Ozone Sensitivity Research Articles

Ozone sensitivity of four Pakchoi cultivars with different leaf colors: physiological and biochemical mechanisms

Ozone (O3) is important air pollutant inducing severe losses of horticultural production. Cultivars of the same species, but with different leaf colors, may differ in their ozone sensitivity. However, it has not been clarified yet if different leaf coloration influences such a sensitivity. In this study, two purple-leafed and two green-leafed cultivars of Pakchoi were selected for ozone fumigation (240 ± 20 nmol mol–1, 09:00–16:00 h). Elevated O3 decreased chlorophyll content, increased anthocyanin (Ant) content, damaged cell membrane integrity, enhanced antioxidative enzyme activities, depressed photosynthetic rate (P N) and stomatal conductance (g s), inhibited maximal quantum yield (Fv/Fm) and effective quantum yield [YII] of PSII photochemistry, and caused visible injury. Purple-leafed cultivars with higher Ant contents were more tolerant than green-leafed cultivars as indicated by lower relative enhancement in malondialdehyde content and lower relative losses in P N, g s, Fv/Fm, and YII. The higher ability to synthesize Ant in the purple-leafed cultivars contributed to their higher photoprotective ability.

A Dominant Mutation in the HT1 Kinase Uncovers Roles of MAP Kinases and GHR1 in CO2-Induced Stomatal Closure.

Activation of the guard cell S-type anion channel SLAC1 is important for stomatal closure in response to diverse stimuli, including elevated CO2 The majority of known SLAC1 activation mechanisms depend on abscisic acid (ABA) signaling. Several lines of evidence point to a parallel ABA-independent mechanism of CO2-induced stomatal regulation; however, molecular details of this pathway remain scarce. Here, we isolated a dominant mutation in the protein kinase HIGH LEAF TEMPERATURE1 (HT1), an essential regulator of stomatal CO2 responses, in an ozone sensitivity screen of Arabidopsis thaliana The mutation caused constitutively open stomata and impaired stomatal CO2 responses. We show that the mitogen-activated protein kinases (MPKs) MPK4 and MPK12 can inhibit HT1 activity in vitro and this inhibition is decreased for the dominant allele of HT1. We also show that HT1 inhibits the activation of the SLAC1 anion channel by the protein kinases OPEN STOMATA1 and GUARD CELL HYDROGEN PEROXIDE-RESISTANT1 (GHR1) in Xenopus laevis oocytes. Notably, MPK12 can restore SLAC1 activation in the presence of HT1, but not in the presence of the dominant allele of HT1. Based on these data, we propose a model for sequential roles of MPK12, HT1, and GHR1 in the ABA-independent regulation of SLAC1 during CO2-induced stomatal closure.

Ozone sensitivity to isoprene chemistry and emissions and anthropogenic emissions in central California

Ozone formation in California in year 2017 was simulated using three chemical mechanisms: the Statewide Air Pollution Research Center 2007 mechanism with updated toxics and isoprene chemistry (S07TIC); the Carbon Bond 6, revision 2 (CB6r2) mechanism; a modified CB6r2 mechanism with increased hydroxyl radical (OH) production from isoprene oxidation at low nitrogen oxide (NOx) concentrations (CB6r2OH). The simulations with a photochemical grid model (PGM) showed little difference in ozone between CB6r2 and CB6r2OH. Further analysis with a box model found little sensitivity of ozone to OH production in the isoprene chemistry of all three mechanisms under conditions representative of California. The S07TIC generally predicts greater ozone than the CB6r2, and the difference in the predicted concentrations exceeds the uncertainty estimated from uncertainties in the emissions inventory. The sensitivity of ozone to anthropogenic volatile organic compound (VOC), NOx and carbon monoxide (CO) emissions and to isoprene emissions was also calculated with the PGM. Accounting for uncertainties in the emissions inventory, the sensitivity to NOx emissions is significantly different between S07TIC and CB6r2 in central and northern California; the sensitivity to isoprene emissions is significantly different in southern California. All mechanisms give a negative sensitivity of ozone to isoprene emissions in areas of northern California where NOx emissions are small. The CB6r2 and S07TIC differ in the sensitivity of ozone to organic nitrate (ON) formation from isoprene oxidation, likely because all ONs recycle to NOx in the S07TIC mechanism but only first-generation ONs do so in the CB6r2. For current California conditions, uncertainties in OH production from isoprene have little impact on ozone, but the extent to which isoprene ONs recycle NOx does impact ozone concentration and ozone sensitivity to NOx emissions.

Photosynthetic Characteristics and Ozone Dose-response Relationships for Different Genotypes of Poplar

The open top chambers were used to explore the photosynthetic characteristics of three genotypes of poplar ('546', '90' and '84K') in response to different ozone exposures. The results showed that net photosynthetic rate (<i>P</i>n), transpiration rate (<i>T</i>r), water use efficiency (WUE), apparent electron transport rate (ETR), excitation energy capture efficiency of PSⅡ reaction center (<i>F</i>'v/<i>F</i>'m), coefficient of photochemical quenching (qP), actual photochemical efficiency of PSⅡ in the light (PhiPS2), chlorophyll a (Chla), chlorophyll b (Chlb), total chlorophyll (Chla+b) and carotenoid (Car)contents were significantly decreased with the increasing ozone concentrations. However, intercellular CO2 concentration (<i>c</i>i) was significantly increased and stomatal conductance (<i>G</i>s) remained unchanged. There was significant difference in photosynthetic characteristics among three genotypes of poplar. The genotype'546' showed a significant linear correlation (<i>P</i><0.01) between photosynthetic parameters (except <i>G</i>s) and the ozone dose index AOT40(accumulated hourly O3 concentration over a threshold of 40 nmol·mol^-1 during daylight hours). Among the three genotypes of poplar, photosynthesis pigments contents in '546' significantly declined with the increase of ozone concentration but not in '90' and '84K'. According to the linear relationship of most photosynthetic parameters and AOT40, especially the total chlorophyll, '546' showed the maximum slope, follows by '90' and then '84K'. So the order of the ozone sensitivity of three poplar genotypes was '546'> '90'> '84K'. The results of this study can provide an important basis for breeding ozone resistant genotype of poplar as well as protecting poplar from ozone damage.

Differences in ozone sensitivity among woody species are related to leaf morphology and antioxidant levels.

Ozone (O3) sensitivity varies greatly among plant species. Leaf traits such as stomatal conductance, antioxidant capacity and leaf morphology and anatomy may play important roles in controlling this variation, but the relative contributions of each trait remain elusive. In this study, we examined the differences in O3 sensitivity among 29 deciduous and evergreen woody species used for urban greening in China in an open-top chamber experiment. Elevated O3 caused visible injury and reductions in net photosynthesis, and these effects differed significantly among species. The deciduous species Sorbaria sorbifolia, Hibiscus syriacus and Fraxinus chinensis were the most sensitive, while evergreen species ranked among the most tolerant. O3 sensitivity was linked to both low leaf mass per area (LMA) and low leaf area-based antioxidant levels, but not to variation in leaf mass-based antioxidant levels or stomatal conductance. The well-known and easily measured leaf trait LMA thus represents a potentially useful metric for O3 risk assessment and for selecting appropriate species for urban greening in O3-polluted areas.

The role of surface electron accumulation and bulk doping for gas-sensing explored with single-crystalline In2O3 thin films

Single crystalline and textured In2O3 thin films with (111) surface orientation, grown by plasma-assisted molecular beam epitaxy, were used as a model system to study the role of bulk and surface electron accumulation layer conductance for ozone sensing. Both conductance contributions, which add to the total film conductance, were systematically varied. The resulting ozone sensitivity was determined by total conductance measurements in synthetic air with defined ozone concentration using UV irradiation instead of heating to regenerate the In2O3 surface. Depletion of the surface electron accumulation by an oxygen plasma treatment, confirmed by X-ray photoelectron spectroscopy, rendered the films ozone insensitive. The ozone response of films with an accumulation layer was increased by thickness reduction or by designing the bulk of the film semi-insulating using deep acceptor doping by Mg. Our results of using electron accumulation layers for gas sensing and bulk doping by deep acceptors to increase sensitivity can be generalized to other gas sensing materials. The use of single crystalline films allows selecting the most sensitive crystallographic surface orientation and may have further advantages over polycrystalline films, such as increased stability and sensing speed.

Modeled response of ozone to electricity generation emissions in the northeastern United States using three sensitivity techniques

ABSTRACTElectrical generation units (EGUs) are important sources of nitrogen oxides (NOx) that contribute to ozone air pollution. A dynamic management system can anticipate high ozone and dispatch EGU generation on a daily basis to attempt to avoid violations, temporarily scaling back or shutting down EGUs that most influence the high ozone while compensating for that generation elsewhere. Here we investigate the contributions of NOx from individual EGUs to high daily ozone, with the goal of informing the design of a dynamic management system. In particular, we illustrate the use of three sensitivity techniques in air quality models—brute force, decoupled direct method (DDM), and higher-order DDM—to quantify the sensitivity of high ozone to NOx emissions from 80 individual EGUs. We model two episodes with high ozone in the region around Pittsburgh, PA, on August 4 and 13, 2005, showing that the contribution of 80 EGUs to 8-hr daily maximum ozone ranges from 1 to >5 ppb at particular locations. At these locations and on the two high ozone days, shutting down power plants roughly 1.5 days before the 8-hr ozone violation causes greater ozone reductions than 1 full day before; however, the benefits of shutting down roughly 2 days before the high ozone are modest compared with 1.5 days. Using DDM, we find that six EGUs are responsible for >65% of the total EGU ozone contribution at locations of interest; in some locations, a single EGU is responsible for most of the contribution. Considering ozone sensitivities for all 80 EGUs, DDM performs well compared with a brute-force simulation with a small normalized mean bias (–0.20), while this bias is reduced when using the higher-order DDM (–0.10).Implications: Dynamic management of electrical generation has the potential to meet daily ozone air quality standards at low cost. We show that dynamic management can be effective at reducing ozone, as EGU contributions are important and as the number of EGUs that contribute to high ozone in a given location is small (<6). For two high ozone days and seven geographic regions, EGUs would best be shut down or their production scaled back roughly 1.5 days before the forecasted exceedance. Including online sensitivity techniques in an air quality forecasting model can provide timely and useful information on which EGUs would be most beneficial to shut down or scale back temporarily.

Stratospheric ozone change and related climate impacts over 1850–2100 as modelled by the ACCMIP ensemble

Abstract. Stratospheric ozone and associated climate impacts in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) simulations are evaluated in the recent past (1980–2000), and examined in the long-term (1850–2100) using the Representative Concentration Pathways (RCPs) low- and high-emission scenarios (RCP2.6 and RCP8.5, respectively) for the period 2000–2100. ACCMIP multi-model mean total column ozone (TCO) trends compare favourably, within uncertainty estimates, against observations. Particularly good agreement is seen in the Antarctic austral spring (−11.9 % dec−1 compared to observed ∼ −13.9 ± 10.4 % dec−1), although larger deviations are found in the Arctic's boreal spring (−2.1 % dec−1 compared to observed ∼ −5.3 ± 3.3 % dec−1). The simulated ozone hole has cooled the lower stratosphere during austral spring in the last few decades (−2.2 K dec−1). This cooling results in Southern Hemisphere summertime tropospheric circulation changes captured by an increase in the Southern Annular Mode (SAM) index (1.3 hPa dec−1). In the future, the interplay between the ozone hole recovery and greenhouse gases (GHGs) concentrations may result in the SAM index returning to pre-ozone hole levels or even with a more positive phase from around the second half of the century (−0.4 and 0.3 hPa dec−1 for the RCP2.6 and RCP8.5, respectively). By 2100, stratospheric ozone sensitivity to GHG concentrations is greatest in the Arctic and Northern Hemisphere midlatitudes (37.7 and 16.1 DU difference between the RCP2.6 and RCP8.5, respectively), and smallest over the tropics and Antarctica continent (2.5 and 8.1 DU respectively). Future TCO changes in the tropics are mainly determined by the upper stratospheric ozone sensitivity to GHG concentrations, due to a large compensation between tropospheric and lower stratospheric column ozone changes in the two RCP scenarios. These results demonstrate how changes in stratospheric ozone are tightly linked to climate and show the benefit of including the processes interactively in climate models.

Impact of climate and land cover changes on tropospheric ozone air quality and public health in East Asia between 1980 and 2010

Abstract. Understanding how historical climate and land cover changes have affected tropospheric ozone in East Asia would help constrain the large uncertainties associated with future East Asian air quality projections. We perform a series of simulations using a global chemical transport model driven by assimilated meteorological data and a suite of land cover and land use data to examine the public health effects associated with changes in climate, land cover, land use, and anthropogenic emissions between the 5-year periods 1981–1985 and 2007–2011 in East Asia. We find that between these two periods land cover change alone could lead to a decrease in summertime surface ozone by up to 4 ppbv in East Asia and ~ 2000 fewer ozone-related premature deaths per year, driven mostly by enhanced dry deposition resulting from climate- and CO2-induced increase in vegetation density, which more than offsets the effect of reduced isoprene emission arising from cropland expansion. Climate change alone could lead to an increase in summertime ozone by 2–10 ppbv in most regions of East Asia and ~ 6000 more premature deaths annually, mostly attributable to warming. The combined impacts (−2 to +12 ppbv) show that while the effect of climate change is more pronounced, land cover change could offset part of the climate effect and lead to a previously unknown public health benefit. While the changes in anthropogenic emissions remain the largest contributor to deteriorating ozone air quality in East Asia over the past 30 years, we show that climate change and land cover changes could lead to a substantial modification of ozone levels, and thus should come into consideration when formulating future air quality management strategies. We also show that the sensitivity of surface ozone to land cover change is more dependent on dry deposition than on isoprene emission in most of East Asia, leading to ozone responses that are quite distinct from that in North America, where most ozone-vegetation sensitivity studies to date have been conducted.

Spatial and temporal variability of ozone sensitivity over China observed from the Ozone Monitoring Instrument

AbstractSurface ozone (O3) air pollution in populated regions has been attributed to emissions of nitrogen oxides (NO + NO2 = NOx) and reactive volatile organic compounds (VOCs). These constituents react with hydrogen oxide radicals (OH + HO2 = HOx) in the presence of sunlight and heat to produce O3. The question of whether to reduce NOx emissions, VOC emissions, or both is complicated by spatially and temporally heterogeneous ozone‐NOx‐VOC sensitivity. This study characterizes spatial and temporal variations in O3 sensitivity by analyzing the ratio of formaldehyde (HCHO, a marker of VOCs) to nitrogen dioxide (NO2), a metric known as the formaldehyde nitrogen ratio (FNR). Level 3 gridded retrievals from the Ozone Monitoring Instrument (OMI) aboard the NASA Aura satellite were used to calculate FNR, with our analysis focusing on China. Based on previous studies, we take FNR &lt; 1.0 as indicating VOC‐limited regimes, FNR &gt; 2.0 as indicating NOx‐limited regime, and FNR between 1.0 and 2.0 as indicating transitional regime (where either NOx reductions or VOC reductions would be expected to reduce O3). We find that the transitional regime is widespread over the North China Plain (NCP), the Yangtze River Delta, and the Pearl River Delta during the ozone season (defined as having near‐surface air temperatures &gt;20°C at the early afternoon OMI overpass time). Outside of these regions, the NOx‐limited regime is dominant. Because HCHO and NO2 have distinct seasonal patterns, FNR also has a pronounced seasonality, consistent with the seasonal cycle of surface O3. Examining trends from 2005 to 2013 indicates rapid growth in NO2, especially over less‐developed areas where O3 photochemistry is NOx limited. Over this time period, HCHO decreased in southern China, where VOC emissions are dominated by biogenic sources, but increased slightly over the NCP, where VOC emissions are dominated by anthropogenic sources. A linear regression approach suggests that most of China (70% of grid cells) will be characterized by a transitional regime during the O3 season by 2030. However, in megacities such as Guangzhou, Shanghai, and Beijing, NO2 has decreased such that the chemical regime has shifted from VOC limited in 2005 to transitional in 2013.

Inter-annual variations in satellite observations of nitrogen dioxide and formaldehyde over India

Nitrogen dioxide (NO2) and formaldehyde (HCHO) are important reactive trace gases due to their role regulating the oxidation capacity of the troposphere through ozone (O3) production and because they are pollutants causing health hazards. Over the last two decades, satellite and ground observations have reported a clear increase in the tropospheric HCHO and NO2 over India, with larger increases over the urban regions due to an increase in anthropogenic emissions. We compare observations from four different satellites for a period covering 1995–2013 over India. Some differences are observed in the calculated growth trends between the different satellites for both HCHO and NO2, although an increasing trend is seen by all the satellites. The mean growth rate calculated for the HCHO vertical column density (VCD) is 1.51 ± 0.44% yr−1, while tropospheric NO2 VCDs are calculated to calculated to grow faster at 2.20 ± 0.73% yr−1, indicating that NOx emissions are increasing faster than the emissions for volatile organic compounds (VOCs). The faster increase in NOx as compared to VOCs is however expected considering the large fraction of natural VOCs. The ratio of HCHO/NO2, which is an indicator of the relative sensitivity of surface ozone to emissions of nitrogen oxides (NOx = NO + NO2) and VOCs, is also studied. The satellite-derived ratios indicate that over most of India, O3 production is limited by NOx, although in urban regions and over the Indo-Gangetic Plain, the O3 production is VOC limited, especially during the winter season. We also compare the modeled HCHO and NO2 VCDs from the ECHAM5-HAMMOZ model using the RETRO emission inventory and the results indicate that the VOC emissions in the model are overestimated leading to larger modeled HCHO VCDs.

Sensitivity of tropical stratospheric ozone to rotational UV variations estimated from UARS and Aura MLS observations during the declining phases of solar cycles 22 and 23

The correlation between tropical stratospheric ozone and UV radiation on solar rotational time scales is investigated using daily satellite ozone observations and reconstructed solar spectra. We consider two 3-year periods falling within the descending phases of two 11-year solar cycles 22 (1991–1994) and 23 (2004–2007). The UV rotational cycle is highly irregular and even disappears for half a year during cycle 23. For the 1991–1994 period, ozone and 205nm UV flux are found to be correlated between about 10 and 1hPa with a maximum of 0.29 at ~5hPa; ozone sensitivity (percentage change in ozone for 1% change in UV) peaks at ~0.4. Correlation during cycle 23 is weaker with a peak ozone sensitivity of 0.2. The correlation is found to vary widely, not only with altitude, but also from one year to the next with a rotational signal in ozone appearing almost intermittent. Unexpectedly, the correlation is not found to bear any relation with the solar rotational forcing. For instance, solar rotational fluctuations are by far the strongest during 1991–1992 whereas the correlation peaks at the end of 1993, a rotationally quiescent period. When calculated over sliding intervals of 1-year, the sensitivity is found to vary very strongly within both 3-year periods; it is almost negligible over the entire vertical profile during some 1-year intervals or reaches close to 1 around 2–5mb for other intervals. Other sources of variability, presumably of dynamical origin, operate on the rotational spectral range and determine to a large extent the estimated solar rotational signal. Even considering 3 years of observations (corresponding to about 40 solar cycles), the extraction of the rotational solar signal does not appear to be robust during declining phases of 11-year solar cycles. As observational studies cover at best three 11-year solar cycles, it must be challenging to produce a reliable estimation of the 11-year solar cycle signal in stratospheric ozone, especially in the presence of decadal climate variability.

Positive but variable sensitivity of August surface ozone to large-scale warming in the southeast United States

The sensitivity of surface ozone, a major pollutant, to climate warming is shown to be positive but variable over the southeast United States.

Varietal screening of ozone sensitivity in Mediterranean durum wheat (Triticum durum, Desf.)

This study investigated the ozone (O3) sensitivity of five cultivars of durum wheat (Triticum durum) grown in Open-Top Chambers (OTC) during the 2013 growing season. Two levels of ozone were applied during daylight hours: +50% and −50% of ambient ozone concentration respectively in O3-enriched OTC and charcoal-filtered OTC. Results suggest that the significant differences observed in agronomic parameters, were more cultivar-dependent rather than ozone-dependent. Two cultivars showed a significant reduction of aboveground biomass due to ozone (−19.7% and −25%), however only one of them showed also a significant reduction in grain yield (−16%). Stomatal conductance was significantly reduced by ozone fumigation up to −33% in the afternoon measuring cycle. No significant effects on chlorophyll fluorescence were found, nor correlation was observed between ozone-like symptoms severity (leaf chlorotic/necrotic spots) and yield reduction, suggesting that these parameters cannot be indicative of ozone sensitivity/tolerance. These results may be useful for the selection of durum wheat genotypes more adapted for the cultivation in geographical areas where tropospheric ozone is particularly high, but also for the future definition of consistent dose–response relationships to be used in the ozone risk assessment evaluation for the Mediterranean countries.

Ensemble simulations of the role of the stratosphere in the attribution of northern extratropical tropospheric ozone variability

Abstract. Despite the need to understand the impact of changes in emissions and climate on tropospheric ozone, the attribution of tropospheric interannual ozone variability to specific processes has proven difficult. Here, we analyze the stratospheric contribution to tropospheric ozone variability and trends from 1953 to 2005 in the Northern Hemisphere (NH) mid-latitudes using four ensemble simulations of the free running (FR) Whole Atmosphere Community Climate Model (WACCM). The simulations are externally forced with observed time-varying (1) sea-surface temperatures (SSTs), (2) greenhouse gases (GHGs), (3) ozone depleting substances (ODS), (4) quasi-biennial oscillation (QBO), (5) solar variability (SV) and (6) stratospheric sulfate surface area density (SAD). A detailed representation of stratospheric chemistry is simulated, including the ozone loss due to volcanic eruptions and polar stratospheric clouds. In the troposphere, ozone production is represented by CH4–NOx smog chemistry, where surface chemical emissions remain interannually constant. Despite the simplicity of its tropospheric chemistry, at many NH measurement locations, the interannual ozone variability in the FR WACCM simulations is significantly correlated with the measured interannual variability. This suggests the importance of the external forcing applied in these simulations in driving interannual ozone variability. The variability and trend in the simulated 1953–2005 tropospheric ozone from 30 to 90° N at background surface measurement sites, 500 hPa measurement sites and in the area average are largely explained on interannual timescales by changes in the 30–90° N area averaged flux of ozone across the 100 hPa surface and changes in tropospheric methane concentrations. The average sensitivity of tropospheric ozone to methane (percent change in ozone to a percent change in methane) from 30 to 90° N is 0.17 at 500 hPa and 0.21 at the surface; the average sensitivity of tropospheric ozone to the 100 hPa ozone flux (percent change in ozone to a percent change in the ozone flux) from 30 to 90° N is 0.19 at 500 hPa and 0.11 at the surface. The 30–90° N simulated downward residual velocity at 100 hPa increased by 15% between 1953 and 2005. However, the impact of this on the 30–90° N 100 hPa ozone flux is modulated by the long-term changes in stratospheric ozone. The ozone flux decreases from 1965 to 1990 due to stratospheric ozone depletion, but increases again by approximately 7% from 1990 to 2005. The first empirical orthogonal function of interannual ozone variability explains from 40% (at the surface) to over 80% (at 150 hPa) of the simulated ozone interannual variability from 30 to 90° N. This identified mode of ozone variability shows strong stratosphere–troposphere coupling, demonstrating the importance of the stratosphere in an attribution of tropospheric ozone variability. The simulations, with no change in emissions, capture almost 50% of the measured ozone change during the 1990s at a variety of locations. This suggests that a large portion of the measured change is not due to changes in emissions, but can be traced to changes in large-scale modes of ozone variability. This emphasizes the difficulty in the attribution of ozone changes, and the importance of natural variability in understanding the trends and variability of ozone. We find little relation between the El Niño–Southern Oscillation (ENSO) index and large-scale tropospheric ozone variability over the long-term record.

An assessment of enhanced biogenic emissions influence on ozone formation in central Alberta, Canada

Emissions from biogenic sources are the primary source of isoprene and monoterpene that contribute to the formation of ozone and secondary organic aerosol (SOA). In this study, we used a regional air quality model to examine the sensitivity of simulated ozone to biogenic emission estimates. We created a new regional database of plant functional type (PFT) and land use and land cover (LULC) based on two satellite data products, the Alberta Vegetation Inventory (AVI) and Earth Observation for Sustainable Development of forests (EOSD).The Model for Emissions for Gases and Aerosols from Nature (MEGAN) biogenic emissions model was used with the new PFT data as well as the default Moderate Resolution Imaging Spectroradiometer (MODIS) PFT to generate biogenic emissions in Alberta. The comparison revealed that the new LULC increased isoprene (ISOP) emissions by 30–40 %, decreased monoterpene emissions by 7–8 %, and increased NO emissions by 65–90 % associated with the new regional plant functional type fractional (PFTf) database. This study further investigated the impact of using Alberta-specific biogenic emission on ambient ozone concentration through the Community Multi-scale Air Quality (CMAQ) modeling system against the default MEGAN emissions. In addition, the result from using the new LULC on the predicted fourth highest daily maximum 8-h ozone concentration were examined, which showed a substantial reduction (6 ppb) in ozone in the urbanized capital region area when compared to the default the LULC with less ozone changes in the rural areas. This is likely due to ozone formation in the urban areas being more sensitive to changes in volatile organic compound (VOC) emissions than the rural areas. As CMAQ tended to overestimate the observed ozone peaks in the urban areas, the use of the enhanced LULC resulted in improved model performance compared to the default LULC database. This study results will be primarily used to understand impact of biogenic emission into air on ambient air quality and secondary to provide strategic advice on air quality management plan and initiatives regarding air issues (e.g., ozone) in the region. Results also can be implied to the relationship between climate change-induced increases in biogenic VOC emissions and ozone concentrations.

Effect ofGlomus aggregatumon photosynthetic function of snap bean in response to elevated ozone

SUMMARYSnap bean genotypes (Phaseolus vulgarisL.) with different ozone (O3) sensitivities (line S156: O3-sensitive; line R123: O3-tolerant) were grown for 70 days with or without inoculation of arbuscular mycorrhizal (AM) fungi under ambient (CAMB = 20 nanolitres (nl)/l and elevated (CMID = '50 nl/l andCHIG = 80 nl/l) O3. Sequential determinations (leaf injury, pigment concentration, chlorophyll fluorescence, photosynthesis, etc) were carried out during plant growth to evaluate mycorrhizal influence on the photosynthetic function of the two genotypes under elevated O3. Inoculation with AM fungi alleviated leaf injury in both genotypes and delayed time of injury manifestation (TIM) in the R123 line at the blooming stage (growth stage (GS): 61-65 (Zadoks scale, Zadokset al. 1974), 30–35 days after the onset of O3fumigation), but mycorrhizal effect was slight at the initial growth stage (GS 11–13, 0–5 days after onset of O3fumigation). Relative to the non-mycorrhizal plant, AM fungi inoculation increased the concentrations of chlorophyll (Chl) a, Chl b and carotenoids in S156 plants, regardless of O3levels, while in R123 plants a similar effect was observed only in theCAMBtreatment. At the blooming (GS 61–65) and the pod filling (GS 71–77, 45–50 days after starting O3fumigation) stages, photosynthetic rate, stomatal conductance and transpiration rate for the two genotypes decreased with elevated O3in all treatments, although the effect was reduced inCAMBandCMIDtreatments in AM-inoculated plants; however, the mycorrhizal effect was slight in theCHIGtreatment. Intercellular carbon dioxide concentration increased with elevated O3regardless of AM fungi inoculation, but it was lower in the mycorrhizal plants than in the non-mycorrhizal plants, in most cases. Furthermore, AM fungi inoculation significantly increased the maximum quantum yield of photosystem II (PS II) photochemistry (Fv/Fm) and electron transport rate in both genotypes in theCHIGtreatment. The present study indicated that in some cases, AM fungi inoculation can enhance plant tolerance to elevated O3through improving plant photosynthetic function, but the effect was reduced by serious O3stress.

Towards the retrieval of tropospheric ozone with the Ozone Monitoring Instrument (OMI)

Abstract. We have assessed the sensitivity of the operational Ozone Monitoring Instrument (OMI) ozone profile retrieval algorithm to a number of a priori and radiative transfer assumptions. We studied the effect of stray light correction, surface albedo assumptions and a priori ozone profiles on the retrieved ozone profile. Then, we studied how to modify the algorithm to improve the retrieval of tropospheric ozone. We found that stray light corrections have a significant effect on the retrieved ozone profile but mainly at high altitudes. Surface albedo assumptions, on the other hand, have the largest impact at the lowest layers. Choice of an ozone profile climatology which is used as a priori information has small effects on the retrievals at all altitudes. However, the usage of climatological a priori covariance matrix has a significant effect. Based on these sensitivity tests, we made several modifications to the retrieval algorithm: the a priori ozone climatology was replaced with a new tropopause-dependent climatology, the a priori covariance matrix was calculated from the climatological ozone variability values, and the surface albedo was assumed to be linearly dependent on wavelength in the 311.5–330 nm channel. As expected, we found that the a priori covariance matrix basically defines the vertical distribution of degrees of freedom for a retrieval. Moreover, our case study over Europe showed that the modified version produced over 10% smaller ozone abundances in the troposphere which reduced the systematic overestimation of ozone in the retrieval algorithm and improved correspondence with Infrared Atmospheric Sounding Instrument (IASI) retrievals. The comparison with ozonesonde measurements over North America showed that the operational retrieval performed better in the upper troposphere/lower stratosphere (UTLS), whereas the modified version improved the retrievals in the lower troposphere and upper stratosphere. These comparisons showed that the systematic biases in the OMI ozone profile retrievals are not caused by the a priori information but by some still unidentified problem in the radiative transfer modelling. Instead, the a priori information pushes the systematically wrong ozone profiles towards the true values. The smaller weight of the a priori information in the modified retrieval leads to better visibility of tropospheric ozone structures, because it has a smaller tendency to damp the variability of the retrievals in the troposphere. In summary, the modified retrieval unmasks systematic problems in the radiative transfer/instrument model and is more sensitive to tropospheric ozone variation; that is, it is able to capture the tropospheric ozone morphology better.

Tropospheric Ozone Response on Climate Change in Malaysia

Ozone at the tropospheric level is considered as pollutants and harms the human health. As the chemistry of tropospheric ozone is sensitive to solar radiation and temperature, one may expect significant changes to the tropospheric ozone variability due to climate change. In this study, the authors have explored the impact of regional climate change to the tropospheric ozone in a number of urban, rural and remote areas in Malaysia. This paper aims to develop a climate change scenario for A2 emissions over Malaysia using RCM PRECIS model and used the climate output as input to CiTTyCAT, a tropospheric chemistry model. At the end of this century, the surface temperature and precipitation were found to increase both during wet season (winter monsoon) and dry season (summer monsoon). In response to climate change relative to the observed ozone concentrations in year 2008, tropospheric ozone concentrations have been found to increase in urban areas (Kuala Lumpur, Sg. Petani and Kota Kinabalu), while in rural and remote areas (Kapit and Danum Valley) concentrations have been found to decrease. These projections were observed in both seasons. This study has suggested that tropospheric ozone sensitivity to climate change shows a degree of response variability.

A cautionary note on the use of EESC-based regression analysis for ozone trend studies

Equivalent effective stratospheric chlorine (EESC) construct of ozone regression models attributes ozone changes to EESC changes using a single value of the sensitivity of ozone to EESC over the whole period. Using space-based total column ozone (TCO) measurements, and a synthetic TCO time series constructed such that EESC does not fall below its late 1990s maximum, we demonstrate that the EESC-based estimates of ozone changes in the polar regions (70–90°) after 2000 may, falsely, suggest an EESC-driven increase in ozone over this period. An EESC-based regression of our synthetic “failed Montreal Protocol with constant EESC” time series suggests a positive TCO trend that is statistically significantly different from zero over 2001–2012 when, in fact, no recovery has taken place. Our analysis demonstrates that caution needs to be exercised when using explanatory variables, with a single fit coefficient, fitted to the entire data record, to interpret changes in only part of the record.