Ozone Sensitivity Research Articles

Applying model simulation and photochemical indicators to evaluate ozone sensitivity in southern Taiwan

Abstract Ozone sensitivity was investigated using CAMx simulations and photochemical indicator ratios at three sites (Pingtung City, Chao-Chou Town, and Kenting Town) in Pingtung County in southern Taiwan during 2003 and 2004. The CAMx simulations compared fairly well with the hourly concentrations of ozone. Simulation results also showed that Pingtung City was mainly a volatile organic compounds (VOC)-sensitive regime, while Chao-Chou Town was either a VOC-sensitive or a NO x-sensitive regime, depending on the seasons. Measurements of three photochemical indicators (H 2O 2, HNO 3, and NOy) were conducted, and simulated three transition ranges of H 2O 2/HNO 3 (0.5-0.8), O 3/HNO 3 (10.3-16.2) and O 3/NOy (5.7-10.8) were adopted to assess the ozone sensitive regime at the three sites. The results indicated that the three transition ranges yield consistent results with CAMx simulations at most times at Pingtung City. However, both VOC-sensitive and NO x-sensitive regimes were important at the rural site Chao-Chou Town. Kenting Town, a touring site at the southern end of Taiwan, was predominated by a NO x-sensitive regime in four seasons.

Influence of vertical mixing uncertainties on ozone simulation in CMAQ

Abstract This study explores the extent to which uncertainties in the formulation of vertical diffusion schemes and in associated model parameters affect predictions of ozone levels and their responsiveness to emission controls in the Community Multiscale Air Quality (CMAQ) model. CMAQ is applied with two vertical diffusion schemes, eddy viscosity (K-theory) and the asymmetric convective model, version 2 (ACM2), to simulate ozone during the Second Texas Air Quality Study (TexAQS II) in 2006, enabling comparisons with a rich array of both ground-level and aloft ozone measurements. The high-order decoupled direct method (HDDM) was implemented into ACM2, and was extended to quantify the influence of parametric uncertainties in dry deposition velocity and eddy diffusivity in both vertical diffusion schemes in CMAQ. Choices of vertical diffusion scheme and parameter values did not strongly influence model performance in simulating ozone concentrations or predicted ozone-precursor responsiveness over much of the domain. However, in some high ozone locations, results show the 8-h ozone sensitivity to NOx may vary by approximately 20% due to the choice of vertical mixing scheme and by 5–10% due to the uncertainty in dry deposition velocities.

In Situ Measurements of Hydrogen Peroxide, Nitric Acid and Reactive Nitrogen to Assess the Ozone Sensitivity in Pingtung County, Taiwan

This study was aimed to investigate the concentration of hydrogen peroxide (H2O2), nitric acid (HNO3) and reactive nitrogen (NOy) at three sites in Southern Taiwan during 2003–2004. The mean H2O2 concentrations were 1.0–2.7 ppbv, 1.6–2.8 ppbv and 1.0–2.6 ppbv at Pingtung, Chao-Chou and Kenting, respectively. Meanwhile, the mean HNO3 concentrations were 2.7–5.5 ppbv at Pingtung, 1.9–4.6 ppbv at Chao-Chou and 1.2–3.0 ppbv at Kenting. The NOy mean concentrations were 61.0–85.0 ppbv, 16.0–75.0 ppbv and 4.2–12.0 ppbv at Pingtung, Chao-Chou and Kenting, respectively. The hourly data of H2O2, HNO3, NOy and O3 were then used to determine the ratio of H2O2 to HNO3, O3 to HNO3, O3 to NOy and the extent of reaction (E) in Smog Production Model (SPM) to evaluate the NOx and VOC sensitivity of ozone formation in Southern Taiwan. The results show that Pingtung city was primarily VOC-sensitive regime in four seasons. At Chao-Chou, the percentages of VOC-sensitive regime exceed those in NOx-sensitive regime in H2O2/HNO3 and O3/NOy in four seasons; but O3/HNO3 indicates NOx-sensitive regime in autumn, winter and spring. Kenting was mainly dominated by NOx-sensitive by use of three indicators in four seasons. The SPM results are consistent with those determined by the photochemical indicator ratios although the percentages of dominance may vary among these analyses.

Attribution of stratospheric ozone trends to chemistry and transport: a modelling study

Abstract. The decrease of the concentration of ozone depleting substances (ODSs) in the stratosphere over the past decade raises the question to what extent observed changes in stratospheric ozone over this period are consistent with known changes in the chemical composition and possible changes in atmospheric transport. Here we present a series of ozone sensitivity calculations with a stratospheric chemistry transport model (CTM) driven by meteorological reanalyses from the European Centre for Medium-Range Weather Forecasts, covering the period 1978–2009. In order to account for the reversal in ODS trends, ozone trends are analysed as piecewise linear trends over two periods, 1979–1999 and 2000–2009. Modelled column ozone (TO3) inter-annual variability and trends are in excellent agreement with observations from the Total Ozone Mapping Spectrometer (TOMS) and Solar Backscatter UV (SBUV/2) as well as the Global Ozone Monitoring Experiment (GOME/GOME2) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instruments. In the period 1979–1999, modelled TO3 trends at mid-latitudes are dominated by changes in in situ gas-phase chemistry, which contribute to about 50% or more of the TO3 trend in most seasons. Changes in meteorology contribute around 35% to mid-latitude TO3 trends, with strong differences between different seasons. In springtime, export of ozone depleted air from polar latitudes contributes about 35–50% to the modelled TO3 trend at SH mid-latitudes and about 15–30% at NH mid-latitudes. Over the period 2000–2009 positive linear trends in modelled TO3, which agree well with observed TO3 trends, are dominated by changes in meteorology, as expected for the yet small decrease in stratospheric halogen loading over this period. While the TO3 trends themselves are not statistically significant over the period 2000–2009, changes in linear trends between 1978–1999 and 2000–2009 are significant at mid- and high latitudes of both hemisphere during most seasons. However, changes in meteorology have contributed substantially to these TO3 trend changes.

Decadal regional air quality simulations over Europe in present climate: near surface ozone sensitivity to external meteorological forcing

Abstract. Regional climate-air quality decadal simulations over Europe were carried out with the RegCM3/CAMx modeling system for the time slice 1991–2000, in order to study the impact of different meteorological forcing on surface ozone. The RegCM3 regional climate model was firstly constrained by the ERA40 reanalysis dataset which is considered as an experiment with perfect meteorological boundary conditions and then it was constrained by the global circulation model ECHAM5. A number of meteorological parameters were examined including the 500 mb geopotential height, solar radiation, temperature, cloud liquid water path, planetary boundary layer height and surface wind. The different RegCM meteorological forcing resulted in changes of near surface ozone over Europe ranging between ± 4 ppb for winter and summer. The area showing the greatest sensitivity in O3 during winter is central and southern Europe while in summer central north continental Europe. The different meteorological forcing impacts on the atmospheric circulation, which in turn affects cloudiness and solar radiation, temperature, wind patterns and the meteorology depended biogenic emissions. For comparison reasons, the impact of chemical boundary conditions on surface ozone was additionally examined with a series of sensitivity studies, indicating that surface ozone changes are comparable to those caused by the different meteorological forcing. These findings suggest that, when it comes to regional climate-air quality simulations, the selection of external meteorological forcing can be as important as the selection of adequate chemical lateral boundary conditions.

회화나무 8 가계간 오존 내성 차이에 대한 생리적 지표의 적합성

본 연구는 오존에 노출된 회화나무 8 가계에서 측정한 생리적 지표들을 대상으로, 오존에 대한 민감성을 평가하고, 이 결과들을 종합하여 가계 간 차이를 구명하고자 실시하였다. 회화나무(Sophora japonica L.) 8가계를 대상으로 오존 처리 후, 광합성 특성, 엽록소 함량, 항산화효소 활성 및 MDA 함량을 측정하였고, 각 측정 지표들의 표준화 지수를 이용하여 내성 순위를 결정하였다. 탄소고정효율은 6번 가계를 제외한 모든 가계에서 오존 처리 후 뚜렷하게 감소하였으며, 탄소고정효율의 감소율은 -38%에서 -67% 범위를 보였다. 또한 순양자수율은 7번 가계를 제외한 모든 가계에서 오존 처리 후 뚜렷한 감소를 보였으며, 감소율은 -27%에서 -61%를 나타냈다. 엽록소 a를 비롯한 광색소 함량의 가계 간 차이는 컸으나, 오존 처리 효과는 나타나지 않았다. 오존 처리 후, SOD 활성의 증가율은 7%에서 64%로, 가계 간 차이가 뚜렷하였다. APX 활성은 모든 가계에서 오존 처리 후 증가하였으며, 7번 가계가 가장 큰 활성 증가율(218%)을 보였다. 표준화 지수를 기준으로 할 때, 6번 가계의 내성 수준이 가장 낮았으며, 7번 가계의 내성 수준이 가장 높았다. 6번 가계는 오존 처리 후 탄소고정효율을 비롯한 광합성 특성의 감소율과 광색소 함량의 감소율이 높게 나타난 반면, 내성을 나타내는 항산화효소의 활성 증가가 매우 적었다. 반대로 내성 수준이 높은 7번 가계는 오존 처리 후 광합성 특성의 감소율이 다른 가계에 비해 적었으며, 광색소 함량은 오히려 오존처리 후 증가하였고, 항산화효소의 증가율도 다른 가계에 비해 높게 나타났다. This study was conducted to investigate ozone sensitivity of physiological indicators and the difference in ozone tolerance of 8 families of Sophora japonica seedlings on the basis of the standardized physiological indicators. After ozone treatment, photosynthetic parameters, photosynthetic pigments and malondialdehyde (MDA) content, and antioxidative enzyme activities were analyzed from the leaves of S. japonica seedlings. Ozone tolerance indices among 8 families were calculated with the standardized physiological parameters. In addition, the reduction of carboxylation efficiency and apparent quantum yield were observed in the leaves of seven families, except for family No. 6 and 7, respectively. The apparent quantum yield varied from -27% to -61% of the control seedlings. Photosynthetic pigment content differed significantly among 8 families, but was not affected significantly by ozone treatment. Superoxide dismutase (SOD) activity increased from 7% to 64% after ozone exposure, and significant difference existed among 8 families. Ascorbate-peroxidase (APX) activity of 8 families increased by ozone treatment, and the activity of family No. 7 showed the highest increase (218%) in comparison to their respective control plants. On the basis of the standardized indices, family No. 6 showed the lowest tolerance by indicating higher reduction of both photosynthetic parameters and pigment content and lower increase of antioxidative enzyme activities. On the contrary, family No. 7 showed the highest tolerance as indicated by lower reduction of photosynthetic parameters, higher amounts of photosynthetic pigments, and higher enzyme activity.

Sensitivity of polar ozone to sea surface temperatures and halogen amounts

Coupled chemistry‐climate model simulations are presented for the period 1951–2099 and 1951–2007. The model includes a tested parameterization for the production of active halogens from the source molecules. In run 1 the observed levels of chlorine and bromine are specified, as well as the sea surface temperatures (SSTs) from a coupled ocean‐atmosphere model. Run 2 is identical to run 1 but observed SSTs are specified instead of model SSTs. In run 3 the bromine amount is reduced by 25% but otherwise the simulation is identical to run 2. The results show that the ozone hole is sensitive to SSTs and bromine amounts. For the period 1990–2007, when the ozone hole was fully developed, the area of the ozone hole was simulated to be largest in run 1 (11% smaller than observed), compared with underpredictions of 17% and 27% for runs 2 and 3, respectively. The effect of SSTs (difference between runs 1 and 2) is shown to arise from changes in the strength of the Brewer‐Dobson circulation, which is weaker for the simulation with model SSTs. The sensitivity of the model results to bromine (difference between runs 2 and 3) indicates the need to include realistic bromine amounts as well as chlorine and may explain, in part, the substantial underpredictions of the ozone hole area in previous simulations. The results also suggest that a small residual ozone hole may still be present after 2070 and that the ozone hole may not disappear entirely this century.

Apoplastic ascorbate contributes to the differential ozone sensitivity in two varieties of winter wheat under fully open-air field conditions

We studied leaf apoplastic ascorbates in relation to ozone (O 3) sensitivity in two winter wheat ( Triticum aestivum L.) varieties: Yangfumai 2 (Y2) and Yangmai 16 (Y16). The plants were exposed to elevated O 3 concentration 27% higher than the ambient O 3 concentration in a fully open-air field from tillering stage until final maturity. The less sensitive variety Y16 had higher concentration of reduced ascorbate in the apoplast and leaf tissue by 33.5% and 12.0%, respectively, than those in the more sensitive variety Y2, whereas no varietal difference was detected in the decline of reduced ascorbate concentration in response to elevated O 3. No effects of O 3 or variety were detected in either oxidized ascorbate or the redox state of ascorbate in the apoplast and leaf tissue. The lower ascorbate concentrations in both apoplast and leaf tissue should have contributed to the higher O 3 sensitivity in variety Y2.

Contrasting ozone sensitivity in related evergreen and deciduous shrubs

Plant responses to enhanced ozone levels have been studied in two pairs of evergreen-deciduous species ( Pistacia terebinthus vs. P. lentiscus; Viburnum lantana vs. V. tinus) in Open Top Chambers. Ozone induced widespread visible injury, significantly reduced CO 2 assimilation and stomatal conductance ( g s ), impaired Rubisco efficiency and regeneration capacity ( V c,max, J max) and altered fluorescence parameters only in the deciduous species. Differences in stomatal conductance could not explain the observed differences in sensitivity. In control plants, deciduous species showed higher superoxide dismutase (SOD) activity than their evergreen counterparts, suggesting metabolic differences that could make them more prone to redox imbalances. Ozone induced increases in SOD and/or peroxidase activities in all the species, but only evergreens were able to cope with the oxidative stress. The relevancy of these results for the effective ozone flux approach and for the current ozone Critical Levels is also discussed.

Sensitivity of 21st century stratospheric ozone to greenhouse gas scenarios

To understand how greenhouse gas (GHG) emissions may affect future stratospheric ozone, 21st century projections from four chemistry‐climate models are examined for their dependence on six different GHG scenarios. Compared to higher GHG emissions, lower emissions result in smaller increases in tropical upwelling with resultant smaller reductions in ozone in the tropical lower stratosphere and less severe stratospheric cooling with resultant smaller increases in upper stratospheric ozone globally. Increases in reactive nitrogen and hydrogen that lead to additional chemical ozone destruction mainly play a role in scenarios with higher GHG emissions. Differences among the six GHG scenarios are found to be largest over northern midlatitudes (∼20 DU by 2100) and in the Arctic (∼40 DU by 2100) with divergence mainly in the second half of the 21st century. The uncertainty in the return of stratospheric column ozone to 1980 values arising from different GHG scenarios is comparable to or less than the uncertainty that arises from model differences in the larger set of 17 CCMVal‐2 SRES A1B simulations. The results suggest that effects of GHG emissions on future stratospheric ozone should be considered in climate change mitigation policy and ozone projections should be assessed under more than a single GHG scenario.

Simulation of the impact of thunderstorm activity on atmospheric gas composition

A chemistry-climate model of the lower and middle atmosphere has been used to estimate the sensitivity of the atmospheric gas composition to the rate of thunderstorm production of nitrogen oxides at upper tropospheric and lower stratospheric altitudes. The impact that nitrogen oxides produced by lightning have on the atmospheric gas composition is treated as a subgrid-scale process and included in the model parametrically. The natural uncertainty in the global production rate of nitrogen oxides in lightning flashes was specified within limits from 2 to 20 Tg N/year. Results of the model experiments have shown that, due to the variability of thunderstorm-produced nitrogen oxides, their concentration in the upper troposphere and lower stratosphere can vary by a factor of 2 or 3, which, given the influence of nitrogen oxides on ozone and other gases, creates the potential for a strong perturbation of the atmospheric gas composition and thermal regime. Model calculations have shown the strong sensitivity of ozone and the OH hydroxyl to the amount of lightning nitrogen oxides at different atmospheric altitudes. These calculations demonstrate the importance of nitrogen oxides of thunderstorm origin for the balance of atmospheric odd ozone and gases linked to it, such as ozone and hydroxyl radicals. Our results demonstrate that one important task is to raise the accuracy of estimates of the rate of nitrogen oxide production by lightning discharges and to use physical parametrizations that take into account the local lightning effects and feedbacks arising in this case rather than climatological data in models of the gas composition and general circulation of the atmosphere.

NMOC, ozone, and organic aerosol in the southeastern United States, 1999–2007: 2. Ozone trends and sensitivity to NMOC emissions in Atlanta, Georgia

Non-methane organic carbon (NMOC) measurements made in Atlanta, Georgia from 1999–2007 are used with nitrogen oxide (NO x or NO y) and ozone (O 3) data to investigate relationships between O 3 precursors and peak 8-hour O 3 concentrations in the city. Data from a WNW-to-ENE transect of sites illustrate that the mean urban peak 8-hour O 3 excess constitutes about 20% of the peak 8-hour O 3 measured at the area-wide maximum O 3 site when air-mass movement is from the northwest quadrant; local influence is potentially greater on days with more stagnation or recirculation. The peak 8-hour O 3 concentrations in Atlanta increase as (1) surface temperature (T), ambient NMOC and NO y concentrations, and previous-day peak O 3 concentrations increase, and as (2) relative humidity, surface wind speeds, and ratios of NMOC-to-NO y decrease. An observation-based statistical model is introduced to relate area-wide peak 8-hour O 3 concentrations to ambient NMOC and NO y concentrations, while accounting for the non-linear dependences of peak 8-hour O 3 concentrations on meteorological factors. On the majority of days when the area-wide peak 8-hour O 3 exceeds 75 ppbv, meteorologically-adjusted peak 8-hour O 3 concentrations increase as ambient NMOC concentrations increase (NMOC sensitive) and ambient NO y concentrations decrease. This result contrasts with regional conditions in which O 3 formation appears to be NO x-sensitive in character. The results offer observationally-based information of relevance to O 3 management strategies in the Atlanta area, potentially contributing to “weight-of-evidence” assessments.

Ozone predictabilities due to meteorological uncertainties in the Mexico City basin using ensemble forecasts

Abstract. The purpose of the present study is to investigate the sensitivity of ozone (O3) predictions in the Mexico City Metropolitan Area (MCMA) to meteorological initial uncertainties and planetary boundary layer (PBL) parameterization schemes using state-of-the-art meteorological and photochemical prediction models through ensemble forecasts. The simulated periods (3, 9, 15 and 29 March 2006) represent four typical meteorological episodes ("South-Venting", "O3-North", "O3-South" and "Convection-North", respectively) in the Mexico City basin during the MCMA-2006/MILAGRO campaign. Our results demonstrate that the uncertainties in meteorological initial conditions have significant impacts on O3 predictions, including peak time O3 concentrations ([O3]), horizontal and vertical O3 distributions, and temporal variations. The ensemble spread of the simulated peak [O3] averaged over the city's ambient monitoring sites can reach up to 10 ppb. The increasing uncertainties in meteorological fields during peak O3 period contribute to the largest unpredictability in O3 simulations, while the impacts of wind speeds and PBL height on [O3] are more straightforward and important. The magnitude of the ensemble spreads varies with different PBL schemes and meteorological episodes. The uncertainties in O3 predictions caused by PBL schemes mainly come from their ability to represent the mixing layer height; but overall, these uncertainties are smaller than those from the uncertainties in meteorological initial conditions.

Influence of nocturnal vertical stability on daytime chemistry: A one-dimensional model study

Nocturnal chemistry can play an important role in determining the initial morning conditions for daytime chemistry in urban areas. However, the impact on daytime O 3 levels is difficult to assess as the suppression of vertical trace gas transport leads to highly altitude dependent nocturnal chemistry, in particular with respect to the removal and conversion of nitrogen oxides (NO x) and volatile organic compounds (VOC). One-dimensional (1-D) chemical transport model calculations for different nighttime vertical stabilities and different ozone formation regimes (i.e. NO x- vs. VOC-sensitive) were performed assuming a 1000 m high daytime boundary layer and a growing nocturnal boundary layer reaching 200 m height at the end of the night. Exclusion of NO 3 chemistry from the model leads to daytime O 3 concentration changes from −4% to +16% for different O 3 sensitivities. In all cases strong nocturnal vertical concentration profiles of NO x, O 3, NO 3 and N 2O 5 and a dependence of these profiles on vertical stability were found at night. The nocturnal NO x loss averaged over the lowest 1000 m changes by 9–24% for different vertical stabilities and ozone sensitivities. The impact of nocturnal vertical stability leads to 7–12% difference in O 3 concentration in the morning and ∼0–2.5% in the afternoon.

Sensitivity of ozone to precursor emissions in urban Beijing with a Monte Carlo scheme

In order to understand the formation mechanisms of high surface ozone and identify the main contributor sources in Beijing, this study investigates the sensitivity of surface ozone to NO, NO 2 and nine types of NMVOC emissions during a photochemical smog episode. Monte Carlo sensitivity analysis scheme with fifty simulations is established based on the Nested Air Quality Prediction Model System (NAQPMS). At every simulation, each of the eleven precursor emissions is perturbed with a distinct set of perturbations. The sensitivities of ozone to emissions are identified by multiple linear regressions. The stability of sensitivity results is validated by two experiments with standard deviations of log-normal perturbations set as 30% and 50% respectively. The sensitivity results suggest that the current high surface ozone is strongly stimulated by NMVOC emissions. Among NMVOC emissions, formaldehyde, ethylene and olefins emissions present the greatest impacts on ozone. On the other hand, NOx emissions have a strong inhibitory effect on ozone formation, even after 50% NOx emission reduction. This indicates that the current ozone formation in Beijing is under NOx-saturated conditions. A transition of ozone formation is observed from NOx-saturated to NOx-limited sensitivity behavior with a 75% reduction of NOx emissions. This study gives the implication that abatement of the four NMVOC types mentioned above could be efficient on reducing the high levels of surface ozone in central urban Beijing, while inadequate abatement in NOx emissions probably induces reverse effects.

Influence of uncertain reaction rates on ozone sensitivity to emissions

Air quality models rely upon simplified photochemical mechanisms to efficiently represent the thousands of chemical species that interact to form air pollution. Uncertainties in the chemical reaction rate constants and photolysis frequencies that comprise those mechanisms can generate uncertainty in the estimation of pollutant concentrations and their responsiveness to emission controls. A high-order sensitivity analysis technique is applied to quantify the extent to which reaction rate uncertainties influence estimates of ozone concentrations and their sensitivities to precursor emissions during an air pollution episode in Houston, Texas. Several reactions were found to have much larger proportional effects on ozone’s sensitivities to emissions than on its concentrations. In particular, uncertainties in photolysis frequencies and in the rate of reaction between NO 2 and OH to form nitric acid can significantly influence the magnitude and sign of peak ozone sensitivity to nitrogen oxide (NO x) emissions. Ozone sensitivity to VOCs exhibits a much more muted response to uncertainties in the reaction rate constants and photolysis frequencies considered here. The results indicate the importance of accurate reaction rate constants to predicting the ozone impacts resulting from NO x emission controls.

Natural variation in ozone sensitivity among Arabidopsis thaliana accessions and its relation to stomatal conductance

Genetic variation between naturally occurring populations provides a unique source to unravel the complex mechanisms of stress tolerance. Here, we have analysed O(3) sensitivity of 93 natural Arabidopsis thaliana accessions together with five O(3)-sensitive mutants to acute O(3) exposure. The variation in O(3) sensitivity among the natural accessions was much higher than among the O(3)-sensitive mutants and corresponding wild types. A subset of nine accessions with major variation in their O(3) responses was studied in more detail. Among the traits assayed, stomatal conductance (g(st)) was an important factor determining O(3) sensitivity of the selected accessions. The most O(3)-sensitive accession, Cvi-0, had constitutively high g(st), leading to high initial O(3) uptake rate and dose received during the first 30 min of exposure. Analyzing O(3)-induced changes in stress hormone concentrations indicated that jasmonate (JA) concentration was also positively correlated with leaf damage. Quantitative trait loci (QTL) mapping in a Col-0 x Cvi-0 recombinant inbred line (RIL) population identified three QTLs for O(3) sensitivity, and one for high water loss of Cvi-0. The major O(3) QTL mapped to the same position as the water loss QTL further supporting the role of stomata in regulating O(3) entry and damage.

2009년 봄, 여름철 광양만 지역 오존의 광화학적 특성 분석

We examined high ozone episodes observed during the intensive measurement periods (11 May~21 June and 30 July~11 August 2009) in the Gulf of Gwangyang. During that period, there were a few events (or days) in which 1 hr averaged ozone concentrations were greater than 100 ppbv. The analysis of ozone budget and photochemical characteristics related to the ozone production was carried out using a photochemical box model. Ozone sensitivity to <TEX>$NO_x$</TEX> and VOCs was also examined in the study area during the measurement period. Diurnal variation of ozone during the episodes was similar to that of odd hydrogen radicals (<TEX>$HO_2,CH_3O_2$</TEX>, and <TEX>$RO_2$</TEX>), suggesting significant correlation with photochemical production of ozone during the episodes. In general, ozone concentration in the study area during the measurement period was sensitive to VOCs, whereas ozone was sensitive to <TEX>$NO_x$</TEX> under certain conditions. Ozone sensitivity assessment using a radical budget analysis and <TEX>$NO_x$</TEX>/VOCs-control strategy was consistent with that using indicator species (<TEX>$H_2O_2/HNO_3$</TEX> ratio).

Differences in Ozone Sensitivity at Different NPK Levels of Three Tropical Varieties of Mustard (Brassica campestris L.): Photosynthetic Pigments, Metabolites, and Antioxidants

The effects of ambient O3 at two different levels of nitrogen, phosphorus, and potassium, (recommended and 1.5 times the recommended NPK) on three tropical varieties of mustard (Brassica campestris L. var. Kranti, Aashirwad and Vardan) were explored to unravel the mechanism of protection under higher NPK level at a rural experimental site using open top chambers. Ambient O3 concentrations ranged from 27.7 to 59.04 ppb. Lipid peroxidation, antioxidative enzymes, and metabolites were higher, whereas photosynthetic pigments and protein were lower in all the varieties of mustard grown in non-filtered chambers than in filtered chambers. The magnitude of response varied with varieties, NPK levels and ages. Vardan showed a maximum stimulation in the antioxidative defense system, thus efficient scavenging of ROS produced by O3 and consequently conferred greater tolerance in terms of least reductions in pigments and protein as compared to Kranti and Aashirwad. The antioxidant defense system was not stimulated in response to 1.5 times the recommended NPK, but higher levels of pigments and protein were maintained compared to the recommended NPK under ambient O3 levels.

Understanding of regional air pollution over China using CMAQ, part II. Process analysis and sensitivity of ozone and particulate matter to precursor emissions

Following model evaluation in part I, this part II paper focuses on the process analysis and chemical regime analysis for the formation of ozone (O 3) and particulate matter with aerodynamic diameter less than or equal to 10 μm (PM 10) in China. The process analysis results show that horizontal transport is the main contributor to the accumulation of O 3 in Jan., Apr., and Oct., and gas-phase chemistry and vertical transport contribute to the production and accumulation of O 3 in Jul. Removal pathways of O 3 include vertical and horizontal transport, gas-phase chemistry, and cloud processes, depending on locations and seasons. PM 10 is mainly produced by primary emissions and aerosol processes and removed by horizontal transport. Cloud processes could either decrease or increase PM 10 concentrations, depending on locations and seasons. Among all indicators examined, the ratio of P HNO 3 / P H 2 O 2 provides the most robust indicator for O 3 chemistry, indicating a VOC-limited O 3 chemistry over most of the eastern China in Jan., NO x-limited in Jul., and either VOC- or NO x-limited in Apr. and Oct. O 3 chemistry is NO x-limited in most central and western China and VOC-limited in major cities throughout the year. The adjusted gas ratio, AdjGR, indicates that PM formation in the eastern China is most sensitive to the emissions of SO 2 and may be more sensitive to emission reductions in NO x than in NH 3. These results are fairly consistent with the responses of O 3 and PM 2.5 to the reductions of their precursor emissions predicted from sensitivity simulations. A 50% reduction of NO x or AVOC emissions leads to a reduction of O 3 over the eastern China. Unlike the reduction of emissions of SO 2, NO x, and NH 3 that leads to a decrease in PM 10, a 50% reduction of AVOC emissions increases PM 10 levels. Such results indicate the complexity of O 3 and PM chemistry and a need for an integrated, region-specific emission control strategy with seasonal variations to effectively control both O 3 and PM 2.5 pollution in China.