Ozone Control Research Articles

Analysis of the photochemical characteristics and sensitivity of ozone pollution in Xi’an

<p indent="0mm">The Fenwei Plain is an important agricultural production base and transportation hub in China with a residential population of over 55 million. With rapid industrialization and urbanization, this area has experienced serious photochemical pollution in the summer season. In this study, a field campaign was conducted in summer 2019 with measurements of ozone and photochemical precursors in Xi’an, a megacity in the Fenwei Plain. An explicit case was performed to explore O₃-NO_{<italic>x</italic>}-VOCs sensitivity and the local ozone budget using an observation-based model. Results revealed that precursors significantly promoted ozone production. The positive matrix factorization (PMF) model combined with the relative incremental reactivity (RIR) method was applied to identify the key VOC sources that affect ozone formation. An ozone pollution episode lasting <sc>11 d</sc> was selected and divided into three periods: Initial (July 8–11), polluted (July 12–15), and sweep (July 16–18) periods. It was found that strong solar radiation intensity, high temperature, low relative humidity, and low pressure prevailed during the polluted period, which favored ozone production. The maximum O₃ concentrations at the upwind CB site and urban DHS site were found to be 125 ppbv during the polluted period, whereas at the QL site, the maximum O₃ concentrations were much lower (98 ppbv). The maximum local ozone production rate <sc>(<italic>P</italic>(O_{<italic>x</italic>}))</sc> of the three sites during the polluted period was significantly higher than that in the initial and sweep periods. The <italic>P</italic>(O_{<italic>x</italic>}) was 17.7, 33.9, and 14.9 ppbv/h for the CB, DHS, and QL sites, respectively. The <italic>in situ</italic> O_{<italic>x</italic>}<italic> </italic>budget demonstrated that ozone pollution at the CB and DHS sites was mainly attributed to local photochemical production, whereas the regional transportation effect could not be ignored at the QL site. The O₃-NO_{<italic>x</italic>}-VOCs sensitivity analysis revealed that ozone production regimes were transitional, VOCs-limited, and NO_{<italic>x</italic>}-limited at the CB, DHS, and QL sites, respectively, and the regimes stayed unchanged for all the three sites during the entire ozone pollution episode. However, during the initial period at the DHS site, NO_{<italic>x</italic>} reduction led to a negative effect on ozone control. The ozone formation regime obtained from the emission rate box model was consistent with that of the RIR method. From the proportion of grouped VOCs, the alkane and OVOCs were the dominant species in the mixing ratio (78%–86%), whereas the contribution of aromatics to OFP (16%–24%) was second only to that of OVOCs. Finally, by combining the PMF model and RIR method, ozone production was found to be more sensitive to precursors reduction in the initial period than in the polluted period at the three sites, which indicated that pollutants control measures for ozone pollution mitigation will be more effective in the initial than in polluted periods. Therefore, during an ozone pollution episode, the time to take action for ozone pollution control is not during the polluted period when the ozone concentrations peak, but should be brought forward, when controlling the concentration of precursors has the highest efficiency in reducing ozone production.

Summertime Clean-Background Ozone Concentrations Derived from Ozone Precursor Relationships are Lower than Previous Estimates in the Southeast United States.

Background ozone in this study is defined as the amount of ozone that is not affected by the emissions of ozone precursors in the region of study and is transported from the distant troposphere or the stratosphere. It is one of the factors that must be considered in regional ozone control strategies. Different methods have been applied to define the background ozone level. We develop a new method based on the O3-CO-HCHO relationships, which can be applied to both observation and modeling data for regions with high isoprene emission ozone, such as the Southeast United States. We make use of the extensive aircraft and surface observations in the Southeast in the summer of 2013. Compared to the diagnostic results using the relationship of O3-NOz (total reactive nitrogen excluding nitrogen oxides), zero-emission (model-only), and 5th percentile methods, the new method is most consistent using observation or model data and the resulting background ozone concentrations are 4-50% lower than the other methods for field campaigns. Using this method, we find that the summertime background ozone at the surface is in the range of 10-15 ppbv in the inland areas of the Southeast, which is lower than that reported in previous studies. This background ozone tends to increase from urban centers to rural regions and from the surface to higher altitude due to changing ozone lifetime driven by anthropogenic emissions and dry deposition to the surface. The better quantification of background ozone using the new method highlights the importance of the contributions by natural emissions to ozone and the necessity to control anthropogenic emissions in ozone nonattainment areas of the Southeast.

Large scale control of surface ozone by relative humidity observed during warm seasons in China

Rising air pollution by surface ozone (O3) in China has induced extensive efforts to control ozone generation in major urban and industrial areas, yet mechanisms ruling the ozone production and loss are not well understood. In particular, ozone levels are strongly influenced by meteorological factors such as relative humidity, but this has been explored only in local situations, and the effect of relative humidity on ozone levels in warm seasons on a large scale in China is still unknown. Here we studied surface ozone, relative humidity, temperature, and other meteorological variables in 74 major cities in China during 2017–2018, focusing on the warm seasons in seven regions. Results show that ozone levels decrease with increasing relative humidity in all cities, with an average correlation coefficient of − 0.58, ranging from − 0.17 in Zhangjiakou to − 0.84 in Hengshui. At high relative humidity levels, above 75%, average ozone levels ranged from 44.6 to 122.5 μg m−3, which is lower than Chinese quality threshold of hourly average ozone level of 200 μg m−3. The decreases of ozone with relative humidity were more pronounced at high temperature, above 30 °C, than below 25 °C. The increases of ozone with temperature were more pronounced at low relative humidity, below 40%. Overall, our findings reveal that mechanisms ruling surface ozone levels are similar on a large scale. This is promising to design common methods of climate engineering to protect human health.

A newly integrated dataset of volatile organic compounds (VOCs) source profiles and implications for the future development of VOCs profiles in China

Volatile organic compounds (VOCs) source profiles can be used for a number of purposes, such as creating speciated air pollutant emission inventories and providing inputs to receptor and air quality models. In this study, we first collected and schematically evaluated more than 500 Chinese domestic source profiles from literature and field measurements, and then established a most up-to-date dataset of VOCs source profiles in China by integrating 363 selective VOCs profiles into 101 sector-based source profiles. The profile dataset covers eight major source categories and contains 447 VOCs species including non-methane hydrocarbons (NMHCs) species and oxygenated VOCs (OVOCs) species. The results shown that (1) VOCs composition characteristics exhibit variations for most Level-II source sectors and Level-III sub-sectors even under the same Level-I source category; (2) OVOCs, which were significantly missing in previous profiles, account for more than 95% in cooking and 20– 40% in non-road mobile, biomass burning and solvent use sources; (3) aromatics account for 20%–40% in most emission sources except cooking source, alkenes and alkynes account for ~20% in combustion sources (stationary combustion, mobile source and biomass burning), alkanes are abundant in gasoline-related emission sources(on-road mobile source and fuel oil storage and transportation); (4) missing OVOCs species could bring 30%–50% to ozone formation potentials in most emission sources; and (5) there are considerable differences in VOCs chemical groups and individual species for most emission sources between this dataset and the widely used U.S. SPECIATE database, indicating the importance of developing domestic VOCs source profiles. The dataset developed in this study can help support reactive VOCs species-based ozone control strategy and provide domestic profile data for source apportionment and air quality modeling in China and other countries or regions with similar emission source characteristics.

Association of ambient ozone with pneumonia hospital admissions in Hong Kong and Taipei: A tale of two Southeast Asian cities.

Ozone (O3) is a reactive oxidant exerting both inflammatory and oxidative damages to the respiratory system. With the ground-level O3 progressively increasing in the past decade, the reevaluation of the pneumonia hospitalization risk from exposure to O3 is of public health interest. We conducted an ecological time-series study to examine the city-specific association between short-term O3 exposure and pneumonia hospitalizations in Hong Kong and Taipei, respectively. We linked the daily pneumonia hospitalization count to air pollution concentrations and weather conditions according to the date of admission during 2010-2017. We applied a generalized additive distributed lag model to examine the association while adjusting for time-varying covariates. Stratified analysis by age group and the potential harvesting effect of O3 were evaluated. We observed the harvesting effects of O3 on pneumonia hospitalizations in children in both cities and adults in Taipei. The short-term effect of O3 lasted for around one week. An interquartile range (IQR) increment of daytime 8-hour mean concentration of O3 distributed over 0-6 lag days in Hong Kong (42.4μg/m3) was associated with a 7.04% (95% CI: 5.35-8.76%) increase in hospital admissions for elderly pneumonia, while the corresponding cumulative excess risk per IQR increment of O3 in Taipei (38.7μg/m3) was 3.41% (95% CI: 1.63-5.22%). Different O3 metrics, varying degrees of freedom for filtering the temporal trend, and three-pollutant models supported the robustness of the associations. We concluded that short-term O3 exposure was associated with pneumonia hospitalizations in the elderly population. Understanding the pneumonia hospitalization risk of O3 will help to inform public health policies in the planning of ozone control strategies and intervention measures to prevent ozone-related pneumonia in vulnerable elderly populations.

A new approach for health-oriented ozone control strategy: Adjoint-based optimization of NOx emission reductions using metaheuristic algorithms

While levels of particulate matters in the Pearl River Delta Region (PRD) show a significant reduction, ozone (O3) has an opposite increasing trend, becoming the critical air quality target in this decade. Emission control strategies are typically formulated sector by sector, spatial variability in emissions reductions and health impacts of air pollutants may not be taken into account, affecting the overall effectiveness of control strategies. This study proposes an adjoint-based optimization framework to facilitate health-oriented O3 control over PRD. The location-specific adjoint sensitivity coefficients, which reflect the spatiotemporal influences from emissions of nitrogen dioxide (NOx) on O3 health impacts, are combined with metaheuristic algorithms to minimize the O3-related premature mortalities over receptor regions. Using the proposed optimization methodology, the regional O3 health benefits under current emission reduction policy can be increased by 16–27%. The results show that relatively larger NOx emissions reductions occurred at highly developed and populated areas. Particularly, significant reductions in NOx emissions are observed at Shenzhen and urban Guangzhou. Furthermore, implementing regional NOx emissions abatement has advantages to achieve an overall O3 health benefits for all cities. The interregional influences of NOx emissions abatement between cities indicate a promising strategy of health-oriented O3 control in PRD.

Study on the variation characteristics of tropospheric ozone in Northeast China.

The goal of this study was to understand the current status of ozone pollution in Northeast China and to distinguish the main influencing factors of ozone, in order to provide a scientific basis for the future prevention and control of ozone in this region. In this study, the Ozone Monitoring Instrument data product was used as the source data, and the pixel space analysis method and grey correlation analysis method were utilized to examine the tropospheric ozone column concentration in Northeast China from 2010 to 2018. The results revealed that the ozone column concentration in Northeast China was relatively high compared to other parts of the country. The high-value areas were primarily distributed in Tahe County, Heihe City, Hegang City, and Qiqihar City. The temporal variation of the ozone column concentration in Northeast China exhibited an obvious periodicity of 9 years, and its interannual change displayed a downward trend. The maximum value occurred in 2010, and the minimum value was found in 2016. The seasonal changes manifested a relative trend of spring > winter > summer > autumn, which was contrary to the research results for other parts of China, which showed a summer maximum. Among the influencing factors, atmospheric pressure, relative humidity, sunshine hours, GDP, and primary and secondary industries exhibited the closest relationships with ozone. The high concentration of ozone in Northeast China was determined to result from the superimposed effects of long-distance atmospheric transport and anthropogenic emissions.

Residual ozone in microorganisms enhanced organics removal and shaped microbial community

The residual ozone played an important role in enhancing the organics removal by stimulate subsequent biological processes. However, how the residual ozone affects the biological process is not well studied. In this work, a pilot scale integrated O3-BAF, ordinary BAF and separated O3-BAF were compared in advanced treatment of real bio-treated petrochemical wastewater. Results showed that residual ozone with 0.05–0.10 mg L−1 in the BAF demonstrated relatively high chemical oxygen demand (COD) removal efficiency of 48.4%, which was 1.5-fold higher than that obtained by separated O3-BAF and 3-fold higher than that obtained by ordinary BAF. The stimulative effect of low dosage of O3 on biological treatment additionally donated 33.9% of the COD removal in the BAF. The COD removal amount per dosage of ozone reached 5.30 mg-COD/mg-O3. The biofilm thickness in the integrated O3-BAF was reduced by 30–50% while the dehydrogenase activity (DHA) was improved by 500%, indicating the stimulate effect on the bioactivity. Additionally, Illumina HiSeq sequencing of 16S rRNA gene amplicons demonstrated significant microbial diversity decreasing. Specially, Gemmatimonadetes and Bacteroidetes are the dominate microorganism in the integrated O3-BAF, having a positive correlation with the proper residual ozone, and increased by 5.4% and 4.2% in comparison with the separated O3-BAF, respectively. The residual ozone higher than 0.22 mg L−1 showed inhibition effect on the bioactivity. In summary, the control of residual ozone introduced to BAF was crucial for stimulative effects and manager the microbial community in the integrated O3-BAF, which still need further detail research.

Association of cardiorespiratory hospital admissions with ambient volatile organic compounds: Evidence from a time-series study in Taipei, Taiwan

As important precursors of ozone and secondary organic aerosols, the harmful impact of exposure to ambient volatile organic compounds (VOCs) is of public health interest. However, few studies have investigated the health risks of numerous individual VOC species. This study linked the daily concentrations of 54 C2–C11 VOC species monitored from the Wanhua Photochemical Assessment Monitoring Station and hospital admissions for cardiorespiratory diseases in Taipei, Taiwan, from the National Health Insurance Research Database. A standard time-series approach entailing a series of sensitivity analyses was applied to investigate the short-term health risks of exposure to VOC subgroups and species. Consistent associations of all VOC subgroups and main species with chronic obstructive pulmonary disease (COPD) hospitalizations were demonstrated. In addition, associations of the C5–C6 alkanes, C2–C3 alkenes, toluene, and xylene with asthma hospitalizations were found, as were associations of aromatic hydrocarbons with hospitalizations for heart failure. An interquartile range increase in total VOC exposure at lag0 day (102.6 parts per billion carbon) was associated with increments of 1.84% (95% confidence interval: 0.54%–3.15%), 1.65% (0.71%–2.60%), and 1.21% (0.36%–2.07%) in hospitalizations for asthma, COPD, and heart failure, respectively. The effect estimates were robust with data excluding extreme values, the second pollutant adjustment for PM2.5 and O3, and the Bonferroni correction. The associations of ambient VOC exposure with cardiorespiratory hospitalizations in Taipei serve as a reference for VOC regulations and ozone control strategies.

Ozone Generation by Ultraviolet Lamps†.

The COVID-19 pandemic has generated a great deal of interest in ultraviolet germicidal irradiation (UVGI) as an important means to disinfect air and surfaces. The traditional lamp employed for UVGI has been the low-pressure mercury-discharge lamp that emits primarily at 254nm in the ultraviolet photobiological band UV-C (100-280nm). The recent development of even shorter-wavelength UV-C lamps, such as the Krypton-Chloride, 222-nm lamp, has led to greater concerns about the UV-C generation of ozone. It is well known that wavelengths below 240nm more readily generate ozone. However, there is a great misunderstanding with regard to the actual generation and dissipation of ozone molecules by UV-C lamps. A review of this subject is much warranted. An overview of the ozone generation of various UV-C light sources is presented to give users a better understanding of risk and how to assure control of ozone when employing UV-C lamps.

Rising surface ozone in China from 2013 to 2017: A response to the recent atmospheric warming or pollutant controls?

With the enactment of Air Pollution Action Plan in 2013, the air quality improved in most Chinese cities, except that surface ozone (O3) increased markedly. Some recent studies have examined this issue and presented controversial opinions, but only focus on summertime ozone increase. This study extends a comprehensive analysis of the influencing factors on China's ozone changes from 2013 to 2017 out of the summer season, combining satellite data, ground measurements and model analyses. The annual trends of air pollutants, e.g., increase in 95th percentile O3 concentration (+1.4–8.7 μg m−3 yr−1), and decreases in fine particulate matter (PM2.5; −4.0~−7.5 μg m−3 yr−1) and sulfur dioxide (−2.6~−9.7 μg m−3 yr−1) are uncovered by satellite and observational data. Model results show that the attributions of surface O3 changes from 2013 to 2017 vary spatially and seasonally, and most regions are more affected by emission changes (−9.5–47.0 μg m−3) rather than meteorological changes (−8.1–21.3 μg m−3). In specific regions and seasons, e.g., south/southwestern and eastern China south of 35°N in May and July, the surface O3 responses to climate variability could have an equal or even greater importance than emission changes. In these major pollution control regions, e.g. northern and mid-eastern China, the precursor emissions control (11–35%) contributes in the same degree as the changes in aerosol effects (35–38%) to surface ozone enhancement in the warm seasons. More scientific emission controls and climate adaptation strategies are required to attain the synergetic control of atmospheric particulate matter and ozone in China.

Experimental investigation of the effect of collection length in a two-stage electrostatic precipitator for removal of PM2.5

• The effect of collection length in a two-stage ESP was investigated in detail under consideration of various factors. • The collection efficiency of sub-micron particles could reach up to be more than 95% at 4 m/s gas velocity. • The sequence of the influence degree of main parameters in governing ozone concentration was obtained. In this work, a laboratory-scale charger, with a single wire electrode of one charging unit for effective ozone control, and collector with a 300 mm length and 5 mm plate-plate distance extremely short for high-efficient capture of noxious particles, was designed and assembled as a two-stage ESP to study the effect of collection length for removal of PM2.5, in particular to these sub-micron particles which had the highest penetration rate during the electrostatic capture process. The influence factors, including the current density of charger, the electric field strength of collector, and gas velocity, were investigated in detail. Multiple channels of the collector were chosen to thoroughly compare the performance difference by detecting the particle concentration in the electric field directly. Besides, the ozone concentration test was carried out in various parameters to explore the influence degree simultaneously. Experimental results showed that the collection efficiency based on the number concentration could reach up to be 92.9%, 96.7%, and 97.7% for 0.25 μm, 0.35 μm, and 0.45 μm diameter particles at 4 m/s gas velocity, respectively, which benefited from the advantages of long collection plate and short migration distance. Compared with the influence factors of charger current density and gas velocity, electric field strength occupied the middle position in effecting the collection efficiency, whose most massive index factor was about 18 at a collection length of 30 cm. While the maximum index factor of current density was 3.7 at a collection length of 15 cm and of gas velocity was 27.5 at a collection length of 10 cm. The ozone concentration test suggested that charger current, gas velocity, collection length, and electric field strength could affect the ozone concentration from strong to weak in sequence.

Concentration monitoring of volatile organic compounds and ozone in Xi'an based on PTR-TOF-MS and differential absorption lidar

Ozone has become a severe ambient pollutant. As the critical precursors of the formation of ozone, volatile organic compounds (VOCs) can adversely affect the atmospheric environment. In order to obtain reliable data on the sources and pollution characteristics of VOCs and ozone in the city for precise emission reduction, the concentrations of VOCs and ozone in Xi'an city were monitored by navigation observation using both a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) and differential absorption lidar. Three different functional areas were selected, including a residential area (RA), a commercial district (CD), and an industrial park (IP). The PTR-TOF-MS measurement results found total concentrations of VOCs (TVOCs) with mean values of 136 ppb, 175 ppb, and 267 ppb at RA, CD, and IP sites, respectively. The dominant category of VOCs was oxygenated VOCs (OVOCs) at all three sites, accounting for 86%, 81%, and 75% of TVOCs at the RA, CD, and IP sites, respectively. Among OVOCs and aromatic hydrocarbons (AHs), acetone and toluene were the predominant chemical species, accounting for 51% and 58% at the IP site, respectively. Propylene was the most abundant aliphatic hydrocarbon (ALH) at the RA and CD sites, accounting for 42% and 48% of the TVOCs, respectively. The average ozone formation potentials (OFP) of the measured VOCs were 546 μg/m3, 574 μg/m3, and 772 μg/m3 at the RA, CD, and IP sites, respectively; OVOCs were the dominant contributors to OFP at all three sites. Ozone concentrations were measured by differential absorption lidar, with mean values of 82 μg/m3, 92 μg/m3, and 117 μg/m3 at the RA, CD, and IP sites, respectively. Ozone concentration was correlated to VOCs concentration. Local meteorological conditions including wind speed and air pressure influenced VOCs and ozone concentrations. The assessment of the measurement results of local environmental protection departments indicated that forming relevant VOCs and ozone control policies and priority strategies should be considered in order to reduce the adverse effects of these pollutants.

Ozone pollution control strategies examined by Empirical Kinetics Modeling Approach over the Beaumont-Port Arthur region in Texas of USA

Ground-level ozone is harmful to both human health and ecological environment, which is formed by reactions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. With the increasingly rigorous ozone standard in the U.S., it is important to examine ozone pollution control strategies to help air-quality management in a concentrated industrial region, such as Beaumont-Port Arthur (BPA) areas in Texas of USA. In this study, the method of Empirical Kinetics Modeling Approach (EKMA) associated with the comprehensive air quality modeling with extensions (CAMx) have been employed to demonstrate feasible air-quality control strategies to examine the effects of VOCs and NOx abatement on ozone concentration in the BPA area. Case studies included base case simulations as well as those with 25%, 50%, and 75% reductions of anthropogenic NOx and/or VOCs emissions in the BPA area, which were based on the TCEQ-provided meteorological and emission inventories for a high ozone episode. Simulation results indicated that NOx abatement is more effective than VOCs abatement in reducing ozone concentrations for BPA area, which suggestively belongs to the NOx-sensitive regime for ozone pollution. The average 8-hr ozone could be reduced 3.3%, 7.0% and 11.1%, respectively, by 25%, 50% and 75% of both NOx and VOCs emission abatement. The effect of pollutant abatement on ozone reduction is observed to be different at eight monitor stations in BPA region. Also, the nonlinear relationship between ozone and its precursors has been observed. This study could be helpful to provide scientific and technological support for the future development of air-quality management and ozone control strategies in a concentrated industrial region.

Field measurement of the organic peroxy radicals by the low-pressure reactor plus laser-induced fluorescence spectroscopy

A low-pressure reactor (LPR) was developed for the measurement of ambient organic peroxy (RO2) radicals with the use of the laser-induced fluorescence (LIF) instrument. The reactor converts all the ROx (= RO2 + HO2 + RO + OH) radicals into HO2 radicals. It can conduct different measurement modes through altering the reagent gases, achieving the speciated measurement of RO2 and RO2# (RO2 radicals derived from the long-chain alkane, alkene and aromatic hydrocarbon). An example of field measurement results was given, with a maximum concentration of 1.88 × 108 molecule/cm3 for RO2 and 1.18 × 108 molecule/cm3 for RO2#. Also, this instrument quantifies the local ozone production rates directly, which can help to deduce the regional ozone control strategy from an experimental perspective. The new device can serve as a potent tool for both the exploration of frontier chemistry and the diagnosis of the control strategies.

Synoptic condition-driven summertime ozone formation regime in Shanghai and the implication for dynamic ozone control strategies

Regarding the continuous worsening of tropospheric ozone pollution, the scenario in Shanghai is a microcosm of the entire China. Understanding the ozone formation regimes (OFRs), their variations, and driving factors is a prerequisite for formulating effective ozone control strategies. Traditional OFR estimation by numerical model, which often involves sensitivity analysis on at least tens of scenarios, is labor-intensive and time-consuming; therefore, it is not appropriate to make OFR forecasts to guide ozone contingency control. In this study, by using a localized modeling system consisting of the Weather Research and Forecasting, Sparse Matrix Operator Kernel Emissions, and Community Multiscale Air Quality models and considering the latest emission inventory over the Yangtze River Delta of China, we discovered a strong connection between the variations of large-scale circulation (LSC) and OFRs over Shanghai in July 2017, thereby providing an alternative way to infer OFR. During the northward movement of Western Pacific Subtropical High from South China Sea, the wind field over Shanghai changed from weak westerly to moderate southwesterly and to one without a distinct direction. The local OFR shifted from anthropogenic volatile organic compounds (AVOCs)-limited to NOx-limited and ultimately to the transitional regime. Such a variation in OFR is essentially driven by the spatial heterogeneity of NOx and AVOC emissions in different directions of Shanghai, brought on by the wind under different LSC patterns. With the existing weather forecasting technology, the LSC patterns can be well-predicted 48–72 h in advance. Hence, we propose the adoption of a dynamic ozone control strategy for Shanghai with the priority control target on AVOC or NOx emission sources adjusted according to the LSC pattern and OFR forecasts in a forthcoming O3 pollution episode. This would serve to maximize the peak ozone reduction under varying pollution conditions.

Ozone Trends from Two Decades of Ground Level Observation in Malaysia

We examine the change in surface ozone and its precursor behavior over 20 years at four locations in western Peninsular Malaysia which have undergone urban-commercial development. Trend and correlation analyses were carried out on ozone and oxides of nitrogen observation data over the periods of 1997–2016 as well as the decadal intervals of 1997–2006 and 2007–2016. Diurnal variation composites for decadal intervals were also plotted. Significant increasing ozone concentrations were observed at all locations for the 20-year period, with a range between 0.09 and 0.21 ppb yr−1. The most urbanized location (S3) showed the highest ozone trend. Decadal intervals show that not all stations record significant increasing trends of ozone, with S1 recording decreasing ozone at a rate of −0.44 ppb yr−1 during the latter decade. Correlation analysis showed that only oxides of nitrogen ratios (NO/NO2) had significant inverse relationships with ozone at all stations corresponding to control of ozone by photostationary state reactions. The diurnal composites show that decadal difference in NO/NO2 is mostly influenced by change in nitric oxide concentrations.

Calculation of maximum incremental reactivity scales based on typical megacities in China

<p indent=0mm>Ozone pollution is becoming increasingly serious in China, the accurate calculation of the volatile organic compounds (VOCs) contributions to ozone formation potential is the precondition for scientific and effective ozone control strategies. Maximum incremental reactivity (MIR) is an effective tool to evaluate VOCs’ reactivities, which may vary significantly because of different atmospheric conditions, VOCs compositions, and the relative abundances of VOCs and NO_{<italic>x</italic>}. Nevertheless, the most widely used MIR calculated by Carter based on 39 urban areas in the United States reflected the ozone formation potential of each VOCs species under atmospheric conditions in US. Whether their MIR values are appropriate under atmospheric conditions in China or not is still under discussion. In order to calculate the real contribution of VOCs to ozone formation, we firstly calculated the indigenized MIR values for Chinese megacities. Box model based on the second Regional Atmospheric Chemistry Mechanism (RACM2) was used to calculate the indigenized MIR for China. Observed data of four megacities (Beijing-Tianjin-Hebei, Yangtze River Delta, Pearl River Delta and Chengdu-Chongqing) which represent the typical atmospheric conditions in China were used as input parameters in calculation. We set two scenarios (Base scenarios and MIR scenarios) for MIR calculation, where Base scenarios were established by selecting the fourth highest ozone day during three years’ observed data, MIR scenarios were set by adjusting the NO_{<italic>x</italic>} availability to obtain the scenarios where ozone formation was most sensitive to VOCs. MIR values were calculated via the ratio of the change in ozone concentration due to the change in VOCs concentration divided by the change of VOCs concentrations in MIR scenarios. MIR_CHN (MIR values for four megacities) was obtained by averaging the normalized MIR values of all sites, with an uncertainty of 25%. Compared to the MIR calculated by Carter (MIR_USA in this study), our results showed a larger range values between the most active VOCs and the most inert VOCs. The MIR_CHN values of highly reactive VOCs (such as internal alkenes, butadiene, anthropogenic dienes, terminal alkenes, isoprene and o/m/p-xylene) were higher than MIR_USA values. Whereas MIR_CHN values of low reactive VOCs (HC5 and acetylene) were lower than MIR_USA values. Values of MIR_CHN and values of MIR_UAS were comparable for the moderate reactive VOCs. The differences between MIR_CHN and MIR_USA may be caused by differences in simulation time, reaction mechanism, and proportion of ozone precursors, NO_{<italic>x</italic>} availability, and VOCs compositions. Ozone formation potential of four megacities calculated by the MIR_CHN were much higher than that calculated by the MIR_USA, which meant that using MIR_USA may not only underestimate ozone formation potential, but also miss the key VOCs species in ozone formation in China. The key VOCs were isoprene, internal alkenes and m/p-xylene in ozone formation in China based on MIR_CHN calculation.

Membrane fouling potential of the denitrification filter effluent and the control mechanism by ozonation in the process of wastewater reclamation

A process of denitrification filter (DNF) coupled with ultrafiltration (UF) and ozonation (DNF-UF-O3) has been widely applied to advanced nitrogen removal for wastewater reclamation. Despite of the effective removal of nitrogen by DNF, the influence of DNF stage on the operation of UF was still unclear. In this study, a laboratory filtration system was used to investigate the membrane fouling potential of DNF effluent and the fouling control of ozonation. The membrane fouling potential was proved to be increased significantly after DNF stage and alleviated with ozonation treatment. With the help of UV–vis, fluorescence spectroscopy, scanning electron microscopy (SEM) and molecular weight (MW) analysis, the change of DOM component characteristics was proved to be in accordance with the change of fouling potential. The water samples were further fractionated into six hydrophobic/hydrophilic acidic/basic/neutral fractions, among which hydrophobic acids (HOA) and hydrophobic neutrals (HON) dominated the membrane fouling potential of DNF effluent. Detailed study of each fraction revealed that higher MW components in HOA and HON played a crucial role in the fouling of UF membrane. The dominant component of membrane fouling could be degraded and removed by ozonation, and therefore significant fouling alleviation was achieved. These results indicated that in the process of wastewater reclamation, besides conventional water quality indexes, more detailed water features should also be taken into consideration to optimize the whole process. Moreover, the control effects by ozonation could be monitored simply according to the change of specific UV absorbance (SUVA) and fluorescence intensity as surrogates in engineering applications. According to these results, a modified DNF-O3-UF process with O3 dosage of 3 mg/L was proposed simply by reversing the sequence of UF and O3 with no more infrastructure. This modified DNF-O3-UF process was expected to enlarge the produce capacity of reclaimed water with much lower electricity costs and chemical consumption.

Features of stratospheric ozone distribution in Kazakhstan

Ozone control and monitoring are very important because they provide the world’s population with a basis for making informed decisions and policies to protect life on earth. Since the thinning of the ozone layer is harmful to nature and human health, the study of the spatial and temporal dynamics of stratospheric ozone on the territory of Kazakhstan does not lose its significance. Based on aerological data obtained from observations of the world ozone and ultraviolet data center and the University of Wyoming, the total amount of ozone and its relationship with other meteorological parameters (air temperature above 20 km altitude, relative humidity and wind speed) at stations where ozone observations are carried out in Kazakhstan were investigated and the correlation between them was calculated. Correlation analysis of control series was used to study the relationships between values, hypotheses were made about possible mechanisms of their interaction, and the method of statistical processing was used as a research method. The average annual moves of the considered characteristics are given. As a result, it was found that each of the considered meteorological parameters affects the ozone concentration, especially in close connection with changes in air temperature. Under the influence of strong heating of the stratosphere, a positive relationship between the air temperature and the total ozone was revealed, while under normal conditions it has a negative relationship.