Surface O3 Levels Research Articles

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

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 Ozone Monitoring Instrument (OMI)-derived summertime VCD HCHO, NO2, and FNRs in the Northern Hemisphere from 2005 to 2021. FNR trends were analyzed for polluted regions, 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 by ∼ 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 it was determined that 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.

A Comprehensive Review of Surface Ozone Variations in Several Indian Hotspots

Ozone at ground level (O3) is an air pollutant that is formed from primary precursor gases like nitrogen oxides (NOx) and volatile organic compounds (VOCs). It plays a significant role as a precursor to highly reactive hydroxyl (OH) radicals, which ultimately influence the lifespan of various gases in the atmosphere. The elevated surface O3 levels resulting from anthropogenic activities have detrimental effects on both human health and agricultural productivity. This paper provides a comprehensive analysis of the variations in surface O3 levels across various regions in the Indian subcontinent, focusing on both spatial and temporal changes. The study is based on an in-depth review of literature spanning the last thirty years in India. Based on the findings of the latest study, the spatial distribution of surface O3 indicates a rise of approximately 50–70 ppbv during the summer and pre-monsoon periods in the northern region and Indo-Gangetic Plain. Moreover, elevated levels of surface O3 (40–70 ppbv) are observed during the pre-monsoon/summer season in the western, southern, and peninsular Indian regions. The investigation also underscores the ground-based observations of diurnal and seasonal alterations in surface O3 levels at two separate sites (rural and urban) in Kannur district, located in southern India, over a duration of nine years starting from January 2016. The O3 concentration exhibits an increasing trend of 7.91% (rural site) and 5.41% (urban site), ascribed to the rise in vehicular and industrial operations. This review also presents a succinct summary of O3 fluctuations during solar eclipses and nocturnal firework displays in the subcontinent.

AIRS and MODIS Satellite-Based Assessment of Air Pollution in Southwestern China: Impact of Stratospheric Intrusions and Cross-Border Transport of Biomass Burning

The exacerbation of air pollution during spring in Yunnan province, China, has attracted widespread attention. However, many studies have focused solely on the impacts of anthropogenic emissions while ignoring the role of natural processes. This study used satellite data spanning 21 years from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Atmospheric Infrared Sounder (AIRS) to reveal two natural processes closely related to springtime ozone (O3) and PM2.5 pollution: stratospheric intrusions (SIs) and cross-border transport of biomass burning (BB). We aimed to assess the mechanisms through which SIs and cross-border BB transport influence O3 and PM2.5 pollution in Southwestern China during the spring. The unique geographical conditions and prevalent southwest winds are considered the key driving factors for SIs and cross-border BB transport. Frequent tropopause folding provides favorable dynamic conditions for SIs in the upper troposphere. In the lower troposphere, the distribution patterns of O3 and stratospheric O3 tracer (O3S) are similar to the terrain, indicating that O3 is more likely to reach the surface with increasing altitude. Using stratospheric tracer tagging methods, we quantified the contributions of SIs to surface O3, ranging from 6 to 31 ppbv and accounting for 10–38% of surface O3 levels. Additionally, as Yunnan is located downwind of Myanmar and has complex terrain, it provides favorable conditions for PM2.5 and O3 generation from cross-border BB transport. The decreasing terrain distribution from north to south in Yunnan facilitates PM2.5 transport to lower-elevation border cities, whereas higher-elevation cities hinder PM2.5 transport, leading to spatial heterogeneity in PM2.5. This study provides scientific support for elucidating the two key processes governing springtime PM2.5 and O3 pollution in Yunnan, SIs and cross-border BB transport, and can assist policymakers in formulating optimal emission reduction strategies.

Benefits of air quality for human health resulting from climate change mitigation through dietary change and food loss prevention policy

Food production, particularly cattle husbandry, contributes significantly to air pollution and its associated health hazards. However, making changes in dietary habits, such as reducing red meat consumption and minimizing food waste, can lead to substantial improvements in both air quality and human health. In this study, we explored the impact of dietary changes on future air quality and human wellbeing. We also assessed the influence of dietary transformation policies in the context of climate change mitigation, with the objective of understanding how policies can effectively complement each other. We used a chemical transport model and an integrated assessment model to determine changes in fine particulate matter (PM2.5) and ozone (O3) concentrations. Then, an exposure model was applied to estimate premature deaths as a consequence of air pollution. Our results showed that dietary changes could play a crucial role in mitigating air pollution, particularly in regions where agricultural activities emit significant quantities of ammonia. In the European Union, for example, dietary changes could lead to a reduction of 5.34% in PM2.5 by 2050. Similarly, in Asia, the models projected a reduction of 6.23% in PM2.5 by 2100. Ground surface O3 levels in Southeast Asia were projected to drop by as much as 12.93% by 2100. Our results further showed that dietary changes could lead to significant reductions in global mortality associated with PM2.5 and O3, with 187,500 and 131,110 avoided deaths per year expected by 2100. A combined approach that integrates dietary changes with climate change mitigation measures could lead to more comprehensive air quality improvements in specific regions. However, careful consideration is needed to address any potential adverse effects on O3 concentrations in some areas.

Ozone variability driven by the synoptic patterns over China during 2014–2022 and its implications for crop yield and economy

China has experienced increasingly serious ozone (O3) pollution in recent years, posing a great threat to agricultural ecosystem and economy. In this study, the decadal records of surface ozone concentrations across China (2014–2022), combined with the spatial synoptic classification (SSC) and multiple linear regression (MLR) methods are used to determine the surface ozone variability driven by the synoptic weather patterns. The maximum daily average 8-h (MDA8) ozone concentrations increase significantly from 2014 to 2019 at 2.5–5.2 μg m−3 yr−1 and decrease over the years 2019–2021, with a rebound in 2022. Strong connections between surface O3 levels and SSC synoptic weather patterns are identified, with the dry tropical (DT) weather pattern featured by dry and hot air masses as the main contributor to 35.3% of the high ozone occurrences and partly explaining the observed ozone trends in recent decade (e.g., +9.7% ozone increase per tripling of the DT frequency). Quantitative MLR analysis further confirms that meteorological conditions play an important role in the seasonal ozone trends from 2014 to 2022 (up to a 28.6% contribution), and daily-maximum air temperature and solar radiation could explain 11.3–51.0% and 11.1–37.4% of the meteorological-driven ozone trends. Using the agricultural statistical data and empirical algorithms, it is estimated that the annual yields of winter wheat, single-cropping rice, double-cropping early rice and late rice are reduced by 9.0–17.0%, 6.0−8.2%, 4.8−9.4% and 3.9−7.0%, respectively, in China during 2014–2022 due to the ozone exposure, along with a total economic loss of 74.9–171.9 billion yuan per year. This study is meaningful to understand the driving factors for the increasingly serious ozone pollution and is beneficial for the synergetic control of air pollution and climate mitigation.

Relationships between ozone and particles during air pollution episodes in arid continental climate

For human health, tropospheric ozone (O3), particles (PM2.5 and PM10, particles with aerodynamic diameter <2.5 and 10 μm), and nitrogen dioxide (NO2) are the most harmful air pollutants. We have investigated the simultaneity of PM2.5, PM10, NO2, and O3 occurrence by using data from 21 ground-based monitoring stations in a megacity of the Middle East, Tehran (Iran), between 2011 and 2022. In Tehran, the daily PM2.5 (21–45 μg m−3), PM10 (52–108 μg m−3) and NO2 (75–146 μg m−3) mean concentrations have largely exceeded the 24-h limit value established by the 2021 World Health Organization for the protection of human health, i.e., 15, 45 and 25 μg m−3, respectively, in particular for NO2. The ground-level daily O3 concentrations ranged from 26 to 47 μg m−3. Changes in aerosols burden (e.g., PM2.5 and PM10) affect surface O3 through changes in aerosol chemistry and photolysis rates. Following the dust events and for the days with PM2.5 and PM10 exceeding 50 and 100 μg m−3, respectively, we observed a reduction of surface O3 levels (- 30.0% and - 13.5%), concurrently to surface NO2 (+27.9% and +16.6%) levels increases compared to the non-dusty clear-sky days over Tehran city. Surface O3 formation is suppressed under high particulate matter (PM) levels in the atmosphere, in particular PM2.5, likely due to weakened photochemical reactions (lower solar radiation and air temperature), dilution effect, and heterogeneous chemical processes occurring onto the PM2.5 surface (reactive uptake of nitrogen oxides, NOx, and hydrogen oxide radicals, HOx). To achieve O3-PM co-improvement in cities, we recommend reductions in NOx emissions concurrently with significant reductions in PM and Volatile Organic Compounds emissions, for instance by suitable greening and re-naturing programs.

Assessing surface ozone risk to human health and forests over time in Poland

Hourly ground-level ozone (O3) data from 52 monitoring stations in Poland were analyzed over a ten-year pre-COVID19 period (2010–2019) to map and define areas at risk for human health and vegetation, and to calculate trends over the study period. Annual O3 metrics (24-h average concentrations, 50th percentiles, and hourly maxima), human health metrics (Sum Of daily maximum 8-h Means Over 35 ppb, SOMO35, summertime average of the daily 8-h maximum O3 concentrations, O3 MDA8, and number of daily maximum 8-h values above 60 ppb, EU60) and vegetation exposure metrics (AOT40, i.e., accumulation of hourly O3 concentrations exceeding 40 ppb during the growing season for agricultural crops AOT40c and forests AOT40f) were investigated. Higher O3 levels occurred in rural areas than in cities. Between 2010 and 2019, the O3 levels were rising in both urban and rural areas. Despite the reduction of nitrogen oxides (NOx: - 2.33% year-1) and volatile organic compounds emissions (VOCs: - 0.95% year-1), annual O3 mean levels (+0.81 and +0.12% year-1), 50th percentiles (+1.06 and ∼0% year-1), hourly maxima (- 0.10 and +0.23% year-1), SOMO35 (+2.86 and +1.50% year-1), summertime O3 MDA8 (+0.49 and +0.48% year-1), EU60 (+0.09 and +0.15 days year-1), AOT40c (+3.79 and +3.29% year-1) and AOT40f (+4.47 and +4.34% year-1) commonly increased in urban and rural stations. The O3 levels increased at 75.0% of urban stations and 62.5% of rural stations. A slight decline of the number of O3 peaks occurred in cities, likely driven by the recent reductions in NOx emissions by on-road transport. For all metrics, the increase can be attributed to higher regional photochemical O3 formation and rising background O3 levels likely driven by imported O3 and its precursors by long-range transport, climate change, and lower O3 titration by NOx emissions decline. The failure to attain the target value for O3 for protecting vegetation and human health and vegetation persists. Southeastern Poland, where coal stoves are still used for residential heating, faces the highest O3 risk. This study reports new information on surface O3 levels, exceedances, and trends in Poland to develop effective policies to mitigate O3 effects.

The effect of anthropogenic emission, meteorological factors, and carbon dioxide on the surface ozone increase in China from 2008 to 2018 during the East Asia summer monsoon season

Abstract. Despite the implementation of the Clean Air Action Plan by the Chinese government in 2013, the issue of increasing surface ozone (O3) concentrations remains a significant environmental concern in China. In this study, we used an improved regional climate–chemistry–ecology model (RegCM-Chem-YIBs) to investigate the impact of anthropogenic emissions, meteorological factors, and CO2 changes on summer surface O3 levels in China from 2008 to 2018. Compared to its predecessor, the model has been enhanced concerning the photolysis of O3 and the radiative impacts of CO2 and O3. The investigations showed anthropogenic emissions were the primary contributor to the O3 increase in China, responsible for 4.08–18.51 ppb in the North China Plain. However, changed meteorological conditions played a crucial role in decreasing O3 in China and may have a more significant impact than anthropogenic emissions in some regions. Changed CO2 played a critical role in the variability of O3 through radiative forcing and isoprene emissions, particularly in southern China, inducing an increase in O3 on the southeast coast of China (0.28–0.46 ppb) and a decrease in southwest and central China (−0.51 to −0.11 ppb). Our study comprehensively analyzed O3 variation across China from various perspectives and highlighted the importance of considering CO2 variations when designing long-term O3 control policies, especially in high-vegetation-coverage areas.

Divergent summertime surface O3 pollution formation mechanisms in two typical Chinese cities in the Beijing-Tianjin-Hebei region and Fenwei Plain

Recently, severe summertime ozone (O3) pollution has swept across most areas of China, especially the Beijing-Tianjin-Hebei (BTH) region and Fenwei Plain. By focusing on Beijing and Yuncheng, which are two typical cities in the BTH region and the Fenwei Plain, we intended to reveal the neglected fact that they had disparate emission features and atmospheric movements but suffered from similar high-O3 pollution levels. Field observations indicated that Yuncheng had lower volatile organic compound (VOC) and NOx concentrations but higher background O3 levels. The model simulation verified that both photochemical reactions and net O3 generation were stronger in Beijing. Ultimately, faster net O3 generation rates (8.4 ppbv/h) plus lower background O3 values in Beijing and lower net O3 generation rates (6.2 ppbv/h) plus higher background O3 values in Yuncheng caused both regions to reach similar O3 peak values in July 2020. However, different O3 control measures were appropriate for the two cities according to the different simulated O3-VOCs-NOx responses. Additionally, as surface O3 levels are greatly affected by the ongoing O3 production/depletion process that occurs in three dimensions, exploring the effects of spatially distributed O3 on surface O3 should be high on the agenda in the future.

Traffic-Related Air Pollution and Ground-Level Ozone Associated Global DNA Hypomethylation and Bulky DNA Adduct Formation.

Studies have indicated that air pollution, including surface-level ozone (O3), can significantly influence the risk of chronic diseases. To better understand the carcinogenic mechanisms of air pollutants and identify predictive disease biomarkers, we examined the association between traffic-related pollutants with DNA methylation alterations and bulky DNA adducts, two biomarkers of carcinogen exposure and cancer risk, in the peripheral blood of 140 volunteers-95 traffic police officers, and 45 unexposed subjects. The DNA methylation and adduct measurements were performed by bisulfite-PCR and pyrosequencing and 32P-postlabeling assay. Airborne levels of benzo(a)pyrene [B(a)P], carbon monoxide, and tropospheric O3 were determined by personal exposure biomonitoring or by fixed monitoring stations. Overall, air pollution exposure was associated with a significant reduction (1.41 units) in global DNA methylation (95% C.I. -2.65-0.04, p = 0.026). The decrement in ALU repetitive elements was greatest in the policemen working downtown (95% C.I. -3.23--0.49, p = 0.008). The DNA adducts were found to be significantly increased (0.45 units) in the municipal officers with respect to unexposed subjects (95% C.I. 0.02-0.88, p = 0.039), mainly in those who were controlling traffic in downtown areas (95% C.I. 0.39-1.29, p < 0.001). Regression models indicated an increment of ALU methylation at higher B(a)P concentrations (95% C.I. 0.03-0.60, p = 0.032). Moreover, statistical models showed a decrement in ALU methylation and an increment of DNA damage only above the cut-off value of 30 µg/m3 O3. A significant increment of 0.73 units of IL-6 gene methylation was also found in smokers with respect to non-smokers. Our results highlighted the role of air pollution on epigenetic alterations and genotoxic effects, especially above the target value of 30 µg/m3 surface-level O3, supporting the necessity for developing public health strategies aimed to reduce traffic-related air pollution molecular alterations.

Ozone pollution threatens the production of major staple crops in East Asia

East Asia is a hotspot of surface ozone (O3) pollution, which hinders crop growth and reduces yields. Here, we assess the relative yield loss in rice, wheat and maize due to O3 by combining O3 elevation experiments across Asia and air monitoring at about 3,000 locations in China, Japan and Korea. China shows the highest relative yield loss at 33%, 23% and 9% for wheat, rice and maize, respectively. The relative yield loss is much greater in hybrid than inbred rice, being close to that for wheat. Total O3-induced annual loss of crop production is estimated at US$63 billion. The large impact of O3 on crop production urges us to take mitigation action for O3 emission control and adaptive agronomic measures against the rising surface O3 levels across East Asia.

Characteristics of boundary layer ozone and its effect on surface ozone concentration in Shenzhen, China: A case study

In late September 2019, the longest and most extensive ozone (O3) pollution process occurred at Pearl River Delta. Base on the observational data, surface-level O3, vertical distribution characteristics boundary layer O3 as well as its effect on surface-level O3 are thoroughly analyzed. The O3 lidar results showed similar vertical O3 profiles both in pollution episodes and clean periods, from which a high O3 concentration layer between 300 and 500 m and a sub-high O3 concentration layer between 1300 and 1700 m (near the top of the mixing layer) can be found. Besides, the downward O3 transport paths from the high/sub-high O3 concentration layers could be observed along with the boundary layer evolution: At nighttime, large amounts of O3 were effectively stored into the residual layer (RL). Due to the upward development of Mixing layer (ML) in early morning, atmospheric vertical mixing carried the O3 inside the RL down to the surface, which led to a rapid increase in the surface-level O3. The sub-high O3 layer began the downward mixing at noon, and became well-mixed after the boundary layer was fully developed in the afternoon, by which the near surface O3 pollution deteriorated again. Further analysis of the heavy O3 pollution episodes show that, the high O3 concentration inside the RL contributed 54% ± 6% of the surface-level O3 at 9:00 LT and the average contribution of O3 in the sub-high concentration layer to the surface-level O3 at 14:00 LT was 26% ± 9%. Based on the quantitative analysis of the observational data, this paper focus to reveal the importance of the contribution of O3 inside the RL and near the top of the ML to the surface O3.

Impact of Biomass Burning on Ozone, Carbon Monoxide, and Nitrogen Dioxide in Northern Thailand

The problem of smoke haze pollution in Northern Thailand affects both the environment and residents. The main sources of smoke are wildfires and open burning during the dry season, which release many pollutants, especially surface O3, impacting health and causing an air pollution crisis. The aim of this research was to study the impact of biomass burning on the surface O3, CO, and NO2 levels in Northern Thailand using the Weather Research and Forecasting Model with Chemistry (WRF-Chem). The simulation domain was configured with two domains with a grid spacing of 50 and 10 km in March 2014. To elucidate the effect of biomass burning, the model simulation was conducted for two cases: 1) a simulation with anthropogenic, biogenic, and biomass burning emissions; and 2) a simulation excluding biomass burning emissions. Owing to the model performance, the diurnal temperature and precipitation were consistent with observations, as indicated by the index of agreement (IOA) ranges of 0.74–0.76, while those of O3, CO, and NO2 were in the ranges of 0.12–0.71. The results show that biomass burning increased O3, CO, and NO2 levels by 9, 51, and 96%, respectively.

Impacts of Nocturnal Cloud Top Radiative Cooling on Surface O3 in Sichuan Basin, Southwestern China

AbstractNighttime ozone (O3) reserved over the stable boundary layer (SBL) could contribute significantly to surface O3 levels. While many studies have revealed that daytime convective eddies and turbulence induced by nighttime low‐level jets can mix O3‐rich air over the SBL down to the surface, increasing nocturnal surface O3 within the cloud topped boundary layer has rarely been examined. In this study, we used measurements and a single‐column photochemistry model to investigate O3 variations within the nighttime cloud topped boundary layer over the Sichuan Basin, which is the cloudiest region in southwest China. The Santa Barbara Distort Atmospheric Radiative Transfer radiation model was coupled into the single‐column photochemistry model to investigate the nighttime radiative effects of clouds. The results showed that the nocturnal cloud top radiative cooling generated turbulence and enhanced vertical mixing below the cloud top layer. The cloud‐driven turbulent eddies even penetrated through the SBL to the surface. Consequently, it weakened the decoupling of the SBL from the residual layer. O3‐rich air over the SBL was entrained downwards to the surface, decreasing O3 aloft and increasing surface O3 at nighttime. The cloud top radiative cooling rates were enhanced with the increase in the cloud liquid water path. Higher cooling rates produced stronger turbulent transport of O3, leading to higher nocturnal surface O3 levels. The turbulent transport of O3 induced by cloud top radiative cooling is revealed as an important mechanism of vertical transport of O3 within a cloud topped boundary layer, contributing to the maximum nocturnal surface O3, which has great implications for understanding atmospheric O3 variation.

Long-range transport of Siberian biomass burning emissions to North America during FIREX-AQ

Biomass burning from wildfires is a significant global source of aerosol and trace gases which impact air quality, tropospheric and stratospheric composition, and climate. During the summer of 2019, wildfire activity in central and eastern Siberia occurred during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign conducted in the United States between July 24 and September 6, 2019. Ground-based lidar observations from the Autonomous Mobile Ozone Lidar for Tropospheric Experiments (AMOLITE) system in Alberta, Canada retrieved frequent ozone (O3) and aerosol lamina in the free troposphere during the campaign. Simulated data from NASA's GEOS Composition Forecast (GEOS-CF) coupled chemistry meteorology model, TROPOspheric Monitoring Instrument (TROPOMI), and ground-based in situ measurements were applied to define the trans-Pacific and trans-Arctic transport pathways of Siberian biomass burning emissions resulting in the enhanced O3 and aerosol lamina observed by AMOLITE in western Canada. Siberian wildfires had some influence on North American air quality resulting in enhancements of surface carbon monoxide (CO) and fine particulate matter (PM2.5) concentrations in western Canada; however, minimal increases in surface-level O3 were measured as well as modeled by GEOS-CF. The impact in western Canada was larger in the free troposphere, demonstrated by GEOS-CF modeled and AMOLITE observed O3 lamina >20 ppb above background values and coincident model-predicted PM2.5 lamina >30 μg m−3. This study demonstrated that the Siberian biomass burning emissions in the summer of 2019 impacted tropospheric composition in western Canada, and potentially could have influenced areas in the vicinity of FIREX-AQ airborne and ground-based measurements in the United States, and should be considered in future studies.

Discrepancies between MICS-Asia III simulation and observation for surface ozone in the marine atmosphere over the northwestern Pacific Asian Rim region

Abstract. In order to identify the causes of overestimate of the surface-level O3 mixing ratio simulated by three regional chemical-transport models, NAQPMS v.3 (abbreviated as NAQM in this paper), CMAQ v.5.0.2, and CMAQ v.4.7.1, compared to the EANET observational data at a marine remote site at Oki in July 2010, analyses of hourly O3 mixing ratios and net ozone production were made in the context of MICS-Asia III. In addition to Oki, model-simulated and observational data for two other EANET marine sites, Hedo and Ogasawara, were also examined. Three factors, i.e., long-range transport from the continent, in situ photochemical formation, and dry deposition of O3 on seawater, have been identified as contributing to the overestimate by these regional models at Oki. The calculated O3 mixing ratios during long-range transport from the continent were much higher for all three models than those of the observation. In situ photochemical formation, demonstrated by a distinct diurnal variation which was not discerned in the observational data, was seen in the simulated data of all three models and ascribed to the virtual transport of NOx from the southern urban areas of the main island of Japan. The overestimate of the O3 mixing ratio in the background oceanic air mass has been discussed referring to dry deposition velocity (Vd) of O3 over oceanic water. Sensitivity analysis of the dry deposition velocity to the concentration of O3 was made for Oki in July. An increase in Vd from 0.0005 to 0.001 cm s−1 used in the standard runs for CMAQ by a factor of 10 decreases the O3 mixing ratio by more than 20 ppbv on an event basis in certain periods of time and by ca. 4.9 ppbv as a monthly mean in July. The dry deposition velocity of O3 in Bohai Bay and the Yellow Sea has been assumed to be comparable to that of the open ocean in all three models, which could have resulted in the overestimate of O3 mixing ratios in this area and also in the long-range transport of O3 from the continent to Oki. A higher value of dry deposition velocity in this marine area is expected considering the higher content of organics in the surface sea layer brought by rivers and atmospheric wet deposition. Empirical measurements of the mixing ratios and dry deposition flux of O3 in this area are highly recommended, since they would affect the simulated mixing ratios in the downwind region in the Pacific Rim region.

Transport and boundary layer interaction contribution to extremely high surface ozone levels in eastern China.

Vertical measurements of ozone (O3) within the 3000-m lower troposphere were obtained using an O3 lidar to investigate the contribution of the interactions between the transport and boundary layer processes to the surface O3 levels in urban Shanghai, China during July 23-28, 2017. An extremely severe pollution episode with a maximum hourly O3 mixing ratio of 160.4ppb was observed. In addition to enhanced local photochemical production, both downward and advection transport in the lower troposphere may have played important roles in forming the pollution episode. The O3-rich air masses in the lower free troposphere primarily originated from central China and the northern Yangtze River Delta (YRD) region. The downward transport of O3 from the lower free troposphere may have an average contribution of up to 49.1% to the daytime (09:00-16:00 local time) surface O3 in urban Shanghai during the pollution episode (July 23-26, 2017). As for the advection transport, large amounts of O3 were transported outward from Shanghai in the planetary boundary layer under the influence of southeasterly winds during the field study. In this condition, the boundary-layer O3 that was transported downward from the free troposphere in Shanghai could be transported back to the northern YRD region and accumulated therein, leading to the occurrence of severe O3 pollution events over the whole YRD region. Our results indicate that effective regional emission control measures are urgently required to mitigate O3 pollution in the YRD region.

Significant ground-level ozone attributed to lightning-induced nitrogen oxides during summertime over the Mountain West States

Using lightning flash data from the National Lightning Detection Network with an updated lightning nitrogen oxides (NOx) emission estimation algorithm in the Community Multiscale Air Quality (CMAQ) model, we estimate the hourly variations in lightning NOx emissions for the summer of 2011 and simulate its impact on distributions of tropospheric ozone (O3) across the continental United States. We find that typical summer-time lightning activity across the U.S. Mountain West States (MWS) injects NOx emissions comparable to those from anthropogenic sources into the troposphere over the region. Comparison of two model simulation cases with and without lightning NOx emissions show that significant amount of ground-level O3 in the MWS during the summer can be attributed to the lightning NOX emissions. The simulated surface-level O3 from a model configuration incorporating lightning NOx emissions showed better agreement with the observed values than the model configuration without lightning NOx emissions. The time periods of significant reduction in bias in simulated O3 between these two cases strongly correlate with the time periods when lightning activity occurred in the region. The inclusion of lightning NOx increased daily maximum 8 h O3 by up to 17 ppb and improved model performance relative to measured surface O3 mixing ratios in the MWS region. Analysis of model results in conjunction with lidar measurements at Boulder, Colorado during July 2014 corroborated similar impacts of lightning NOx emissions on O3 air quality. The magnitude of lightning NOx emissions estimated for other summers is comparable to the 2011 estimates suggesting that summertime surface-level O3 levels in the MWS region could be significantly influenced by lightning NOx.

Impacts of meteorology and emissions on summertime surface ozone increases over central eastern China between 2003 and 2015

Abstract. Recent studies have shown that surface ozone (O3) concentrations over central eastern China (CEC) have increased significantly during the past decade. We quantified the effects of changes in meteorological conditions and O3 precursor emissions on surface O3 levels over CEC between July 2003 and July 2015 using the GEOS-Chem model. The simulated monthly mean maximum daily 8 h average O3 concentration (MDA8 O3) in July increased by approximately 13.6 %, from 65.5±7.9 ppbv (2003) to 74.4±8.7 ppbv (2015), comparable to the observed results. The change in meteorology led to an increase in MDA8 O3 of 5.8±3.9 ppbv over the central part of CEC, in contrast to a decrease of about -0.8±3.5 ppbv over the eastern part of the region. In comparison, the MDA8 O3 over the central and eastern parts of CEC increased by 3.5±1.4 and 5.6±1.8 ppbv due to the increased emissions. The increase in averaged O3 in the CEC region resulting from the emission increase (4.0±1.9 ppbv) was higher than that caused by meteorological changes (3.1±4.9 ppbv) relative to the 2003 standard simulation, while the regions with larger O3 increases showed a higher sensitivity to meteorological conditions than to emission changes. Sensitivity tests indicate that increased levels of anthropogenic non-methane volatile organic compounds (NMVOCs) dominate the O3 increase over the eastern part of CEC, and anthropogenic nitrogen oxides (NOx) mainly increase MDA8 O3 over the central and western parts and decrease O3 in a few urban areas in the eastern part. Budget analysis showed that net photochemical production and meteorological conditions (transport in particular) are two important factors that influence O3 levels over the CEC. The results of this study suggest a need to further assess the effectiveness of control strategies for O3 pollution in the context of regional meteorology and anthropogenic emission changes.

A novel bagging ensemble approach for predicting summertime ground-level ozone concentration

ABSTRACTOzone pollution appears as a major air quality issue, e.g. for the protection of human health and vegetation. Formation of ground level ozone is a complex photochemical phenomenon and involves numerous intricate factors most of which are interrelated with each other. Machine learning techniques can be adopted to predict the ground level ozone. The main objective of the present study is to develop the state-of-the-art ensemble bagging approach to model the summer time ground level ozone in an industrial area comprising a hazardous waste management facility. In this study, the feasibility of using ensemble model with seven meteorological parameters as input variables to predict the surface level O3 concentration. Multilayer perceptron, RTree, REPTree, and Random forest were employed as the base learners. The error measures used for checking the performance of each model includes IoAd, R2, and PEP. The model results were validated against an independent test data set. Bagged random forest predicted the ground level ozone better with higher Nash-Sutcliffe coefficient 0.93. This study scaffolded the current research gap in big data analysis identified with air pollutant prediction.Implications: The main focus of this paper is to model the summer time ground level O3 concentration in an Industrial area comprising of hazardous waste management facility. Comparison study was made between the base classifiers and the ensemble classifiers. Most of the conventional models can well predict the average concentrations. In this case the peak concentrations are of importance as it has serious effect on human health and environment. The models developed should also be homoscedastic.