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Missing hydroxyl radical (OH) reactivity from unknown/unmeasured trace species empirically accounts for 10%-30% of total OH reactivity and may cause significant uncertainty regarding estimation of photochemical ozone production. T...
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Missing hydroxyl radical (OH) reactivity from unknown/unmeasured trace species empirically accounts for 10%-30% of total OH reactivity and may cause significant uncertainty regarding estimation of photochemical ozone production. Thus, it is essential to unveil the missing OH reactivity for developing an effective ozone mitigation strategy. In this study, we conducted simultaneous observations of total OH reactivity and 54 reactive trace species in a suburban area as part of the Air QUAlity Study (AQUAS)-Tsukuba campaign for the summer of 2017 to gain in-depth insight into total OH reactivity in an area that experienced relatively high contributions of secondary pollutants. The campaign identified on average 35.3% of missing OH reactivity among total OH reactivity (12.9 s~(-1)). In general, ozone-production potential estimation categorized ozone formation in this area as volatile organic compound (VOC)-limited conditions, and missing OH reactivity may increase ozone production potential 40% on average if considered. Our results suggest the importance of photochemical processes of both AVOCs and BVOCs for the production of missing OH reactivity and that we may underestimate the importance of reducing precursors in approach to suppressing ozone production if we ignore the contribution of their photochemical products.
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Tropospheric ozone (O_3) continues to be a threat to human health and agricultural productivity. While O_3 control is challenging, tracking underlying formation mechanisms provides insights for regulatory directions. Here, we desc...
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Tropospheric ozone (O_3) continues to be a threat to human health and agricultural productivity. While O_3 control is challenging, tracking underlying formation mechanisms provides insights for regulatory directions. Here, we describe a comprehensive analysis of the effects of changing emissions on O_3 formation mechanisms with observational evidence. We present a new approach that provides a quantitative metric for the ozone production rate (OPR) and its sensitivity to precursor levels by interpreting two decades of in situ observations of the six criteria air pollutants(2001-2018). Applying to the South Coast Air Basin (SoCAB), California, we show that by 2016-2018, the basin was at the transition region between nitrogen oxide (NO_x)-limited and volatile organic compound (VOC)-limited chemical regimes. Assuming future weather conditions are similar to 2016-2018, we predict that NO_x-focused reduction is required to reduce the number of summer days the SoCAB is in violation of the National Ambient Air Quality Standard (70 ppbv) for O_3. Roughly, ～40% (～60%) NO_x reductions are required to reduce the OPR by ～1.8 ppb/h (～3.3 ppb/h). This change would reduce the number of violation days from 28 to 20% (10%) in a year, mostly in summertime. Concurrent VOC reductions which reduce the production rate of HO_x radicals would also be beneficial.
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This study presents the results of a bench experiment on the formation of aldehydes during the ozonation process. the objective of this research is to investigate the influence of source of organic matter on aldehyde production an...
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This study presents the results of a bench experiment on the formation of aldehydes during the ozonation process. the objective of this research is to investigate the influence of source of organic matter on aldehyde production and compare the amounts of aldehydes produced by the ozon- ation of humic and fulvic acids. Our results show that fulvic acids are major precursors of aldehydes generated during oxidation of humic substances by ozone.
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An observation-based method (OBM) is developed to evaluate the ozone (O_3) production efficiency (O_3 molecules produced per NO_x molecule consumed) and O_3 production rate (P(O_3)) during a field campaign in southern Taiwan. The ...
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An observation-based method (OBM) is developed to evaluate the ozone (O_3) production efficiency (O_3 molecules produced per NO_x molecule consumed) and O_3 production rate (P(O_3)) during a field campaign in southern Taiwan. The method can also provide an estimate of the concentration of OH. A key step in the method is to use observed concentrations of two aromatic hydrocarbons, namely ethylbenzene and m,p-xylene, to estimate the degree of photochemical processing and amounts of photochemically consumed NO_x and NMHCs by OH. In addition, total oxidant (O_3 + NO_2) instead of O_3 itself turns out to be very useful for representing ozone production in the OBM approach. The average O_3 production efficiency during the field campaign in Fall (2003) is found to be about 10.2 ± 3.9. The relationship of P(O_3) with NO_X is examined and compared with a one-dimensional (1D) photochemical model. Values of P(O_3) derived from the OBM are slightly lower than those calculated in the 1D model. However, OH concentrations estimated by the OBM are about a factor of 2 lower than the 1D model. Fresh emissions, which affect the degree of photochemical processing appear to be a major cause of the underestimate. We have developed a three-dimensional (3D) OBM O_3 production diagram that resembles the EKMA ozone isopleth diagram to study the relationship of the total oxidant versus O_3 precursors. The 3D OBM O_3 production diagram suggests that reducing emissions of NMHCs are more effective in controlling O_3 than reducing NO_X. However, significant uncertainties remain in the OBM, and considerable more work is required to minimize these uncertainties before a definitive control strategy can be reached. The observation-based approach provides a good alternative to measuring peroxy radicals for evaluating the production of O_3 and formulating O_3 control strategy in urban and suburban environments.
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The Soberanes Fire burned 53,470 ha (132,127 acres) along the central California coast between 22 July and 12 October 2016, generating dense smoke and a variety of gaseous compounds that drifted eastward into the San Joaquin Valle...
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The Soberanes Fire burned 53,470 ha (132,127 acres) along the central California coast between 22 July and 12 October 2016, generating dense smoke and a variety of gaseous compounds that drifted eastward into the San Joaquin Valley Air Basin (SJVAB), an “extreme” nonattainment area for ozone (O_3). These gases included nitrogen oxides (NO_x) and volatile organic compounds, the photochemical precursors of O_3. The fire started during the California Baseline Ozone Transport Study, a field campaign that brought aircraft, surface, and remote sensing measurements of O_3 and related species to central California. In this paper, we use the California Baseline Ozone Transport Study measurements to assess the impact of the Soberanes Fire on ozone and particulate air quality in the SJVAB. We focus our analysis on 27 July to 2 August when the smoke haze was heaviest and the highest O_3 concentrations in the SJVAB during 2016 were recorded. Our analyses suggest that while 40 to 60 ppbv of fire-generated O_3 was transported to the eastern SJVAB in the 1- to 3-km-altitude range, relatively little smoke or fire-generated O_3 reached the surface in the Visalia area.
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Triclosan is an antimicrobial agent widely used in many household and personal care products. Widespread use of this compound has led to the elevated concentrations of triclosan in wastewater, wastewater treatment plants and recei...
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Triclosan is an antimicrobial agent widely used in many household and personal care products. Widespread use of this compound has led to the elevated concentrations of triclosan in wastewater, wastewater treatment plants and receiving waters. In this study removal of triclosan by aqueous ozone was investigated and the degradation products formed during ozonation of an aqueous solution of triclosan were analyzed by GC-MS and HPLC-MS/MS. The following transformation products have been identified: 2,4-dichlorophenol, chloro-catecol, mono-hydroxy-triclosan and di-hydroxy-triclosan during treatment process. Cyto-toxicity and genotoxirity of pure triclosan and 2,4-dichlorophenol have been investigated and the results showed reduced genotoxic effects after ozonation, though the respective chlor-ophenol is harmful to aquatic organisms.
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We present a comprehensive field campaign conducted in Beijing, September 2016, to elucidate the photochemical smog pollution, i.e. Ozone (O_3). The observed daily maximum hydroxyl radical (OH) and hydroperoxy radical (HO_2) conce...
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We present a comprehensive field campaign conducted in Beijing, September 2016, to elucidate the photochemical smog pollution, i.e. Ozone (O_3). The observed daily maximum hydroxyl radical (OH) and hydroperoxy radical (HO_2) concentrations were up to 1 × 10~7 cm~(-3) and 6 × 10~8 cm~(-3), respectively, indicating the active photochemistry in autumn Beijing. Photolysis of nitrous acid (HONO) and O_3 contributed 1-2 ppbv h~(-1) to OH primary production during daytime. OH termination were dominated by the reaction with nitric oxide (NO) and nitrogen dioxide (NO_2), which were in general larger than primary production rates, indicating other primary radical sources maybe important. The measurement of radicals facilitates the direct determination of local ozone production rate P (O_x) (O_x = O_3 + NO_2).The integrated P(O_x) reached 75 ppbv in afternoon (for 4 h) when planetary boundary layer was well developed. At the same time period, the observed total oxidant concentrations O_x, increased significantly by 70 ppbv. In addition, the O_x measurement showed compact increase in 12 stations both temporally and spatially in Beijing, indicating that active photochemical production happened homogenously throughout the city. The back-trajectory analysis showed that Beijing was isolated from the other cities during the episode, which further proved that the fast ozone pollution was contributed by local photochemical production rather than regional advection.
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Ozone degradation of a mixture containing methylparaben, ethylparaben, propylparaben, butylparaben and benzylparaben was carried out in aqueous solution. The degradation followed the pseudo-first-order kinetic model and occurs wit...
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Ozone degradation of a mixture containing methylparaben, ethylparaben, propylparaben, butylparaben and benzylparaben was carried out in aqueous solution. The degradation followed the pseudo-first-order kinetic model and occurs with two ozonation stages with the observed rate constants of second stage ozonation, k_(obs2), being higher than the observed rate constants in first stage, k_(obs1). The k_(obs1)of parabens was found to increase exponentially whilst k_(obs2) was found to maximize at 35°C. Both k_(obs1) and k_(obs2) were found to decrease exponentially with respect to the initial concentration of parabens. Both pH and ozone dose showed positive effects on the rate of degradation. It was also observed that an ozone dose of 0.67 g/h resulted in the removal of 99% of parabens in 12 min, and also the removal of 61 and 32% of chemical oxygen demand (COD) and total organic carbon (TOC), respectively, in 3 h of ozonation time for a 500 μM of solution of parabens.
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Ozone degradation of a mixture containing methylparaben, ethylparaben, propylparaben, butylparaben and benzylparaben was carried out in aqueous solution. The degradation followed the pseudo-first-order kinetic model and occurs wit...
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Ozone degradation of a mixture containing methylparaben, ethylparaben, propylparaben, butylparaben and benzylparaben was carried out in aqueous solution. The degradation followed the pseudo-first-order kinetic model and occurs with two ozonation stages with the observed rate constants of second stage ozonation, k_(obs2), being higher than the observed rate constants in first stage, k_(obs1). The k_(obs1)of parabens was found to increase exponentially whilst k_(obs2) was found to maximize at 35°C. Both k_(obs1) and k_(obs2) were found to decrease exponentially with respect to the initial concentration of parabens. Both pH and ozone dose showed positive effects on the rate of degradation. It was also observed that an ozone dose of 0.67 g/h resulted in the removal of 99% of parabens in 12 min, and also the removal of 61 and 32% of chemical oxygen demand (COD) and total organic carbon (TOC), respectively, in 3 h of ozonation time for a 500 μM of solution of parabens.
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The consumption of ozone by pine wood with a water content of 7 to 85% is investigated. The specific ozone consumption and degree of ozone conversion during the ozonation of wood with different contents of water are determined. IR...
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The consumption of ozone by pine wood with a water content of 7 to 85% is investigated. The specific ozone consumption and degree of ozone conversion during the ozonation of wood with different contents of water are determined. IR absorption spectra of ozonated lignocellulosic material (LCM) produced from wood are analyzed. Destruction of the lignin aromatic structure and the formation of carbonyl- and carboxyl- containing compounds are observed. The content of cellulose in a sample of ozonated LCM grows along with the specific ozone consumption. Products of the ozonolysis of lignin (glyoxylic, formic, and oxalic acids) form during ozonation of the wood, as determined via HPLC. It is shown that the oxidation of acids by ozone proceeds in the water phase of the sample. Based on the data for the destruction of lignin and the results from investigating the process of wood ozonation, it is concluded that the optimum content of water for wood treatment is 60-63%. It was shown that the destruction of lignin during wood ozonation proceeds via ozonolysis and with the participation of radicals formed in the reaction between ozone and water.
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