may also be affected by other variables such as tropopause height and STE as well as LRT. Decreasing or increasing trends in TrC-NO2 have varying effects on TrC-O3, which is related to the different local chemistry in each region. We also shed light on the contribution of NOx lightning and soil NO and nitrous acid (HONO) emissions to trends of tropospheric ozone on regional and global scales.
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This content will become publicly available on January 1, 2026
Tropical upper-tropospheric trends in ozone and carbon monoxide (2005–2020): observational and model results
Abstract. We analyze tropical ozone (O3) and carbon monoxide (CO) distributions in the upper troposphere (UT) for 2005–2020 using Aura Microwave Limb Sounder (MLS) observations and simulations from the Whole Atmosphere Community Climate Model (WACCM) and two variants of the Community Atmosphere Model with Chemistry (CAM-chem), with each variant using different anthropogenic CO emissions. Trends and variability diagnostics are obtained from multiple linear regression. The MLS zonal mean O3 UT trend for 20° S–20° N is +0.39 ± 0.28 % yr−1; the WACCM and CAM-chem simulations yield similar trends, although the WACCM result is somewhat smaller. Our analyses of gridded MLS data yield positive O3 trends (up to 1.4 % yr−1) over Indonesia and east of that region, as well as over Africa and the Atlantic. These positive mapped O3 trends are generally captured by the simulations but in a more muted way. We find broad similarities (and some differences) between mapped MLS UT O3 trends and corresponding mapped trends of tropospheric column ozone. The MLS zonal mean CO UT trend for 20° S–20° N is −0.25 ± 0.30 % yr−1, while the corresponding CAM-chem trend is 0.0 ± 0.14 % yr−1 when anthropogenic emissions are taken from the Community Emissions Data System (CEDS) version 2. The CAM-chem simulation driven by CAMS-GLOB-ANTv5 emissions yields a tropical mean CO UT trend of 0.22 ± 0.19 % yr−1, in contrast to the slightly negative MLS CO trend. Previously published analyses of total column CO data have shown negative trends. Our tropical composition trend results contribute to continuing international assessments of tropospheric evolution.
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- Award ID(s):
- 2128446
- PAR ID:
- 10567528
- Publisher / Repository:
- Copernicus
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 25
- Issue:
- 1
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 597 to 624
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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