Diverging Ozone Trends Above Western North America: Boundary Layer Decreases Versus Free Tropospheric Increases

Chang, Kai‐Lan; Cooper, O. R.; Rodriguez, Gavin; Iraci, L. T.; Yates, E. L.; Johnson, Matthew S.; Gaudel, Audrey; Jaffe, Dan; Bernays, Noah; Clark, Hannah; Effertz, Peter; Leblanc, Thierry; Petropavlovskikh, Irina; Sauvage, Bastien; Tarasick, D. W.

doi:10.1029/2022jd038090

JGR Atmospheres

2023

DOI: 10.1029/2022jd038090

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Diverging Ozone Trends Above Western North America: Boundary Layer Decreases Versus Free Tropospheric Increases

Kai‐Lan Chang

O. R. Cooper

Gavin Rodriguez

et al.

Abstract: From a climate change perspective, ozone is the third most important greenhouse gas (after CO 2 and CH 4 ) and its radiative forcing is proportional to the global tropospheric ozone burden, which contributes to global warming on relatively long timescales of decades (see Chapter 7 of IPCC AR6, 2021). Therefore, long-term ozone trends at remote sites and in the free troposphere are typically based on observations from all months of the year, in addition to seasonal-based analyses (

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Cited by 5 publications

References 103 publications

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On ozone's weekly cycle for different seasons in Arizona

Greenslade,

Guo,

Betito

et al. 2024

Atmospheric Environment

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On ozone's weekly cycle for different seasons in Arizona

Greenslade,

Guo,

Betito

et al. 2024

Atmospheric Environment

View full text Add to dashboard Cite

Fingerprints of the COVID-19 economic downturn and recovery on ozone anomalies at high-elevation sites in North America and western Europe

Putero,

Cristofanelli,

Chang

et al. 2023

Atmos. Chem. Phys.

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Abstract. With a few exceptions, most studies on tropospheric ozone (O3) variability during and following the COrona VIrus Disease (COVID-19) economic downturn focused on high-emission regions or urban environments. In this work, we investigated the impact of the societal restriction measures during the COVID-19 pandemic on surface O3 at several high-elevation sites across North America and western Europe. Monthly O3 anomalies were calculated for 2020 and 2021, with respect to the baseline period 2000–2019, to explore the impact of the economic downturn initiated in 2020 and its recovery in 2021. In total, 41 high-elevation sites were analyzed: 5 rural or mountaintop stations in western Europe, 19 rural sites in the western US, 4 sites in the western US downwind of highly polluted source regions, and 4 rural sites in the eastern US, plus 9 mountaintop or high-elevation sites outside Europe and the United States to provide a “global” reference. In 2020, the European high-elevation sites showed persistent negative surface O3 anomalies during spring (March–May, i.e., MAM) and summer (June–August, i.e., JJA), except for April. The pattern was similar in 2021, except for June. The rural sites in the western US showed similar behavior, with negative anomalies in MAM and JJA 2020 (except for August) and MAM 2021. The JJA 2021 seasonal mean was influenced by strong positive anomalies in July due to large and widespread wildfires across the western US. The polluted sites in the western US showed negative O3 anomalies during MAM 2020 and a slight recovery in 2021, resulting in a positive mean anomaly for MAM 2021 and a pronounced month-to-month variability in JJA 2021 anomalies. The eastern US sites were also characterized by below-mean O3 for both MAM and JJA 2020, while in 2021 the negative values exhibited an opposite structure compared to the western US sites, which were influenced by wildfires. Concerning the rest of the world, a global picture could not be drawn, as the sites, spanning a range of different environments, did not show consistent anomalies, with a few sites not experiencing any notable variation. Moreover, we also compared our surface anomalies to the variability of mid-tropospheric O3 detected by the IASI (Infrared Atmospheric Sounding Interferometer) satellite instrument. Negative anomalies were observed by IASI, consistent with published satellite and modeling studies, suggesting that the anomalies can be largely attributed to the reduction of O3 precursor emissions in 2020.

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Dynamical drivers of free-tropospheric ozone increases over equatorial Southeast Asia

Stauffer,

Thompson,

Kollonige

et al. 2024

Atmos. Chem. Phys.

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Abstract. Positive trends in tropical free-tropospheric (FT) ozone are frequently ascribed to emissions growth, but less is known about the effects of changing dynamics. Extending a prior study (Thompson et al., 2021; https://doi.org/10.1029/2021JD034691; “T21”), we re-examine Southern Hemisphere Additional Ozonesondes (SHADOZ) ozone trends over equatorial Southeast Asia (ESEA), one of Earth's most convectively active regions, using 25 years (1998–2022) of ozone soundings. T21 posited that early-year positive FT ozone trends at equatorial SHADOZ stations are related to decreasing convection. The 25-year analysis of Kuala Lumpur and Watukosek SHADOZ records finds that FT ozone trends of +5 % to +15 % (+2 to +6 nmol mol−1) per decade from ∼ February–April coincide with large increases in satellite infrared brightness temperatures and outgoing longwave radiation, indicators of declining convective activity. MERRA-2 reanalyses exhibit increases in upper-tropospheric velocity potential and decreases in precipitable water, also indicating diminished convection. In contrast, trends in ozone and convective indicators are weak the rest of the year. These results suggest that decreases in convective intensity and frequency are primary drivers of FT ozone build-up over ESEA early in the year; i.e., waning convection suppresses lofting and dilution of ozone. Decreasing convection promotes accumulation of biomass burning emissions typical of boreal spring even though satellite FT carbon monoxide trends (2002–2022) over ESEA follow a global decrease pattern. Finally, our results demonstrate the advantages of monthly or seasonally resolved analyses over annual means for robust attribution of observed ozone trends, challenging models to reproduce these detailed features in simulations of the past 25 years.

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Diverging Ozone Trends Above Western North America: Boundary Layer Decreases Versus Free Tropospheric Increases

Cited by 5 publications

References 103 publications

On ozone's weekly cycle for different seasons in Arizona

On ozone's weekly cycle for different seasons in Arizona

Fingerprints of the COVID-19 economic downturn and recovery on ozone anomalies at high-elevation sites in North America and western Europe

Dynamical drivers of free-tropospheric ozone increases over equatorial Southeast Asia

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