High O3 Exposure Research Articles

Glycerophospholipid metabolism changes association with ozone exposure

Exposure to ozone (O3) has been associated with cardiovascular outcomes in humans, yet the underlying mechanisms of the adverse effect remain poorly understood. We aimed to investigate the association between O3 exposure and glycerophospholipid metabolism in healthy young adults. We quantified plasma concentrations of phosphatidylcholines (PCs) and lysophosphatidylcholines (lysoPCs) using a UPLC-MS/MS system. Time-weighted personal exposures were calculated to O3 and co-pollutants over 4 time windows, and we employed orthogonal partial least squares discriminant analysis to discern differences in lipids profiles between high and low O3 exposure. Linear mixed-effects models and mediation analysis were utilized to estimate the associations between O3 exposure, lipids, and cardiovascular physiology indicators. Forty-three healthy adults were included in this study, and the mean (SD) time-weighted personal exposures to O3 was 9.08 (4.06) ppb. With shorter exposure durations, O3 increases were associated with increasing PC and lysoPC levels; whereas at longer exposure times, the opposite relationship was shown. Furthermore, two specific lipids, namely lysoPC a C26:0 and lysoPC a C17:0, showed significantly positive mediating effects on associations of long-term O3 exposure with pulse wave velocity and systolic blood pressure, respectively. Alterations in specific lipids may underlie the cardiovascular effects of O3 exposure.

Long-term ozone exposure and all-cause mortality: Cohort evidence in China and global heterogeneity by region

BackgroundCohort evidence linking long-term ozone (O3) exposure to mortality remained largely mixed worldwide and was extensively deficient in densely-populated Asia. This study aimed to assess the long-term effects of O3 exposure on all-cause mortality among Chinese adults, as well as to examine potential regional heterogeneity across the globe. MethodsA national dynamic cohort of 42153 adults aged 16+ years were recruited from 25 provinces across Chinese mainland and followed up during 2010–2018. Annual warm-season (April–September) O3 and year-round co-pollutants (i.e., nitrogen dioxide [NO2] and fine particulate matter [PM2.5]) were simulated through validated spatial-temporal prediction models and were assigned to each enrollee in each calendar year. Cox proportional hazards models with time-varying exposures were employed to assess the O3-mortality association. Concentration-response (C-R) curves were fitted by natural cubic spline function to investigate the potential nonlinear association. Both single-pollutant model and co-pollutant models additionally adjusting for PM2.5 and/or NO2 were employed to examine the robustness of the estimated association. The random-effect meta-analysis was adopted to pool effect estimates from the current and prior population-based cohorts (n = 29), and pooled C-R curves were fitted through the meta-smoothing approach by regions. ResultsThe study population comprised of 42153 participants who contributed 258921.5 person-years at risk (median 6.4 years), of whom 2382 death events occurred during study period. Participants were exposed to an annual average of 51.4 ppb (range: 22.7−74.4 ppb) of warm-season O3 concentration. In the single-pollutant model, a significantly increased hazard ratio (HR) of 1.098 (95% confidence interval [CI]: 1.023−1.179) was associated with a 10-ppb rise in O3 exposure. Associations remained robust to additional adjustments of co-pollutants, with HRs of 1.099 (95% CI: 1.023−1.180) in bi-pollutant model (+PM2.5) and 1.093 (95% CI: 1.018−1.174) in tri-pollutant model (+PM2.5+NO2), respectively. A J-shaped C-R relationship was identified among Chinese general population, suggesting significant excess mortality risk at high ozone exposure only. The combined C-R curves from Asia (n = 4) and North America (n = 17) demonstrated an overall increased risk of all-cause mortality with O3 exposure, with pooled HRs of 1.124 (95% CI: 0.966−1.307) and 1.023 (95% CI: 1.007−1.039) per 10-ppb rise, respectively. Conversely, an opposite association was observed in Europe (n = 8, HR: 0.914 [95% CI: 0.860−0.972]), suggesting significant heterogeneity across regions (P < 0.01). ConclusionsThis study provided national evidence that high O3 exposure may curtail long-term survival of Chinese general population. Great between-region heterogeneity of pooled O3-mortality was identified across North America, Europe, and Asia.

Interaction between ozone and paternal smoking on fetal congenital heart defects among pregnant women at high risk: a multicenter maternal-fetal medicine study.

Evidence remains limited on the association between maternal ozone (O3) exposure and congenital heart defects (CHDs) in offspring, and few studies have investigated the interaction and modification of paternal smoking on this association. Using a sample including pregnant women at high risk of fetal CHD (with metabolic disease, first-trimester viral infection, family history of CHD, etc.) from a maternal-fetal medicine study covering 1313 referral hospitals in China during 2013-2021, we examined the associations between maternal O3 exposure during 3-8 weeks of gestational age and fetal CHD in offspring and investigated the interaction and modification of paternal smoking on this association. CHD was diagnosed by fetal echocardiograms, maximum daily 8-hour average O3 exposure data at a 10 km × 10 km spatial resolution came from the Tracking Air Pollution in China dataset, and paternal smoking was collected using questionnaires. Logistic regression models were used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). Among 27,834 pregnant women at high risk of fetal CHD, 17.4% of fetuses were diagnosed with CHD. Each 10 μg/m3 increase in maternal O3 exposure was associated with a 17% increased risk of CHD in offspring (OR= 1.17, 95% CI =1.14-1.20). Compared with paternal nonsmoking and maternal low O3 exposure, the ORs (95% CI) of CHD for smoking and low O3 exposure, nonsmoking and high O3 exposure, and smoking and high O3 exposure were 1.25 (1.08-1.45), 1.81 (1.56-2.08), and 2.23 (1.84-2.71), respectively. Paternal smoking cessation seemingly mitigated the increased risk of CHD. Maternal O3 exposure and paternal smoking were interactively associated with an increased risk of fetal CHD in offspring, which calls for effective measures to decrease maternal exposure to O3 pollution and secondhand smoke for CHD prevention.

Association between air pollution exposure and outpatient visits for dermatomyositis in a humid subtropical region of China: a time-series study.

In recent years, a growing number of studies have found that air pollution plays critical roles in the onset and development of autoimmune diseases, but few studies have shown an association between air pollutants and dermatomyositis (DM). We sought to investigate the relationship between short-term exposure to air pollution and outpatient visits for DM and to quantify the burden of DM due to exposure to air pollutants in Hefei, China. Daily records of hospital outpatient visits for DM, air pollutants and meteorological factors data in Hefei from January 1, 2018 to December 31, 2021 were obtained. We used a distributed lag non-linear model (DLNM) in conjunction with a generalized linear model (GLM) to explore the association between air pollution and outpatient visits for DM, and conducted stratified analyses by gender, age and season. Moreover, we used attributable fraction (AF) and attributable number (AN) to reflect the burden of disease. A total of 4028 DM clinic visits were recorded during this period. High concentration nitrogen dioxide (NO2) exposure was associated with increased risk of DM outpatient visits (relative risk (RR) 1.063, 95% confidence interval (CI) 1.015-1.114, lag 0-5). Intriguingly, exposure to high concentration ozone (O3) was associated with reduced risk of outpatient visits for DM (RR 0.974, 95% CI 0. 0.954-0.993, lag 0-6). The results of stratified analyses showed that the cold season (vs. warm season) were more susceptible to outpatient visits for DM associated with NO2 and O3 exposure. In addition, we observed that an increased risk of DM outpatient visits was attributable to high concentration NO2 exposure, while high concentration O3 exposure was associated with a decreased risk of DM outpatient visits. This study provided a scientific basis for the etiology research and health protection of DM.

A life course approach to asthma and wheezing among young children caused by ozone: A prospective birth cohort in northern China

BackgroundGiven differences in vulnerability of children in early life, a life course approach to asthma and wheezing (AW) in young children caused by ozone (O3) is not fully understood. MethodsWe conducted a birth cohort in Jinan, China from 2018 to 2021 to elucidate the onset model of childhood AW due to O3 exposure. An inverse distance weighted model was used for individual exposure assessment. The time-dependent Cox proportional-hazard model and logistic model were used to investigate the effects of O3 exposure on AW. Principal component analysis, interaction analysis, and distributed lag model were used to analyze the life course approach. ResultsThe cumulative incidence rate for AW among 6501 children aged 2 was 1.4%. A high level of O3 was related to AW (HR: 2.10, 95% CI: 1.31, 3.37). Only O3 exposure after birth was associated with AW, with an OR of 1.82 (1.08, 3.12), after adjusting for the effect before birth. Furthermore, adjusting for other air pollutants, the HR for the individual effect of high O3 exposure on AW was 2.44 (1.53, 3.89). Interestingly, P values for interactions for O3 and the principal components of other pollutants, as well as the characteristic variable of open windows were less than 0.1. Moreover, an increase in the IQR of O3 exposure at the 31st to 37th weeks before birth and the 1st to 105th weeks after birth was associated with an increase in the HRs for AW. ConclusionsHigh-level of O3 exposure after birth could lead to AW among young children. Importantly, the AW onset model may include the risk factors accumulation and the sensitive period model. Specifically, there are two sensitive windows in early life, and the correlated insults between the high level of O3 and other pollutants as well as open windows in the asthma-inducing effect.

The ozone–climate penalty over South America and Africa by 2100

Abstract. Climate change has the potential to increase surface ozone (O3) concentrations, known as the “ozone–climate penalty”, through changes to atmospheric chemistry, transport and dry deposition. In the tropics, the response of surface O3 to changing climate is relatively understudied but has important consequences for air pollution and human and ecosystem health. In this study, we evaluate the change in surface O3 due to climate change over South America and Africa using three state-of-the-art Earth system models that follow the Shared Socioeconomic Pathway 3-7.0 emission scenario from CMIP6. In order to quantify changes due to climate change alone, we evaluate the difference between simulations including climate change and simulations with a fixed present-day climate. We find that by 2100, models predict an ozone–climate penalty in areas where O3 is already predicted to be high due to the impacts of precursor emissions, namely urban and biomass burning areas, although on average, models predict a decrease in surface O3 due to climate change. We identify a small but robust positive trend in annual mean surface O3 over polluted areas. Additionally, during biomass burning seasons, seasonal mean O3 concentrations increase by 15 ppb (model range 12 to 18 ppb) in areas with substantial biomass burning such as the arc of deforestation in the Amazon. The ozone–climate penalty in polluted areas is shown to be driven by an increased rate of O3 chemical production, which is strongly influenced by NOx concentrations and is therefore specific to the emission pathway chosen. Multiple linear regression finds the change in NOx concentration to be a strong predictor of the change in O3 production, whereas increased isoprene emission rate is positively correlated with increased O3 destruction, suggesting NOx-limited conditions over the majority of tropical Africa and South America. However, models disagree on the role of climate change in remote, low-NOx regions, partly because of significant differences in NOx concentrations produced by each model. We also find that the magnitude and location of the ozone–climate penalty in the Congo Basin has greater inter-model variation than that in the Amazon, so further model development and validation are needed to constrain the response in central Africa. We conclude that if the climate were to change according to the emission scenario used here, models predict that forested areas in biomass burning locations and urban populations will be at increasing risk of high O3 exposure, irrespective of any direct impacts on O3 via the prescribed emission scenario.

Ambient air pollution during pregnancy and cardiometabolic biomarkers in cord blood

Background/Objectives:Prenatal air pollution exposure has been associated with adverse childhood cardiometabolic outcomes. It is unknown whether evidence of metabolic disruption associated with air pollution is identifiable at birth. We examined exposure to prenatal ambient air pollution and cord blood cardiometabolic biomarkers among 812 mother-infant pairs in the Healthy Start study.Methods:Using inverse-distance-weighted interpolation of ambient concentrations obtained from stationary monitors, we estimated daily particulate matter ≤2.5 micrometers (PM2.5) and ozone (O3) concentrations at participant residences. Daily estimates were averaged by trimester, full-pregnancy, and the 7 and 30 days prior to delivery. Associations of air pollution with the following cord blood biomarkers were estimated via multivariable linear regression: glucose, insulin, glucose/insulin ratio (GIR), leptin, high-density lipoprotein (HDL) cholesterol, non-HDL cholesterol, free fatty acids, and triglycerides.Results:In this Denver-based cohort, PM2.5 concentrations were lower than in many US urban areas, but O3 concentrations regularly exceeded federal air quality standards. Higher O3 concentrations during pregnancy were consistently associated with higher insulin and lower GIR in cord blood. For example, an interquartile range increase in full pregnancy O3 (6.3 parts per billion [ppb]) was associated with 0.13 log-µIU/ml (95% confidence interval [CI] = 0.04, 0.22) higher cord blood insulin, after adjusting for PM2.5 and other confounders. We found positive, but generally nonsignificant, associations between PM2.5 and leptin and isolated associations between pollutants during certain exposure periods and lipids.Conclusions:In this cohort with moderately high O3 exposure, prenatal concentrations of O3 were positively associated with cord blood insulin. Future studies should examine the implications for offspring long-term health.

Impacts of Ozone‐Vegetation Interactions on Ozone Pollution Episodes in North China and the Yangtze River Delta

AbstractPersistent ozone (O3) pollution episodes (OPEs, with regionally averaged maximum daily 8‐h average (MDA8) O3 concentration exceeding 80 ppbv and lasting for 5 days or longer) occurred frequently in megalopolis over eastern China in recent years. Here, we apply a newly developed chemistry‐biosphere model (GEOS‐Chem‐YIBs) to comprehensively quantify the vegetation contributions to OPEs in North China and Yangtze River Delta (YRD) over May to October in 2014–2017. The simulated MDA8 O3 concentrations increases 16.7 and 16.6 ppbv) during OPEs in North China and YRD, of which about 1.4 ppbv (8.4%) and 3.8 ppbv (22.9%) are caused by the processes including increased BVOC emissions and reduced stomatal dry deposition. Furthermore, the O3 damages to vegetation stomata slightly increase seasonal‐mean O3 concentrations by &lt;1 ppbv, but such effects are not exacerbated during OPEs despite the high O3 exposure.

Short-term effects of ambient temperature and pollutants on the mortality of respiratory diseases: A time-series analysis in Hefei, China

BackgroundThe air pollution has become an important environmental health problem due to its adverse health effect. The objective of this study was to investigate the effects of ambient temperature and pollutants on mortality of respiratory diseases (RD) in Hefei, China, a typical inland city. MethodsNonlinear exposure–response dependencies and delayed effects of urban daily mean temperature (DMT) and pollutants were evaluated by distributed lag non-linear models (DLNM). To further explore this effect, different genders and ages were also examined by stratified analysis. ResultsA total of 12876 deaths from RD were collected from January 1, 2014 to December 31, 2018 in Hefei, China. There was a U-shaped correlation between DMT and RD mortality, and the RD mortality rised by 11.6% (95% CI: 2.2–22.0%) when the DMT was 35.8 °C (reference temperature is 20 °C). The results show that risk of death with short-term exposure to elevated concentrations of PM10 and SO2 was not significant. The maximum hysteresis and cumulative relative risk (RR) of RD mortality were 1.012 (95% CI: 1.003 ~ 1.021, lag 0 day) and 1.072 (95% CI: 1.014 ~1.133, lag 10 days) for each 10 μg/m3 augment in NO2; 1.005 (95% CI: 1.001–1.009, lag 0 day) and 1.027 (95% CI: 1.004–1.051, lag 10 days) for each 10 μg/m3 augment in O3; a negative association between CO exposure and the cumulative risk of death was observed (RR = 0.964, 95% CI: 0.935–0.993, lag 07 days). Subgroup analysis showed the effect of high temperatures, NO2, O3 and CO exposure was still statistically significant for the elderly and male. ConclusionThe present study found that short-term exposure to high temperature, NO2, O3 and CO were significantly associated with the risk of RD mortality and male as well as elderly are more susceptible to these factors.

Impact of Ambient Particulate Matter and Ozone Exposure of Heart Transplant Recipients on All-Cause Mortality after Heart Transplant

Purpose There is limited evidence on role of air quality on chronic rejection after heart transplant (HT). We investigated the impact of particulate matter concentration (PM≥2.5 μm/m3) and ozone (O3) exposure of recipients on all-cause mortality after HT in the US. Methods UNOS Standard Transplant Analysis and Research (STAR) database (June 30, 2017) identified adult HT recipients between 2005 and 2015, and their zip code of residence at HT. Average ambient PM and daily maximum 8-hour average O3 associated with recipient residencies 1 year after HT were estimated by mapping each zip code to a census tract, using a crosswalk from HUD, downscaled from a 12 × 12-km sq grid resolution detailed chemistry - transport model application using a Bayesian space-time downscaler, and then fused with surface observations. PM concentration was classified into low ( 12 μg/m3); O3 was similarly categorized (low: 42 ppb). Inverse-probability of treatment weighted Cox regression and Kaplan-Meier curves assessed the impact of PM and O3 on 1-year and long-term incidence of all-cause mortality. Results Overall, 17,893 HT patients were included; Median follow-up was 1529 days (IQR 737-2586). 21% of HT recipients had high PM exposure and 20% had high O3 exposure. While estimates were imprecise, both high exposure levels of PM and O3, compared to low exposure, appeared to increase long-term mortality (Table). High PM exposure may also increase 1-year mortality; O3 had no impact on 1-year mortality. Conclusion PM2.5 and O3 conc are only 2 aspects of air quality and appear to increase long term risk of death after HT. Additional research on other air quality measures including isolating primary and secondary components of PM2.5 and focusing on traffic-related air pollutants is warranted for all transplant recipients.

Effects of foam fractionation and chemical disinfection on the removal of different microalgae cultures

The recent development of recirculation aquaculture systems (RAS) potentially allows more sustainable and controlled rearing conditions. However, control of suspended microparticles and microalgae in RAS is challenging, as uncontrolled blooms of toxic algae or heterotrophic dinoflagellates can have catastrophic impacts on the production of fish. In this study, we tested the potential of protein skimmers to remove microalgae. In 100 L batch tests, protein skimmers were tested separately and in combination with ozone (O3), ultraviolet (UV) or hydrogen peroxide (H2O2). Three different and distinct microalgae cultures were tested with densities from 30,000 to 120,000 algae cells/ml in a triplicated experimental setup. Trial 1 included twelve 24-hr replicated tests where protein skimmers with air or with two levels of ozone (low and high O3 exposure) were compared. The protein skimmer with air alone had a limited effect on the removal of microalgae compared to the untreated control algae tanks. When ozone and protein skimmers were combined, a clear additive effect was found, and all added microalgae were removed. Low O3 dosage and protein skimmers completely removed the algae cultures within 12 hr, while more than 95% of the algae were removed within 7 hr when a higher ozone dose was used. The second trial compared the removal capacity of protein skimmers in combination with UV, H2O2 and O3. These experiments showed no to limited additive effect of UV combined with protein skimming, but significantly increased removal efficiency (270% and 1,300%, respectively) was found when H2O2 and ozone were combined with a protein skimmer. The study showed an algae species-specific response to a protein skimmer with ozonation and provided information on the transition from reactivity and consumption to accumulation of ozone-produced oxidants.

Heterogeneous Ozonolysis of Squalene: Gas-Phase Products Depend on Water Vapor Concentration.

Previous work examining the condensed-phase products of squalene particle ozonolysis found that an increase in water vapor concentration led to lower concentrations of secondary ozonides, increased concentrations of carbonyls, and smaller particle diameter, suggesting that water changes the fate of the Criegee intermediate. To determine if this volume loss corresponds to an increase in gas-phase products, we measured gas-phase volatile organic compound (VOC) concentrations via proton-transfer-reaction time-of-flight mass spectrometry. Studies were conducted in a flow-tube reactor at atmospherically relevant ozone (O3) exposure levels (5-30 ppb h) with pure squalene particles. An increase in water vapor concentration led to strong enhancement of gas-phase oxidation products at all tested O3 exposures. An increase in water vapor from near zero to 70% relative humidity (RH) at high O3 exposure increased the total mass concentration of gas-phase VOCs by a factor of 3. The observed fraction of carbon in the gas-phase correlates with the fraction of particle volume lost. Experiments involving O3 oxidation of shirts soiled with skin oil confirms that the RH dependence of gas-phase reaction product generation occurs similarly on surfaces containing skin oil under realistic conditions. Similar behavior is expected for O3 reactions with other surface-bound organics containing unsaturated carbon bonds.

Changes of Cinnamomum camphora root characteristics and soil properties under ozone stress in South China.

High O3 exposure affects the forest growth and soil characteristics. Although there is substantial evidence that O3 does impose a stress on forest trees, the effects of O3 on roots and soil of evergreen broad-leaved tree species in South China remain unknown. The effects of ozone (O3) fumigation on the root biomass, root morphology, root nutrient, soil physical, and chemical properties were examined in Cinnamomum camphora seedlings grown under four O3 treatments (charcoal-filtered air (CF) or O3 at 1×, 2× and 4× ambient concentration). O3 significantly decreased root biomass and root carbon (C). Regardless of O3 level, elevated O3 significantly resulted in reduced root surface area, volume, number of forks, and specific root length (SRL). The percentages of fine to total root in terms of root surface area and root volume of seedlings under the CF and 1 × O3 treatments were significantly higher than those of seedlings under the 4 × O3 treatment, indicating that high O3 level impaired the growth performance of fine roots. O3 affected root growth and structures, which increased soil bulk density and reduced soil total porosity and void ratio. The soil pH under all O3 fumigation treatments significantly increased compared with CF treatment, whereas the organic matter significantly decreased. In conclusion, although the increased O3 level enhanced root N and P under 2 and 4 × O3 treatments compared with 1 × O3 treatment as compensation mechanisms to prevent O3-induced decrease in root C gain and root functions, O3 still decreased the root biomass and root tips, and changed the soil physical and chemical properties.

How does elevated ozone reduce methane emissions from peatlands?

The effects of increased tropospheric ozone (O3) pollution levels on methane (CH4) emissions from peatlands, and their underlying mechanisms, remain unclear. In this study, we exposed peatland mesocosms from a temperate wet heath dominated by the sedge Schoenus nigricans and Sphagnum papillosum to four O3 treatments in open-top chambers for 2.5years, to investigate the O3 impacts on CH4 emissions and the processes that underpin these responses. Summer CH4 emissions, were significantly reduced, by 27% over the experiment, due to summer daytime (8hday-1) O3 exposure to non-filtered air (NFA) plus 35ppb O3, but were not significantly affected by year-round, 24hday-1, exposure to NFA plus 10ppb or NFA plus 25ppb O3. There was no evidence that the reduced CH4 emissions in response to elevated summer O3 exposure were caused by reduced plant-derived carbon availability below-ground, because we found no significant effect of high summer O3 exposure on root biomass, pore water dissolved organic carbon concentrations or the contribution of recent photosynthate to CH4 emissions. Our CH4 production potential and CH4 oxidation potential measurements in the different O3 treatments could also not explain the observed CH4 emission responses to O3. However, pore water ammonium concentrations at 20cm depth were consistently reduced during the experiment by elevated summer O3 exposure, and strong positive correlations were observed between CH4 emission and pore water ammonium concentration at three peat depths over the 2.5-year study. Our results therefore imply that elevated regional O3 exposures in summer, but not the small increases in northern hemisphere annual mean background O3 concentrations predicted over this century, may lead to reduced CH4 emissions from temperate peatlands as a consequence of reductions in soil inorganic nitrogen affecting methanogenic and/or methanotrophic activity.

Canopy-level stomatal narrowing in adult Fagus sylvatica under O3 stress – Means of preventing enhanced O3 uptake under high O3 exposure?

Spatio-temporally consistent O3 doses are demonstrated in adult Fagus sylvatica from the Kranzberg Forest free-air fumigation experiment, covering cross-canopy and whole-seasonal scopes through sap flow measurement. Given O3-driven closure of stomata, we hypothesized enhanced whole-tree level O3 influx to be prevented under enhanced O3 exposure. Although foliage transpiration rate was lowered under twice-ambient O3 around noon by 30% along with canopy conductance, the hypothesis was falsified, as O3 influx was raised by 25%. Nevertheless, the twice-ambient/ambient ratio of O3 uptake was smaller by about 20% than that of O3 exposure, suggesting stomatal limitation of uptake. The O3 response was traceable from leaves across branches to the canopy, where peak transpiration rates resembled those of shade rather than sun branches. Rainy/overcast-day and nightly O3 uptake is quantified and discussed. Whole-seasonal canopy-level validation of modelled with sap flow-derived O3 flux becomes available in assessing O3 risk for forest trees.

Growth and photosynthetic responses of four landscape shrub species to elevated ozone

Attention should be paid to ozone (O3) sensitivity of greening plant since ground-level O3 concentrations are increasing especially in urban and suburban area. We studied the ecophysiological responses to elevated O3 of four shrub species [Euonymus bungeanus Maxim. (EB), Photinia × fraseri (PF), Chionanthus retusus Lindl. & Paxt. (CR) and Cornus alba L. (CA)], which are often used for garden greening in China. Saplings of those species were exposed to high O3 concentration (70 nmol mol-1, 7 h d-1 for 65 d) in open-top growth chambers. Responses to O3 were assessed by gas exchanges, chlorophyll (Chl) fluorescence and dry mass. We found that elevated O3 significantly decreased lightsaturated net photosynthetic rate (P Nsat), transpiration rate (E) and stomatal conductance (g s). The ratio of intercellular CO2 to ambient CO2 concentration (C i/C a) did not reduce under O3 fumigation which suggested that the O3-induced depressions of P Nsat under O3 fumigation were probably due to limitation of mesophyll processes rather than stomatal limitation. High O3 exposure also significantly depressed the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (Fv/Fm) which meant the O3-induced photoinhibition. Both root dry mass and root/shoot ratios were significantly decreased under ozone fumigation, but the total mass was unchanged. The responses of gas exchange such as P Nsat in these four shrubs to O3 exposure were species-specific. Highest loss of P Nsat was observed in EB (-49.6%), while the CR had the lowest loss (-36.5%). Moreover, the O3-exposed CR showed similar g s as CF, reflecting that its O3 flux might be unchanged under elevated O3 environment. Ozone drastically decreased actual quantum yield of PSII (ΦPSII) and electron transport rate (ETR) in EB while increased ΦPSII and ETR in CR. Furthermore, the relative losses in P Nsat positively correlated with the relative decreases in ΦPSII and ETR which indicated that the impairment of photosynthesis was probably affected by the light reaction process. The light reaction of EB was impaired most seriously but that of CR was not damaged. All results indicated that EB was probably the most sensitive shrub species to O3 while CR the most tolerant one. Therefore, CR might be an ideal choice for greening in ozone-polluted areas.

Risk assessment of ozone impact on the carbon absorption of Japanese representative conifers

A risk assessment of ozone (O3) impact on the annual carbon absorption (ACA) of Japanese representative conifers was conducted based on the results of an experimental study, monitoring data of oxidant concentrations and vegetation surveys. The areas with high O3-induced reduction in ACA did not necessarily correspond to the areas with relatively high O3-exposure. Widespread distribution of O3-sensitive tree species such as Pinus densiflora and Larix kaempferi, and high ACA were important factors that induced a high risk of O3 impact on the ACA. Therefore, we concluded that not only the accumulated O3-exposure but also the variety of tree habitat, the tree sensitivity to O3 and the ACA among the tree species must be taken into account to assess the risk of O3 impact on the ACA of Japanese conifers. The O3-induced reduction in the total ACA of the three tree species in Japan was estimated to be 0.8%.

Photosynthetic and yield responses of an old and a modern winter wheat cultivars to short-term ozone exposure

In order to study the responses of winter wheat cultivars released in different years to short-term high O3 exposure, an old cultivar ('Nongda 311', released in 1960s) and a modern one ('Yannong 19', released in 1990s) were treated with an O3 exposure (145 &plusmn; 12 mm3 m-3, 4 h d-1 for 3 d) shortly after anthesis stage (&gt; 50 % main stems blossomed). During the O3 exposure, light-saturated photosynthetic rate (P N) and stomatal conductance (g s) of both cultivars decreased considerably. Elevated O3 did not decrease dark-adapted maximum photochemical efficiency, but induced significant reduction in actual photochemical efficiency and thereby considerably increase in non-photochemical quenching. P N, g s of the modern cultivar 'Yannong 19' decreased more than the older one 'Nongda 311', indicating the former exhibited higher sensitivity to O3 than the latter. After O3 exposure, P N, g s and chlorophyll (Chl) content in flag leaf decreased more quickly than control, indicating induction of faster premature leaf senescence. As a result, the short-term O3 exposure caused substantial yield loss, with larger reduction in 'Yannong 19' (-19.2 %) than in 'Nongda 311' (-8.4 %). Our results indicated that high O3 exposure at grain filling stage would have greater negative impacts on the high yielding modern cultivar relative to the old one with lower yield.

Visible Foliar Injury and Physiological Responses to Ozone in Italian Provenances ofFraxinus excelsiorandF. ornus

We compared leaf visible injury and physiological responses (gas exchange and chlorophyll a fluorescence) to high O3 exposure (150 nmol mol–1 h, 8 h day–1, 35–40 days) of two woody species of the same genus with different ecological features: the mesophilic green ash (Fraxinus excelsior) and the xerotolerant manna ash (F. ornus). We also studied how provenances from northern (Piedmont) and central (Tuscany) Italy, within the two species, responded to O3 exposure. Onset and extent of visible foliar injury suggested that F. excelsior was more O3 sensitive than F. ornus. The higher stomatal conductance in F. ornus than in F. excelsior suggested a larger potential O3 uptake, in disagreement to lower visible foliar injury. The higher carbon assimilation in F. ornus suggested a higher potential of O3 detoxification and/or repair. Contrasting geographical variations of ash sensitivity to O3 were recorded, as Piedmont provenances reduced gas exchange less than Tuscan provenances in F. excelsior and more in F. ornus. Visible injury was earlier and more severe in F. excelsior from Piedmont than from Tuscany, while the provenance did not affect visible injury onset and extent in F. ornus.

Effects of ambient ozone on lung function in children over a two-summer period.

There is a general consensus that short term exposure to ozone (O3) causes a decrease in lung function parameters such as forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). The objective of this study was to assess the reproducibility of lung function decrements after ambient O3 exposure over a two-summer period. The authors studied 797 children with a mean age of 8.2 yrs (95% confidence interval: 6.9-9.5) from the second and third grades of ten elementary schools in Austria and southwestern Germany. At the outset the various study locations were stratified into three groups with low (L), medium (M) and high (H) O3 exposure (range of mean O3 concentration in the locations April-October 1994: 24-30 (L); 33-38 (M); 44-52 (H) parts per billion (ppb)). Four lung function tests were performed on each child between March 1994 and November 1995. The increases in FVC and FEV1 recorded from one test period to the next were expressed as mL x day(-1). A significantly lower FVC and FEV1 increase was observed in children exposed to high ambient O3 concentration during the summer season. (FVC in summer 1994: 0.83 (L); 0.56 (M); 0.55 (H) mL x day(-1); p=0.004; and summer 1995: 0.80 (L); 0.63 (M); 0.56 (H) mL x day(-1); p=0.011; FEV1 in summer 1994: 0.48 (L); 0.34 (M); 0.18 (H) mL x day(-1); p=0.004 and summer 1995: 0.68 (L); 0.45 (M); 0.41 (H) mL x day(-1), p=0.006). There was no significant difference in FVC or FEV1 increase between the groups during the winter period. Adjusting for sex, age, height and passive smoke exposure, linear regression revealed a statistically significant negative association of average ambient O3 concentration with the FVC and FEV1 increase in both summers. During the winter period no association of O3 with FVC or FEV1 was observed. In conclusion, in two consecutive summer periods the authors found reproducible lung function decrements in children exposed to high levels of ambient ozone. Reoccurrence of ozone associated lung function deficits might increase the likelihood of persisting effects on the childrens' airways.