Background Tropospheric Ozone Research Articles

A new biostimulant derived from soybean by-products enhances plant tolerance to abiotic stress triggered by ozone

BackgroundTropospheric ozone is an air pollutant that causes negative effects on vegetation, leading to significant losses in crop productivity. It is generated by chemical reactions in the presence of sunlight between primary pollutants resulting from human activity, such as nitrogen oxides and volatile organic compounds. Due to the constantly increasing emission of ozone precursors, together with the influence of a warming climate on ozone levels, crop losses may be aggravated in the future. Therefore, the search for solutions to mitigate these losses becomes a priority.Ozone-induced abiotic stress is mainly due to reactive oxygen species generated by the spontaneous decomposition of ozone once it reaches the apoplast. In this regard, compounds with antioxidant activity offer a viable option to alleviate ozone-induced damage. Using enzymatic technology, we have developed a process that enables the production of an extract with biostimulant properties from okara, an industrial soybean byproduct. The biostimulant, named as OEE (Okara Enzymatic Extract), is water-soluble and is enriched in bioactive compounds present in okara, such as isoflavones. Additionally, it contains a significant fraction of protein hydrolysates contributing to its functional effect.Given its antioxidant capacity, we aimed to investigate whether OEE could alleviate ozone-induced damage in plants. For that, pepper plants (Capsicum annuum) exposed to ozone were treated with a foliar application of OEE.ResultsOEE mitigated ozone-induced damage, as evidenced by the net photosynthetic rate, electron transport rate, effective quantum yield of PSII, and delayed fluorescence. This protection was confirmed by the level of expression of genes associated with photosystem II. The beneficial effect was primarily due to its antioxidant activity, as evidenced by the lipid peroxidation rate measured through malondialdehyde content. Additionally, OEE triggered a mild oxidative response, indicated by increased activities of antioxidant enzymes in leaves (catalase, superoxide dismutase, and guaiacol peroxidase) and the oxidative stress index, providing further protection against ozone-induced stress.ConclusionsThe present results support that OEE protects plants from ozone exposure. Taking into consideration that the promotion of plant resistance against abiotic damage is an important goal of biostimulants, we assume that its use as a new biostimulant could be considered.

Long-Term Trends in Inferred Continental Background Ozone in Eastern Australia

A better understanding of background tropospheric ozone delivers multiple benefits. Robust estimates of regional background ozone are required to understand the limits of anthropogenic emissions controlling ozone reduction. Long-term estimates of background ozone assist in characterising changes in atmospheric composition and can help quantify the influence of human activity on the atmosphere. Background tropospheric ozone measurements representative of continental air masses are scarce in Australia. Here, we use k-means clustering to identify a cluster of measurements from the long-term air quality monitoring station at Oakdale, NSW, which are likely to be representative of background air. The cluster is associated with NOx-limited air masses of continental origin. From this analysis, we estimate background ozone representative of Eastern Australia. We find recent (2017–2022) mean ozone mixing ratios of 28.5 ppb and identify a statistically significant (α = 0.05) trend in the mean of +1.8 (1.0–2.8) ppb/decade. Our methods demonstrate that some long-term monitoring stations within or near urban areas can provide suitable conditions and datasets for regional Global Atmosphere Watch monitoring.

Technical note: Northern midlatitude baseline ozone – long-term changes and the COVID-19 impact

Abstract. A nonlinear change in baseline ozone concentrations at northern midlatitudes has been quantified over preceding decades. During the past few years, several studies, using linear trend analyses, report relatively small trends over selected time periods – results inconsistent with the earlier developed picture. We show that reported COVID-19-related ozone changes in the background troposphere based on the linear analysis are significantly larger than those derived considering recent long-term decreases in background ozone, which the linear trend analyses do not quantify. We further point out that the extensive loss of lower stratospheric ozone in the unprecedented 2020 springtime Arctic stratospheric ozone depletion event likely reduced the natural source to the troposphere, rendering the background anomalously low that year. Consideration of these two issues indicates that the COVID-19 restrictions had a much smaller impact on background tropospheric ozone in 2020 than previously reported. A consensus understanding of baseline ozone changes and their causes is important for formulating policies to improve ozone air quality; cooperative, international emission control efforts aimed at continuing or even accelerating the ongoing decrease in hemisphere-wide background ozone concentrations may be the most effective approach to further reducing urban and rural ozone in the more developed northern midlatitude countries, as well as improving ozone air quality in all countries within these latitudes. Analysis of baseline ozone measurements over several years following the COVID-19 impact is expected to provide a firm basis for resolving the inconsistencies between the two views of long-term northern midlatitude ozone changes and better quantifying the COVID-19 impact.

Cloud-scale modelling of the impact of deep convection on the fate of oceanic bromoform in the troposphere: a case study over the west coast of Borneo

Abstract. This paper presents a modelling study on the fate of CHBr3 and its product gases in the troposphere within the context of tropical deep convection. A cloud-scale case study was conducted along the west coast of Borneo, where several deep convective systems were triggered on the afternoon and early evening of 19 November 2011. These systems were sampled by the Falcon aircraft during the field campaign of the SHIVA project and analysed using a simulation with the cloud-resolving meteorological model C-CATT-BRAMS at 2×2 km resolution that represents the emissions, transport by large-scale flow, convection, photochemistry, and washout of CHBr3 and its product gases (PGs). We find that simulated CHBr3 mixing ratios and the observed values in the boundary layer and the outflow of the convective systems agree. However, the model underestimates the background CHBr3 mixing ratios in the upper troposphere, which suggests a missing source at the regional scale. An analysis of the simulated chemical speciation of bromine within and around each simulated convective system during the mature convective stage reveals that >85 % of the bromine derived from CHBr3 and its PGs is transported vertically to the point of convective detrainment in the form of CHBr3 and that the remaining small fraction is in the form of organic PGs, principally insoluble brominated carbonyls produced from the photo-oxidation of CHBr3. The model simulates that within the boundary layer and free troposphere, the inorganic PGs are only present in soluble forms, i.e. HBr, HOBr, and BrONO2, and, consequently, within the convective clouds, the inorganic PGs are almost entirely removed by wet scavenging. We find that HBr is the most abundant PG in background lower-tropospheric air and that this prevalence of HBr is a result of the relatively low background tropospheric ozone levels at the regional scale. Contrary to a previous study in a different environment, for the conditions in the simulation, the insoluble Br2 species is hardly formed within the convective systems and therefore plays no significant role in the vertical transport of bromine. This likely results from the relatively small quantities of simulated inorganic bromine involved, the presence of HBr in large excess compared to HOBr and BrO, and the relatively efficient removal of soluble compounds within the convective column.

High spatial resolution ozone risk-assessment for Asian forests

Background tropospheric ozone (O3) is increasing particularly over China and India, and becomes a major threat to Asian forests. By using the coupled WRF-Chem model at high spatial resolution (8 km) over Asia in 2015, we showed that both standards AOT40 (European) and W126 (United States) underestimated the O3 risk to deciduous forests and overestimated it to evergreen forests compared to the biologically based metric POD1. Both metrics AOT40 and W126 showed different spatial distribution and exceedance extent with respect to POD1. We found very high potential of O3 impacts on deciduous forest growth in Asia, while potential O3 impacts on evergreen forest types were lower. The most limiting factors were light availability, soil water content and air temperature (65%, 29% and 6%, respectively), making this region of the globe at high O3 risk for deciduous species and at medium O3 risk for evergreen species. For the first time, the O3 risk to Asian forests was quantified at high spatial resolution; and our results suggested: (i) a relevant overestimation of O3 risk to evergreen forests when using AOT40 and W126 relative to the more biologically based POD1 metric; and (ii) a significant underestimation of O3 risk to the boreal deciduous forests when using AOT40 and W126 relative to POD1 because of stomatal aperture permissive condition.

Using Visual Ozone Damage Scores and Spectroscopy to Quantify Soybean Responses to Background Ozone

Remotely-sensed identification of ozone stress in crops can allow for selection of ozone resistant genotypes, improving yields. This is critical as population, food demand, and background tropospheric ozone are projected to increase over the next several decades. Visual scores of common ozone damage have been used to identify ozone-stress in bio-indicator plants. This paper evaluates the use of a visual scoring metric of ozone damage applied to soybeans. The scoring of the leaves is then combined with hyperspectral data to identify spectral indices specific to ozone damage. Two genotypes of soybean, Dwight and Pana, that have shown different sensitivities to ozone, were grown and visually scored for ozone-specific damage on multiple dates throughout the growing season. Leaf reflectance, foliar biophysical properties, and yield data were collected. Additionally, ozone bio-indicator plants, snap beans, and common milkweed, were investigated with visual scores and hyperspectral leaf data for comparison. The normalized difference spectral index (NDSI) was used to identify the significant bands in the visible (VIS), near infrared (NIR), and shortwave infrared (SWIR) that best correlated with visual damage score when used in the index. Results were then compared to multiple well-established indices. Indices were also evaluated for correlation with seed and pod weight. The ozone damage scoring metric for soybeans evaluated in August had a coefficient of determination of 0.60 with end-of-season pod weight and a Pearson correlation coefficient greater than 0.6 for photosynthetic rate, stomatal conductance, and transpiration. NDSI [R558, R563] correlated best with visual scores of ozone damage in soybeans when evaluating data from all observation dates. These wavelengths were similar to those identified as most sensitive to visual damage in August when used in NDSI (560 nm, 563 nm). NDSI [R560, R563] in August had the highest coefficient of determination for individual pod weight (R2 = 0.64) and seed weight (R2 = 0.54) when compared against 21 well-established indices used for identification of pigment or photosynthetic stress in plants. When evaluating use of spectral bands in NDSI, longer wavelengths in SWIR were identified as more sensitive to ozone visual damage. Trends in the bands and biophysical properties of the soybeans combined with evaluation of ozone data indicate likely timing of significant ozone damage as after late-July for this season. This work has implications for better spectral detection of ozone stress in crops and could help with efforts to identify ozone tolerant varieties to increase future yield.

Widespread changes in UK air quality observed from space

Previous studies have used surface observations of pollutants (e.g., nitrogen dioxide [NO2] and aerosols) to evaluate improvements in United Kingdom (UK) air quality over recent decades. However, surface monitoring networks provide limited spatial coverage and are not always representative of air quality over a wider region. Satellite observations, such as tropospheric column NO2 (TCNO2), aerosol optical depth (AOD) and sub‐column (0–6 km) ozone (SCO3), provide widespread monitoring of air quality on a national scale. In this study, we use such observations to analyse trends in UK air quality, between 2005 and 2015, finding significant decreases in TCNO2 and AOD over UK pollution hotspots. The largest changes in short‐lived NO2 are located over populated (i.e., source) regions, associated with large emissions of nitrogen oxides (NO x). AOD changes are more spread out, and less strongly associated with source regions, due to a longer aerosol lifetime, secondary aerosol formation and non‐urban aerosol sources. SCO3 shows no significant trends over England/Wales, but significant positive trends over Scotland, which is consistent with previous studies of changes in background tropospheric ozone in other remote regions of north‐western Europe.

Summertime free-tropospheric ozone pool over the eastern Mediterranean/Middle East

Abstract. Observations show that the Mediterranean troposphere is characterized by a marked enhancement in summertime ozone, with a maximum over the eastern Mediterranean. This has been linked to enhanced photochemical ozone production and subsidence under cloud-free anticyclonic conditions. The eastern Mediterranean is among the regions with the highest levels of background tropospheric ozone worldwide. A 12 yr climatological analysis (1998–2009) of free-tropospheric ozone was carried out over the region based on the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA-Interim reanalysis data and simulations with the EMAC (ECHAM5–MESSy) atmospheric chemistry–climate model. EMAC is nudged towards the ECMWF analysis data and includes a stratospheric ozone tracer. A characteristic summertime pool with high ozone concentrations is found in the middle troposphere over the eastern Mediterranean–Middle East (EMME) in the ERA-Interim ozone data, Tropospheric Emission Spectrometer (TES) satellite ozone data and simulations with EMAC. The enhanced ozone over the EMME during summer is a robust feature, extending down to lower free-tropospheric levels. The investigation of ozone in relation to potential vorticity and water vapour and the stratospheric ozone tracer indicates that the dominant mechanism causing the free-tropospheric ozone pool is the downward transport from the upper troposphere and lower stratosphere, in association with the enhanced subsidence and the limited horizontal divergence observed over the region. The implications of these high free-tropospheric ozone levels on the seasonal cycle of near-surface ozone over the Mediterranean are discussed.

Distinct transcriptional profiles of ozone stress in soybean ( Glycine max ) flowers and pods

BackgroundTropospheric ozone (O3) is a secondary air pollutant and anthropogenic greenhouse gas. Concentrations of tropospheric O3 ([O3] have more than doubled since the Industrial Revolution, and are high enough to damage plant productivity. Soybean (Glycine max L. Merr.) is the world’s most important legume crop and is sensitive to O3. Current ground-level [O3] are estimated to reduce global soybean yields by 6% to 16%. In order to understand transcriptional mechanisms of yield loss in soybean, we examined the transcriptome of soybean flower and pod tissues exposed to elevated [O3] using RNA-Sequencing.ResultsElevated [O3] elicited a strong transcriptional response in flower and pod tissues, with increased expression of genes involved in signaling in both tissues. Flower tissues also responded to elevated [O3] by increasing expression of genes encoding matrix metalloproteinases (MMPs). MMPs are zinc- and calcium-dependent endopeptidases that have roles in programmed cell death, senescence and stress response in plants. Pod tissues responded to elevated [O3] by increasing expression of xyloglucan endotransglucosylase/hydrolase genes, which may be involved with increased pod dehiscence in elevated [O3].ConclusionsThis study established that gene expression in reproductive tissues of soybean are impacted by elevated [O3], and flowers and pods have distinct transcriptomic responses to elevated [O3].

Multi-site tropospheric ozone measurements across the North Tropical Atlantic during the summer of 2010

Ozone soundings are launched during two Intensive Observing Periods (IOPs) from Dakar, Senegal; Sao Vicente, Cape Verde; and St James, Barbados to investigate ozone variability across the North Tropical Atlantic during June/July and August/September 2010. Two objectives of the campaign are to compare background tropospheric ozone mixing ratios and its variability associated with the Saharan Air Layer (SAL) and African Easterly Waves (AEWs) at sites located in the Eastern and Western Tropical Atlantic Ocean. During IOP1 (June–July), reduced ozone mixing ratios are found in the SAL with elevated ozone levels at the SAL's base and above it. During IOP I, the tropospheric column ozone (TCO) is higher at Cape Verde (27.5 DU) when compared to Barbados (19.8 DU). During IOP II (August–September) ozone-rich air is found above 500 hPa prior to the passage of AEW or developing tropical cyclones. The observed larger mixing ratios of middle/upper tropospheric ozone are most prominent at Dakar prior to the passage of an AEW, which we attribute to lightning NOx. During IOP II the tropospheric column ozone is highest at Dakar (30.5 DU) when compared to Cape Verde (20.2 DU) and Barbados (17.2 DU).

Megacity ozone air quality under four alternative future scenarios

Abstract. The impact of the megacities of the world on global tropospheric ozone, and conversely, the extent to which megacities are influenced by emissions of ozone precursors from outside of the megacities is examined under the four alternative RCP ("Representative Concentration Pathway") emissions scenarios. Despite accounting for about 6% of present-day anthropogenic emissions of ozone precursor species, the contribution of emissions from megacities to global tropospheric ozone is calculated to be 0.84%. By 2100 this contribution falls to between 0.18% and 0.62% depending on the scenario, with the lower value being for the most-polluting of the four future emissions scenarios due to stringent controls on ozone precursor emissions from highly populated areas combined with a stronger tropospheric background ozone field. The higher end of this range is from the least-polluting of the four emissions scenarios, due to lower background tropospheric ozone combined with the use of a simpler downscaling methodology in the construction of the scenario, which results in higher emissions from megacities. Although the absolute impact of megacities on global ozone is small, an important result of this study is that under all future scenarios, future air quality in megacities is expected to be less influenced by local emissions within the cities, but instead more influenced by emission sources outside of the cities, with mixing ratios of background ozone projected to play an increasing role in megacity air quality throughout the 21st century. Assumptions made when downscaling the emissions scenarios onto the grids used in such modelling studies can have a large influence on these results; future generations of emissions scenarios should include spatially explicit representations or urban development suitable for air quality studies using global chemical transport models.

Ozone Air Pollution: How Low Can You Go?

Ozone Air Pollution: How Low Can You Go?

Background ozone in the southern Europe and Mediterranean area: Influence of the transport processes

The troposphere is subject to continuous inputs, production and removal processes of ozone and its precursors from natural processes and human activities acting together within a very complex system. In order to assess the behaviour of background ozone in the Mediterranean area, a description of trends, seasonal and diurnal behaviours of free tropospheric ozone is provided. In the Mediterranean area and southern Europe the background tropospheric ozone concentration appears significantly affected by three main air mass transport processes: (i) transport of polluted air masses on regional and long-range scales, (ii) downward transport of stratospheric air masses, and (iii) transport of mineral dust from the Sahara desert. In this review of the literature of the last two decades, we present an overview of these phenomena, mainly monitored at high baseline mountain stations representative of background atmospheric conditions.

Transcriptomic changes induced by acute ozone in resistant and sensitive Medicago truncatula accessions.

BackgroundTropospheric ozone, the most abundant air pollutant is detrimental to plant and animal health including humans. In sensitive plant species even a few hours of exposure to this potent oxidant (200–300 nL. L-1) leads to severe oxidative stress that manifests as visible cell death. In resistant plants usually no visible symptoms are observed on exposure to similar ozone concentrations. Naturally occurring variability to acute ozone in plants provides a valuable resource for examining molecular basis of the differences in responses to ozone. From our earlier study in Medicago truncatula, we have identified cultivar Jemalong is ozone sensitive and PI 464815 (JE154) is an ozone-resistant accession. Analyses of transcriptome changes in ozone-sensitive and resistant accession will provide important clues for understanding the molecular changes governing the plant responses to ozone.ResultsAcute ozone treatment (300 nL L-1 for six hours) led to a reactive oxygen species (ROS) burst in sensitive Jemalong six hours post-fumigation. In resistant JE154 increase in ROS levels was much reduced compared to Jemalong. Based on the results of ROS profiling, time points for microarray analysis were one hour into the ozone treatment, end of treatment and onset of an ozone-induced ROS burst at 12 hours. Replicated temporal transcriptome analysis in these two accessions using 17 K oligonucleotide arrays revealed more than 2000 genes were differentially expressed. Significantly enriched gene ontologies (GOs) were identified using the Cluster Enrichment analysis program. A striking finding was the alacrity of JE154 in altering its gene expression patterns in response to ozone, in stark contrast to delayed transcriptional response of Jemalong. GOs involved in signaling, hormonal pathways, antioxidants and secondary metabolism were altered in both accessions. However, the repertoire of genes responding in each of these categories was different between the two accessions. Real-time PCR analysis confirmed the differential expression patterns of a subset of these genes.ConclusionThis study provided a cogent view of the unique and shared transcriptional responses in an ozone-resistant and sensitive accession that exemplifies the complexity of oxidative signaling in plants. Based on this study, and supporting literature in Arabidopsis we speculate that plants sensitive to acute ozone are impaired in perception of the initial signals generated by the action of this oxidant. This in turn leads to a delayed transcriptional response in the ozone sensitive plants. In resistant plants rapid and sustained activation of several signaling pathways enables the deployment of multiple mechanisms for minimizing the toxicity effect of this reactive molecule.

Long‐range transport and tropospheric ozone variability in the western Mediterranean region during the Intercontinental Transport of Ozone and Precursors (ITOP‐2004) campaign

Two ground‐based ozone lidars have been operated at Observatoire de Haute Provence (OHP) for 11 days during the Intercontinental Transport of Ozone and Precursors (ITOP‐2004) measurement campaign. Ozone and scattering ratio vertical profiles have been measured from the boundary layer up to the tropopause. At first order, tropospheric ozone temporal variability is due to local pollution within the planetary boundary layer and to stratosphere‐troposphere exchange. Remaining ozone rich layers within the free troposphere are related to long‐range transport processes. Transport pathways are discussed combining Lagrangian particle dispersion modeling analysis and upstream airborne in situ measurements of the chemical composition of these air masses. High ozone and CO mixing ratios measured within polluted plumes aboard the aircraft correspond to ozone and aerosol layers seen by the lidar. Most of these layers have their origin in North America where they are uplifted either by forest fires or by warm conveyor belts in the vicinity of frontal regions. During the campaign, these polluted and thin (<1 km) layers remain coherent and are transported in a Lagrangian manner over the Atlantic Ocean. The layers observed above OHP in the lower free troposphere exhibit ozone mixing ratio 50% larger than background values. With an ozone content of 3 to 6 Dobson Units, these layers increase by 5 to 10% the background tropospheric ozone column.

Linking ozone pollution and climate change: The case for controlling methane

Methane (CH4) emission controls are found to be a powerful lever for reducing both global warming and air pollution via decreases in background tropospheric ozone (O3). Reducing anthropogenic CH4 emissions by 50% nearly halves the incidence of U.S. high‐O3 events and lowers global radiative forcing by 0.37 W m−2 (0.30 W m−2 from CH4, 0.07 W m−2 from O3) in a 3‐D model of tropospheric chemistry. A 2030 simulation based upon IPCC A1 emissions projections shows a longer and more intense U.S. O3 pollution season despite domestic emission reductions, indicating that intercontinental transport and a rising O3 background should be considered when setting air quality goals.

Tropical tropospheric ozone from total ozone mapping spectrometer by a modified residual method

A modified residual method for deriving time‐averaged tropical tropospheric ozone (TTO) from total ozone mapping spectrometer (TOMS) has been refined [cf Kim et al., 1996] and applied to a 2‐year period, 1991–1992. This period was selected because of the availability of a unique sonde record at tropical Atlantic and near‐Atlantic sites: Natal, Brazil; Ascension Island; and Brazzaville. The essentials of the modified‐residual method are (1) Fourier analysis to identify the latitude range for use of the method; (2) use of the wave‐like pattern to estimate stratospheric ozone column and a background tropospheric ozone column, which is defined as the amount of ozone expected in the absence of chemical pollution; (3) assumption that the wave‐one feature is tropospheric; and (4) the stratospheric and background tropospheric ozone amounts consistent with the constraint of the three station ozonesonde measurements for total tropospheric ozone. An excess ozone (pollution) signal is also derived from TOMS total ozone. Parameters derived from the modified residual method are evaluated with independent data to verify the quality of the TTO. Derived tropical stratospheric column ozone for 1991–1992 agrees very well with the corresponding UARS Microwave Limb Sounder and Stratospheric Aerosol and Gas Experiment records (to within 5 Dobson units (DU) for the latter). Background tropospheric ozone, which exhibits a seasonally in 1991–1992, has a 24±4.8 DU mean value at wave maximum (∼0° longitude) and a 15.2±6.0 DU mean value at 180° longitude. The Atlantic value is remarkably similar to the climatological 26 DU previously inferred from subtropical sondes [Kim et al., 1996; Komhyr et al., 1989]. The ∼5 DU standard deviation is the accuracy of the modified‐residual method and is the best that can be achieved given the 15‐day averaging of the sondes (1σ = 5.3 DU). The wave‐like pattern in 1991–1992 has a semiannual periodicity with zero wave amplitude in June and December.

Climate change and pollutant impacts on Scottish vegetation

Summary By the 2050s the UK is projected to be about 1.6°C warmer, when the atmospheric CO2 concentration will be 525 ppmv. These changes will have profound effects on the Scottish flora and fauna. Vegetation primary productivity will increase, except in dry regions, and the productivity of upland forest plantations may increase by several Yield Classes. The spread of plant species may be less than expected, but a number of slow-growing ‘stress-tolerant’ species, including montane/alpine species, are likely to be lost. Nitrogen deposited as a result of emission of NOX from vehicles and NH3 from agriculture is now a major source of acidity, and problems of acidification and eutrophication are linked. Despite reductions in sulphur emissions, critical loads of acid deposition are likely to be exceeded for soils in most of the Scottish uplands until at least 2005. Critical levels affecting tree growth may be exceeded where forests are in cloud for 10% of the time in areas of the Great Glen. Much of the Scottish uplands receives 25–30 kg N ha-1 yr-1, which may be causing change in species composition. Background tropospheric ozone concentrations are increasing. Much of the Scottish uplands experiences mean summer ozone concentrations exceeding those in southern England, but with fewer exceedances of critical levels. However, many crops and some sensitive native species are probably being adversely affected.

Retrieval of tropospheric ozone from simulations of nadir spectral radiances as observed from space

The global remote sensing of tropospheric ozone profiles is a critical environmental measurement to be performed by future satellite experiments. We have applied the method of nonlinear least squares in conjunction with an efficient and accurate line‐by‐line radiative transfer model to directly retrieve vertical profiles of tropospheric ozone from simulated clear sky, nadir‐viewing radiances covering the entire 9.6‐μm ozone band. The simulations have been generated for the specifications of the tropospheric emission spectrometer (TES), a Fourier transform spectrometer with 0.032 cm−1 resolution (half width at half maximum (HWHM), unapodized) being developed for NASA's Earth Observing System. Profile retrieval errors for background tropospheric ozone levels are characterized as a function of measurement noise, spectral resolution, and vertical resolution based on a linear error analysis and an initial guess profile with minimal constraint, hence negligible potential profile bias at all altitudes. The main conclusions of the study are that (1) for the TES experiment design, ozone profiles are retrievable to approximately ±5% (1σ) for a vertical resolution of 5 km in the middle and upper troposphere, (2) the stratospheric portion of the profile must be retrieved directly from the measured nadir spectrum, (3) for equal measurement times and considering the effects of both systematic error and source radiance noise, an optimal spectral interferometer resolution exists that is close to the TES resolution (0.032 cm−1; HWHM unapodized), and (4) ozone boundary layer retrievals are highly dependent on the contrast between that layer and the surface. The results from an ozone retrieval utilizing simulated radiances from an atmosphere defined by a radiosonde observation at Ascension Island are considered in the context of the solution of the nonlinear problem and the linear error analysis. The ozone retrieval analyses presented in this paper are principally concerned with the effects of measurement error and thus represent the optimal retrieval capability for the assumed design. However, the availability of the full high‐resolution spectrum will enable the detection and mitigation of the systematic errors.

A two-year study of ozone behaviour at rural and forested sites in Eastern France

Abstract Ozone and other gases measurements in three rural sites of different altitudes in eastern France (an area with important forest decline) were used as a basis to understand the mechanisms controlling the ozone behaviour in the lower troposphere. An analysis is presented of the annual variation of the background tropospheric ozone level in order to evaluate its contribution to the surface ozone level. The frequency of occurrence of simultaneous elevated ozone episodes at one urvan and the three rural sites was examined in order to determine the major cause of high ozone levels. The relation between elevated ozone concentrations and wind direction was also investigated. It was found that the majority of high ozone concentration episodes take place simultaneously at the three sites, showing an elevated occurrence of episodes of regional origins. Most of the episodes are associated with the east wind sector.