Tropospheric O3 Concentrations Research Articles

Revising VOC emissions speciation improves the simulation of global background ethane and propane

Abstract. Non-methane volatile organic compounds (NMVOCs) generate ozone (O3) when they are oxidised in the presence of oxides of nitrogen, modulate the oxidative capacity of the atmosphere and can lead to the formation of aerosol. Here, we assess the capability of a chemical transport model (GEOS-Chem) to simulate NMVOC concentrations by comparing ethane, propane and higher-alkane observations in remote regions from the NOAA flask Network and the World Meteorological Organization's Global Atmosphere Watch (GAW) network. Using the Community Emissions Data System (CEDS) inventory, we find a significant underestimate in the simulated concentration of both ethane (35 %) and propane (64 %), consistent with previous studies. We run a new simulation in which the total mass of anthropogenic NMVOC emitted in a grid box is the same as that used in CEDS but with the NMVOC speciation derived from regional inventories. For US emissions, we use the National Emissions Inventory (NEI); for Europe, we use the UK National Atmospheric Emissions Inventory (NAEI); and for China, we use the Multi-resolution Emission Inventory model for Climate and air pollution research (MEIC). These changes lead to a large increase in the modelled concentrations of ethane, improving the mean model bias from −35 % to −4 %. Simulated propane also improves (from −64 % to −48 % mean model bias), but there remains a substantial model underestimate. There were relatively minor changes to other NMVOCs. The low bias in simulated global ethane concentration is essentially removed, resolving one long-term issue in global simulations. Propane concentrations are improved but remain significantly underestimated, suggesting the potential for a missing global propane source. The change in the NMVOC emission speciation results in only minor changes in tropospheric O3 and OH concentrations.

Temporal and Spatial Characteristics of Troposphere O3 and Precursors HCHO and NO2 in East China

Based on OMI remote sensing satellite data, the temporal and spatial characteristics of tropospheric ozone (O3), nitrogen dioxide (NO2), and formaldehyde (HCHO) concentrations in East China from 2005 to 2021 were analyzed, and the backward trajectory (HYSPLIT) model was used to explore their sources. The results showed that ① during the 17 years, the tropospheric O3 concentration steadily increased, reached the maximum value in 2010, and then showed a fluctuating and undulating state. NO2 showed an increasing trend from 2005 to 2012 and slowly decreased from 2012 to 2021. The average HCHO concentration showed an increasing trend from 1.15×1016molec·cm-2 in 2005 to 1.8×1016 molec·cm-2 in 2021. ② In terms of spatial characteristics, the concentrations of the three pollutants generally showed a pattern of high concentration in the north and low concentration in the south, with a high concentration in the north, uncharacteristic concentration in the middle, and low concentration in the south. ③ The sensitivity of O3 was as follows:η<2.3 in spring, which belonged to the VOCs control area; η<4.2 in summer, showing that most areas were NOx-VOCs coordinated control areas and a few areas were VOCs control areas; η<4.2 in autumn, which was primarily controlled by VOCs, with a few of them being NOx-VOC synergistic control areas; and η<2.3 in winter, which was a VOCs-controlled area. VOCs were primarily controlled in Shandong Province. ④ Owing to the high concentration of O3 in Shandong Province from 2005 to 2021, Jinan, the capital city of Shandong Province in 2021, was selected for ozone source analysis. The O3 concentration increased in Jinan in 2021 owing to two aspects. First, the long-distance air transportation primarily originated from Lianyungang City in Jiangsu Province and Cangzhou City in Hebei Province. Second, the close air mass transport originated from the pollution of cities near Jinan and the economic zones of the Yellow Sea and Bohai Sea, and the aggregation analysis results corresponded with those of the potential source contribution factor algorithm (PSCF) and the weighted trajectory analysis (CWT).

Global reanalysis products cannot reproduce seasonal and diurnal cycles of tropospheric ozone in the Congo Basin

Tropospheric ozone (O3) is a secondary pollutant and a greenhouse gas with a positive radiative forcing. Many studies have documented its negative impacts on plant growth and human health. Historically, studies have focused on determining levels of exposure in mid- and high-latitude regions. In the tropics, high O3 concentrations are expected due to large concurrent and future precursor emissions. In Africa, seasonal biomass burning (from both natural and anthropogenic fires) during the dry season plays a crucial role in O3 precursor production. However, O3 observational studies in tropical Africa are currently missing. To fill this major knowledge gap, we established in November 2019 a continuous monitoring of near-surface O3 in the Congo Basin at the Yangambi research centre in the Democratic Republic of the Congo. Using this unique dataset in the heart of the second-largest tropical forest in the world, we assessed the ability of current remote sensing products to capture the magnitude and temporal dynamics of in situ tropospheric O3 concentrations, especially O3 concentration variation between dry and wet seasons until March of 2022. We compared near-surface atmospheric O3 measurements collected in Yangambi and four different reanalysis products: European Centre for Medium-Range Weather Forecasts Reanalysis (ECMWF) v5 (ERA5), Copernicus Atmospheric Monitoring Service reanalysis (CAMSRA), Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) and Japanese Reanalysis (JRA-55). The results show that reanalysis products overestimated the magnitude of near-surface O3 across the region with a mean bias of 27.3 ppbv, 19.9 ppbv, 10.8 ppbv and 1.0 ppbv for ERA5, CAMSRA, MERRA-2 and JRA-55, respectively. ERA5 and CAMSRA reanalysis were the only products able to capture, to some extent, the observed annual variation, showing higher O3 concentrations during dry season months, despite the inability to reproduce the daily cycle of near-surface O3.

NOx‐Induced Changes in Upper Tropospheric O3 During the Asian Summer Monsoon in Present‐Day and Future Climate

AbstractThe upper tropospheric ozone (O3) strongly influences the atmosphere's radiative budget. Using the Aerosol and Chemistry Model Intercomparison Project simulations, we study the influence of present‐day and future anthropogenic nitrogen oxides (NOx) emissions on the upper tropospheric O3 concentrations over India during the Asian summer monsoon (ASM). We observe that the upper tropospheric O3 concentrations increased 1.5 times over the ASM anticyclone region during the ASM due to higher NOx emissions in 2014 compared to 1850, and their transport due to convection. These NOx‐induced O3 changes exert a regional positive radiative forcing of 0.6 Wm−2 at the top of the atmosphere. The upper tropospheric O3 increases in the future with increasing NOx emissions. However, air quality policies to reduce surface NOx emissions also reduce the upper tropospheric O3 over India during the ASM.

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.

Air Quality during the COVID–19 Lockdown and Unlock Periods in India Analyzed Using Satellite and Ground-based Measurements

A nationwide lockdown was imposed in India from 24 March 2020 to 31 May 2020 to contain the spread of COVID-19. The lockdown has changed the atmospheric pollution across the continents. Here, we analyze the changes in two most important air quality related trace gases, nitrogen dioxide (NO2) and tropospheric ozone (O3) from satellite and surface observations, during the lockdown (April–May 2020) and unlock periods (June–September 2020) in India, to examine the baseline emissions when anthropogenic sources were significantly reduced. We use the Bayesian statistics to find the changes in these trace gas concentrations in different time periods. There is a strong reduction in NO2 during the lockdown as public transport and industries were shut during that period. The largest changes are found in IGP (Indo-Gangetic Plain), and industrial and mining areas in Eastern India. The changes are small in the hilly regions, where the concentrations of these trace gases are also very small (0–1 × 1015 molec./cm2). In addition, a corresponding increase in the concentrations of tropospheric O3 is observed during the period. The analyses over cities show that there is a large decrease in NO2 in Delhi (36%), Bangalore (21%) and Ahmedabad (21%). As the lockdown restrictions were eased during the unlock period, the concentrations of NO2 gradually increased and ozone deceased in most regions. Therefore, this study suggests that pollution control measures should be prioritized, ensuring strict regulations to control the source of anthropogenic pollutants, particularly from the transport and industrial sectors.Highlights• Most cities show a reduction up to 15% of NO2 during the lockdown• The unlock periods show again an increase of about 40–50% in NO2• An increase in tropospheric O3 is observed together with the decrease in NO2Supplementary InformationThe online version contains supplementary material available at 10.1007/s40710-022-00585-9.

ENSO modulation of summertime tropospheric ozone over China

Ozone (O3) is one of the most critical pollutants affecting air quality in China in recent years. In this study, different impacts of the El Niño–Southern Oscillation (ENSO) warm/cold phases on summertime tropospheric O3 over China are examined based on model simulations, ground measurements, and reanalysis data. Summertime surface O3 concentrations in China show a positive correlation with ENSO index during years 1990–2019, with the largest increases by 20% over southern China in El Niño (warm phase) relative to La Niña (cold phase) years. The ENSO modulation extends to the middle and even upper troposphere. Our analysis indicates that O3 flux convergence associated with weakened southerlies is the primary reason for the increase in tropospheric O3 over southern China. In addition, the O3 increase during El Niño years is mainly from domestic emissions in China. This study highlights the potential significance of ENSO in modulating tropospheric O3 concentrations in China, with great implications for O3 pollution mitigation.

Time series analysis and spatial distribution map of aggregate risk index due to tropospheric NO2 and O3 based on satellite observation

A high increase in human activities has led to more emission of air pollutants in metropolises and industrial areas. Recently, remotely sensed data of tropospheric pollutants is used for environmental management and decision-making on large scale. The purpose of this study was a time series analysis of nitrogen dioxide Vertical Column Density (NO2 VCD) and Ozone (O3) using Ozone Monitoring Instrument (OMI) from 2005 to 2016 by Mann-Kendall test. Also, the aggregate risk index (ARI) was calculated to estimate the overall impact of exposure to tropospheric NO2 and O3 concentrations at the national scale in 2016. To estimate the surface NO2 related drivers, The Radial Basis Function (RBF) neural network modeling was performed for different months of 2016. Results of Mann-Kendall test showed that tropospheric ozone concentration had an increasing trend in all parts of Iran and this increasing trend was significantly higher in the southern region of Iran and lower in the northern parts of Iran. NO2 VCD in most parts of Iran had a significant increasing trend. The result of sensitivity analysis showed that NO2 VCD (1.25), the distance to the industrial area, (1.20) and wind speed (1.07) were the most important variables for the estimation of surface NO2 concentration. Spatial ARI with the highest risks is mainly located in the Northern half of Iran, especially in Tehran, Alborz, and Khorasan-e− Razavi provinces, where NO2 and O3 concentrations are very severe. In northern Iran and central cities, the ARI values are calculated from 1.5 to 2.08, indicating the highest human health risks in these regions. The human health risks based on OMI observation were obtained higher in comparison to AQM data because the satellite data coverage is larger than AQM station and monitors transmitted air pollution by the wind in addition to local pollution. Based on this research, using satellite observation for air quality monitoring is a suitable tool for environmental management on a national scale.

COVID-19 lockdown closures of emissions sources in India: Lessons for air quality and climate policy

Reduced anthropogenic activities during the COVID-19 pandemic caused significant reductions in ambient fine particulate matter (PM2.5), SO2 and NOx concentrations across India. However, tropospheric O3 concentrations spiked over many urban regions. Moreover, reductions in SO2 and NOx (atmospheric cooling agents) emissions unmask heating exerted by warming forcers. Basing governmental guidelines, we model daily emissions reductions in CO2 and short-lived climate forcers (SLCFs) during different lockdown periods using bottom-up regional emission inventory. The transport sector, with maximum level of closure, followed by power plants and industry reduced nearly −50% to −75% emissions of CO2, primary PM2.5, SO2 and NOx, while warming SLCFs (black carbon, CH4, CO and non-methane VOCs) showed insignificant reduction from continuing activity in residential and agricultural sectors. Consequently, the analysis indicates that reduction in the emission ratio of NOx to NMVOC coincided spatially with observed increases in O3, consistent with reduced uptake of O3 from night-time NOx reactions. Also, similar reductions, occurring for longer timescales (say, a year), can potentially increase the annual warming rate over India from the positive regional temperature response, estimated using climate metric. Further, by linking ongoing policies to sectoral reductions during lockdown, this study shows that the relative pacing of implementation among policies is crucial to avoid counter-productive results. A key policy recommendation is introduction and improving efficacy of programs targeting reduction of NMVOC and warming SLCF emissions (shifts away from biomass cooking technologies, household electrification and curbing open burning of crop residues), must precede the strengthening of policies targeting NOx and SO2 dominated sectors.

Nitrate aerosol formation and source assessment in winter at different regions in Northeast China

To fully identify the formation and source characteristics of aerosol nitrate during winter which accompanied by frequent haze in Northeast China, the nitrate concentrations, δ15N–NO3- and δ18O–NO3- characteristics of PM2.5 samples from four sites of different types including the (a) urban area, (b) suburban area, (c) suburban-rural transition area and (d) rural area in Northeast China were analyzed in this work. δ15N isotope fractionation (εN) during the conversion of atmospheric NOX (δ15N-NOX) to nitrate (δ15N–NO3-) was discussed on the basis of the estimated contributions of the gas phase oxidation pathway of OH radical (·OH) (γOH) and the heterogeneous hydrolysis pathway of N2O5 (γN2O5) to nitrate formation. Besides, the contribution of biological soil, coal combustion, biomass burning and motor vehicles to NOX emissions had also been analyzed using Bayesian isotope mixing model. Results showed that different types of sites had inconsistent source contributions. Obviously, coal combustion plays an absolutely indispensable role in the production of NOX in all the sites, especially in rural areas (d), where coal combustion contributed up to 89.8%. In addition, biomass burning still has a great effect on NOX emissions in the Northeast, showing a contribution of 5.2%–35.8%. It is worth noting that in urban site (a) where the tropospheric O3 concentration (34±9 μg m−3) was significantly lower than the other regions ((b): 54 ± 16 μg m−3, (c): 101 ± 21 μg m−3, (d): 98 ± 17 μg m−3), the contribution of the ·OH pathway to nitrate was as high as 69.4%, which was very different from the other three sites. The different formation mechanisms of nitrate in urban and non-urban may be due to different O3. Haze not only affects the sources of nitrate, but also changes the contribution of nitrate formation. Except for rural site (d), the contribution of the heterogeneous reaction (N2O5 pathway) of the other three sites during the haze period was greater (a: 35.1%, b: 60.0%, c: 59.0%, d: 60.8%) than in the non-haze period (a: 22.5%, b: 44.7%, c: 41.9%, d: 64.2%).

Variation and correlation between ultraviolet index and tropospheric ozone during COVID-19 lockdown over megacities of India.

Worldwide spread out of COVID-19 in a short-time has brought a significant decline of road traffic, tourist flow and industrial ventures. During this emergency period, the restricted human dealings with nature have appeared as blessing for health of the total environment. The variation of atmospheric O3 may modulate the range of UV index (UVI) at any region of the earth. The objective of the study is to examine the variation of UV index over the megacities of India with respect to tropospheric O3 level modification during COVID-19 lockdown. The meteorological or environmental data (temperature in °C, gust in km/h, wind speed km/h, relative humidity in %, air pressure in mb and cloud cover in okta) of four selective megacities of India (Kolkata, Chennai, Delhi, Mumbai) during and pre lockdown period have been obtained to comprehend about the variation of UV index and tropospheric O3. The descriptive statistical applications i.e. standard deviation, standard errors and K-means clustering have been done through standard statistical software. In the present study, t-test has been used to understand level of significance of surface O3 and UVI during pre-lockdown (2019) and lockdown (2020) phase. The result shows that the four major megacities in India namely New Delhi, Mumbai, Kolkata and Chennai have experienced the vibrant diminution in terms of the concentration of UV index with slightly increasing the tropospheric O3 level during the lockdown phase. The higher accumulation of O3 during the lockdown in the lower atmosphere of four megacities does not exceed the permissible limit. The excess amount of O3 has remarkably contributed to trap the harmful UV radiation which has lowered the UVI in these worst polluted megacities of India. In the meantime, the prominent reduction of NOx during the lockdown period decreases the titration impact to O3 and this mechanism helps to revitalize the ozone concentration level. The uniqueness of the current study is highlighted the ground reality regarding reduction of UV index and amplification of tropospheric O3 concentration during lockdown phase. This study definitely assists to make new environmental policy, act and law for recover the health of the total environment.

Investigating the biophysical and socioeconomic determinants of China tropospheric O3 pollution based on a multilevel analysis approach.

Severe tropospheric O3 pollution has swept across China in recent years. Consequently, investigation of tropospheric O3 concentration influencing mechanism is of significance for O3 pollution control in China. Previous studies have rarely detected combined impacts of natural factors and anthropogenic activities behind tropospheric O3 concentration in China at a national scale. Moreover, there is significant spatiotemporal heterogeneity of O3 pollution distribution in China due to the temporal and regional differences of socioeconomic and natural environmental condition in the vast territory. The targeted O3 control recommendations for different regions and seasons should be put forward in terms of the spatiotemporal heterogeneity of O3 concentration determinants. In this context, a three-level regression model integrating multi-scale biophysical and socioeconomic variables was proposed to explore the determinants of O3 pollution in China. The results showed that the tropospheric O3 concentration in the eastern and southeastern regions of China was strongly affected by meteorological conditions. In contrast, tropospheric O3 pollution concentrated in inland areas mainly depended on the emission intensity from anthropogenic sources.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10653-020-00797-8.

Influence of NO2, NO and meteorological conditions on the tropospheric O3 concentration at an industrial station

Combustion of fossil fuels (even biomass combustion) to produce energy and heat for the industry is the most important anthropogenic source of nitrogen oxides (NOx=NO+NO2). Although NO2 is not a greenhouse gas, it is the precursor to the formation of such a gas, namely tropospheric ozone. Energy-intensive industries contribute up to 45% to the global greenhouse gas emissions, so to keep global warming below 1.5 °C according to the Paris Agreement requirements, CO2 emissions must be close to zero by 2050, so the industrial sector must be decarbonized. All decisions on reducing pollutant emissions and not just those of CO2 (by capturing and storing them), will lead to lower fossil fuel consumption and will increase energy efficiency in the industry and reduce greenhouse gas (GHG) emissions. The paper analyzes the synergistic effects of pollutants (NO2, NO), emitted by industry energy use, and meteorological factors in the formation of tropospheric ozone at an industrial site using Pearson’s correlation. Pearson’s correlation showed that the ozone concentration was significantly correlated with NO2, NO pollutants and the meteorological factors. Among them, NO2, NO, and relative humidity were negatively correlated with the O3 concentration. We observed a significant positive correlation between solar radiations, air temperature and wind speed with O3 concentration during the study period.

Ozone structure in Caribbean hurricanes

Using ozone data from model-assimilated satellite measurements in the eastern Caribbean 15–20N, 60–68W, cases were studied when upper tropospheric O3 values declined below 60 ppb. Secondary criteria on convection and circulation isolated two hurricanes for analysis (Irma and Maria 2017). Winds at 150 hPa (14 km) show divergence over the vortex characterized by ozone <50 ppb. Upper tropospheric O3 concentrations >100 ppb appear west of hurricanes, where sinking motions interact with vortex outflow. Past work suggests that high values are important, but here low ozone concentrations near the core are more conspicuous. The low O3 layer formed over the ocean and lifted by the hurricane circulation and convection, indicates vortex – environment interaction, vertical motion and storm intensity. Upper tropospheric O3 concentrations <50 ppb cover an area about double the radius of heavy rainfall >10 mm/h, appearing as a protective envelope around the core.

The Interplay Between Ozone and Urban Vegetation—BVOC Emissions, Ozone Deposition, and Tree Ecophysiology

Tropospheric ozone (O3) is one of the most prominent air pollution problems in Europe and other countries worldwide. Human health is affected by O3 via the respiratory as well the cardiovascular systems. Even though trees are present in relatively low numbers in urban areas, they can be a dominant factor in the regulation urban O3 concentrations. Trees affect the O3 concentration via emission of biogenic volatile organic compounds (BVOC), which can act as a precursor of O3, and by O3 deposition on leaves. The role of urban trees with regard to O3 will gain further importance as NOx concentrations continue declining and climate warming is progressing—rendering especially the urban ozone chemistry more sensitive to BVOC emissions. However, the role of urban vegetation on the local regulation of tropospheric O3 concentrations is complex and largely influenced by species-specific emission rates of BVOCs and O3 deposition rates, both highly modified by tree physiological status. In this review, we shed light on processes related to trees that affect tropospheric ozone concentrations in metropolitan areas from rural settings to urban centers, and discuss their importance under present and future conditions. After a brief overview on the mechanisms regulating O3 concentrations in urban settings, we focus on effects of tree identity and tree physiological status, as affected by multiple stressors, influencing both BVOC emission and O3 deposition rates. In addition, we highlight differences along the rural-urban gradient affecting tropospheric O3 concentrations and current knowledge gaps with the potential to improve future models on tropospheric O3 formation in metropolitan areas.

Impact of El Niño–Southern Oscillation on the interannual variability of methane and tropospheric ozone

Abstract. The interannual variability of the greenhouse gases methane (CH4) and tropospheric ozone (O3) is largely driven by natural variations in global emissions and meteorology. The El Niño–Southern Oscillation (ENSO) is known to influence fire occurrence, wetland emission and atmospheric circulation, affecting sources and sinks of CH4 and tropospheric O3, but there are still important uncertainties associated with the exact mechanism and magnitude of this effect. Here we use a modelling approach to investigate how fires and meteorology control the interannual variability of global carbon monoxide (CO), CH4 and O3 concentrations, particularly during large El Niño events. Using a three-dimensional chemical transport model (TOMCAT) coupled to a sophisticated aerosol microphysics scheme (GLOMAP) we simulate changes to CO, hydroxyl radical (OH) and O3 for the period 1997–2014. We then use an offline radiative transfer model to quantify the climate impact of changes to atmospheric composition as a result of specific drivers. During the El Niño event of 1997–1998, there were increased emissions from biomass burning globally, causing global CO concentrations to increase by more than 40 %. This resulted in decreased global mass-weighted tropospheric OH concentrations of up to 9 % and a consequent 4 % increase in the CH4 atmospheric lifetime. The change in CH4 lifetime led to a 7.5 ppb yr−1 increase in the global mean CH4 growth rate in 1998. Therefore, biomass burning emission of CO could account for 72 % of the total effect of fire emissions on CH4 growth rate in 1998. Our simulations indicate that variations in fire emissions and meteorology associated with El Niño have opposing impacts on tropospheric O3 burden. El Niño-related changes in atmospheric transport and humidity decrease global tropospheric O3 concentrations leading to a −0.03 W m−2 change in the O3 radiative effect (RE). However, enhanced fire emission of precursors such as nitrogen oxides (NOx) and CO increase O3 and lead to an O3 RE of 0.03 W m−2. While globally the two mechanisms nearly cancel out, causing only a small change in global mean O3 RE, the regional changes are large – up to −0.33 W m−2 with potentially important consequences for atmospheric heating and dynamics.

Isotopic constraint on the twentieth-century increase in tropospheric ozone.

Tropospheric ozone (O3) is a key component of air pollution and an important anthropogenic greenhouse gas1. During the twentieth century, the proliferation of the internal combustion engine, rapid industrialization and land-use change led to a global-scale increase in O3 concentrations2,3; however, the magnitude of this increase is uncertain. Atmospheric chemistry models typically predict4-7 an increase in the tropospheric O3 burden of between 25 and 50 per cent since 1900, whereas direct measurements made in the late nineteenth century indicate that surface O3 mixing ratios increased by up to 300 per cent8-10 over that time period. However, the accuracy and diagnostic power of these measurements remains controversial2. Here we use a record of the clumped-isotope composition of molecular oxygen (18O18O in O2) trapped in polar firn and ice from 1590 to 2016 AD, as well as atmospheric chemistry model simulations, to constrain changes in tropospheric O3 concentrations. We find that during the second half of the twentieth century, the proportion of 18O18O in O2 decreased by 0.03±0.02 parts per thousand (95 per cent confidence interval) below its 1590-1958 AD mean, which implies that tropospheric O3 increased by less than 40 per cent during that time. These results corroborate model predictions of global-scale increases in surface pollution and vegetative stress caused by increasing anthropogenic emissions of O3 precursors4,5,11. We also estimate thatthe radiative forcing of tropospheric O3 since 1850 AD is probably less than +0.4 watts per square metre, consistent with results from recent climate modelling studies12.

Tropospheric ozone and skin aging: Results from two German cohort studies

During the last two decades, it has been well established that a short-term exposure to ozone (O3) elicits an oxidative stress response in human and mouse skin, which leads to aberrant transcriptional expression of genes consistent with increased skin aging. Whether a long-term exposure to ambient O3 is associated with any skin aging traits, has remained unclear. We addressed this question in two elderly German cohorts: the SALIA study (806 women aged 66–79 years), and the BASE-II study (1207 men and women aged 60–84 years). Five-year mean residential exposure to O3 was modeled as the number of days with maximum daily 8-h mean O3 concentrations ≥120 μg/m3 per year in the wider neighborhood (5-digit postcode) of a participant's residence. Extrinsic (environmentally induced) skin aging traits – coarse wrinkles and pigment spots (lentigines) on the face – were assessed by means of SCINEXA™, a validated visual score previously shown to be well suited to measure extrinsic facial skin aging in cohort studies. We observed positive associations of O3 exceedances with coarse wrinkles in the face, but not with pigment spots. These associations were present in each cohort as well as in the combined sample of both cohorts. They were independent of chronic ultraviolet radiation exposure as the most obvious confounder, and also of co-pollutants such as particulate matter and nitrogen dioxide. Thus, long-term exposure to elevated concentrations of tropospheric O3 appears to contribute to skin aging.

Effects of Elevated Ozone on Biogenic Volatile Organic Compounds (BVOCs) Emission: A Review

With the global increase of tropospheric ozone (O3) and complex interactions between biogenic volatile organic compounds (BVOCs) emissions and tropospheric O3 concentrations, this review summarizes current research progress and future research prospects in terms of the effects of elevated O3 on BVOCs emissions. The main progress included impacts of BVOCs categories, plant functional types, O3 sensitivity of plants, the O3 stress level on the response of BVOCs emissions to single O3 stress, and the combined effects of elevated O3 and temperature, carbon dioxide (CO2), drought, and nitrogen (N) deposition. Results indicated that most published results reported no change in BVOCs emissions in response to increasing O3 concentration. Specifically, decreasing effects of O3 on BVOCs emissions were more obvious in studies on isoprene and deciduous species, whereas studies on monoterpenes and evergreen plant species showed more results with an increasing trend as well as acute O3 exposure experiments. There was an increased tendency of monoterpene emissions to the combined effects of O3 and temperature or N deposition. However, the combined effects of O3 and CO2 decreased isoprene emissions. Given that studies on the effects of O3 on BVOCs emissions remain scarce, more complete experiments are needed that consider differences between short-term and long-term or individual-level and ecosystem-level. Furthermore, future research should strengthen the multi-factor interactive studies, particularly on O3 and other global change components and biotic and abiotic stresses, to assess BVOCs emissions from terrestrial ecosystems in response to O3 pollution both currently and in the future, which will provide valuable theoretical support to air pollution control.

Ozone time scale decomposition and trend assessment from surface observations in Switzerland

Regulation for ozone (O3) precursor emissions began in Europe around 1990 with control measures primarily targeting industries and traffic. To understand how these measures have affected air quality, it is important to investigate the temporal evolution of tropospheric O3 concentrations in different types of environments. In this study, we analyze long-term trends of the concentrations of O3 and the sum of oxidants Ox (O3 + NO2) in Switzerland for the last 25 years. Statistical decomposition of the observed time series is used to extract the underlying time scales, i.e. the long-term, seasonal and short-term variability. This allows subtraction of the seasonal variation of O3 and Ox from the observations and estimation of long-term changes of de-seasonalized O3 and Ox with reduced uncertainties. A two-regime trend calculation based on the long-term variability accounts for non-monotonic temporal evolution of O3. In addition, adjustment of the higher frequency meteorological influence was applied, based on the time series containing the short-term variability. This led to an uncertainty reduction in the trend estimation, but only by a small factor. We observe that, despite the implementation of regulations and reduction of nitrogen oxides concentrations, for all studied sites daily mean O3 values increased until mid-2000s. Afterwards, a decline or a leveling-off in the concentrations is observed. The start of change in the trend depends on the site type; the more polluted the site, the later is the onset of the change in trend behavior. At locations close to sources, the observed trend can mainly be explained by the reduced titration of O3 by NO due to the strong reductions in nitrogen oxides emissions. At remote locations (such as the high alpine station in Jungfraujoch) that are influenced by hemispheric transport of O3 an increase during 1990s and a decline after early 2000s is observed. The calculated temporal trends exhibit distinct differences depending on the characteristics and pollution burdens of the measurement sites; such differences have become smaller following emission reductions.