Tropospheric Ozone Concentrations Research Articles

Evaluation of the impacts of ozone on the vegetation productivity of woodland and grassland ecosystems in China

In the context of global warming, with the increasing tropospheric ozone concentration and the obvious trend of aridity, terrestrial ecosystems are experiencing multiple pressures. However, there are still many uncertainties in modeling the effects of ozone on ecosystem productivity. In this study, an ozone uptake module was coupled to the BEPS (Boreal Ecosystem Productivity Simulator) model, and the new version, the BEPS-O3 model, was used to simulate the impacts of ozone on the gross primary productivity (GPP) of woodland and grassland ecosystems in China. Observational data from four sites were used to verify and improve the models, namely, DXG (grassland), HBG (shrub), DHS (evergreen broad-leaved) and CBS (coniferous forest). The regional results show that the total GPP of forest, grassland and shrub in China was 3.62 Pg C, 0.75 Pg C 0.33 Pg C in 2016, respectively. The GPP loss of forests, grasslands and shrubs caused by ozone was 2.8% and 1.1% and 1.5% of the GPP in woodland and grassland ecosystems, respectively (excluding farmland). Subtropical regions experienced the worst GPP losses, although ozone concentrations were not high. However, higher stomatal conductance leads to higher ozone absorption. By comparing the parameters of previous studies, we conclude that the ozone uptake function was better than the ozone exposure function in modeling. Furthermore, the selection of the ozone uptake function will have a significant impact on the final simulation results, especially for grassland.

Impact of introducing net-zero carbon strategies on tropospheric ozone (O3) and fine particulate matter (PM2.5) concentrations in Japanese region in 2050

In this study, we estimated the future emission inventory of primary air pollutants in Japan in 2050 after introducing low-carbon technology based on the results of the socio-economic model provided by the Japanese government. The results suggested that introducing net-zero carbon technology would contribute to a 50–60 % decrease in primary NOx, SO2, and CO emissions and a ~30 % decrease in primary emissions of volatile organic compounds (VOCs) and PM2.5. The estimated emission inventory and future meteorological conditions in 2050 were applied as inputs to a chemical transport model. A scenario involving the application of future reduction strategies with relatively moderate global warming (RCP4.5) was evaluated. The results showed that the concentration of tropospheric ozone (O3) was highly reduced compared with that in 2015 after applying net-zero carbon reduction strategies. On the other hand, the fine particulate matter (PM2.5) concentration under the 2050 scenario was expected to be equal or higher because of the growth in secondary aerosol formation caused by the increase in short-wave radiation. Finally, the premature mortality change from 2015 to 2050 was analyzed, and the change in air quality contributed by net-zero carbon technology will contribute to a ~4000 decrease in premature deaths in Japan.

Short-term effects of tropospheric ozone and other environmental factors on emergency admissions due to pregnancy complications: A time-series analysis in the Madrid Region

Air pollution has been linked to adverse neonatal outcomes, mainly in the case of prolonged exposures. This study focuses on the short-term effects on maternal health.We conducted a retrospective ecological time-series study in the Madrid Region covering the period 2013–2018. The independent variables were mean daily concentrations of tropospheric ozone (O3), particulate matter (PM10/PM2.5) and nitrogen dioxide (NO2), as well as noise levels. The dependent variables were daily emergency hospital admissions due to complications in pregnancy, childbirth and the puerperium. Poisson generalised linear regression models were fitted to quantify the relative and attributable risks, controlling for trend, seasonality, the autoregressive nature of the series, and a number of meteorological factors.There were 318 069 emergency hospital admissions due to obstetric complications across the 2191 days of study. Of this total: 13 164 (95%CI: 9930–16 398) admissions were attributable to exposure to O3, the only pollutant to show a statistically significant (p < 0.05) association with admissions due to hypertensive disorders; and 10 575 (95%CI: 3573–17 566) admissions were attributable to daytime noise levels, while admissions due to hyperemesis gravidarum and vomiting were related to exposure to night noise. Other pollutants which also displayed statistically significant associations were: NO2 concentrations, with admissions due to vomiting and preterm labour; PM10 concentrations, with premature rupture of membranes: and PM2.5 concentrations, with total complications.Exposure to a range of air pollutants, and ozone in particular, is associated with a higher number of emergency hospital admissions due to gestational complications. Hence, surveillance of environmental effects on maternal health should be intensified, and plans and strategies to minimise these should be drawn up.

Assessment of the differential trade-off between growth, subsistence, and productivity of two popular Indian hybrid mango varieties under elevated ozone exposure

The multifunctionality of plants is well known to be compromised in the areas experiencing higher concentrations of tropospheric ozone (O3). Mango (Mangifera indica L.) cultivation is essential to the economy of tropical regions, including India. Mango, widely grown in suburban and rural areas, experiences production loss due to air pollutants. Ozone, the most important phytotoxic gas in mango growing areas, warrants an investigation of its effects. Therefore, we assessed the differential sensitivity of mango saplings (two-year-old hybrid and regular-bearing mango varieties, Amrapali and Mallika) at two levels of O3: ambient and elevated (ambient + 20 ppb) using open-top chambers from September 2020 to July 2022. Under elevated O3, both varieties showed similar seasonal responses (winter and summer) for all the growth parameters but differed in their height-diameter allocation pattern. A decrease in stem diameter and an increase in plant height were observed in Amrapali, whereas Mallika showed a reverse response. Early emergence of phenophases was noticed during the reproductive growth of both varieties under elevated O3 exposure. However, these changes were more pronounced in Amrapali. Stomatal conductance was more negatively affected in Amrapali than in Mallika under elevated O3 during both seasons. Furthermore, leaf morpho-physiological traits (leaf nitrogen concentration, leaf area, leaf mass per area, and photosynthetic nitrogen use efficiency) and inflorescence parameters responded variably in both varieties under elevated O3 stress. A decrease in photosynthetic nitrogen use efficiency, further enhanced yield loss which was more pronounced in Mallika than in Amrapali under elevated O3 exposure. The results of this study could be useful in selecting a better-performing variety based on its productivity, which will be economically more beneficial in achieving the goal of sustainable production at the anticipated high O3 levels under a climate change scenario.

Rapid increase in tropospheric ozone over Southeast Asia attributed to changes in precursor emission source regions and sectors

Observations indicate that tropospheric ozone (O3) concentrations over Southeast Asia have been increasing rapidly since the 1990s. Here, we quantify source contributions from geographical regions and emission sectors of the two distinct types of O3 precursors, i.e., nitrogen oxides (NOx) and volatile organic compounds (VOCs), to the increase in tropospheric O3 in Southeast Asia during 1990–2019 using an O3 source tagging technique implemented in a global chemistry-climate model. The results show that although local anthropogenic emission of NOx in Southeast Asia only contributes 18% of the annual averaged near-surface O3 concentration, the increase in local NOx emission dominates the increasing trend of O3 concentration in Southeast Asia, accounting for 107% of the regional averaged trend of 1.07 ppb decade−1. Increases in NOx emissions from East Asia and South Asia explain 29% of the increasing trend, but 9% is offset by the emission reduction in North America. The vertical O3 trends in the troposphere contributed by individual source regions are consistent with those near the surface. Ground transportation is responsible for 79% of the rapid O3 increase, followed by 39% contribution from international shipping. Because an increase in anthropogenic NOx emissions enhances the O3 production efficiency by VOCs, the increase in O3 concentrations in Southeast Asia is thereby largely contributed by methane and biogenic VOCs.

Distribution and Long-Term Trends of Tropospheric Ozone Concentrations in Ireland

Tropospheric ozone (O3) is highly variable over space and time reflecting local production and destruction as well as addition and loss through regional and long-range transport. In this study, O3 concentrations at 11 stations in Ireland and their long-term trends (7–9 sites) were evaluated; O3 concentrations (2015–2019) varied spatially, with the highest annual mean concentrations along the Atlantic west coast (69–75 µg/m3), and the lowest in urban centres (39–43 µg/m3). Ozone followed a seasonal pattern of spring and winter maximum and summer–autumn minimum. Significant long-term (2005–2019) increases were observed in annual O3 concentration at two rural stations, while increases were larger and more frequent during winter with increases at four out of seven stations. During the decade 2010–2019, significant annual increases were observed at four out of nine stations. Observed site- and season-specific increasing trends in O3 concentrations likely reflected changes in regional precursor gas emissions sources. Despite reported decreases in background concentrations in the marine boundary layer in northern mid-latitudes in recent decades, O3 concentrations at some sites in Ireland have increased significantly primarily driven by changes in winter concentrations. There were no significant decreasing trends at any site or in any season.

Air pollution as a substantial threat to the improvement of agricultural total factor productivity: Global evidence

ObjectiveThis study aims to provide empirical evidence about whether and to what extent air pollution affects the global agricultural total factor productivity (TFP). MethodsThe research sample covers 146 countries all over the world during 2010–2019. Two-way fixed effects panel regression models are used to estimate air pollution’s impacts. A random forest analysis is conducted to assess the relative importance of independent variables. ResultsThe results show that, on average, a 1% increase in fine particulate matter (PM2.5) and tropospheric ozone (O3) concentration would cause the agricultural TFP to decline by 0.104% and 0.207%, respectively. Air pollution’s adverse impact widely exists in various countries with different development levels, pollution degrees, and industrial structures. This study also finds that temperature has a moderating effect on the relationship between PM2.5 and agricultural TFP. PM2.5 pollution’s detrimental impact is weaker (stronger) in a warmer (cooler) climate. In addition, the random forest analysis confirms that air pollution is among the most crucial predictors of agricultural productivity. ConclusionsAir pollution is a substantial threat to the improvement of global agricultural TFP. Worldwide actions should be taken to ameliorate air quality, for the sake of agricultural sustainability and global food security.

Current Status and Future Forecast of Short-lived Climate-Forced Ozone in Tehran, Iran, derived from Ground-Based and Satellite Observations.

In this study, the distribution and alterations of ozone concentrations in Tehran, Iran, in 2021 were investigated. The impacts of precursors (i.e., CO, NO2, and NO) on ozone were examined using the data collected over 12months (i.e., January 2021 to December 2021) from 21 stations of the Air Quality Control Company (AQCC). The results of monthly heat mapping of tropospheric ozone concentrations indicated the lowest value in December and the highest value in July. The lowest and highest seasonal concentrations were in winter and summer, respectively. Moreover, there was a negative correlation between ozone and its precursors. The Inverse Distance Weighting (IDW) method was then implemented to obtain air pollution zoning maps. Then, ozone concentration modeled by the IDW method was compared with the average monthly change of total column density of ozone derived from Sentinel-5 satellite data in the Google Earth Engine (GEE) cloud platform. A good agreement was discovered despite the harsh circumstances that both ground-based and satellite measurements were subjected to. The results obtained from both datasets showed that the west of the city of Tehran had the highest averaged O3 concentration. In this study, the status of the concentration of ozone precursors and tropospheric ozone in 2022 was also predicted. For this purpose, the Box-Jenkins Seasonal Autoregressive Integrated Moving Average (SARIMA) approach was implemented to predict the monthly air quality parameters. Overall, it was observed that the SARIMA approach was an efficient tool for forecasting air quality. Finally, the results showed that the trends of ozone obtained from terrestrial and satellite observations throughout 2021 were slightly different due to the contribution of the tropospheric ozone precursor concentration and meteorology conditions.

Nitrogen oxides in the free troposphere: implications for tropospheric oxidants and the interpretation of satellite NO2 measurements

Abstract. Satellite-based retrievals of tropospheric NO2 columns are widely used to infer NOx (≡ NO + NO2) emissions. These retrievals rely on model information for the vertical distribution of NO2. The free tropospheric background above 2 km is particularly important because the sensitivity of the retrievals increases with altitude. Free tropospheric NOx also has a strong effect on tropospheric OH and ozone concentrations. Here we use observations from three aircraft campaigns (SEAC4RS, DC3, and ATom) and four atmospheric chemistry models (GEOS-Chem, GMI, TM5, and CAMS) to evaluate the model capabilities for simulating NOx in the free troposphere and attribute it to sources. NO2 measurements during the Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS) and Deep Convective Clouds and Chemistry (DC3) campaigns over the southeastern U.S. in summer show increasing concentrations in the upper troposphere above 10 km, which are not replicated by the GEOS-Chem, although the model is consistent with the NO measurements. Using concurrent NO, NO2, and ozone observations from a DC3 flight in a thunderstorm outflow, we show that the NO2 measurements in the upper troposphere are biased high, plausibly due to interference from thermally labile NO2 reservoirs such as peroxynitric acid (HNO4) and methyl peroxy nitrate (MPN). We find that NO2 concentrations calculated from the NO measurements and NO–NO2 photochemical steady state (PSS) are more reliable to evaluate the vertical profiles of NO2 in models. GEOS-Chem reproduces the shape of the PSS-inferred NO2 profiles throughout the troposphere for SEAC4RS and DC3 but overestimates NO2 concentrations by about a factor of 2. The model underestimates MPN and alkyl nitrate concentrations, suggesting missing organic NOx chemistry. On the other hand, the standard GEOS-Chem model underestimates NO observations from the Atmospheric Tomography Mission (ATom) campaigns over the Pacific and Atlantic oceans, indicating a missing NOx source over the oceans. We find that we can account for this missing source by including in the model the photolysis of particulate nitrate on sea salt aerosols at rates inferred from laboratory studies and field observations of nitrous acid (HONO) over the Atlantic. The median PSS-inferred tropospheric NO2 column density for the ATom campaign is 1.7 ± 0.44 × 1014 molec. cm−2, and the NO2 column density simulated by the four models is in the range of 1.4–2.4 × 1014 molec. cm−2, implying that the uncertainty from using modeled NO2 tropospheric columns over clean areas in the retrievals for stratosphere–troposphere separation is about 1 × 1014 molec. cm−2. We find from GEOS-Chem that lightning is the main primary NOx source in the free troposphere over the tropics and southern midlatitudes, but aircraft emissions dominate at northern midlatitudes in winter and in summer over the oceans. Particulate nitrate photolysis increases ozone concentrations by up to 5 ppbv (parts per billion by volume) in the free troposphere in the northern extratropics in the model, which would largely correct the low model bias relative to ozonesonde observations. Global tropospheric OH concentrations increase by 19 %. The contribution of the free tropospheric background to the tropospheric NO2 columns observed by satellites over the contiguous U.S. increases from 25 ± 11 % in winter to 65 ± 9 % in summer, according to the GEOS-Chem vertical profiles. This needs to be accounted for when deriving NOx emissions from satellite NO2 column measurements.

Vertical distribution of tropospheric ozone and its sources of precursors over Beijing: Results from ∼ 20 years of ozonesonde measurements based on clustering analysis

This study comprehensively analyzed nearly 20 years of ozonesonde data from Beijing on the North China Plain collected between 2001 and 2019 to determine the vertical structure of tropospheric ozone as well as its sources of precursors through a combination of radiosonde data, satellite products, and ERA5 reanalysis data. Quantitative analysis involved the self-organizing map (SOM) algorithm, calculating backward trajectories, and applying the Potential Source Contribution Function (PSCF) algorithm. The SOM clustering results (3 × 3 classes) showed that the ozone profiles over Beijing were primarily affected by seasonal variability, and the vertical ozone structure and its precursors exhibited obvious seasonal patterns (high VOCs in warm seasons and high NOx in cold seasons). The tropospheric ozone concentrations in Beijing, which were influenced by both ozone precursors and seasonal meteorological factors, were high in warm seasons and low in cold seasons. Further detailed investigations of SOM clustering results found that biomass burning, pollutant transport and stratospheric intrusion contributed significantly to tropospheric ozone over Beijing. Ozone in spring and summer was influenced by biomass burning activities south of Beijing, resulting in an increase in tropospheric ozone concentrations (at 0–10 km) of 60.6 ppbv. Biomass burning activities on the North China Plain have been adequately controlled since the implementation of the Clean Air Action Plan in 2013, which greatly reduced the frequency of ultrahigh tropospheric ozone concentrations in Beijing during the spring and summer. Stratospheric intrusions, which are closely associated with ozone transport from high latitudes (including the influence of Brewer-Dobson circulation subsidence), occur more frequently during spring and winter and increase ozone concentrations in the middle and upper troposphere in Beijing.

Evidence of NOx and O3 concentration reduction by kudzu (Pueraria lobata) invasion at a Japanese highway

Generally, urban green infrastructure aids in the mitigation of air pollution. However, little is known about the role of densely packed vegetation canopies, such as Pueraria lobata (Willd.) Ohwi (kudzu) in air pollution mitigation. Here, we conducted field measurements of tropospheric ozone (O3) and nitrogen oxides (NOx) concentrations on a highway embankment slope with and without kudzu canopies in Japan. We measured O3 and NOx concentrations above and within the kudzu canopies by using a passive sampler several times during the growing season in 2019. The results demonstrated that both O3 and NOx concentrations reduced within the kudzu canopy throughout the growing season, suggesting that kudzu generally acts as “vegetation barrier” for both gas pollutants along the highway roadside. Depending on meteorological and vegetative surface conditions, the reduction rate within the canopy ranged from 11% to 64% and from −2% to 33% for O3 and NOx concentrations, respectively. Considering lower canopy height but higher leaf area density of kudzu than those for urban tree plantations or forest patches along the roadside, kudzu can be useful as green infrastructure depending on situations. We also found that the higher the leaf area index of kudzu canopies, the higher the reduction rates of O3 and NOx. Depending on the maintenance cost for roadside tree planting, the minimal management without targeting the eradication of kudzu over a certain area can be an option for realizing green infrastructure at least for maintaining local air quality during the growing season.

Short-Term Exposure of Dactylis glomerata Pollen to Atmospheric Gaseous Pollutants Is Related to an Increase in IgE Binding in Patients with Grass Pollen Allergies.

The concentrations of nitrogen dioxide (NO2) and tropospheric ozone (O3) in urban and industrial site atmospheres are considered key factors associated with pollen-related respiratory allergies. This work studies the effects of NO2 and O3 on the protein expression profile and IgE binding in patients with grass allergies to Dactylis glomerata pollen extracts. Pollens were collected during the flowering season and were exposed to NO2 and O3 in a controlled environmental chamber. The amount of soluble protein was examined using the Bradford method, and the protein expression profile and antigenic properties were analysed using the immunoblotting and enzyme-linked immunosorbent assay (ELISA), respectively. Our results showed apparent inter-sera differences concerning the number and intensity of IgE reactivity, with the most prominent at bands of 55 kDa, 35, 33, and 13 kDa. In the 13 kDa band, both gases tend to induce an increase in IgE binding, the band at 33 kDa showed a tendency towards a reduction, particularly pollen exposed to O3. Reactive bands at 55 and 35 kDa presented an increase in the IgE binding pattern for all the patient sera samples exposed to NO2, but the samples exposed to O3 showed an increase in some sera and in others a decrease. Regarding the ELISA results, out of the 21 tested samples, only 9 showed a statistically significant increase in total IgE reactivity after pollen exposure to the pollutants. Our study revealed that although airborne pollen allergens might be affected by air pollution, the possible impacts on allergy symptoms might vary depending on the type of pollutant and the patient's sensitisation profile.

Physicochemical characteristics of lodging susceptibility of rice cultivars in response to ozone exposure

High tropospheric ozone concentrations reduce rice yield and grain quality, which imposes a serious threat to food security in Asia. This study aimed at determining the effect of ozone on rice lodging, an unpredictable constraint for achieving high yield and good quality in rice production under climate change. Two rice cultivars with different ozone sensitivity were exposed to ozone concentration of 80 ppb (8 h per day) and control conditions (13 ppb) in natural-light fumigation chambers from tillering to maturity. The pushing resistance of intact plants and the lodging-related culm traits were examined. Ozone exposure significantly decreased the in-situ pushing resistance of intact plant or single culm in the ozone-sensitive cultivar YD6, but had no effects in the ozone-tolerant cultivar WYJ27. Ozone reduced breaking resistance and bending moment to a similar magnitude, resulting in no change of lodging index when averaged across all rice basal internodes. In general, WYJ27 was less responsive to ozone than YD6. Negative ozone effects on lodging-related culm traits of YD6 included reductions in the internode dry weight as well as the dry weight per unit internode length, decreases in internode diameter, cross section area and culm wall thickness of basal internodes, and reduced concentrations of soluble sugar and starch. Correlation analysis indicated that ozone-induced decrease in culm strength of YD6 was mainly attributed to the thinner internodes and the smaller culm density due to less nonstructural carbohydrate deposition. The ozone-sensitivity of YD6 was confirmed by its high yield reduction of 25 %, caused by an 11 % decrease in spikelet number per panicle and a 10 % decrease in fulfilled grain weight. The results suggested that rice ozone sensitivity in yield was in consistent with that in stem strength, which could result in no change of lodging index under greenhouse conditions. The realistic lodging susceptibility of these cultivars in response to ozone pollution in open paddy fields, where rice was often subjected to wind and rain during ripening stage, needs further investigation.

The Earth Summit Mission-2022: Successful ozone soundings contribute to source identification in the north Mt. Qomolangma region

As part of “The Earth Summit Mission-2022” during the second Tibetan Plateau Scientific Expedition and Research (STEP) in April and May 2022, we conducted the ozone sounding experiment (an ozonesonde mated to a radiosonde) at Mt. Qomolangma Base Camp (MQBC; 86.85°E, 28.14°N; 5200 m), a location at an extremely high altitude. A total of ten sounding profiles were obtained between April 30 and May 06, 2022, of which seven profiles were above 35 km in altitude, with a maximum detection altitude up to 39.0 km. This study presents the temporal variation and vertical distributions of atmospheric temperature, humidity, and ozone during the MQBC campaign. The averaged ozone concentration was high (68.3 ppbv) at the surface and then increased smoothly until peaking (∼110 ppbv) in the middle troposphere (approximately 10 km), and afterward, the ozone concentration increased rapidly from the upper troposphere to a maximum of ∼10 ppmv at ∼30 km. The enhanced ozone concentration in the middle troposphere was associated with the blocking high pressure, and transport from the southern flank of the Himalayas occurred during the campaign period. The average total ozone column was 291.9±21.4 DU for the seven profiles exceeding 35 km in altitude. The ozonesonde measurements were also compared with the vertical ozone profiles retrieved from the space-borne ozone products from the Microwave Limb Sounder (MLS) onboard the Aura satellite and the Atmospheric Infrared Sounder (AIRS) onboard the Aqua satellite.

Tropospheric Ozone Concentration on the Territory of Russia in 2021

Ozone is one of the most toxic admixtures in the troposphere. Therefore, it is among the main pollutants and its concentration is monitored. This work represents an overview of continuous measurements of the ozone content in the troposphere on the territory of Russia throughout 2021 carried out on an initiative of scientific and educational institutions at 17 stations in different Russian regions. The monitoring results showed that the daily average ozone concentration exceeded the MPCd.a level during a major part of the year at all observation sites, and by a factor of two or even three at a number of stations. At six stations, concentrations in excess of the maximum permissible one-time concentration MPCm.o were recorded. This requires a more comprehensive analysis of the composition and concentration of ozone precurcors and the development of measures to reduce their emission into the atmosphere.

Sources of surface O3 in the UK: tagging O3 within WRF-Chem

Abstract. Tropospheric ozone (O3) concentrations depend on a combination of hemispheric, regional, and local-scale processes. Estimates of how much O3 is produced locally vs. transported from further afield are essential in air quality management and regulatory policies. Here, a tagged-ozone mechanism within the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) is used to quantify the contributions to surface O3 in the UK from anthropogenic nitrogen oxide (NOx) emissions from inside and outside the UK during May–August 2015. The contribution of the different source regions to three regulatory O3 metrics is also examined. It is shown that model simulations predict the concentration and spatial distribution of surface O3 with a domain-wide mean bias of −3.7 ppbv. Anthropogenic NOx emissions from the UK and Europe account for 13 % and 16 %, respectively, of the monthly mean surface O3 in the UK, as the majority (71 %) of O3 originates from the hemispheric background. Hemispheric O3 contributes the most to concentrations in the north and the west of the UK with peaks in May, whereas European and UK contributions are most significant in the east, south-east, and London, i.e. the UK's most populated areas, intensifying towards June and July. Moreover, O3 from European sources is generally transported to the UK rather than produced in situ. It is demonstrated that more stringent emission controls over continental Europe, particularly in western Europe, would be necessary to improve the health-related metric MDA8 O3 above 50 and 60 ppbv. Emission controls over larger areas, such as the Northern Hemisphere, are instead required to lessen the impacts on ecosystems as quantified by the AOT40 metric.

Evaluation of Ambient Ozone Effect in Bean and Petunia at Two Different Sites under Natural Conditions: Impact on Antioxidant Enzymes and Stress Injury

Tropospheric ozone is a harmful air pollutant and greenhouse gas that adversely affects living organisms. The effect of long-term ozone stress on the activity of SOD, APX, and GuPX, as well as lipid peroxidation and membrane injury in bean and petunia growing at a city site and in a forest, characterised by different ozone concentrations, was examined. The experiments were conducted in three growing seasons with different tropospheric ozone concentrations and meteorological conditions. Plants’ exposition to increased ozone concentration resulted in enhanced activity of antioxidant enzymes, level of lipid peroxidation, and membrane injury. In all years, higher ozone levels and solar radiation were observed at the forest site. The pattern of the changes in enzyme activity was dependent on ozone concentrations as well as on environmental conditions and varied from year to year. In the second year with the highest ozone concentration, the activity of GuPX and SOD increased the most. However, despite higher ozone concentration in the forest, a larger increase in APX and SOD activity in both species and GuPX activity in bean was recorded at the city site. The present results revealed that plant response to ozone might vary in different locations not only due to differences in ozone concentration but also because of the impact of other environmental factors, such as solar radiation and temperature.

Changes in tropospheric ozone concentration over Indo-Gangetic Plains: the role of meteorological parameters

This study seeks to understand and quantify the changes in tropospheric ozone (O3) in lower troposphere (LT), middle troposphere (MT) and upper middle troposphere (UMT) over the Indo-Gangetic Plains (IGPs), India during the COVID-19 lockdown 2020 with that of pre-lockdown 2019. The gridded datasets of ozone from the European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis product, ERA5 in combination with statistical interpolated (IDWs) surface NO2 observations, present a consistent picture and indicate a significant tropospheric ozone enhancement over IGP during COVID-19 lockdown restrictions in May 2020. The Paper also examines the influencing role of meteorological parameters on increasing ozone concentration. Over LT, an increase in O3 concentration (23%) is observed and in MT to UMT an enhancement of about 9–18% in O3 concentration have been seen during May 2020 with respect to May 2019. An investigation on causes of increasing ozone concentration (35–85 ppbv) from MT to UMT during May 2020 reveals that there was significant rise (by 1–6%) in low cloud cover (LCC). Notably, higher LCC increases the backscattering of upward solar radiation from the top of the atmosphere. A positive difference of 5–25 W/m2 in upward solar radiation (USR) is observed across the entire study region. The result suggests that higher LCC significantly contributed to the enhanced USR. Thereby, resulting in higher photolysis rate that lead to an increase in mid tropospheric ozone concentration during May 2020. The results highlight the importance of LCC as an important pathway in ozone formation and aid in scientific understanding of it.

Retrieval of tropospheric ozone profiles using ground-based MAX-DOAS

In recent years, surface ozone concentrations have increased in many cities in China. Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) is a powerful technique for retrieving the profiles of tropospheric trace gases, such as NO2, SO2, and HCHO. However, since the difficulties in deducting the effects of stratospheric ozone, there are few studies on the retrieval of tropospheric ozone profiles using MAX-DOAS measurements. Here, we developed an accurate inversion method to retrieve tropospheric ozone concentrations during the PRIDE-GBA Campaign, wherein the ozone differential slant column densities (DSCDs) were retrieved in QDOAS software using the “time-interpolated zenith spectrum” as the reference spectrum. The tropospheric DSCDs (DSCDstrop) were then calculated by subtracting the simulated stratospheric DSCDs (DSCDsstr, simulated from the SCIATRAN model) from the DSCDs. Tropospheric ozone profiles were retrieved from the DSCDstrop using the optimal estimation method (OEM). The results showed that high values of tropospheric ozone were mainly distributed below 1 km, which is consistent with lidar measurements. In addition, the observed surface ozone concentrations were highly correlated with the in-situ measurements, with correlation coefficients (R) of 0.75 and 0.81, respectively. Combined with the retrieved NO2 and HCHO profiles using the MAX-DOAS measurements, we found that the planetary boundary layer ozone pollution of HeShan Observatory during the PRIDE-GBA Campaign are controlled by the NOx-limited regime. The results of this study indicate that the MAX-DOAS technique has the potential to retrieve tropospheric ozone profiles with high temporal and spatial resolution.

A remote sensing based study of tropospheric ozone concentration amid COVID-19 lockdown over India using Sentinel-5P satellite data

Amid the COVID-19 crisis, governments all over the world, and not excluding India, took to lockdown measures to deaccelerate the spread of the COVID-19 virus. This led to reduction of atmospheric pollution by declining the harmful Nitrogen and Sulphur Oxide (NOX and SOX) concentrations. However, one hand while the stratospheric Ozone (O3) showed repair, the lower atmospheric O3 concentrations demonstrated a remarkable increase during lockdown phase over India. This study aims to estimate the O3 concentration during the Covid-19 lockdown over Pune city in India using freely available Sentinel-5P satellite datasets. The study makes use of the Ordinary Least Squares (OLS) and Random Forest (RF) regressions and compares the findings of the two algorithms based on estimation results. This study utilizes lower atmospheric O3 concentration data from Sentinel-5P satellite of the European Space Agency (ESA) over the Indian mainland for a month of lockdown scenario (March 22nd, 2020, to April 25th, 2020) and shows the remarkable increase in concentration of O3 gas as a pollutant. Despite the complete lockdown over India during this given time frame, there has been enough emission of O3 precursors from other sources such as stubble burning. The estimates of tropospheric O3 concentration for May 2020 for Pune city, using OLS and RF Regressions, have been validated with May 2020 data. The results have provided a RMSE of 1.05 and 1.23 with R2-statistics of 0.90 and 0.857 in training and testing phases for OLS and RMSE of 0.98 and MAE of 1.07 with R2-statistics of 0.968 and 0.895 in training and testing phases of the RF. The outcome of this study has proven that O3 gas concentrations in the atmosphere depends upon various other causative factors apart from the precursor gases. The study also shows that the remotely sensed Sentinel-5P datasets, supplemented with ground-based sensor data can help in time and cost saving estimation of O3 concentrations in the troposphere with considerable accuracy.