Audrey Gaudel

We use an offline radiative transfer model driven by IAGOS aircraft observations to estimate the tropospheric ozone radiative forcing (RF) at decadal time scale (three time intervals with a common starting period in 1994–2004 and ending periods: 2011–2016, 2017–2019 and 2020–2023), over 11 selected Northern Hemispheric regions. We found a positive trend in the tropospheric ozone column (TOC) for the three time intervals, even if decadal trends are progressively reduced from 2011–2016 (ΔTOC +3.6 ± 2.0 DU, +14.8 ± 11.5 %, 2.5 ± 1.4 DU per decade) to 2017–2019 (ΔTOC +3.9 ± 3.9 DU, +17.5 ± 22.1 %, 2.0 ± 2.0 DU per decade) to 2020–2023 (ΔTOC +3.5 ± 2.8 DU, +13.8 ± 12.1 %, 1.5 ± 1.2 DU per decade). The progressively reduced average TOC decadal trends in 2020–2023 and 2017–2019, with respect to 2011–2016, originate from stagnation in ΔTOC in more recent time intervals (especially in the COVID and post-COVID crisis periods) and decreases of trends of the more radiative efficient upper tropospheric ozone. These average trend reductions are accompanied with reductions of the tropospheric ozone RF, from 2011–2016 (41.6 ± 24.0 mW m⁻² per decade) to 2017–2019 (27.6 ± 36.7 mW m⁻² per decade) to 2020–2023 (14.6 ± 25.6 mW m⁻² per decade). The total tropospheric ozone RF sensitivity varies between 18.4 ± 7.4 mW m⁻² DU⁻¹, in 2011–2016, and 11.1 ± 10.4 mW m⁻² DU⁻¹, in 2020–2023. Our decadal RF estimates vary from being ∼ 25 %–90 % larger (2011–2016 and 2017–2019 ending periods) to ∼ 30 % smaller (2020–2023 ending period) than the most recent global average RF estimates with online modelling. Our study underlines the importance of the evolution of ozone vertical profiles for the tropospheric ozone RF.

Quantifying long-term free-tropospheric ozone trends is essential for understanding the impact of human activities and climate change on atmospheric chemistry. However, this is complicated by two key challenges: the differences among existing satellite-derived tropospheric ozone products, which are not yet fully understood or reconciled, and the limited temporal and spatial coverage of ground-based reference measurements. Here, we explore if a more consistent understanding of the geographical distribution of tropospheric ozone column (TrOC) trends can be obtained by focusing on regional trends from ground-based measurements. Regions were determined with a correlation analysis between modeled TrOCs at the site locations. For those regions, TrOC trends were estimated with quantile regression for the Trajectory-mapped Ozonesonde dataset for the Stratosphere and Troposphere (TOST) and with a linear mixed-effects modeling (LMM) approach to calculate synthesized trends from homogenized HEGIFTOM (Harmonization and Evaluation of Ground-based Instruments for Free-Tropospheric Ozone Measurements) individual site trends. For different periods (1990–2021/22, 1995–2021/22, 2000–2021/22), both approaches give increasing (partial) tropospheric ozone column amounts over almost all Asian regions (median confidence) and negative trends over Arctic regions (very high confidence). Trends over Europe and North America are mostly weakly positive (LMM) or negative (TOST). For both approaches, the 2000–2021/22 trends decreased in magnitude compared to 1995–2021/22 for most regions; and for all time periods and regions, the pre-COVID trends are larger than the post-COVID trends. Our results enable the validation of global satellite TrOC trends and assessment of the performance of atmospheric chemistry models to represent the distribution and variation of TrOC.

We use an offline radiative transfer model driven by IAGOS aircraft observations, to estimate the tropospheric ozone radiative forcing (RF) at decadal time scale (two time intervals between 1994–2004 and 2011–2016 or 2019), over 11 selected Northern Hemispheric regions. On average, we found a systematic positive trend in the tropospheric ozone column (TOC) for both time intervals, even if trends are reduced in 2019 (∆TOC +2.5±1.7 DU, +9.3±7.7 %) with respect to 2011–2016 (∆TOC +3.6±2.0 DU, +14.9±11.5 %). The reduced TOC average trend in 2019 with respect to 2011–2016, originates mostly from decreases of the lower tropospheric ozone column (LTOC) trends and limited variations for upper tropospheric ozone column (UTOC) trends, in the tropics. These average reductions in TOC trends are not accompanied with reductions of the tropospheric ozone RF, between 2011–2016 (4.2±2.4 mW m^-2 per year) and 2019 (3.8±3.6 mW m^-2 per year). This disconnection depends by the smaller RF sensitivity to LTOC than UTOC changes. Correspondingly, the total tropospheric ozone RF sensitivity varies between 18.4±7.4 mW m^-2 per DU, in 2011–2016, and 31.6±20.3 mW m^-2 per DU, in 2019. About 84–85 % of the tropospheric ozone RF occurs in the longwave, with ~4–6 % larger values of this proportion in the tropics than in the extra-tropics. Our estimates are 60–90 % larger than the most recent global average tropospheric ozone RF estimates with online modelling. Our study underlines the importance of the evolution of ozone vertical profiles for the tropospheric ozone RF.

We use an offline radiative transfer model driven by IAGOS aircraft observations, to estimate the tropospheric ozone radiative forcing (RF) at decadal time scale (two time intervals between 1994–2004 and 2011–2016 or 2019), over 11 selected Northern Hemispheric regions. On average, we found a systematic positive trend in the tropospheric ozone column (TOC) for both time intervals, even if trends are reduced in 2019 (∆TOC +2.5±1.7 DU, +9.3±7.7 %) with respect to 2011–2016 (∆TOC +3.6±2.0 DU, +14.9±11.5 %). The reduced TOC average trend in 2019 with respect to 2011–2016, originates mostly from decreases of the lower tropospheric ozone column (LTOC) trends and limited variations for upper tropospheric ozone column (UTOC) trends, in the tropics. These average reductions in TOC trends are not accompanied with reductions of the tropospheric ozone RF, between 2011–2016 (4.2±2.4 mW m^-2 per year) and 2019 (3.8±3.6 mW m^-2 per year). This disconnection depends by the smaller RF sensitivity to LTOC than UTOC changes. Correspondingly, the total tropospheric ozone RF sensitivity varies between 18.4±7.4 mW m^-2 per DU, in 2011–2016, and 31.6±20.3 mW m^-2 per DU, in 2019. About 84–85 % of the tropospheric ozone RF occurs in the longwave, with ~4–6 % larger values of this proportion in the tropics than in the extra-tropics. Our estimates are 60–90 % larger than the most recent global average tropospheric ozone RF estimates with online modelling. Our study underlines the importance of the evolution of ozone vertical profiles for the tropospheric ozone RF.

Air quality remains a serious threat to urban residents; it is the primary contributor to respiratory illnesses. Those living in densely populated neighborhoods are particularly vulnerable. Despite considerable advancements in our overall understanding of urban air pollution, our insights into neighborhood- and street-level pollution remain insufficient. Dense urban neighborhoods are dominated by tall buildings and high levels of traffic, leading to complex flow patterns and uneven distribution of primary pollutants. Herein, we delve into the street and neighborhood-scale pollution dynamics in New York City, harnessing both mobile and in-situ observations. We used a backpack fitted with research-grade instruments to monitor particulate matter (PM2.5) and ozone in the summer of 2023. Between July and August, nearly 50 runs were conducted, sampling multiple neighborhoods during various time periods. In-situation observations from multiple public air quality networks were also included in our analysis. Our results show a high degree of uniformity in street-level ozone concentration in NYC, while the particulate matter concentration varied significantly. On days impacted by synoptic disturbances, both ozone and particulate matter concentrations were nearly uniform throughout the city. The fixed ground stations were able to adequately capture the median PM2.5 concentration. However, they missed the extremes, which were, in some cases, two to five times the median value. The observations were also used to validate an urbanized WRF-Chem model and satellite-derived measurements. The numerical simulations conducted at 4km X 4km resolution performed better than the current forecast model in predicting both PM2.5 and ozone concentration.

We use an offline radiative transfer model driven by IAGOS aircraft observations, to estimate the tropospheric ozone radiative forcing (RF) at decadal time scale (two time intervals between 1994–2004 and 2011–2016 or 2019), over 11 selected Northern Hemispheric regions. On average, we found a systematic positive trend in the tropospheric ozone column (TOC) for both time intervals, even if trends are reduced in 2019 (∆TOC +2.5±1.7 DU, +9.3±7.7 %) with respect to 2011–2016 (∆TOC +3.6±2.0 DU, +14.9±11.5 %). The reduced TOC average trend in 2019 with respect to 2011–2016, originates mostly from decreases of the lower tropospheric ozone column (LTOC) trends and limited variations for upper tropospheric ozone column (UTOC) trends, in the tropics. These average reductions in TOC trends are not accompanied with reductions of the tropospheric ozone RF, between 2011–2016 (4.2±2.4 mW m^-2 per year) and 2019 (3.8±3.6 mW m^-2 per year). This disconnection depends by the smaller RF sensitivity to LTOC than UTOC changes. Correspondingly, the total tropospheric ozone RF sensitivity varies between 18.4±7.4 mW m^-2 per DU, in 2011–2016, and 31.6±20.3 mW m^-2 per DU, in 2019. About 84–85 % of the tropospheric ozone RF occurs in the longwave, with ~4–6 % larger values of this proportion in the tropics than in the extra-tropics. Our estimates are 60–90 % larger than the most recent global average tropospheric ozone RF estimates with online modelling. Our study underlines the importance of the evolution of ozone vertical profiles for the tropospheric ozone RF.

The quantification of long-term free-tropospheric ozone trends is essential for understanding the impact of human activities and climate change on atmospheric chemistry, but is challenged by the diversity between satellite tropospheric ozone records and the sparse temporal and spatial sampling of ground-based measurements. Here, we explore if a more consistent understanding of the geographical distribution of tropospheric ozone column (TrOC) trends can be obtained by focusing on regional trends calculated from ground-based measurements. Regions were determined with a correlation analysis between modelled TrOCs at the site locations. For those regions, TrOC trends were estimated with Quantile Regression and Dynamical Linear Modelling for the Trajectory-mapped Ozonesonde dataset for the Stratosphere and Troposphere (TOST), and with a linear mixed-effects modelling (LMM) approach to calculate synthesized trends from the homogenized HEGIFTOM (Harmonization and Evaluation of Ground-based Instruments for Free-Tropospheric Ozone Measurements) individual site trends. For different periods (1990–2021/22, 1995–2021/22, 2000–2021/22), both approaches give increasing (partial) tropospheric ozone column amounts over almost all Asian regions (median confidence), and negative trends over the Arctic regions (very high confidence). Trends over Europe and North America are mostly weakly positive (LMM method) or negative (TOST). For both approaches, the 2000–2021/22 trends decreased in magnitude compared to the 1995–2021/22 for most of the regions, and for all time periods and regions, the pre-COVID trends are larger than the post-COVID trends. Our results enable the validation of global satellite TrOC trends, and assessment of the performance of atmospheric chemistry models to represent the distribution and variation of TrOC.

The quantification of long-term free-tropospheric ozone trends is essential for understanding the impact of human activities and climate change on atmospheric chemistry, but is challenged by the diversity between satellite tropospheric ozone records and the sparse temporal and spatial sampling of ground-based measurements. Here, we explore if a more consistent understanding of the geographical distribution of tropospheric ozone column (TrOC) trends can be obtained by focusing on regional trends calculated from ground-based measurements. Regions were determined with a correlation analysis between modelled TrOCs at the site locations. For those regions, TrOC trends were estimated with Quantile Regression and Dynamical Linear Modelling for the Trajectory-mapped Ozonesonde dataset for the Stratosphere and Troposphere (TOST), and with a linear mixed-effects modelling (LMM) approach to calculate synthesized trends from the homogenized HEGIFTOM (Harmonization and Evaluation of Ground-based Instruments for Free-Tropospheric Ozone Measurements) individual site trends. For different periods (1990–2021/22, 1995–2021/22, 2000–2021/22), both approaches give increasing (partial) tropospheric ozone column amounts over almost all Asian regions (median confidence), and negative trends over the Arctic regions (very high confidence). Trends over Europe and North America are mostly weakly positive (LMM method) or negative (TOST). For both approaches, the 2000–2021/22 trends decreased in magnitude compared to the 1995–2021/22 for most of the regions, and for all time periods and regions, the pre-COVID trends are larger than the post-COVID trends. Our results enable the validation of global satellite TrOC trends, and assessment of the performance of atmospheric chemistry models to represent the distribution and variation of TrOC.

We use an offline radiative transfer model driven by IAGOS aircraft observations, to estimate the tropospheric ozone radiative forcing (RF) at decadal time scale (two time intervals between 1994–2004 and 2011–2016 or 2019), over 11 selected Northern Hemispheric regions. On average, we found a systematic positive trend in the tropospheric ozone column (TOC) for both time intervals, even if trends are reduced in 2019 (∆TOC +2.5±1.7 DU, +9.3±7.7 %) with respect to 2011–2016 (∆TOC +3.6±2.0 DU, +14.9±11.5 %). The reduced TOC average trend in 2019 with respect to 2011–2016, originates mostly from decreases of the lower tropospheric ozone column (LTOC) trends and limited variations for upper tropospheric ozone column (UTOC) trends, in the tropics. These average reductions in TOC trends are not accompanied with reductions of the tropospheric ozone RF, between 2011–2016 (4.2±2.4 mW m^-2 per year) and 2019 (3.8±3.6 mW m^-2 per year). This disconnection depends by the smaller RF sensitivity to LTOC than UTOC changes. Correspondingly, the total tropospheric ozone RF sensitivity varies between 18.4±7.4 mW m^-2 per DU, in 2011–2016, and 31.6±20.3 mW m^-2 per DU, in 2019. About 84–85 % of the tropospheric ozone RF occurs in the longwave, with ~4–6 % larger values of this proportion in the tropics than in the extra-tropics. Our estimates are 60–90 % larger than the most recent global average tropospheric ozone RF estimates with online modelling. Our study underlines the importance of the evolution of ozone vertical profiles for the tropospheric ozone RF.

The quantification of long-term free-tropospheric ozone trends is essential for understanding the impact of human activities and climate change on atmospheric chemistry, but is challenged by the diversity between satellite tropospheric ozone records and the sparse temporal and spatial sampling of ground-based measurements. Here, we explore if a more consistent understanding of the geographical distribution of tropospheric ozone column (TrOC) trends can be obtained by focusing on regional trends calculated from ground-based measurements. Regions were determined with a correlation analysis between modelled TrOCs at the site locations. For those regions, TrOC trends were estimated with Quantile Regression and Dynamical Linear Modelling for the Trajectory-mapped Ozonesonde dataset for the Stratosphere and Troposphere (TOST), and with a linear mixed-effects modelling (LMM) approach to calculate synthesized trends from the homogenized HEGIFTOM (Harmonization and Evaluation of Ground-based Instruments for Free-Tropospheric Ozone Measurements) individual site trends. For different periods (1990–2021/22, 1995–2021/22, 2000–2021/22), both approaches give increasing (partial) tropospheric ozone column amounts over almost all Asian regions (median confidence), and negative trends over the Arctic regions (very high confidence). Trends over Europe and North America are mostly weakly positive (LMM method) or negative (TOST). For both approaches, the 2000–2021/22 trends decreased in magnitude compared to the 1995–2021/22 for most of the regions, and for all time periods and regions, the pre-COVID trends are larger than the post-COVID trends. Our results enable the validation of global satellite TrOC trends, and assessment of the performance of atmospheric chemistry models to represent the distribution and variation of TrOC.