Trihalomethane formation in ozonated and chlorinated surface water

The relatively recent discovery of disinfection by-products has driven the main regulatory organisms to set maximum contaminant levels for certain substances in drinking water. Trihalomethanes can be deemed as the most important group of by-products in chlorinated surface waters. The present work has focused on trihalomethane formation in a full-scale water treatment plant. We studied the effect of several factors, including ozonation, on trihalomethane levels in chlorinated treated water. The treatment scheme also includes an ozonation step. Electronic Publication     

Characterization of a new smog chamber for evaluating SAPRC gas-phase chemical mechanism

A new state-of-the-art indoor smog chamber facility (CAPS-ZJU) has been constructed and characterized at Zhejiang University, which is designed for chemical mechanism evaluation under well-controlled conditions. A series of characterization experiments were performed to validate the well-established experimental protocols, including temperature variation pattern, light spectrum and equivalent intensity (J_NO2), injection and mixing performance, as well as gases and particle wall loss. In addition, based on some characterization experiments, the auxiliary wall mechanism has been setup and examined. Fifty chamber experiments were performed across a broad range of experimental scenarios, and we demonstrated the ability to utilize these chamber data for evaluating SAPRC chemical mechanism. It was found that the SAPRC-11 can well predict the O₃ formation and NO oxidation for almost all propene runs, with 6 hr Δ(O₃ – NO) model error of –3% ± 7%, while the final O₃ was underestimated by ~20% for isoprene experiments. As for toluene and p-xylene experiments, it was confirmed that SAPRC-11 has significant improvement on aromatic chemistry than earlier version of SAPRC-07, although the aromatic decay rate was still underestimated to some extent. The model sensitivity test has been carried out, and the most sensitive parameters identified are the initial concentrations of reactants and the light intensity as well as HONO offgasing rate and O₃ wall loss rate. All of which demonstrated that CAPS-ZJU smog chamber could derive high quality experimental data, and could provide insights on chamber studies and chemical mechanism development.     

Kinetic and mechanism studies of the ozonolysis of three unsaturated ketones

Reaction rate constants and products of 1-octen-3-one, 3-octen-2-one and 4-hexen-3-one with ozone were studied in a 100-L fluorinated ethylene propylene (FEP) Teflon film bag using absolute rate method at 298 ± 1 K and atmospheric pressure. The rate constants were (1.09 ± 0.12) × 10^?17, (3.48 ± 0.36) × 10^?17 and (5.70 ± 0.60) × 10^?17 cm³/(molecule?sec), respectively. According to the obtained rate constants, the effects of carbonyl were discussed. The carbonyl group in β position has a net withdrawing effect with respect to an olefinic bond, then causing the decline of rate constants. The quantum chemical calculation was used to explain the results of rate constants. The products of ozonolysis were mainly aldehydes, which have significant influence on the formation of SOA, and hence play an important role in the atmosphere. In this work, we detected the main products of reaction and proposed the reaction mechanism by combining the results of quantum chemical calculations. Atmospheric lifetime for three unsaturated ketones reacted with ozone was 36.4, 11.4 and 6.9 hr for 1-octen-3-one, 3-octen-2-one and 4-hexen-3-one, respectively.     

Reactor characterization and primary application of a state of art dual-reactor chamber in the investigation of atmospheric photochemical processes

Increasing attention has been paid to the air pollution more recently. Smog chamber has been proved as a necessary and effective tool to study atmospheric processes, including photochemical smog and haze formation. A novel smog chamber was designed to study the atmospheric photochemical reaction mechanism of typical volatile organic compounds (VOCs) as well as the aging of aerosols. The smog chamber system includes an enclosure equipped with black lights as the light source, two parallel reactors (2 m³ of each) with separate control of light source and temperature, with a series of coupled instruments for online monitoring of gas phase and particle phase reactants and products. Chamber characterization, including air source stability, effective light intensity, temperature stability, as well as gas phase and particle phase wall losses, were carried out before further research. The results showed that our smog chamber systems developed by other domestic and international groups. It was also observed that the wall loss of aromatic VOCs varied with different functional groups as well as the isomerism. The results of preliminary simulation experiment from styrene-NO_x demonstrated that the chamber can be well utilized to simulate gas-particle conversion progresses in the atmosphere.     

Large variability in ambient ozone sensitivity across 19 ethylenediurea-treated Chinese cultivars of soybean is driven by total ascorbate

The sensitivity of Chinese soybean cultivars to ambient ozone(O3) in the field is unknown,although soybean is a major staple food in China. Using ethylenediurea(EDU) as an O3 protectant, we tested the gas exchange, pigments, antioxidants and biomass of 19 cultivars exposed to 28 ppm·hr AOT40(accumulated O3 over an hourly concentration threshold of40 ppb) over the growing season at a field site in China. By comparing the average biomass with and without EDU, we estimated the cultivar-specific sensitivity to O3 and ranked the cultivars from very tolerant( 10% change) to highly sensitive( 45% change), which helps in choosing the best-suited cultivars for local cultivation. Higher lipid peroxidation and activity of the ascorbate peroxidase enzyme were major responses to O3 damage, which eventually translated into lower biomass production. The constitutional level of total ascorbate in the leaves was the most important parameter explaining O3 sensitivity among these cultivars. Surprisingly, the role of stomatal conductance was insignificant. These results will guide future breeding efforts towards more O3-tolerant cultivars in China, while strategies for implementing control measures of regional O3 pollution are being implemented. Overall, these results suggest that present ambient O3 pollution is a serious concern for soybean in China, which highlights the urgent need for policy-making actions to protect this critical staple food.     

Strong ozone production at a rural site in theNorth China Plain: Mixed effects of urban plumesand biogenic emissions

Regional ozone (O₃) pollution has drawn increasing attention in China over the recent decade, but the contributions from urban pollution and biogenic emissions have not been clearly elucidated. To better understand the formation of the regional O₃ problem in the North China Plain (NCP), intensive field measurements of O₃ and related parameters were conducted at a rural site downwind of Ji'nan, the capital city of Shandong province, in the summer of 2013. Markedly severe O₃ pollution was recorded, with the O₃ mixing ratios exceeding the Chinese national ambient air quality standard on 28?days (a frequency of 78%) and with a maximum hourly value of 198 ppbv. Extensive regional transport of well-processed urban plumes to the site was identified. An observation-constrained chemical box model was deployed to evaluate in situ photochemical O₃ production on two episodes. The results show that the in situ formation accounted for approximately 46% of the observed O₃ accumulation, while the remainder (~ 54%) was contributed by regional transport of the O₃-laden urban plumes. The in situ ozone production was in a mixed controlled regime that reducing either NOx or VOCs would lead to a reduction of ozone formation. Biogenic VOCs played an important role in the local ozone formation. This study demonstrates the significant mixed effects of both anthropogenic pollution from urban zones and biogenic emission in rural areas on the regional O₃ pollution in the NCP region, and may have general applicability in facilitating the understanding of the formation of secondary pollution over China.     

Responses of evergreen and deciduous Quercus species to enhanced ozone levels

Plants of one evergreen oak (Quercus ilex) and three deciduous oaks (Q. faginea, with small leaves; Q. pyrenaica and Q. robur, with large leaves) were exposed both to filtered air and to enhanced ozone levels in Open-Top Chambers. Q. faginea and Q. pyrenaica were studied for the first time. Based on visible injury, gas exchange, chlorophyll content and biomass responses, Q. pyrenaica was the most sensitive species, and Q. ilex was the most tolerant, followed by Q. faginea. Functional leaf traits of the species were related to differences in sensitivity, while accumulated ozone flux via stomata (POD_1.6) partly contributed to the observed differences. For risk assessment of Mediterranean vegetation, the diversity of responses detected in this study should be taken into account, applying appropriate critical levels.     

How the redox state of tobacco 'Bel-W3' is modified in response to ozone and other environmental factors in a sub-tropical area?

This study intended to determine whether the redox state in plants of Nicotiana tabacum ‘Bel-W3’ fluctuates in response to the environmental factors in a sub-tropical area contaminated by ozone (São Paulo, SE - Brazil) and which environmental factors are related to this fluctuation, discussing their biomonitoring efficiency. We comparatively evaluated the indicators of redox state (ascorbic acid, glutathione, superoxide dismutase, ascorbate peroxidase, and glutathione reductase) and leaf injury in 17 field experiments performed in 2008. The redox state was explained by the combined effects of chronic levels of O₃ and meteorological variables 4-6 days prior to the plant sampling. Moderate leaf injury was observed in most cases. The redox state of tobacco decreases few days after their placement in the sub-tropical environment, causing them to become susceptible to oxidative stress imposed by chronic doses of O₃. Its bioindicator efficiency would not be diminished in such levels of atmospheric contamination.     

Plant phenology, growth and nutritive quality of Briza maxima: responses induced by enhanced ozone atmospheric levels and nitrogen enrichment

An assessment of the effects of tropospheric ozone (O₃) levels and substrate nitrogen (N) supplementation, singly and in combination, on phenology, growth and nutritive quality of Briza maxima was carried out. Two serial experiments were developed in Open-Top Chambers (OTC) using three O₃ and three N levels. Increased O₃ exposure did not affect the biomass-related parameters, but enhanced senescence, increased fiber foliar content (especially lignin concentration) and reduced plant life span; these effects were related to senescence acceleration induced by the pollutant. Added N increased plant biomass production and improved nutritive quality by decreasing foliar fiber concentration. Interestingly, the effects of N supplementation depended on meteorological conditions and plant physiological activity. N supplementation counteracted the O₃-induced senescence but did not modifiy the effects on nutritive quality. Nutritive quality and phenology should be considered in new definitions of the O₃ limits for the protection of herbaceous vegetation.     

Leaf size and surface characteristics of Betula papyrifera exposed to elevated CO2 and O3

Betula papyrifera trees were exposed to elevated concentrations of CO₂ (1.4 × ambient), O₃ (1.2 × ambient) or CO₂ + O₃ at the Aspen Free-air CO₂ Enrichment Experiment. The treatment effects on leaf surface characteristics were studied after nine years of tree exposure. CO₂ and O₃ increased epidermal cell size and reduced epidermal cell density but leaf size was not altered. Stomatal density remained unaffected, but stomatal index increased under elevated CO₂. Cuticular ridges and epicuticular wax crystallites were less evident under CO₂ and CO₂ + O₃. The increase in amorphous deposits, particularly under CO₂ + O_3, was associated with the appearance of elongated plate crystallites in stomatal chambers. Increased proportions of alkyl esters resulted from increased esterification of fatty acids and alcohols under elevated CO₂ + O₃. The combination of elevated CO₂ and O₃ resulted in different responses than expected under exposure to CO₂ or O₃ alone.