Ozone is a greenhouse gas and, after water, the second most relevant contributor to global warming in the upper troposphere. Therefore, understanding and monitoring the processes contributing to ozone production is an important tool in observing the progression of climate change. The two main tropospheric precursors to ozone formation are nitrogen oxides (NO_x = NO + NO₂) and volatile organic compounds (VOC). Depending on their availability, ozone production can be limited by either of its precursors. In our study, we focus on processes contributing to ozone formation and loss in the upper tropical troposphere, where changes in ozone have one of the largest impacts on the radiative forcing. Based on modeled trace gas concentrations and meteorological parameters by the EMAC atmospheric chemistry - general circulation model, we analyze a variety of metrics including net ozone production rates (NOPR), the formaldehyde (HCHO) to NO₂ ratio and the share of methyl peroxyradicals (CH₃O₂) forming HCHO (α_CH3O2) in their ability to indicate the dominating ozone regime in the upper troposphere between 30°N and 30°S latitude.

How to cite: Nussbaumer, C. M., Pozzer, A., Lelieveld, J., and Fischer, H.: Ozone production and chemical regime analysis in the upper tropical troposphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-905, https://doi.org/10.5194/egusphere-egu23-905, 2023.

Ozone is a highly oxidative gas affecting human health, especially the impacts on the cardiovascular and respiratory systems. Ozone is usually formed through photochemical reactions outdoors and transported to the indoor environment. Occupants indoors might face an accumulated irritant issue due to high ozone reacting with human skin to produce several volatile organic compounds (VOCs), such as geranyl acetone (Ga), 6-methyl-5-hepten-2-one (6-MHO) and 4-oxopentanal (4-OPA), which might irritate skin and respiratory tract. In this study, the indoor air quality in a university classroom was monitored using air quality boxes (AQBs) comprising low-cost sensors for various gas species, including ozone, CO₂, NO_x, etc. The interaction processes between outdoor and indoor air, and human interference were investigated via a box model simulation of CO₂ and ozone temporal profiles. Both indoor CO₂ and ozone were significantly affected by the ventilation and number of occupants. CO₂ is primarily produced via human respiration and diluted via ventilation in the classroom, so the simulation of CO₂ profiles retrieves the ventilation efficiency and occupancy variation. With the derived parameters, ozone, mainly transported from the outdoors and consumed by room and human surface, is estimated to have deposition velocities of 0.028±0.0053 cm s^-1 and 0.45±0.15 cm s^-1 for room and human surface, respectively, consistent with the literature. The generation of Ga, 6-MHO, and 4-OPA depends on ozone consumption on human surfaces, and those VOCs might accumulate indoors for several ppb in a crowned room with poor ventilation. The integration of observation using low-cost sensors with the model simulation quantifies the physical and chemical processes controlling indoor ozone and organic ozonolysis. Furthermore, it might provide proper ventilation strategies to maintain good indoor air quality with energy efficiency based on the occupants.

How to cite: Chen, F., Huang, W.-C., Hwang, W.-C., and Hung, H.-M.: The Interaction and Health Impacts between Ozone and Occupants Indoor: Observation and Model Simulation in a University Classroom, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1564, https://doi.org/10.5194/egusphere-egu23-1564, 2023.

In all areas of research, robust, versatile and high-performance data infrastructures are needed.

TOAR is a global research project to analyze the spatial distribution and temporal evolution of ozone in the troposphere and to provide data of surface ozone measurements and its precursors for assessing the impact of ozone on human health, vegetation and climate.

These observational data are collected from various environmental agencies and programs, universities and individual researchers under different requirements for data formats, metadata standards and quality control, and are harmonized and quality-controlled into the TOAR database using our infrastructure. All data in the database are easily accessible through open, freely available and well-documented web services. The TOAR data centre team is committed to the FAIR principles and aims to achieve the highest standards with respect to data curation, archival, and re-use. We established a common approach for data ingestion to ensure that data from different sources is handled in a defined and equal way and that all modifications are recorded in a provenance log. Clear rules are defined how the submitted metadata is mapped into the metadata schema used by the TOAR database. To harmonize the data quality, we employ automated tests of different granularity using statistical methods and heuristics, which assign a score for each data point. Those scores are then translated into categorical data quality flags.

The TOAR data infrastructure has proven that it can handle large amounts of data operationally in a performant way. It not only provides standardized REST-API access to the underlying database but also allows for the integration and linking of additional services. For example, the results of the quality control tool mentioned above can be accessed as interactive charts with tables of aggregated figures. Furthermore, we offer analysis services that implement a variety of statistical evaluations and metrics to allow users to get aggregated, ready-to-use data in a consistent, reproducible, and interoperable manner and also allow for bulk raw data downloads. It is also possible to invoke a service to calculate air pollution trends with quantile regression.

During development, we emphasized the reusability of the database infrastructure code. Therefore, we believe that the database layout, the related workflows for data ingestion and processing, and the service architecture can be transferred to other types of environmental data and perhaps even to data from other disciplines.

With the TOAR database infrastructure, the TOAR community receives a cutting-edge repository and system of web services that allows for easy-to-use, fast, flexible, and reproducible analyses of air pollution and associated data.

How to cite: Schröder, S., Selke, N., and Schultz, M. G.: The TOAR data infrastructure: A generalised database infrastructure for environmental time series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1848, https://doi.org/10.5194/egusphere-egu23-1848, 2023.

Ambient concentrations of 23 volatile organic compounds (VOCs) measured at London Marylebone Road (LMR), an urban traffic site in the UK were analysed over a period of 22 years (1998-2019) to assess the impact of pollution control strategies. A significant decrease in ambient concentration is seen for the majority of VOCs analysed with total VOC burden decreasing by 76% across the period studied, likely as a result of legislative controls. This analysis was extended to consider the contribution of VOCs to ozone formation at this site utilising POCP values. Similarly, the overall reactivity of the VOC burden at LMR has resulted in a significant decrease of just under 12% per year in ozone formation potential over 1998-2019 at this site. The declines in ozone formation potential for VOCs associated with road traffic emissions are all in good agreement at 11-13% decrease per year. VOCs related to non-traffic sources, namely ethane and propane from natural gas leakage, did not see a significant decline over the study period. The variation and composition of the overall VOC burden was compared across three decadal time periods (1998-2000, 2001-2010, 2011-2019) and saw an increase in significance of these pollutants (with ethane and propane moving from the fifth and eleventh largest contributors in 1998-2000 to the first and second largest contributors in 2011-2019, respectively) suggesting they are not sufficiently controlled under current legislation. The increase in significance of ethane and propane was mirrored in their contribution to ozone generation potential but ethene continues to substantially dominate in contribution to ozone formation potential by a factor of 4 and 5 compared with ethane and propane, respectively. Alkanes are typically considered to be less important in the context of ozone formation potential due to their low reactivity in comparison to other VOCs. Analysis presented herein demonstrates the negative impact of ignoring such emissions as their influence begins to grow such that alkanes now represent 3 of the 5 highest contributors to tropospheric ozone formation at this site (in order of contribution: ethene > propene > n-butane > ethane > propane). The importance of high-quality gas-phase kinetic studies to determine the impact of VOCs in ozone production is clear and the usefulness of metrics such as POCPs is demonstrated.

How to cite: Holland, R., Khan, M. A. H., and Shallcross, D.: An investigation of the contributions of VOCs to urban ozone production in the U.K., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2687, https://doi.org/10.5194/egusphere-egu23-2687, 2023.

Carbon monoxide (CO) plays an important role in both air quality and climate. Photochemical oxidation of CO produces ozone (O3) and carbon dioxide (CO2) while also affecting the lifetime of methane (CH4) through reactions with the hydroxyl radical (OH). Because CO2, CH4 and O3 are greenhouse gases, emissions of CO have an indirect radiative forcing, estimated at 0.22 W/m2. Ground-level O3 and CO are also air pollutants that affect human and ecosystem health. Quantifying trends in carbon monoxide is essential for understanding trends in tropospheric ozone, especially in background regions. Using the 22-year data record from MOPITT (Measurements of Pollution In The Troposphere), we show global and regional trends from satellite observations of atmospheric CO. We also examine trends in CO emissions based on model inversions for CO emitted by biomass burning (BB) and fossil fuels (FF) and from chemical production from emissions of biogenic (BG) VOCs (volatile organic compounds). We find that CO concentrations and CO emissions from BB and FF have been mostly decreasing globally, with some notable regional exceptions.

How to cite: Worden, H. and Buchholz, R.: Global and regional trends of atmospheric carbon monoxide – a background ozone precursor, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2952, https://doi.org/10.5194/egusphere-egu23-2952, 2023.

Tropospheric ozone, an important air pollutant and short-lived climate forcer, is changing globally with reported increases over emission regions that can influence ozone downwind. Here, ozone trends are examined in the Arctic troposphere, where surface warming is around four times faster than the global mean. Trends at the surface and in the free troposphere are estimated for 1993-2019 using available surface and ozonesonde data. Observed trends are also compared to modelled trends from the Arctic Monitoring Assessment Project (AMAP) multi-model evaluation, where models were run with the same anthropogenic emissions from 1990 to 2015 (Whaley et al., 2022, ACP). Findings include observed increases in annual mean surface ozone at Arctic coastal sites notably driven by increases during winter that are concurrent with decreasing surface carbon monoxide trends. Positive trends are also diagnosed at most high-Arctic ozonesonde sites in the wintertime free troposphere (up to 400 hPa). These ozone increases, which tend to be overestimated by the multi-model median (MMM) trends, are likely to be due to reductions in anthropogenic emission of nitrogen oxides at mid-latitudes leading to less ozone titration and influencing northern hemispheric ozone. Springtime increases are also found at the surface in northern coastal Alaska/Greenland but not in the MMMs. Causes are unknown but may be related to changing Arctic sea-ice or weather patterns affecting ozone sources or sinks. In contrast, surface ozone trends in northern Scandinavia are negative during spring, likely a response to decreasing ozone precursor emissions in Europe. MMM trends are also negative but generally overestimated. Springtime trends in the free troposphere also tend to be negative while summer trends are positive. Changes in ozone precursor emissions, the downward stratospheric ozone flux or general circulation may be contributing to these seasonal variations in the trends. The implications of these reported trends and model behaviour are discussed.

How to cite: Law, K., Liengaard Hjorth, J., Pernov, J., Whaley, C., Skov, H., Collaud Coen, M., Langner, J., and Arnold, S. and the Arctic tropospheric ozone team: Tropospheric Ozone Trends in the Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3552, https://doi.org/10.5194/egusphere-egu23-3552, 2023.

The first phase of the Tropospheric Ozone Assessment Report (TOAR-I), an activity of the International Global Atmospheric Chemistry Project (IGAC), provided the first comprehensive view of surface ozone’s global distribution and trends, based on all available surface ozone observations.  TOAR-I focused on a present-day period of 2010-2014, and calculated trends for a range of periods, but primarily focused on the most recent years of 2000-2014, plus long-term trends from the 1970s/1980s through 2014.  Subsequent studies of ozone trends using data after the TOAR-I cut-off of 2014, have shown a wide range of trends, both positive and negative, at monitoring sites around the world.  To keep up with the rapid changes of ozone at urban, rural and remote locations this study provides current world-wide ozone trends using observations through 2021, archived in the newly updated TOAR-II Database of Surface Observations.  Focus is placed on two ozone metrics relevant to human health impacts:  1) the annual peak of the 6-month running mean of maximum daily 8-hour average ozone; this metric is used by Global Burden of Disease (GBD) to estimate mortality due to long-term ozone exposure; 2) the number of days per year that exceed 70 ppbv, based on the maximum daily 8-hour average ozone value; this value corresponds to the primary U.S. National Ambient Air Quality Standards for ozone and is relevant to short-term ozone exposure.  Global maps will indicate the regions of the world where the potential for ozone impacts on human health are greatest (and least), and will show regions where ozone air quality is either improving or degrading.  Despite our effort to use all available surface ozone observations, large data gaps exist across many regions of the world, especially in developing nations, and GBD maps generated by data fusion will be used to identify, and to estimate ozone levels in the data-poor regions. 

How to cite: Cooper, O., Chang, K.-L., Schröder, S., Selke, N., West, J. J., and Serre, M.: The global distribution and trends of ozone health-based metrics:  New results from the TOAR-II Database, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3737, https://doi.org/10.5194/egusphere-egu23-3737, 2023.

In response to the severe air pollution issue, the Chinese government implemented two phases (Phase I: 2013-2017, Phase II: 2018-2020) of clean air actions since 2013, resulting in a significant decline in fine particles (PM_2.5) during 2013-2020, while the maximum daily 8 h average ozone (MDA8 O₃) increased by 2.6 μg m^-3 yr^-1 during the same period. Here, we derived the drivers behind the rising O₃ concentrations during the two phases of clean air actions by using a bottom-up emission inventory, a regional chemical transport model, and a multiple linear regression model. We found that both meteorological variations (3.6 μg m^-3) and anthropogenic emissions (6.7 μg m^-3) contributed to the growth of MDA8 O₃ from 2013 to 2020, with the changes in anthropogenic emissions playing a more important role. The anthropogenic contributions to the O₃ rise during 2017-2020 (1.2 μg m^-3) were much lower than that in 2013-2017 (5.2 μg m^-3). The lack of volatile organic compound (VOC) control and the decline in nitrogen oxides (NO_X) emissions were responsible for the O₃ increase in 2013-2017 due to VOC-limited regimes in most urban areas, while the synergistic control of VOC and NO_X in Phase II initially worked to mitigate O₃ pollution during 2018-2020, although its effectiveness was offset by the penalty of PM_2.5 decline. Future mitigation efforts should pay more attention to the simultaneous control of VOC and NO_X to improve O₃ air quality.

How to cite: Liu, Y., Geng, G., Cheng, J., Liu, Y., Xiao, Q., Liu, L., Shi, Q., and Zhang, Q.: Drivers of Increasing Ozone during the Two Phases of Clean Air Actions in China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5103, https://doi.org/10.5194/egusphere-egu23-5103, 2023.

Surface ozone pollution is of great concern in current air quality management in China. The North China Plain (NCP), which is home to 300 million people, has the highest ozone level and increasing trend.  While earlier studies of ozone pollution focused on summer season, here we show that ozone pollution out of summer season over the North China Plain is also very emerging.  Firstly, ozone has been very low during winter haze (particulate) pollution episodes. However, the abrupt decrease of NOx emissions following the COVID-19 lockdown in January 2020 reveals a switch to fast ozone production during winter haze episodes with MDA8 ozone of 60 to 70 ppb. This remarkable switch to an ozone-producing regime in January–February following the lockdown illustrates a more general tendency since 2013 of increasing winter–spring ozone in the North China Plain and increasing association of high ozone with winter haze events, as pollution control efforts have targeted NOx emissions while VOC emissions have limited regulations. Secondly, we find that ozone episodes comparable with those in summer season can also occur in early-autumn over NCP, resulting in the emerging of two-peak ozone pollution (June and September) for some years. The statistical analysis show that this interannual variation is driven by the anomalies in the large-scale sea surface temperature (SST) patterns. These results highlight the urgency of ozone pollution controls out of summer season in China.

How to cite: Li, K., Zhang, D., and Hou, J.: Emerging of surface ozone pollution beyond summer season over the North China Plain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7127, https://doi.org/10.5194/egusphere-egu23-7127, 2023.

High emissions of NOx and anthropogenic VOCs from urban areas are a major source of tropospheric ozone production. Tropospheric ozone is a secondary air pollutant that is harmful to human health as well as crop and ecosystem productivity, and an important greenhouse gas. It is formed from the chemical processing of NOx and VOCs in a non-linear cycle, making ozone reduction strategies challenging. Urban centres across the world are developing at different rates and emitting different combinations and concentrations of chemical species, resulting in location specific drivers of urban ozone concentrations. Alongside this, different countries and cities have implemented a wide range of location specific air quality and climate change measures to reduce air pollution and greenhouse gas emissions. The diversity of these policies over the past few decades has further led to different outcomes for secondary pollutant formation across the globe.

As part of TOAR-II, the Urban Ozone Working Group explores the long-term trends in urban ozone concentrations over the past 20 years on a global scale. Using ground based data from global Air Quality networks, trends in ozone concentrations of > 12 cities across different continents are presented, and temporal changes in ozone trends are identified. This study utilises the TOAR database, accessed via the TOAR Data Portal, which collects hourly data of long-term surface air quality measurements from over 10,000 stations globally. Where sufficient long-term NOx and VOC data are available, ozone concentration trends are compared to trends in its precursor species. 

Trends in ozone concentrations are then related to the state of development of the city using factors such as GDP and the UN City Development Index, and an assessment of how cities in different phases of development are contributing to tropospheric ozone across the world is discussed. Trends in ozone will also be compared to country and city specific changes in air quality and net zero policy interventions.

How to cite: Nelson, B., Lee, J., and Lu, K.: Long-term Ozone Trends in Different Urban Developments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5600, https://doi.org/10.5194/egusphere-egu23-5600, 2023.

As part of the Ozone and Precursors in the Tropics (OPT) working group of the Tropospheric Ozone Assessment Report Phase 2 (TOAR-II), we present the first results on the distribution of tropospheric ozone (O3) and its precursors (carbon monoxide, CO; formaldehyde, HCHO; nitrogen dioxide, NO2) in the tropics over the past 20-25 years. The goal is to give an overview of the seasonal, geographical and vertical variabilities of tropical tropospheric O3 and its precursors. To do so, we use in situ measurements of O3 and its precursors from surface sites, sounding balloons (SHADOZ) and instrumented aircraft (IAGOS and ATOM), as well as ground-based (FTIR) and spatial (IASI, OMI, GOME-2) remote-sensed observations. The observations are averaged monthly over the longest available time-period as well as over the first five years of the time period. The results for these two time periods give the context to interpret distributions and variabilities of O3 and its precursors over the most recent five years as we call it “Present-day”.  Special emphasis is given to the differences of O3 and its precursors’ distributions between remote and polluted regions and to the relationships between the gaseous species. Model output will be included to fill gaps in space and time when necessary to help the interpretation of the analysis based on observations.

From IAGOS measurements, the highest O3 and CO maxima occur in the lower troposphere of Northern Hemisphere Africa, which remains the most influenced by biomass burning. CO maxima are attributed using SOFT-IO model to anthropogenic emissions by 60%. Second maxima are observed in the lower troposphere of Asia, mostly due to anthropogenic emissions. The highest amount of transported CO in the tropics originates from Africa.

How to cite: Sauvage, B., Gaudel, A., Fadnavis, S., Tsivlidou, M., Saxena, P., Barret, B., Li, M., Singh, B. B., Masiwal, R., Sonwani, S., Im, U., Cohen, Y., Singh, S., Hubert, D., Keppens, A., Lambert, J.-C., Wespes, C., Petropavlovskikh, I., Gerosa, G., and Worden, H. and the List of co-authors: Present-day distribution of tropospheric ozone and precursors in the tropics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5293, https://doi.org/10.5194/egusphere-egu23-5293, 2023.

With a few exceptions, most of the studies on tropospheric ozone (O₃) variability following the restriction measures related to the spread of COVID-19 focused on emissions-prone or urban environments. In this work, we investigated the impact of the pandemic restriction measures on surface O₃ at several high-altitude remote and rural sites across North America and Western Europe. O₃ monthly anomalies, computed with respect to the baseline period 2000–2019, were calculated for 2020 and 2021, to explore the impact of the economic downturn in 2020 and the economic recovery in 2021. A total of 41 high-altitude sites were analyzed: 5 remote stations in western Europe, 19 rural sites in the western US, 4 sites in the western US downwind of highly polluted areas, 4 sites in the eastern US, plus 9 remote sites across the globe to provide a "global" picture for comparison. In 2020, most of European high-altitude sites showed persistent negative anomalies for spring (March-May, i.e., MAM; average of -1.8 ppb) and summer (June-August, i.e., JJA; -2.7 ppb), except for April (1.8 ppb). The pattern was similar in 2021 (-1.8 ppb for both MAM and JJA), except for June (1.8 ppb). The sites in the western US showed similar behavior, with negative anomalies in 2020 (-2.1 ppb for MAM and -0.5 ppb for JJA), and 2021 (-0.5 ppb for MAM). However, the JJA seasonal average was influenced by strong positive anomalies in July, due to the large spread of wildfires in the western US. The polluted rural sites in the western US showed a negative O₃ anomaly for MAM 2020, and a slight recovery in 2021, resulting in a positive anomaly for MAM and alternating positive and negative anomalies in JJA. The eastern US sites were characterized by below baseline numbers for both MAM and JJA 2020, while in 2021 the negative values generated a "dipole" structure, with the western sites influenced by the presence of 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 across the globe. A few sites did not experience any relevant variations (e.g., the Antarctic sites), while others showed signals of influence from the surrounding environment, or behaviors like those observed for European and US remote sites. We also attempted anomaly attribution by analyzing the behavior of several O₃ precursors (e.g., surface and columnar CO, NO, and NO₂) from the CAMS reanalysis, and the patterns of emissions reductions for 2019, 2020, and 2021.

How to cite: Putero, D., Cooper, O. R., Beachley, G., Chang, K.-L., Couret, C., Effertz, P., Jaffe, D., Lynch, J., Petropavlovskikh, I., Puchalski, M., Sharac, T., Sive, B. C., Steinbacher, M., Torres, C., and Cristofanelli, P.: Fingerprints of the COVID-19 economic downturn and recovery on ozone anomalies at remote high-altitude sites in North America and Western Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6682, https://doi.org/10.5194/egusphere-egu23-6682, 2023.

Measurements of leaf-level stomatal conductance (g_sto) are central to the ozone (O₃) risk assessment as the allow to recorded environmental response functions that describe how a wheat cultivar responds to different environmental stressors. The calculation of Triticum aestivum yield loss based on the absorbed O₃ phytotoxic dose over a threshold of y (POD_y) has been introduced as a new way to conduct ozone  risk assessment. 

In this study we present environmental response functions of two triticum aestivum cultivars grown as irrigated winter wheat in the state of Punjab, in the North West Indo Gangetic Plain based on measurements conducted during winter 2016-17, 2017-18, and 2018-19. The cultivars PBW550 and HD2967 were directly obtained from breeders and were sown on November 15^th in 2016-17 and 2017-18, and in a relay seeding experiment on November 1^st, 15^th and December 1^st in 2018-19.

We use meteorological observations and ozone measurements obtained at the Central Atmospheric Chemistry facility of IISER Mohali in Punjab, India between November 2016 and April 2019 to derive environmental response function for these two cultivars and estimate triticum aestivum relative yield losses and crop production losses due to ozone. We demonstrate that environmental response functions are not only useful to assess the impact of ozone on plant growth but that they can also be used to assess the impact of heat stress and climate change on yields. We show that modifying the phenology function used in the DO3SE assessment such that it incorporates the impact of heat stress experienced between anthesis to maturity permits a more accurate assessment of the impact of ozone on the wheat yield. We also demonstrate that a thermal time calculation method that is consistent with the temperature response function used in the DO₃SE improves the quality of the assessment.

We evaluate the impact of both heat stress and ozone exposure during different growth stages on several yield parameters including the number of active tillers, 1000-grain weight, flower sterility, number of shrivelled grains.

Late sowing typically not only results into high thermal stress during sensitive growth stages, but also in higher ozone exposure. We find that PBW550 is more sensitive to stress during the grain filling stage than HD2967. However, for both cultivars moderate heat and ozone stress can be associated with superior rather than reduced yields in the real world. We explain this yield-loss yield paradox with the help of meteorological observations.

How to cite: Sinha, B., Saha, S., Meena, A., Singh, S., Kharra, P., Adarsh, A., Ashish, A., Anand, S., and Ram Kishore, Y.: Assessment of crop yield losses for Triticum aestivum in Punjab and Haryana using in-situ measurements, relay seeding experiments and the DO3SE model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7946, https://doi.org/10.5194/egusphere-egu23-7946, 2023.

Several Working Groups have been established within the frame of the second phase of the Tropospheric Ozone Assessment Report (TOAR-II). The Tropospheric Ozone Precursors focus Working Group (TOP WG) aims to examine the current regional and global distribution, variability and trends of ozone precursors. Part of our strategy has been to analyze in greater detail different regions of the globe. In particular, this work addresses South America, a region characterized by densely populated urban areas with high air pollution levels.

We use data from air quality monitoring networks that measure surface-level ozone, nitrogen oxides, carbon monoxide and meteorological variables. To date, we have validated and incorporated monitoring stations from Brazil (51), Chile (18), Colombia (13) and Ecuador (6) into our central database. To evaluate short- and long-term ozone exposure, we use the maximum daily 8-hour average (MDA8) and the peak season guideline proposed by the World Health Organization (WHO) set at 51 and 31 ppbv, respectively. We applied the Quantile Regression (QR) method to analyze ozone and precursor network trends. We also identified points in time series that mark changes in trends through a piecewise function.

The highest MDA8 ozone for 2015-2021 was found in São Paulo (52 ppbv) and Santiago (51 ppbv). In São Paulo, the short-term ozone exposure decreased by 7% compared to the average of the years prior to 2015 (period analyzed in TOAR phase I), while in Santiago, it increased by 10%. In Bogota and Quito, the MDA8 complied with the WHO guidelines (33 and 32 ppbv, respectively). Similarly, the long-term ozone exposure guideline was exceeded in São Paulo (39 ppbv) and Santiago (40 ppbv), while Bogota (25 ppbv) and Quito (26 ppbv) complied. The trend analysis showed that Quito was the only city with a negative ozone trend of -0.10 ppb/year (50th percentile) for the analyzed period. In turn, the São Paulo trend increased after 2008 (0.43 ppbv/year), while Santiago and Bogota have increased since 2017 (0.93 ppbv/year and 1.3 ppbv/year, respectively). We highlight that the positive trend in Santiago is driven mainly by the high percentiles (>70th). Underlying processes that explain trends involve more efficient photochemical ozone formation (e.g., NO₂/NO_x trend) and meteorological factors.

This ongoing work aims to include more South American cities and background stations already available in the new TOAR database. Finally, we will project ozone trends for the next decade using machine learning techniques (random forest) under precursor emission scenarios and temperature projections.

How to cite: Seguel, R., Castillo, L., Opazo, C., Rojas, N., Nogueira, T., Cazorla, M., Gavidia, M., Gallardo, L., Elshorbany, Y., and Menares, C.: Surface ozone trends and precursor attribution in South America, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9772, https://doi.org/10.5194/egusphere-egu23-9772, 2023.

Tropospheric ozone is an important greenhouse gas, is detrimental to human health and crop and ecosystem productivity, and controls the oxidizing capacity of the troposphere. Previous studies, using models, aircraft and remote observation datasets, have shown that the tropospheric ozone has increased significantly in the tropical regions. Sensitivities studies have also showed that the ozone precursor emissions in these tropical regions have been increasing for the past three decades. For this paper, we will work with worldwide scientists to investigate how the emission evolves in the tropical regions from 1995 to 2019, and how these changes have contributed to the global and other receptor regions tropospheric ozone burden increases, by using ensemble state-of-the-art global and regional chemical transport models.

How to cite: Zhang, Y., Li, L., Tang, T., Gaudel, A., Sauvage, B., and West, J. J. and the Yuqiang Zhang: The influences of ozone precursor changes in tropical regions on tropospheric ozone burden, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10700, https://doi.org/10.5194/egusphere-egu23-10700, 2023.

Anthropogenic pollution, including primary compounds such as nitrogen oxides (NOx) and organics, but also secondary pollutants such as ozone, are a threat to sensitive mountain ecosystems, which are already under continued threat of diminished area, due to climate change. This study analyzes two days of volatile organic compound (VOC) concentrations, including a limited set of carbonyls, at the Lulin Atmospheric Background Station (LABS; 2,862 meters asl), which is a well-known remote sub-tropical site that receives long-range transported air masses from various clean and polluted origins. VOCs were sampled in a canister and analyzed by GC-MS/FID, while carbonyls were trapped on Supelco DNPH-coated cartridges and quantified by HPLC-UV. Routine LABS measurements of ozone, CO, and PM_2.5 were also utilized; Copernicus Atmospheric Monitoring Service (CAMS) reanalysis NOx and HNO₃ concentrations were further incorporated into an oxidant modeling analysis. In comparing the two sampling days, the first day was characterized by hazier conditions (~3 times higher PM_2.5 concentrations) and 2-3 times higher VOC and CO concentrations and calculated OH reactivity values. Based on a HYSPLIT back-trajectory analysis, the first day was influenced by air that had a longer residence time at lower altitudes over South China, while the second day was characterized by higher level transport. Also influential at the site are subsidence events that bring drier air that can contain high ozone and NOy species. The measurement and reanalysis data were incorporated into a 0-dimensional modeling analysis (F0AM) of the gas-phase oxidation chemistry in order to further characterize the different air masses that influence this sensitive mountain area. While the first day also was simulated to have higher level of ozone production, the second day captured an afternoon spike in pollutants and ozone production that was likely driven by upslope mountain valley air sourced for lower altitudes in Taiwan. Thus, the oxidation potential in this environment is characterized by large swings driven by local upslope pollution, subsidence events, and long-range transported pollution from the Asian continent, which ultimately dictate the pollutant exposure for this sensitive ecosystem.

How to cite: Griffith, S. M., Liu, W.-T., Chen, F.-I., Hidayati, E., Chang, C.-C., Wang, J.-L., and Lin, N.-H.: Volatile Organic Compound Measurements and Oxidant Modeling at a Remote Mountain Site in the western North Pacific, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10969, https://doi.org/10.5194/egusphere-egu23-10969, 2023.

The variability of ozone (O₃) concentration in China has received wide attention since the emission reduction policies were implemented in 2013. At present, it is still a great challenge to clarify the causes of O₃ change in the Yangtze River Delta (YRD) region. In this work, we applied the Community Multiscale Air Quality (CMAQ) model to investigate the impacts of precursor emissions (such as non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO_X)) and meteorological conditions on the summertime maximum daily 8-h average (MDA8) O₃ variation in Nanjing, a megacity in YRD between 2015 and 2020. The meteorological contribution was quantified by the difference between the sensitive scenario fixing the anthropogenic emission at 2015 level while remaining the meteorology unchanged in 2020 and baseline scenario in 2015. The impact of anthropogenic emissions was then estimated by the difference between the total change of observed MDA8 O₃ and the meteorological contribution. Compared with 2015, the observed MDA8 O₃ in Nanjing decreased by 19.1 μg/m³ during August in 2020, with the meteorological conditions and anthropogenic emissions contributing 8.4 μg/m³ (44%) and 10.7 μg/m³ (56%), respectively. The anthropogenic emissions of VOCs and NO_X in Nanjing in August 2020 decreased by 7.8% and 11.7%. Temperature, relative humidity (RH) and wind filed are key meteorological parameters affecting the O₃ formation. The lower temperature (30.3 ℃ in 2020 compared with 32.4 ℃ in 2015) and higher RH (76.9% in 2020 and 56.9% in 2015) in early August (especially in 4-5) as well as the clean air mass brought by the stronger wind (5.1 m/s in 2020 and 2.5 m/s in 2015) during August 13-14 in 2020 mainly resulted in a drop of O₃. The longer hydroxyl radical (OH) chain length and higher ozone production efficiency (OPE) indicate that the reduction of anthropogenic emissions accelerated the NO_X cycle and makes O₃ more sensitive to NO_X. Using the EKMA diagram, we estimated that O₃ formation has shifted from VOCs-limited in 2015 to a transition regime jointly controlled by VOCs and NO_X in 2020. Our study is consistent with previous ones that in reducing the urban ozone pollution, both the precursor emissions and meteorological conditions should be considered that with the benefit of meteorological conditions, reasonable emission reduction measures could have a positive effect on the reduction of O₃ concentration in Nanjing during August in 2015 and 2020.

How to cite: Li, L., Li, J., Qin, M., Xie, X., and Hu, J.: Impacts of anthropogenic and non-anthropogenic factors on summertime ozone variation from 2015 to 2020 in the Yangtze River Delta, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11130, https://doi.org/10.5194/egusphere-egu23-11130, 2023.

We present an update on the status of the tropospheric ozone data products retrieved from satellite observations. Specifically, we will highlight data from the TRopospheric Ozone and its Precursors from Earth System Sounding (TROPESS) project which is a NASA effort that provides retrievals of atmospheric ozone utilizing radiances from a variety of different satellite instruments. The TROPESS project provides ozone data that provides additional data that can used with record established by the Tropospheric Emission Spectrometer (TES) which flew on NASA’s Aura satellite. The new multispectral retrievals of ozone utilize the (Multi-Spectra, Multi-Species, Multi-Sensors Retrievals of Trace Gases (MUSES) retrieval framework to produce consistent estimations of ozone from different satellite radiances. TROPESS ozone data products include those using data from the Atmospheric Infrared Sounder (AIRS), the Ozone Monitoring Instrument (OMI) and the Cross-track Infrared Sounder (CrIS) instruments. The TROPESS joint-satellite data products provide ozone retrievals with vertical sensitivity similar to that seen in TES observations and allow a continuation of the TES ozone data record. Utilizing satellite instruments that observe with wide swaths will provide much broader spatial sampling than TES was able to provide.

The TROPESS team is currently processing ozone data records using radiances from CrIS, AIRS, OMI, TROPOMI and retrievals using combinations of the different satellites. All of the TROPESS products are being validated through comparisons to ozonesondes as well as comparisons to chemical reanalysis products. We will provide an update on the results from these comparisons as well highlighting the differences in vertical sensitivity and spatial sampling of the different products. We will highlight the differences in the sensitivity of the retrievals to ozone in the troposphere and validation of the satellite retrievals at those pressure levels. We will show statistical analysis for the errors in the satellite retrievals and their comparisons to the ozonesondes.

Lastly, we will present results showing the time record of the different ozone products, including showing how the comparisons to models and ozonesondes change with time. Utilizing the AIRS and OMI instrument data will allow us to examine the tropospheric ozone data record going back to 2005 and we will share results of how the TROPESS products can contribute to determining trends in tropospheric ozone.

How to cite: Osterman, G. and Bowman, K.: Update on the TROPESS ozone data products: Evaluation, validation and a preliminary examination of their utility in tropospheric ozone trend analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11258, https://doi.org/10.5194/egusphere-egu23-11258, 2023.

In the past decade, ozone (O₃) pollution has become a severe environmental problem in major cities in China. Here, based on available observational records, we investigated the long-term trend of ozone pollution in China during 2014–2020. Ozone concentrations were slightly higher in urban areas than in non-urban areas. During these seven years, the highest ozone concentrations primarily occurred in summer in northern China, and in autumn or spring in southern China. Although ozone precursors, including nitrogen oxides (NO_X) and carbon monoxide (CO), continuously decreased, ozone concentrations generally increased throughout the seven years with a slower increasing rate after 2017. The long-term trend of ozone concentrations differed across seasons; especially from 2019 to 2020 when ozone concentrations decreased in summer and increased in winter. To analyze the causes of this observed trend, a photochemical box model was used to investigate the change in ozone sensitivity regime in two representative cities – Beijing and Shanghai. Our model simulations suggest that the summertime ozone sensitivity regime in urban areas of China has changed from a VOC-limited regime to a transition regime during 2014–2020; by 2020, the urban photochemistry is in a transition regime in summer but in a VOC-limited regime in winter. This study helps to understand the distinct trends of ozone in China and provides insights into efficient future ozone control strategies in different regions and seasons.

How to cite: Wang, W., Su, H., Cheng, Y., Parrish, D. D., Wang, S., Bao, F., Ni, R., and Li, X.: Long-term trend of ozone pollution in China during 2014-2020: distinct seasonal and spatial characteristics and ozone sensitivity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13047, https://doi.org/10.5194/egusphere-egu23-13047, 2023.

Ozone concentrations have resulted in significant impacts on both human health and crop production throughout the beginning of the 21st century. Results presented here are from a NASA funded WRF-CMAQ model run at a 12km x 12km gridded horizontal resolution using data assimilation of MODIS AOD and MOPITT CO for a fourteen-year (2005-2018) period to show shifts in atmospheric composition over the continental United States (CONUS). This publicly available data has been aggregated to the maximum daily 8-hour ozone (MDA8) and seasonal ozone (OSDMA8) metrics for each of the EPA regions to show the regional drivers to human health as well as calculation of the accumulated ozone exposure (AOT40 and W126) metrics varying temporally and geographically based on crop data for CONUS available from the United States Department of Agriculture. These aggregation techniques have allowed us to identify both trends and some of the meteorological and atmospheric composition drivers in ozone-related risk for specific outcomes and how they vary geographically. The work presented here will also outline the GIS-based information dissemination platform that can be used by researchers and stakeholders to both access data and assess more detailed collaborative and convergent research questions.

How to cite: Lacey, F., Kumar, R., He, C., Boenhert, J., O'Lenick, C., Wilhelmi, O., Casali, M., and Sampson, K.: Trends in health and agriculture-relevant ozone metrics over the United States from WRF-CMAQ reanalysis simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11274, https://doi.org/10.5194/egusphere-egu23-11274, 2023.

Statistical downscaling models are used to estimate historical and future ozone concentrations in Europe for the summer months from April to September. The basis is formed by over 700 measuring stations from the hourly Air Quality eReporting ozone pollution data from the European Environment Agency. Daily maximum 8-hr running means (MDA8) as well as daily maximum 1-hr values (MDA1) of ozone are the target variables. Meteorological (ERA5) as well as ozone (CAMS) reanalysis data serve as predictors in the perfect prognosis (PP) approaches. A station-specific, individualized predictor screening guarantees site-specific optimums. The predictor selection is performed using regularization with varying shrinkage. Multiple Linear Regression (MLR) is used to model the relationship between all selected predictors and MDA8/ MDA1. An ensemble of seven CMIP6 Earth system models is used to estimate future ozone concentrations. Projections are calculated for the years 2041-2060 and 2081-2100 under two different future scenarios (SSP2-4.5 and SSP3-7.0). The CMIP6 data is bias corrected with a univariate quantile delta mapping method, before being used in the statistical models.

With respect to predictor selection, a sensitivity study is conducted, testing different sets of predictors to examine their influence on future ozone concentrations. Predictor sets with and without ozone, with only thermal and radiative predictors, and additionally thermo-dynamical or circulation-dynamical information are analyzed, in addition to the site-specific optimums described above.

The projection results of the different predictor settings highlight the importance of ozone as predictor. In all predictor sets with included ozone, the results of the two scenarios SSP2-4.5 and SSP3-7.0 differ in their sign depending on the scenario used. The SSP2 scenario, called "Middle of the Road", leads to decreasing ozone concentrations in Europe, while the more pessimistic SSP3 scenario results in partly strong increases of harmful ground-level ozone concentrations. In contrast, all predictor sets that do not take ozone into account show consistently positive change signals.

On the one hand, our results point to the need to include information on emission changes in statistical assessments in order to obtain a realistic picture of future ozone development. Furthermore, our research underscores the need to further reduce air pollution in Europe to better protect human health from direct emissions such as NO_x and indirect pollutants such as ozone.

How to cite: Kaspar-Ott, I., Jahn, S., and Hertig, E.: Future ground-level summer ozone concentrations in Europe: the importance of ozone as predictor in a statistical downscaling approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2204, https://doi.org/10.5194/egusphere-egu23-2204, 2023.

Tropospheric ozone is a greenhouse gas and a secondary pollutant that has negative impact on human health, crop yield and the environment. Therefore information on the long-term trends in surface ozone, particularly in the regional representative site is crucial for assessing the impact on climate and environment. While there are extensive observations of surface ozone in Europe, North America and East Asia, there are very limited observations in South Asia, particularly in the Himalayan regions. In this reference, surface ozone observations were initiated at a mountain site in Nainital (29.40° N, 79.50° E, 1948 m amsl) situated in central Himalaya in October 2006. Here, we present the observed long-term trends in surface ozone over the central Himalayas and underlying factors influencing its diurnal and seasonal variabilities. In general, ozone diurnal variations indicates least daytime photochemical ozone buildup at this remote site, except during episodes of biomass burning in the plain regions of northern India during spring. Instead, ozone levels at this site are primarily influenced by transported air masses, mountain-valley breezes and stratospheric intrusions. The long-term trend found not to be very prominent, but it showed a very slight negative (about 1 ppbv/yr) for 2007-2014 period, while a positive trend (about 0.7 ppbv/yr) for 2014-2022 period. The negative trend during 2007-14 was more prominent in spring while positive trend was prominent in winter. Trend analysis in AIRS ozone data at different pressure levels is being studied and residence time analysis of air-masses, obtained from the back air-trajectories simulations is in progress, which will be presented during the conference. These observations will be very useful for the ongoing efforts by TOAR

How to cite: Tomar, V. and Naja, M.: Long term trends and characteristics of surface ozone at high altitude site in the central Himalayas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15405, https://doi.org/10.5194/egusphere-egu23-15405, 2023.

Ground-based FTIR (Fourier transform infrared) stations contributing to the Network for Detection of Atmospheric Composition Change (NDACC), deliver time-series of ozone and some of its precursors at more than 20 sites, starting from the 90’s for the oldest stations. In the context of the Tropospheric Ozone Assessment Report (TOAR-II), we will present the status of the ground-based FTIR tropospheric ozone, formaldehyde (HCHO), and carbon monoxide (CO) measurements.

From high-resolution solar absorption spectra, O₃, HCHO and CO total columns are obtained with a precision of about 2%, 8%, and 1%, respectively. In addition, the pressure dependence of fully resolved absorption lines allows retrieving low vertical resolution profiles and thus deriving few independent partial columns. For O₃, the degrees of freedom for signal (DOFS) are about 4.5, allowing O₃ amounts to be retrieved in four independent altitude layers: one in the troposphere and three in the stratosphere up to about 45 km, with a precision of 5–6 % for each partial column. For HCHO, the DOFS are only of order 1.0-1.5, with a sensitivity mainly located in the troposphere where most of the HCHO lies. For CO, about 2 DOFS can be obtained, with one of them located in the troposphere.

We will show the variability and trends (when long time-series are available) of O₃, HCHO, and CO tropospheric partial columns at many FTIR stations, covering a wide range of latitudes and pollution conditions. To derive the trends, we use a multiple linear regression model including seasonal cycles and dynamical proxies explaining the species’ variability such as, e.g., the tropopause height, the El Niño-Southern Oscillation (ENSO), or the Quasi-Biennial Oscillation (QBO).

How to cite: Vigouroux, C. and the FTIR data providers: Tropospheric ozone and precursors (HCHO and CO) from the NDACC FTIR ground-based network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11944, https://doi.org/10.5194/egusphere-egu23-11944, 2023.

Tropospheric ozone (O₃) is an important greenhouse gas relevant for global warming projections as well as secondary pollutant affecting air quality on the regional scale. In this Communication, we use halogen version of the CAM-Chem model to investigate the evolution of the O₃ budget during the 21st century following two different climate scenarios (RCP6.0 and RCP8.5) and halogen emissions. Our results indicate that the global ozone net chemical change (NCC) will decrease by ~50%, notwithstanding increasing or decreasing trends in ozone production and loss. However, a wide range of surface NCC variations (from −60% to 150%) are projected over polluted regions depending on the evolution of anthropogenic O₃ precursor emissions. Most notably, water vapor and iodine are found to be key drivers of future tropospheric O₃ destruction, while the largest changes in O₃ production are determined by the future evolution of peroxy radicals. Overall, future surface ozone destruction due to halogens will become more important moving into the future for both scenarios, reaching a net reduction from −30 to −35 Tg (−11 to −15%) on the global O₃ burden.

How to cite: Saiz-Lopez, A.: Influence of Natural Halogens on Global Tropospheric Ozone During the 21st Century, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13226, https://doi.org/10.5194/egusphere-egu23-13226, 2023.

Ozone production and loss in surface air is determined by ambient temperature,  chemical conditions and precursor emissions. Despite efforts to abate surface ozone air pollution, the daily maximum 8-hour average ozone target value for the protection of human health  is regularly exceeded at several monitoring sites in Austria especially during the warm seasons. 

Here we investigate projected changes in the surface ozone burden and effects of climate warming and changes in precursor emissions over the next decades in a series of tailored chemistry-transport model (CTM) experiments, performed with WRF-Chem and CAMx. Specifically we contrast changes in ozone air quality in decadal time slices for 2026-2035 and 2046-2055 with the recent past (2007-2016). Our CTM ensemble comprises simulations following the Representative Concentration Pathways (RCPs) 2.6, 4.5 and 8.5. Our results show a persistent large variability in ozone abundances driven by the large intra- and interannual  variability in meteorological conditions. Overall we find general improvements in the surface ozone burden for low emission scenarios (RCP2.6 and RCP4.5) driven by ambitious NOx controls. In contrast under RCP8.5 we find, on the one hand an increase in the frequency of non-attainment days and on the other a shift in the prime ozone season from summer towards spring. These increases are driven by both a climate penalty and changes in the chemical production regime (NOx vs. VOC limitation) and increasing methane and ozone backgrounds. Furthermore, we investigate impacts of projected ozone changes on human health at the municipal level in Austria.

How to cite: Schmidt, C., Mayer, M., Stähle, C., Kult-Herdin, J., Huszár, P., Karlický, J., Moshammer, H., and Rieder, H.: Evaluating the effects of climate warming and precursor emission changes on surface ozone air quality over coming decades: a case study for Austria, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13237, https://doi.org/10.5194/egusphere-egu23-13237, 2023.

The air pollutant emissions play a decisive role in the control of air quality. In recent years, the anthropogenic emission reduction measures have effectively reduced the PM_2.5 levels over China improving air quality in China. However, due to the complex physical and chemical processes in atmospheric environment, O₃ pollution events still occur frequently. To assess the impact of recent-year emission reduction of emissions on variations of summertime O₃ pollution in the North China Plain, this study conducted the simulations with the air quality model WRF-Chem by using China's Multiresolution Emission Inventory (MEIC) with 0.1° resolution in 2012 and 2019, and we understand the characteristics of summer O₃ pollution in the NCP under the scenario of anthropogenic emission reduction. The results show that the anthropogenic emissions of PM_2.5, PM₁₀, SO₂, CO, black carbon (BC), and organic carbon (OC) in the NCP region decreased significantly from 2012 to 2019, while the emissions of NMVOCs (non-methane volatile organic compounds) increased distinctly in urban areas, and NOx emissions decreased in urban and increased in rural, reflecting the uneven emission reduction of anthropogenic air pollutants in North China. The control of anthropogenic pollutant emissions induced an elevated concentrations of atmospheric oxidants (O₃ and multiple free radicals) in the NCP region, enhancing the atmospheric oxidation capacity, and then strengthening the chemical conversions of SO₂ and NOx to generate sulfate, nitrate, and other secondary particles. As a result, the proportion of secondary PM_2.5 in urban and rural areas markedly raised , especially during the O₃ pollution period, offsetting the reduction of primary PM_2.5 emissions. In addition, these emission reduction measures promote the transformation of O₃ generation mechanism in the NCP from VOC-control to NOx-control. This study reveals the complex effects of anthropogenic emission reduction altering the atmospheric physical and chemical processes on atmospheric environmental change.

How to cite: Luo, Y. and Zhao, T.: Atmospheric environment change in a summertime O3 pollution event over the North China Plain under the influence of recent-year anthropogenic emission reduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14125, https://doi.org/10.5194/egusphere-egu23-14125, 2023.

The first TOAR assessment encountered several observational challenges that limited the confidence in estimates of the burden, short-term variability and long-term changes of ozone in the free troposphere. One of these challenges is the difficulty to interpret tropospheric observations from space, especially when combining data records from multiple satellites with differences in vertical sensitivity, prior information, resolution and spatial domain. Additional confounding factors are time-varying biases and the lack of harmonisation of geophysical quantities, units and definition of the tropospheric top level. All together, these increased the uncertainty on the distribution and trends of tropospheric ozone, impeding firm assessments relevant for policy and science. These challenges motivated the Committee on Earth Observation Satellites (CEOS) to initiate a coordinated activity on improving assessments of tropospheric ozone measured from space. Here, we report on work that contributes to this CEOS activity and to various Working Groups (SOWG, OPT, HEGIFTOM, TOP, ROSTEES, ...) of the ongoing second TOAR assessment.

Our primary objective is to harmonise the vertical perspective of different satellite data records. A first class of tropospheric ozone products is obtained through an inversion of spectral measurements by nadir-viewing sounders into a vertical profile. We describe two complementary approaches (Prior Replacement and Complete Data Fusion) to harmonise the differing profile retrieval set-up for GOME-2, IASI and other UV-visible and infrared nadir sensors, using information conveyed in the prior and the averaging kernels. A second class of products is obtained through subtraction of the stratospheric component from total column retrievals. The stratospheric column is derived with various methods, resulting in differing spatial coverage, tropospheric top level, sampling frequency, etc…  We present how all tropospheric ozone products, from both classes, are harmonised to a common tropospheric top level. We then intercompare all harmonised satellite records, and report on the differences and how these reduce upon harmonisation. Finally, we reflect on the importance of the vertical harmonisation process to improve constraints of the spatial distribution and trends in tropospheric ozone.

Acknowledgements : We are grateful to the sustained effort and committment of the teams, institutes and agencies that collect and provide satellite and ozonesonde data records of high quality.

How to cite: Hubert, D., Keppens, A., Verhoelst, T., Compernolle, S., and Lambert, J.-C.: Harmonisation of Free Tropospheric Ozone Satellite Data Records in Support of TOAR Phase II, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14161, https://doi.org/10.5194/egusphere-egu23-14161, 2023.

Ground-based observations are indispensable for the long-term monitoring of atmospheric constituents. In this work, we take advantage of multiple collocated instruments to analyze potential biases and drifts in ground-based ozone observations, within the context of the HEGIFTOM (Harmonization and Evaluation of Ground-based Instruments for Free Tropospheric Ozone Measurements) working group in the Tropospheric Ozone Assessment Report, Phase II (TOAR-II). This work is performed at Lauder (New Zealand), Boulder (Colorado), and Mauna Loa (Hawaii) where comparisons are made between Fourier Transform Infrared (FTIR) spectroscopy, Dobson Umkehr, and ozonesonde observations. The validation is performed with respect to FTIR as arbitrary reference, while considering the differences between the a priori profile information for the techniques that employ these as well as accounting for the different vertical resolution of each measurement technique. Such intercomparison is done for a handful discrete altitude partial columns, defined to have independent pieces of information also in the case of the low vertical resolution techniques (FTIR and Umkehr). This leads to 4 independent vertical layers to be compared, including one in the troposphere where ozone plays an important role as a greenhouse gas and as a risk to human health. In this tropospheric layer we compare the FTIR, Dobson Umkehr and ozonesonde techniques and derive a consistent bias from the FTIR data of about 5%, which we attribute in part to the assumed spectroscopy. Fitting the time series of the relative measurement differences using multiple linear regression, we obtain a linear trend, which quantifies the drift between pairs of techniques. Within the uncertainties, we find no significant drift between FTIR and Umkehr or ozone sonde data in the troposphere.

How to cite: Björklund, R., Vigouroux, C., Langerock, B., Smale, D., Petropavlovskikh, I., Effertz, P., Hannigan, J., Querel, R., Ortega, I., Koji, M., Robinson, J., Smale, P., Kotkamp, M., Nedoluha, G., Poyraz, D., and Van Malderen, R.: Intercomparison of long-term ground-based tropospheric ozone measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14693, https://doi.org/10.5194/egusphere-egu23-14693, 2023.

As part of the Tropospheric Ozone Assessment Report Phase 2 (TOAR-II), the Ozone and Precursors in Tropics (OPT) working group counts three deliverables dedicated to quantifying 1) the distribution, 2) the trends of tropospheric ozone (O3) and its precursors (carbon monoxide, CO; formaldehyde, HCHO; nitrogen dioxide, NO2) in the tropics over the past 20-25 years, and 3) their impacts on a global scale. This presentation will focus on the trends estimate. We answer the following scientific questions: How have tropical tropospheric ozone and its precursors changed with time? What sources (e.g. anthropogenic emissions, biomass burning, lightning) drive these trends and to what extent?

To accomplish this, we use both observations and model output.  The observations include in situ measurements of O3 and its precursors from surface sites, sounding balloons (SHADOZ) and instrumented aircraft (IAGOS), as well as ground-based (FTIR) and spatial (IASI, OMI, GOME-2) remote-sensed observations. Global model output come from ECHAM6-HAMMOZ, LMDZ-OR-INCA, MIROC-CHASER, CAM4-Chem, GISS-E2 and the CESM2-WACCM6 ensemble.

The trends estimates are based on monthly anomalies and are calculated after considering climate variabilities such as El Niño- Southern oscillation (ENSO) and quasi-biennial oscillation (QBO).

From IAGOS and SHADOZ ozone profiles, we estimate positive ozone trends between 1994 and 2019 throughout the troposphere above the Americas, Africa, India, Southeast Asia and Malaysia/Indonesia. Trends may reach up to 6 ± 1.6 ppb/decade in the free troposphere and up to 12.5 ± 2 ppb/decade in the boundary layer. There is also considerable regional variability. For example, trends are +0 to 4 ppb/decade in the free troposphere above the remote Pacific and Atlantic SHADOZ stations (1998-2019). According to OMI satellite retrievals, tropospheric ozone burden increases between 2004 and 2021 across the tropical latitude band (20˚N-20˚S) and the trends range between 0.09 Tg/yr (OMI CCD retrieval in the southern hemisphere) and 0.3 Tg/year (OMI/MLS retrieval in the northern hemisphere).

The presentation will also include trends estimates of observed ozone’s precursors such as CO, NO₂ and formaldehyde as well as trends estimate of ozone and its precursors from model output.

How to cite: Gaudel, A. and Sauvage, B. and the TOAR-OPT Paper 2 "Trends" Team: Trends of tropical tropospheric ozone and its precursors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9365, https://doi.org/10.5194/egusphere-egu23-9365, 2023.

How to cite: Chang, K.-L. and Cooper, O.: Decreasing trends in extreme ozone events across the United States, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7163, https://doi.org/10.5194/egusphere-egu23-7163, 2023.