High Tropospheric Ozone Research Articles

How to Cope With Stress in the Desert-The Date Palm Approach.

Increasing desertification constitutes a global environmental problem, mainly driven by climate change and inappropriate land-use that limits agriculture, forestry and human colonization. The selection of suitable plant species to mitigate desertification is particularly challenging, as it usually requires simultaneous counteraction against a whole set of unfavourable environmental conditions, including heat, drought, high tropospheric ozone and salinity. It therefore seems useful to identify the survival strategies of plants native in desert environments. Date palm constitutes a plant species native in desert environments and cultivated worldwide in arid regions that have been studied intensively for stress defence during the last decade. The present review summarizes the current state of biochemical stress defence mechanisms including avoidance, osmotic and metabolic adjustments and reactive oxygen species scavenging, addresses whole-plant regulations and trade-off between stress compensation/defence and growth of date palms. The review advances our knowledge about how this typical desert species copes with both individual and multiple environmental stresses at the cellular to the whole-plant level, and identifies areas of future research required to fully understand the strategies of this plant species to survive in the desert, thereby contributing to efforts for the mitigation of climate change and desertification.

Characterization of tropospheric ozone pollution, random forest trend prediction and analysis of influencing factors in South-western Europe

Nowadays, environmental problems have gradually become the focus of world attention. In recent years, heat waves in many parts of Europe have increased ozone concentrations, fuelling ozone pollution. Therefore, this paper investigates the spatial and temporal distribution of tropospheric column ozone concentrations in South-western Europe, future trend changes, influencing factors, and potential source regions based on remotely sensed monitoring data from the OMI (Ozone Monitoring Instrument) from 2011 to 2021. The results show that the areas of high tropospheric column ozone concentrations are mainly concentrated in the northwest, Poland, and southeast coastal areas. At the same time, the monthly variation curve of column ozone concentration is bimodal. Trend change analyses indicate an upward trend in future column ozone concentrations in the southeastern part of the study area. The potential for increases also exists in parts of Germany, France, and Poland, which will need to be monitored. Random forest model projections found a slight decrease in column ozone concentrations in 2022 and 2023 of about 1–4 DU compared to tropospheric column ozone concentrations in 2021. The health risk assessment found that the number of all-cause premature deaths due to exposure to ozone was the highest in Germany. During the summer, when ozone pollution is high, the potential source area in the southeastern part of the study area is located at the border of the three countries, and synergistic management is recommended. In exploring the correlation between the influencing factors and ozone, it was found that there is a significant difference between the long-time and short-time series. In addition, the pathway analysis shows that the population size, distribution density, and forested area in southwestern Europe may be more sensitive to the production of tropospheric ozone.

Effects of elevated ozone on physiology, growth, yield and grain quality of rice (Oryza sativa L.): An ozone gradient experiment

Rice (Oryza sativa L.) as the staple food is widely grown, but the current high tropospheric ozone (O3) pollution has seriously threatened the rice production. We performed an experiment on four rice cultivars widely grown in the Yangtze River Delta region of China, which were exposed to five O3 treatments under open top chambers. The effects of O3 on leaf physiology, growth, yield and grain quality of rice were comprehensively explored, and the results showed that (i) elevated O3 reduced the light-saturated rate of CO2 assimilation (Asat) and stomatal conductance (gs), and the O3-induced decrease in Asat was mainly attributed to stomatal limitation under low O3 treatment whereas stomatal and biochemical co-limitation under high O3 treatment; (ii) elevated O3 did not affected the harvest index since the inhibition of shoot biomass and yield was the same extent, which indicated that O3 does not alter the remobilization of carbon assimilates from vegetative organs to grains; (iii) only ambient air plus 60 ppb O3 treatment (NF60) significantly reduced the yield of rice, which was caused by the combined reduction of individual grain weight, grain number, and panicle number; (iv) elevated O3 did not significantly affect the concentration of mineral nutrients in grains, while the effect of O3 on the concentration of amino acids was consistent with biphasic O3-response profile. NF60 had a greater reduction in the concentration of essential amino acids than non-essential amino acids; (v) NF60 significantly reduced the accumulation of mineral nutrients and amino acid in grain due to a decrease in grain yield. These results are conducive to a comprehensive understanding of the impacts of O3 on rice, and also indicated that the risk assessment of O3 on crops would need to consider both crop yield and grain quality.

Ozone responses to reduced precursor emissions: A modeling analysis on how attainable goals can improve air quality in the Mexico City Metropolitan Area

High tropospheric ozone (O3) concentrations prevent the improvement of the air quality in the Mexico City Metropolitan Area (MCMA). Although the problem has improved considerably since the 1990s, a rebound in O3 levels in recent years has raised concerns about the deteriorating air quality. The nonlinear relationship between O3 formation and the emissions of its main precursors, i.e., volatile organic compounds (VOCs) and nitrogen oxides (NOx), is a challenge when measures are enacted for effective mitigation of the O3 problem. This study evaluated the reduction in precursors, VOCs and NOx, using an up-to-date regional air quality model (HERMES-Mex-WRF-CMAQ). For evaluating realizable scenarios, the decline in VOC achieved in Japan after policy implementation was the targeted VOC reduction (40 % from area sources), and the NOx reduction observed in the MCMA during the COVID-19 pandemic was the targeted NOx reduction (40 % from mobile sources). The analysis evaluated the O3 responses to changes in a single precursor and a combination of both during a period of high O3 concentrations (April 2019). The results showed that 40 % reduction in VOC emissions would decrease the O3 8-h maximum concentrations by 16 %. However, 40 % reduction in NOx emissions would increase O3 by >15 %. The simultaneous reduction of both precursors did not significantly affect O3 levels. The diagnosis of ozone sensitivity using the H2O2/HNO3 ratios reinforced the simulation findings, indicating that VOC emissions limited ozone formation in most MCMA areas. As the simulated scenarios were based on factual case studies, our research offers insights into the realistic aims of MCMA policies to reduce O3 levels.

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.

Synergy of Using Nadir and Limb Instruments for Tropospheric Ozone Monitoring (SUNLIT)

Abstract. Satellite measurements in nadir and limb viewing geometry provide a complementary view of the atmosphere. An effective combination of the limb and nadir measurements can give new information about atmospheric composition. In this work, we present tropospheric ozone column datasets that have been created using a combination of total ozone columns from OMI (Ozone Monitoring Instrument) and TROPOMI (TROPOspheric Monitoring Instrument) with stratospheric ozone column datasets from several available limb-viewing instruments: MLS (Microwave Limb Sounder), OSIRIS (Optical Spectrograph and InfraRed Imaging System), MIPAS (Michelson Interferometer for Passive Atmospheric Sounding), SCIAMACHY (SCanning Imaging Spectrometer for Atmospheric CHartographY), OMPS-LP (Ozone Mapping and Profiles Suite – Limb Profiler), and GOMOS (Global Ozone Monitoring by Occultation of Stars). We have developed further the methodological aspects of the assessment of tropospheric ozone using the residual method supported by simulations with the chemistry transport model SILAM (System for Integrated modeLling of Atmospheric coMposition). It has been shown that the accurate assessment of ozone in the upper troposphere and the lower stratosphere (UTLS) is of high importance for detecting the ground-level ozone patterns. The stratospheric ozone column is derived from a combination of ozone profiles from several satellite instruments in limb-viewing geometry. We developed a method for the data homogenization, which includes the removal of biases and a posteriori estimation of random uncertainties, thus making the data from different instruments compatible with each other. The high-horizontal- and vertical-resolution dataset of ozone profiles is created via interpolation of the limb profiles from each day to a 1∘×1∘ horizonal grid. A new kriging-type interpolation method, which takes into account data uncertainties and the information about natural ozone variations from the SILAM-adjusted ozone field, has been developed. To mitigate the limited accuracy and coverage of the limb profile data in the UTLS, a smooth transition to the model data is applied below the tropopause. This allows for the estimation of the stratospheric ozone column with full coverage of the UTLS. The derived ozone profiles are in very good agreement with collocated ozonesonde measurements. The residual method was successfully applied to OMI and TROPOMI clear-sky total ozone data in combination with the stratospheric ozone column from the developed high-resolution limb profile dataset. The resulting tropospheric ozone column is in very good agreement with other satellite data. The global distributions of tropospheric ozone exhibit enhancements associated with the regions of high tropospheric ozone production. The main datasets created are (i) a monthly 1∘×1∘ global tropospheric ozone column dataset (from ground to 3 km below the tropopause) using OMI and limb instruments, (ii) a monthly 1∘×1∘ global tropospheric ozone column dataset using TROPOMI and limb instruments, and (iii) a daily 1∘×1∘ interpolated stratospheric ozone column from limb instruments. Other datasets, which are created as an intermediate step of creating the tropospheric ozone column data, are (i) a daily 1∘×1∘ clear-sky and total ozone column from OMI and TROPOMI, (ii) a daily 1∘×1∘ homogenized and interpolated dataset of ozone profiles from limb instruments, and (iii) a daily 1∘×1∘ dataset of ozone profiles from SILAM simulations with adjustment to satellite data. These datasets can be used in various studies related to variability and trends in ozone distributions in both the troposphere and the stratosphere. The datasets are processed from the beginning of OMI and TROPOMI measurements until December 2020 and are planned to be regularly extended in the future.

CCMI-1 모형에서의 동아시아 전량오존 및 대류권오존 평가

We assess Total Column Ozone (TCO) and Tropospheric Ozone (TRO) reproduced by the Chemistry Climate Model Initiative phase 1 (CCMI-1) project using ground-based observations and reanalysis datasets from 2003 to 2010 for East Asia. Five models, CESM1-WACCM, CESM1-CAM4Chem, HadGEM3-ES, MRI-CGCM3, and GEOSCCM, are evaluated. The multi-model mean of the five models reproduces a spatial distribution and seasonal cycle of TCO similar to the observation and reanalysis results. CCMI-1 models present a relative bias of TCO in the range of -4.22 to 0.47% against the observation data. Contrary to TCO, TRO shows a comparatively large inter-model spread in spatial pattern and seasonality. Indeed, the relative bias of TRO from the models is from -8.37 to 13.71% compared to the observation data. While CESM1-CAM4Chem and MRI-ESM1r1 produce reasonable spatial and temporal variability of TCO and TRO, HadGEM3-ES and GEOSCCM exhibit a bias with substantially lower and higher TRO in most seasons, respectively. Long-term trends in TCO and TRO are not significant in either reanalysis or CCMI models. These results suggest that TCO and TRO reproduction from CCMI-1 models requires caution and further evaluation, particularly for regional analysis.

Tropospheric ozone rapidly decreases root growth by altering carbon metabolism and detoxification capability in growing soybean roots

High tropospheric ozone (O3) concentrations lead to significant global soybean (Glycine max) yield reductions. Research concerning O3 impacts on soybean has focused on the contributions of above-ground tissues. In this study, Mandarin (Ottawa) (O3-sensitive) and Fiskeby III (O3-tolerant) soybean genotypes provide contrasting materials to investigate O3 effects on root growth. We compared root morphological and proteomic changes when 16-day-old plants were treated with charcoal-filtered (CF) air or elevated O3 (80 ppb O3 for 7 h/day) in continuously stirred-tank reactors (CSTR) for 7 days. Our results showed that in Mandarin (Ottawa), decreased expression of enzymes involved in the tricarboxylic acid (TCA) cycle contributes to reduction of root biomass and diameter under elevated O3. In contrast, O3 tolerance in Fiskeby III roots was associated with O3-dependent induction of enzymes involved in glycolysis and O3-independent expression of enzymes involved in the ascorbate-glutathione cycle. We conclude that a decreased abundance of key redox enzymes in roots due to limited carbon availability rapidly alters root growth under O3 stress. However, maintaining a high abundance of enzymes associated with redox status and detoxification capability contributes to overall O3 tolerance in roots.

Episodes of high tropospheric ozone reduce nodulation, seed production and quality in soybean (Glycine max (L.) merr.) on low fertility soils.

Driven by human activities, air pollution and soil degradation are threatening food production systems. Rising ozone in the troposphere can affect several physiological processes in plants and their interaction with symbiotic microorganisms. Plant responses to ozone may depend on both soil fertility and the ontogenetic stage in which they are exposed. In this work, we studied the effects of ozone episodes and soil fertility on soybean plants. We analysed soybean plant responses in the production of aboveground and belowground biomass, structural and functional attributes of rhizobia, and seed production and quality. The experiment was performed with plants grown in two substrates with different fertility (commercial soil, and soil diluted (50%, v/v) with sand). Plants were exposed to acute episodes of ozone during vegetative and reproductive stages. We observed that ozone significantly reduced belowground biomass (≈25%), nodule biomass (≈30%), and biological nitrogen fixation (≈21%). Plants exposed to ozone during reproductive stage growing in soil with reduced fertility had lower seed production (≈10% lower) and seed protein (≈12% lower). These responses on yield and quality can be explained by the observed changes in belowground biomass and nitrogen fixation. The negative impact of ozone on the symbiotic interaction with rhizobia, seed production and quality in soybean plants were greater in soils with reduced fertility. Our results indicate that food security could be at risk in the future if trends in ozone concentration and soil degradation processes continue to increase.

On the link between the Etesian winds, tropopause folds and tropospheric ozone over the Eastern Mediterranean during summer

The summertime Eastern Mediterranean experiences among the highest worldwide near-surface ozone values often exceeding the EU air-quality standard for human health protection. Downward transport of stratospheric ozone-rich air masses through tropopause folds has been shown to significantly contribute to these high tropospheric ozone levels. The summer circulation over the Eastern Mediterranean is dominated by large-scale subsidence and persistent northerly winds, the Etesians, as well as tropopause fold activity affecting tropospheric ozone levels and variability. This is the first study that directly investigates the connections of the Etesians with tropopause folds and tropospheric ozone over the Eastern Mediterranean region using the state-of-the-art ECHAM5/MESSy Atmospheric Chemistry (EMAC) climate model and a tropopause fold identification algorithm for the period June‐August 1979 to 2013. Model validation against reanalysis and observational measurements indicates that EMAC simulates well the sea level pressure gradient over the Aegean Sea reproducing the occurrence frequency of the Etesians. The shared variance between the simulated and the observed year-to-year frequency of the Etesian winds is higher than 80%. The year-to-year variability of summertime tropopause folds frequency is significantly correlated with the Etesian winds with a correlation coefficient close to 0.7. In addition, a significant increase of the fold activity and the ozone concentrations are observed during intense Etesians. Our findings may have implications for air quality studies and could support human health policy, as the Etesians coincide with favorable conditions for the formation of tropopause folds and stratosphere-to-troposphere transport and therefore, with enhanced ozone levels over the Eastern Mediterranean.

Effects of ethylenediurea (EDU) on regulatory proteins in two maize (Zea mays L.) varieties under high tropospheric ozone phytotoxicity

Rising tropospheric ozone is a major threat to the crops in the present climate change scenario. To investigate the EDU induced changes in proteins, two varieties of maize, the SHM3031 and the PEHM5, (hereafter S and P respectively) were treated with three EDU applications (0= control, 50 and 200 ppm) (hereafter 0= A, 1 and 2 respectively) (SA, S1, S2, PA, P1, P2 cultivar X treatments). Data on the morpho-physiology, enzymatic activity, and protein expression (for the first time) were collected at the vegetative (V, 45 DAG) and flowering (F, 75 DAG) developmental stages. The tropospheric ozone was around 53 ppb enough to cause phytotoxic effects. Protective effects of EDU were recorded in morpho-physiologically and biochemically. SOD, CAT and APX together with GR performed better under EDU protection in SHM3031 variety than PEHM5. The protein expression patterns in SHM3031 at the vegetative stage (28% proteins were increased, 7% were decreased), and at the flowering stage (17% increased, 8% decreased) were found. In PEHM5, a 14% increase and an 18% decrease (vegetative stage) whereas a 16% increase and a 20% decrease (flowering stage) were recorded in protein expression. Some protein functional categories, for instance, photosynthesis, carbon metabolism, energy metabolism, and defense were influenced by EDU. Rubisco expression was increased in SHM3031 whereas differentially expressed in PEHM5. Germin like protein, APX, SOD, and harpin binding proteins have enhanced defense regulatory mechanisms under EDU treatment during prevailing high tropospheric O3. The present study showed EDU protective roles in C4 plants as proven in C3.

Understanding high tropospheric ozone episodes in Bangu, Rio de Janeiro, Brazil.

This study investigates the potential factors that contribute to frequent high levels of ozone in Bangu, one of the most critical areas in the city of Rio de Janeiro, regarding ozone levels and air quality. Speciated non-oxygenated volatile organic compounds (VOCs) were measured using method TO-15 (US EPA). The measured concentrations and kinetic and mechanistic analysis of VOC reactivity showed that alkanes were the most important compounds. Ozone concentrations were simulated for a base case representing a day with high ozone levels. Simulated results and statistical multivariate analysis showed that the high ozone concentrations did not seem to be closely related to local emissions but rather were related to pollutant transport and low measured NOx levels and were triggered by photochemical activity. The differences between weekdays and weekends were also investigated, showing that ozone concentrations were also higher during weekends, mainly on Sunday, when the diesel heavy vehicle fleet was reduced and lower NO emissions were observed. The VOC/NOx ratios correspond to a VOC-limited process, which leads to higher ozone concentrations under low NOx conditions.

A Serum Containing Deschampsia antartica Extract, Ferulic Acid and Vitamin C has Anti-Pollutant Effects on Skin Exposed to High Tropospheric Ozone Levels: A Controlled Single-Blind, Prospective Clinical Trial in Women Living in Urbanized, High Air Pollution Area during the Summer Season

Introduction: Air pollution induces skin damage and accelerating skin aging processes, mainly through oxidative stress. Pollutant substances, such as particulate matter (PM10, PM2.5) and tropospheric ozone (O3), can activate specific intracellular receptors called AhR (Aryl-Hydrocarbon Receptors) and this activation is involved in the skin aging process. Deschampsia antartica aqueous extract (DAE) has shown, in vitro, to reduce the pollutant-induced AhR activation. Ferulic acid (FA) and vitamin C (VC) are well known potent anti-oxidant substances. A dermatological product in serum formulation containing DAE/FA/VC has been recently commercialized. This product has demonstrated in vivo to protect skin from pollution damage during winter season when PM10 levels are very high. No data have been published so far regarding the protective effect of this serum during summer months when the main atmospheric pollutant is O3. Objective and materials and methods: We carried out a prospective, single-blind, controlled 28-day study during the summer season (characterized by elevated O3 tropospheric levels) in 20, photo type II-III, women (mean age 38 years) with mild-moderate skin aging, living in an urbanized, high pollution area (City of Rome) compelling to spend at least 2 hours daily outdoor. The study’s outcomes were to evaluate the effects of treatment on skin barrier function, assessed by TEWL measurement (Tewameter) and corneometry, skin appearance by high resolution photographs with Visioface Quick (Courage and Khazaka) and the effect on squalene peroxide (SQOOH)/squalene (SQ) skin ratio measured with face swabs. Results: The trial was conducted between July the first, and August 2, 2019. All the subjects concluded the trial. During the study period, elevated O3 concentration (>120 microg/m3) were registered in 22 out of 31 days (71%) (The ARPA official database, Agenzia regionale per la protezione ambientale). The product induced, in comparison with baseline values, a significant improvement of skin barrier function and hydration (-14% of TEWL and +16% skin hydration), significant improvements in skin appearance and SQOOH/SQ ratio (-19%) were also observed. The 90% of the subjects involved in the trial evaluated the product very well regarding cosmetic acceptability. Discussion: The results of the present study has demonstrated that a serum containing DAE/FA/VC can improve skin barrier function, skin appearance and counteract skin oxidative stress in women living in high O3 pollution urban area during the summer period.

High tropospheric ozone in Lhasa within the Asian summer monsoon anticyclone in 2013: influence of convective transport and stratospheric intrusions

Abstract. Balloon-borne measurements of ozone in Lhasa (29.66∘ N, 91.14∘ E; 3650 m above sea level) in August 2013 are investigated using backward trajectory calculations performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS). Measurements show three time periods characterized by high ozone mixing ratios (OMRs) in the troposphere on 8, 11, and 18–20 August 2013 during the Asian summer monsoon (ASM) season. Here, we verified two different sources for the enhanced ozone values in the troposphere. First, transport of polluted air from the boundary layer, and second downward transport from the stratosphere by stratospheric intrusions. Air pollution from South Asia through convective and long-range transport plays a key role in enhancing middle tropospheric OMRs up to 90 % on 8 August and up to 125 % on 11 August 2013 compared to monthly mean ozone of August 2013. Stratospheric air intruded from the northern high-latitudes to the southeastern flank of the ASM anticyclone to the troposphere and is identified as the source of enhanced ozone according to backward trajectory calculation and satellite measurements by the Ozone Monitoring Instrument (OMI) and the Atmospheric Infrared Sounder (AIRS). Air parcels with high ozone moved from the high-latitude lower stratosphere to the middle and upper troposphere. These air parcels are then transported to Lhasa over long distances and enhanced upper and middle tropospheric ozone over Lhasa during 18–20 August 2013. Our findings demonstrate that the strong variability of ozone within the ASM anticyclone in the free troposphere is caused by transport from very different regions of the atmosphere.

Evaluation of El Niño-Southern Oscillation influence on 30 years of tropospheric ozone concentrations in Houston

Surface observations collected over the period 1980–2010 at three Continuous Ambient Monitoring Stations located in Houston, Texas were leveraged to create a long-term composite dataset of tropospheric ozone measurements. This dataset was used to evaluate large-scale influences and their relationship to exceedances of the 70 ppbv National Ambient Air Quality Standard for ozone. A linear regression fit to monthly mean daily peak 8-h concentrations for each month revealed a decreasing trend for the duration of the study period. After removal of this temporal trend, 8-h peak values averaged for each month featured peaks in springtime and late-summer with relative minima in mid-summer and winter. Stratification of the database by El Niño-Southern Oscillation phase using the Oceanic Niño Index revealed a statistically significant (α = 0.05) dependence of peak 8-h concentration on ENSO phase, with an enhancement of 5.8, 4.8, and 7.0 for March, April, and June during warm phase years, while cool phase years had statistically significant enhancements of 5.0, 4.0, and 3.6 ppbv in February, October, and December relative to neutral conditions. Importantly, relative to neutral conditions, “El Nino years” produce 26% more exceedences while “La Nina years” produce 23% fewer. The earlier onset of ozone seasons both in spring and late summer during El Nino years leads to more exposure to direct sunlight and more seasonal photochemical production, while the delayed late summer season during La Nina years leads to decreased sunlight and suppressed seasonal photochemical production relative to neutral years. Evaluation of the number of exceedances per month for each ENSO regime also suggests high tropospheric ozone concentrations in the fall and spring, with 4.4 and 6.8 exceedances per month in June and September, respectively for the warm phase. During cool phase conditions, Houston averaged 5.0 exceedances per month in September. Exceedances for neutral conditions ranged from zero exceedances in December to 2.2 exceedances in May and 5.0 in September. Analysis of exceedance data and mean values in light of parameters of the underlying distribution of daily peak 8-h data suggests that ENSO may influence the shape of those distributions, influencing both background ozone concentrations and the number of exceedances. Fast Fourier analysis indicated a common spectral signature for the ENSO and ozone spectra. This finding has implications for air quality mitigation strategies employed during warm phase and cool phase years.

Factors dominating 3-dimensional ozone distribution during high tropospheric ozone period.

Data from an in situ monitoring network and five ozone sondes are analysed during August of 2012, and a high tropospheric ozone episode is observed around the 8th of AUG. The Community Multi-scale Air Quality (CMAQ) model and its process analysis tool were used to study factors and mechanisms for high ozone mixing ratio at different levels of ozone vertical profiles. A sensitive scenario without chemical initial and boundary conditions (ICBCs) from MOZART4-GEOS5 was applied to study the impact of stratosphere-troposphere exchange (STE) on vertical ozone. The simulation results indicated that the first high ozone peak near the tropopause was dominated by STE. Results from process analysis showed that: in the urban area, the second peak at approximately 2km above ground height was mainly caused by local photochemical production. The third peak (near surface) was mainly caused by the upwind transportation from the suburban/rural areas; in the suburban/rural areas, local photochemical production of ozone dominated the high ozone mixing ratio from the surface to approximately 3km height. Furthermore, the capability of indicators to distinguish O3-precursor sensitivity along the vertical O3 profiles was investigated. Two sensitive scenarios, which had cut 30% anthropogenic NOX or VOC emissions, showed that O3-precursor indicators, specifically the ratios of O3/NOy, H2O2/HNO3 or H2O2/NOZ, could partly distinguish the O3-precursor sensitivity between VOCs-sensitive and NOx-sensitive along the vertical profiles. In urban area, the O3-precursor relationship transferred from VOCs-sensitive within the boundary layer to NOx-sensitive at approximately 1-3km above ground height, further confirming the dominant roles of transportation and photochemical production in high O3 peaks at the near-ground layer and 2km above ground height, respectively.

Tropospheric Ozone Climatology in Eastern Equatorial Africa

Tropospheric ozone climatology in eastern Equatorial Africa has been at the core of this study. Seasonal and annual tropospheric ozone distribution and variation have been investigated using SHADOZ network data from Nairobi for the period 1998-2013. Meteorological parameters including air temperature, relative humidity, atmospheric pressure as well as ozone partial pressure have permitted to provide the first comprehensible tropospheric ozone climatology over this region. Mean seasonal tropospheric ozone distribution displays two distinct peaks occurring in winter with 43 DU (July) and 46.8 DU in spring (October). Comparison of mean seasonal ozone partial pressure with relative humidity profiles shows a logarithmic trend with strong regression coefficient for ozone partial pressure (0.81<R2<0.92). Conversely relative humidity variation displays a linear trend with a weak seasonal regression (0.57<R2<0.74). Seasonal vertical tropospheric ozone variation displays two ozone peaks of 121 ppbv in JJA and 126 ppbv in SON at 100 hPa respectively. A minimum photochemical source contribution from local and neighboring countries has been noted at surface to mid latitude. Investigation of individual profiles chosen as case studies for JJA (25/07/2001) and SON (09/10/2002), to assess the origin of high tropospheric ozone concentration has been performed by using back trajectory HYSPLIT model. The strong role played by the Indian Ocean in the long range transport of easterly air mass into eastern Africa at mid and upper troposphere in both seasons has been confirmed. However mean monthly NCEP/NCAR Reanalysis model used to assess the contribution of STE (Stratospheric Tropospheric Exchange), shows a positive mean eddy divergence values during the months of June to July 2001, with evidence of high vorticity 1 sigma values occurring over the same period. In summer higher positive 1 sigma divergence as well as 1 sigma vorticity values have been noted showing stronger STE activity occurring in SON period. These parameters suggest that STE contribution to ozone enhancement in equatorial east Africa is stronger during SON than in JJA. Given the complexity of climate patterns over the equatorial region, in which Nairobi is located, the influence of ENSO (El Nino-Southern Oscillation) and QBO (Quasi Biennial Oscillation) in the STE occurrence cannot be excluded as noted by previous studies.

Heterogeneous responses to ozone and nitrogen alter the species composition of Mediterranean annual pastures.

Air pollution represents a threat to biodiversity throughout the world and particularly in the Mediterranean area, where high tropospheric ozone (O3) concentrations and atmospheric nitrogen (N) deposition are frequently recorded. Mediterranean annual pastures are among the most important ecosystems in southern Europe due to their high biodiversity and extension. Aiming to study the responses of these communities to the main atmospheric pollutants in the Mediterranean region, an experimental study was performed in an open-top chamber (OTC) facility. A mixture of six species representative of annual pastures was grown under field conditions inside the OTC. Plants were exposed for 39days to four O3 treatments and three doses of N. The species responded heterogeneously to both factors. Legumes did not react to N but were very sensitive to O3: Trifolium species responded negatively, while Ornithopus responded positively, taking advantage of the greater sensitivity of clovers to O3. The grasses and the herb were more tolerant of O3 and grasses were the most responsive to N. Significant interactions between factors indicated a loss of effectiveness of N in O3-polluted atmospheres and an ability of O3 to counterbalance the damage induced by N input, but both effects were dependent on O3 and N levels. The inclusion of plant competition in the experimental design was necessary to reveal results that would otherwise be missed, such as the positive growth responses under elevated O3 levels. Surprisingly, competition within the legume family played the most important role in the overall response of the annual community to O3. Both tropospheric O3 and N deposition should be considered important drivers of the structure and biodiversity of Mediterranean annual pastures.

Determining relationships and mechanisms between tropospheric ozone column concentrations and tropical biomass burning in Thailand and its surrounding regions

This study aims to determine the variability and trends of tropical biomass burning, tropospheric ozone levels from 2005–2012 in Thailand and the ozone transport from the surrounding regions. Intense biomass burning and tropospheric ozone in this area have a seasonal variability with the maximum generally occurring during the dry season. The northern part of Thailand was observed to have high tropospheric ozone during the dry peak season in April. Forward trajectory analysis determined that ozone sources due to biomass burning in the northern and western surrounding regions (Myanmar, Laos and India) enhance the tropospheric ozone column in northern Thailand. Seasonal variations were also seen for the middle and northeastern regions of Thailand. During August, most biomass burning occurs in Indonesia and Malaysia. However, forward trajectory analysis showed that the effect in the tropospheric ozone column level in the southern part of Thailand is minimal from these regions. Eight-year trends of tropospheric ozone column were also calculated for the different regions of Thailand. However, statistical analysis showed that these trends were not significant. The interannual variability of the tropospheric ozone column concentrations due to El Niño Southern Oscillation were also investigated. It was observed that the best correlation of the tropospheric ozone column with the Oceanic Niño Index (ONI) occured when ONI was advanced 3 months for the north, northeast and south regions of Thailand and 4 months for the middle region of Thailand.

Tropical tropospheric ozone column retrieval for GOME-2

Abstract. This paper presents the operational retrieval of tropical tropospheric ozone columns (TOCs) from the Second Global Ozone Monitoring Experiment (GOME-2) instruments using the convective-cloud-differential (CCD) method. The retrieval is based on total ozone and cloud property data provided by the GOME Data Processor (GDP) 4.7, and uses above-cloud and clear-sky ozone column measurements to derive a monthly mean TOC between 20° N and 20° S. Validation of the GOME-2 TOC with several tropical ozonesonde sites shows good agreement, with a high correlation between the GOME-2 and sonde measurements, and small biases within ~ 3 DU. The TOC data have been used in combination with tropospheric NO2 measurements from GOME-2 to analyse the effect of the 2009–2010 El Niño–Southern Oscillation (ENSO) on the tropospheric ozone distribution in the tropics. El Niño induced dry conditions in September–October 2009 resulted in relatively high tropospheric ozone columns over the southern Indian Ocean and northern Australia, while La Niña conditions in September–October 2010 resulted in a strong increase in tropospheric NO2 in South America, and enhanced ozone in the eastern Pacific and South America. Comparisons of the GOME-2 tropospheric ozone data with simulations of the ECHAM/MESSy Atmospheric Chemistry (EMAC) model for 2009 El Niño conditions illustrate the usefulness of the GOME-2 TOC measurements in evaluating chemistry climate models (CCMs). Evaluation of CCMs with appropriate satellite observations helps to identify strengths and weaknesses of the model systems, providing a better understanding of driving mechanisms and adequate relations and feedbacks in the Earth atmosphere, and finally leading to improved models.