Preprints
https://doi.org/10.5194/egusphere-2024-583
https://doi.org/10.5194/egusphere-2024-583
21 Mar 2024
 | 21 Mar 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Insights into the long-term (2005–2021) spatiotemporal evolution of summer ozone production sensitivity in the Northern Hemisphere derived with OMI

Matthew S. Johnson, Sajeev Philip, Scott Meech, Rajesh Kumar, Meytar Sorek-Hamer, and Yoichi P. Shiga

Abstract. Tropospheric ozone (O3) formation depends on the relative abundance of precursor species, nitrogen oxides (NOx) and volatile organic compounds (VOCs). Advancements in satellite retrievals of formaldehyde (HCHO) and nitrogen dioxide (NO2) vertical column densities (VCDs), and the corresponding HCHO/NO2 ratios (FNRs), provide the opportunity to diagnose the spatiotemporal evolution of O3 production sensitivity regimes. This study investigates trends of summertime VCD HCHO, NO2, and Ozone Monitoring Instrument (OMI) FNRs in the Northern Hemisphere from 2005 to 2021. FNR trends were analysed for polluted regions, and specifically for 46 highly populated cities, over the entire 17-year period and in 2020 when global anthropogenic emissions were reduced due to COVID-19 lockdown restrictions. It was determined that OMI-derived FNRs have increased on average ~65 % across cities in the Northern Hemisphere. Increasing OMI-derived FNRs indicates a general transition from radical-limited to NOx-limited regimes. The increasing trend is driven by reduced NO2 concentrations because of emission control strategies of NOx. OMI FNR trends were compared to ground-based in situ measurements in US cities and determined they can capture the trends in increasing FNRs (R = 0.91) and decreasing NO2 (R = 0.98) occurring at the surface. OMI FNRs in urban areas were higher (~20 %) in 2020 for most cities studied here compared to 2019 and 2021. In addition to studying the longest period of OMI FNRs across the Northern Hemisphere to-date, the capabilities and challenges of using satellite VCD FNRs to study surface-level O3 production sensitivity regimes are discussed.

Matthew S. Johnson, Sajeev Philip, Scott Meech, Rajesh Kumar, Meytar Sorek-Hamer, and Yoichi P. Shiga

Status: open (until 10 May 2024)

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Matthew S. Johnson, Sajeev Philip, Scott Meech, Rajesh Kumar, Meytar Sorek-Hamer, and Yoichi P. Shiga
Matthew S. Johnson, Sajeev Philip, Scott Meech, Rajesh Kumar, Meytar Sorek-Hamer, and Yoichi P. Shiga

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Short summary
Satellites, such as the Ozone Monitoring Instrument (OMI), retrieve proxy species of ozone (O3) formation (formaldehyde and nitrogen dioxide) and the ratios (FNRs) which can define O3 production sensitivity regimes. Here we investigate trends of OMI FNRs from 2005 to 2021 and they have increased in major cities suggesting a transition from radical- to nitrogen oxide-limited regimes. OMI also observed the impact of reduced emissions during the 2020 COVID-lockdown resulting in increased FNRs.