Source Of O3 Research Articles

Characteristic and Spatiotemporal Variation of Air Pollution in Northern China Based on Correlation Analysis and Clustering Analysis of Five Air Pollutants

AbstractAir quality in Northern China has become a global hot spot issue due to a series of air pollution events in the recent years. In this study, five representative air pollutants (PM2.5, SO2, NO2, CO, and O3) were employed to reveal the spatial and temporal distribution of air pollution in Northern China. Periodic decline in PM2.5, SO2, CO, and NO2 from 2016 to 2018 indicated that air pollution control measures have achieved desired results. In addition, PM2.5 was significantly positively correlated with SO2, CO, and NO2 (p < 0.001), and O3 had negative correlations with the other four pollutants. Furthermore, the heavy pollution phenomenon in Shijiazhuang, Anyang, Xingtai, and Handan was attributed to their industrial structures (e.g., steel industry) and geographical location based on clustering analysis. Contrary to above four pollutants, the annual average concentrations of O3 increased in all the nine cities (1.4–35.9%) from 2016 to 2018. It is necessary to plan mitigation strategy for O3 based on further investigation of source and formation mechanism of O3.

Evaluation of Ozone Generation in Volume Spiral-Tubular Dielectric Barrier Discharge Source

Ozone, due to its high reactivity cannot be stockpiled, and thus requires to be generated on-demand. The paper reports on laboratory studies of O3 generation in a volume dielectric barrier discharge (DBD) tubular flow-through system with a coaxial-spiral electrode arrangement. Its performance is experimentally verified and compared to a commercial surface DBD O3 source fitted with a three-electrode floating supply arrangement. The presented volume DBD design is capable of steadily producing up to 4180 ppmv O3 at 1 Nl/min unprocessed atmospheric air intake and 10 kV 1.6 kHz sinusoidal high voltage supply corresponding to 67 g/kWh O3 production yield increasing to 93 g/kWh at 100 Nl/min air intake. The effects of high voltage supply tuning are also investigated and discussed together with finite element method simulation results.

Characteristic of Surface Ozone and Meteorological Parameters Analysis in Anyang City

This study uses the national ambient air quality station data of Anyang City from 2014 to 2017 to analyze the characteristics and variation rules of ozone (O3) in different functional zones (urban, suburban, and industrial), and also studies meteorological influencing factors and potential source distributions of O3 pollution. The results showed that the O3 concentration in Anyang increased significantly between 2014 and 2017, whereby pollution started to advance from 2015 and the earliest occurrence of an O3 pollution episode was in April 2017. The 90th percentile and average concentrations of O3 in the industrial zone increased at faster rates (average annual growth of 16.0 μg·m-3 and 13.0 μg·m-3, respectively) than of those in the urban and suburban zones. The O3 concentrations at the suburban site showed the fastest increase of all zones at the 5th percentile (average annual growth of 13.2 μg·m-3). The monthly variation in O3 concentrations in Anyang showed an "M" pattern that varied spatially depending on the zone. Temperature played a leading role in O3 concentrations; air temperatures >23℃, relative humidity <58%, and a wind speed of 5 m·s-1 in a south-southwesterly direction were closely related to the occurrence of high O3 concentrations. Potential sources of O3 in different seasons were significantly different, and mainly distributed in southern Hebei, northern Hubei, and northern Shenyang in summer. The first heavy O3 pollution day in the studied period was in May 2017, at which time the highest O3 concentration was found in the industrial zone (up to 405 μg·m-3). This heavy O3 pollution episode was related to the continuous high temperature that was caused by the transfer of a dry, hot air mass in western China.

Source attribution of European surface O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; using a tagged O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; mechanism

Abstract. Tropospheric ozone (O3) is an important air pollutant that affects human health, ecosystems, and climate. The contributions of O3 precursor emissions from different geographical source regions to the O3 concentration can help to quantify the effects of local versus remotely transported precursors on the O3 concentration in a certain area. This study presents a “tagging” approach within the WRF-Chem model that attributes O3 concentration in several European receptor regions to nitrogen oxide (NOx) emissions from within and outside of Europe during April–September 2010. We also examine the contribution of these different precursor sources to various O3 metrics and their exceedance events. Firstly, we show that the spatial distributions of simulated monthly mean MDA8 from tagged O3 source regions and types for late spring, summer, and early autumn 2010 varies with season. For summer conditions, O3 production is dominated by national and intra-European sources, while in the late spring and early autumn intercontinental transported O3 is an important contributor to the total O3 concentration. We have also identified shipping activities in the Mediterranean Sea as an important source of O3 for the Mediterranean countries, as well as the main contributor to high modelled MDA8 O3 concentration in the Mediterranean Basin itself. Secondly, to have a better understanding of the origin of MDA8 O3 exceedances, we compare modelled and observed values of MDA8 O3 concentration in the Po Valley and Germany–Benelux receptor regions, revealing that the contribution from local sources is about 41 % and 38 % of modelled MDA8 O3 during the exceedance days, respectively. By examining the relative contributions of remote NOx sources to modelled and observed O3 exceedance events, we determine that model underrepresentation of long-range O3 transport could be contributing to a general underestimation of modelled O3 exceedance events in the Germany–Benelux receptor region. Thirdly, we quantify the impact of local vs. non-local NOx precursors on O3 production for each European receptor region using different O3 metrics. The comparison between mean, MDA8 and 95th percentile O3 metrics accentuates the importance of large contributions from locally emitted NOx precursors to the high end of the O3 distribution. When we compare the vegetation and health metrics, we notice that the SOMO35 and AOT40 indexes exhibit rather similar behaviour, while the W126 index accentuates the importance of local emissions. Overall, this study highlights the importance of a tagging approach to quantify the contribution of local and remote sources to the MDA8 O3 concentration during several periods as well to different O3 metrics. Moreover, this method could be applied to assess different mitigation options.

Summertime ozone pollution in the Yangtze River Delta of eastern China during 2013–2017: Synoptic impacts and source apportionment

Severe ozone (O3) pollution in China has magnified global concerns over the past years. Exploring the synoptic impacts and quantifying the source contributions are important for mitigating O3 pollution. This study focuses on the summertime O3 pollution over the Yangtze River Delta (YRD) in eastern China. We identify six predominant synoptic weather patterns (SWPs) over the YRD during 2013–2017 using the self-organising map (SOM) approach. We conduct O3 source attribution based on ozone source apportionment technology (OSAT) in a regional transport model. Surface O3 pollution is found to be sensitive to the predominant SWPs, including four O3-polluted types (northeasterly, northerly and southwesterly and anticyclone) and two O3-clean types (cyclone and the Meiyu front). The integrated influences of local chemistry and regional transport are important in O3 pollution under different SWPs. Daily maximum 8-h average (MDA8) O3 holds strong negative and positive correlations with relative humidity and sunshine duration, respectively. Among the six SWPs, the concentration and exceedance of MDA8 O3 reach their maxima under the northerly type on a regional average. Higher O3 levels, particularly under the northerly and northeasterly types, are primarily related to regional transport on various spatial scales. Local production accounts for the largest proportion of O3 sources under the anticyclone type. Under the southwesterly type, favourable weather conditions superimposed on regional transport lead to severe O3 pollution in coastal cities. The impact of super-regional transport is most pronounced along the eastern coast under the cyclone type. Source category analysis shows that transportation and industrial emissions play a prime role in surface O3 formation. This study illustrates the imperative implementation of joint emission control over eastern China to reduce O3 pollution.

Source apportionment of summertime ozone in China using a source-oriented chemical transport model

Contributions of industries, power plants, residential, transportation, open burning, and biogenic sectors to summertime ozone (O3) in China in August 2013 are quantified using an improved O3 source apportionment method implemented in a source-oriented Community Multiscale Air Quality (CMAQ) model. The new O3 source apportionment method attributes in-situ O3 formed in each time step to nitrogen oxides (NOx) and volatile organic compounds (VOCs) with a new attribution scheme that considers NOx-VOC-O3 formation sensitivity in NOx-limited, transition, and VOC-limited regimes (three regimes, 3R). This represents an improvement from the traditional O3 source apportionment models, in which O3 formation sensitivity is divided into two-regimes (2R), either NOx-limited or VOC-limited. An expanded source-oriented gas phase chemical mechanism is developed to concurrently track NOx and primary VOCs and their oxidation products from different sources. The source-resolved NO2 photolysis rates and the NO to NO2 conversion rates by peroxy radicals from the source-oriented chemical mechanism are then used to apportion O3 to NOx (O3_NOx) and VOCs (O3_VOC) from different emission sources.Industries, transportation, power plants and biogenic sources are the major emission sectors to O3. High industrial O3_NOx (8–15 ppb; 20–25% of total O3) is mainly located in north and northeast China, the Yantze River Delta (YRD) and part of the Sichuan Basin (SCB). Transportation O3_NOx accounts for 10–15% of total O3 in most urban areas. Power plants’ contributions to O3_NOx (10–15%) are mostly located in Shanxi, Shaanxi, Ningxia and part of Shandong and Jiangsu. The contribution of soil NOx to O3_NOx is highest in regions in west, central and south China with less direct anthropogenic emission influences. VOC-limited grid cells are mostly located at urban cores and large city clusters in the YRD and Pearl River Delta (PRD) regions. Biogenic and industrial sectors are the most important emission sectors that contribute to O3_VOC, accounting for more than 85% of the O3_VOC in China. In north and east provinces, more than 50% of the O3 is non-background, with the provinces in north China having higher overall O3. The Beijing-Tianjin-Hebei (BTH) region has an area-averaged 8-hr O3 of 75 ppb in August 2013 and about half is non-background. Contributions of industries, transportation, power and biogenic sources to non-background O3 are 37%, 22%, 13% and 23%, respectively. The relative contribution of biogenic emissions to non-background O3 is lower on high 8-hr O3 days. The 2R and 3R approaches show significant differences in assessing the relative importance of O3_NOx and O3_VOC, with the 2-regime approach predicting lower O3_NOx but higher O3_VOC. The new source allocation method for O3_VOC can lead to up to 10% differences for industrial and biogenic sectors.

Ozone source apportionment during peak summer events over southwestern Europe.

It is well established that in Europe, high O3 concentrations are most pronounced in southern/Mediterranean countries due to the more favourable climatological conditions for its formation. However, the contribution of the different sources of precursors to O3 formation within each country relative to the imported (regional and hemispheric) O3 is poorly quantified. This lack of quantitative knowledge prevents local authorities from effectively designing plans that reduce the exceedances of the O3 target value set by the European air quality directive. O3 source attribution is a challenge because the concentration at each location and time results not only from local biogenic and anthropogenic precursors, but also from the transport of O3 and precursors from neighbouring regions, O3 regional and hemispheric transport and stratospheric O3 injections. The main goal of this study is to provide a first quantitative estimation of the contribution of the main anthropogenic activity sectors to peak O3 events in Spain relative to the contribution of imported (regional and hemispheric) O3. We also assess the potential of our source apportionment method to improve O3 modelling. Our study applies and thoroughly evaluates a countrywide O3 source apportionment method implemented in the CALIOPE air quality forecast system for Spain at high resolution (4 × 4 km2) over a 10-day period characterized by typical summer conditions in the Iberian Peninsula (IP). The method tags both O3 and its gas precursor emissions from source sectors within one simulation, and each tagged species is subject to the typical physico-chemical processes (advection, vertical mixing, deposition, emission and chemistry) as the actual conditions remain unperturbed. We quantify the individual contributions of the largest NOx local sources to high O3 concentrations compared with the contribution of imported O3. We show, for the first time, that imported O3 is the largest input to the ground-level O3 concentration in the IP, accounting for 46 %–68 % of the daily mean O3 concentration during exceedances of the European target value. The hourly imported O3 increases during typical northwestern advections (70 %–90 %, 60–80 μg m−3), and decreases during typical stagnant conditions (30 %–40 %, 30–60 μg m−3) due to the local NO titration. During stagnant conditions, the local anthropogenic precursors control the O3 peaks in areas downwind of the main urban and industrial regions (up to 40 % in hourly peaks). We also show that ground-level O3 concentrations are strongly affected by vertical mixing of O3-rich layers present in the free troposphere, which result from local/regional layering and accumulation, and continental/hemispheric transport. Indeed, vertical mixing largely explains the presence of imported O3 at ground level in the IP. Our results demonstrate the need for detailed quantification of the local and remote contributions to high O3 concentrations for local O3 management, and show O3 source apportionment to be an essential analysis prior to the design of O3 mitigation plans in any non-attainment area. Achieving the European O3 objectives in southern Europe requires not only ad hoc local actions but also decided national and European-wide strategies.

Ozone source apportionment over the Yangtze River Delta region, China: Investigation of regional transport, sectoral contributions and seasonal differences

With the stringent emission control measures implemented in recent years, the overall air quality in China has been improved greatly. However, high ozone (O3) concentrations have become a more and more severe air pollution issue in the rapidly developing Yangtze River Delta (YRD) region of eastern China including Shanghai, Jiangsu, Zhejiang and Anhui provinces. The 90th percentile of O3-8 h concentration in the YRD region increased from 144 μg/m3 in 2013 to 168 μg/m3 in 2017. To investigate the sources of O3 within the YRD region, we use a tagged-species method in the Comprehensive Air Quality Model with Extensions (CAMx) called Ozone Source Apportionment Technology (OSAT) to quantify O3 contributions by source regions and sectors in Spring, Summer and Fall. We find that the O3 pollution in Shanghai, southern Jiangsu and northern Zhejiang is caused by the joint effect of local to regional precursor emissions combined with super-regional O3 transport. However, these contributions vary among seasons and pollution events. Super regional transport is the major contributor to average O3 concentration while local and upwind adjacent area contributions can dominate during high O3 concentration episodes. Source sector analysis indicates that industry and vehicle emissions are major anthropogenic sources. Within the industrial sector, power plants, boilers, and petroleum industry are the top three contributors. Reducing super-regional O3 transport is of the most importance to lowering the O3 background but local to regional precursor emission reductions are also of great significance to control O3 episodes with collaboration at the regional level offering potential for synergistic benefits to adjacent cities.

Characteristics and Formation Mechanism of Surface Ozone in a Coastal Island of Southeast China: Influence of Sea-land Breezes and Regional Transport

ABSTRACT The ozone (O3) concentrations in island cities are low due to the relatively low concentrations of O3 precursors. However, Pingtan, a typical island city along the southeast coast of China, suffers from frequent O3 pollution. In this study, one year of hourly O3 concentration data collected from three sites (rural, suburban, and urban) on Pingtan were used to investigate the characteristics and formation mechanism of O3 pollution. The results showed that the minimum O3 concentrations measured at the three sites were larger than 55.53 µg m–3, which was likely caused by low NO titration over Pingtan. The O3 concentrations in summer were low because of the East Asian monsoon. The daily maximum O3 concentrations with sea and land breezes (SLBs) were higher than those without SLBs at all three sites (8.52, 9.84, and 14.30 µg m–3 at the rural, suburban, and urban sites, respectively). In addition, SLBs amplified the diurnal variation in O3 concentrations. Cluster analysis and the analysis of an episode of high O3 concentration indicated that the developed Yangtze River Delta is the main source of O3 in Pingtan. This study helps reveal the characteristics and formation mechanism of O3 pollution in island cities.

Attribution of Tropospheric Ozone to NO x and VOC Emissions: Considering Ozone Formation in the Transition Regime.

An improved three-regime (3R) O3 attribution technique for O3 source apportionment in regional chemical transport models is developed to divide the entire range of VOC-NO x-O3 formation sensitivity to VOC-limited, transition, and NO x-limited regimes based on the value of a regime indicator R. The threshold R values to mark the start ( Rts) and end ( Rte) of the transition regime are defined at the point where O3-NO x sensitivity turns from negative to positive and where O3-NO x sensitivity is ten times higher than O3-VOC sensitivity, respectively. Rts and Rte are determined using NO x and VOC sensitivity simulations in a box model with a modified SAPRC-11 mechanism. For the widely used indicator ration R = ( PH2O2 + PROOH)/ PHNO3, which is based on the production rates of H2O2, HNO3 and organic hydroperoxides (ROOH), the recommended Rts and Rte values are 0.047 and 5.142, respectively. Parameterized attribution functions, depending only on the values of R, are developed to apportion modeled in situ O3 formation in the transition regime to NO x and VOCs. The new 3R and the traditional two-regime (2R) schemes are incorporated into the Community Multiscale Air Quality (CMAQ) model to quantify NO x and VOC contributions to regional O3 concentrations in China in August 2013. The 3R approach predicts approximately 5-10 ppb and up to 15 ppb higher NO x contributions to 8 h O3 in in the North China Plain, the Yangtze River Delta and the Pearl River Delta than the 2R approach. The big differences in O3 attribution between 2R and 3R can have significant policy implications for air pollution emission controls.

Ozonation of pentabromophenol in aqueous basic medium: Kinetics, pathways, mechanism, dimerization and toxicity assessment

Ozonation has been identified effective technique to degrade phenolic compounds, and production of intermediate dimers are major threat. In this study, we systematically investigated the degradation of Pentabromophenol (PBP) in an aqueous medium by using two different ozone generators (sources: air and water). We studied various factors that influenced the degradation kinetics of PBP, including the pH (7.0, 8.0, and 9.0), humic acid (HA) and anions (Cl−, SO42−, NO3−, and HCO3−). PBP was efficiently degraded within 5 min (O3 source: water) and 45 min (O3 source: air) at pH 8.0 maintained by phosphate buffer. Reaction kinetics revealed 17 b y-products with five possible pathways, including dimers with their isomers and lower bromophenols. Furthermore, the frontier molecular orbital theory was employed to confirm the proposed ozonation pathways, including the breakage of the CO bond at C5 and C4 positions, and the cleavage of the CC bond at C3 and C6 position. Product P5, P14 (hydroxyl-nonabromophenyl ether) and P15 (dihydroxyl-octabromophenyl ether) were identified with isomers. Ecological Structure Activity Relationships toxicity assessment resulted into the conversion of highly toxic PBP (acute toxicity: LC50 = 0.11 mg L−1 for fish, LC50 = 0.124 mg L−1 for daphnia, and EC50 = 0.118 mg L−1 for green algae) to less harmful products aside from dimers. P14 (acute toxicity: LC50 = 1.04 × 105) found to be more toxic as compare to PBP. From these findings, we concluded that ozonation is an effective and ideal process for PBP degradation.

Ozone production in a maritime pine forest in water-stressed conditions

During two growing seasons of a maritime pine stand, in 2014 and 2015, ozone (O3) fluxes have been determined using the eddy covariance (EC) method and compared to the outputs of a big-leaf O3 deposition model including stomatal, cuticular and soil pathways. The model developed in this study generally allowed to properly reproduce the measured ozone deposition. Ozone fluxes showed a strong reduction during two water stressed periods in September 2014 and July 2015. The model partly explain this fall due to the reduction of stomatal deposition. Despite this stomatal closure, measured O3 fluxes presented systematically lower negative values than the model outputs, and sometimes even positive values around midday during periods marked by strong water stress. In other words, the difference between observed and modelled O3 fluxes (hereinafter referred to as the residual O3 flux) is systematically positive on daytime during these water-stressed periods.This positive residual flux traduced the existence of an O3 source below the flux measurement level, responsible for positive fluxes that counterbalance deposition fluxes. We developed an O3 production module based on a terpene emission algorithm and an OH concentration proxy, to try to explain the observed ozone production. As this parametrisation allowed us to reproduce well the daily and inter-daily dynamics of the residual O3 flux, it confirms that the latter actually resulted from O3 production processes. This ozone production is here highlighted for the first time using O3 fluxes measurements by the EC method. The chemical reactions possibly involved in O3 production processes in this maritime pine forest have been discussed and different mechanisms are proposed, based on peroxy radicals chemistry or stress-induced BVOCs.

Seasonal influences on surface ozone variability in continental South Africa and implications for air quality.

Although elevated surface ozone (O3) concentrations are observed in many areas within southern Africa, few studies have investigated the regional atmospheric chemistry and dominant atmospheric processes driving surface O3 formation in this region. Therefore, an assessment of comprehensive continuous surface O3 measurements performed at four sites in continental South Africa was conducted. The regional O3 problem was evident, with O3 concentrations regularly exceeding the South African air quality standard limit, while O3 levels were higher compared to other background sites in the Southern Hemisphere. The temporal O3 patterns observed at the four sites resembled typical trends for O3 in continental South Africa, with O3 concentrations peaking in late winter and early spring. Increased O3 concentrations in winter were indicative of increased emissions of O3 precursors from household combustion and other low-level sources, while a spring maximum observed at all the sites was attributed to increased regional biomass burning. Source area maps of O3 and CO indicated significantly higher O3 and CO concentrations associated with air masses passing over a region with increased seasonal open biomass burning, which indicated CO associated with open biomass burning as a major source of O3 in continental South Africa. A strong correlation between O3 on CO was observed, while O3 levels remained relatively constant or decreased with increasing NOx, which supports a VOC-limited regime. The instantaneous production rate of O3 calculated at Welgegund indicated that ~ 40 % of O3 production occurred in the VOC-limited regime. The relationship between O3 and precursor species suggests that continental South Africa can be considered VOC limited, which can be attributed to high anthropogenic emissions of NOx in the interior of South Africa. The study indicated that the most effective emission control strategy to reduce O3 levels in continental South Africa should be CO and VOC reduction, mainly associated with household combustion and regional open biomass burning.

Investigation of high ozone events due to wildfire smoke in an urban area

Using data from the St. Luke's site in Meridian, ID (near Boise) during 2006–2017 and a 2017 summer intensive campaign, we investigate enhancements in ozone (O3) during wildfire events in an urban area. We calculate a wildfire criterion based on the National Oceanic and Atmospheric Administration (NOAA) National Environmental Satellite, Data, and Information Service (NESDIS) Hazard Mapping System (HMS) smoke product and historically averaged PM2.5 data to determine when wildfire emissions are influencing the area (smoke vs. non-smoke events). We also use a Generalized Additive Model (GAM) to investigate anomalous sources of O3, such as wildfires, in this urban area. During the summer 2017 intensive campaign, we find that peroxyacetyl nitrate (PAN), reactive nitrogen (NOy), and maximum daily 8 h average (MDA8) O3 show significant enhancements during smoke events compared with non-smoke periods (65%, 42%, and 32%, respectively). We calculate the 95% confidence interval of ΔPM2.5/ΔCO, ΔNOy/ΔCO, ΔPAN/ΔNOy, and ΔPAN/ΔCO enhancement ratios (ERs) to be 0.129–0.144 μg/m3/ppbv, 0.018–0.022 ppbv/ppbv, 0.152–0.192 ppbv/ppbv, and 3.04–3.76 ppbv/ppmv, respectively, for wildfire smoke influenced events. We also observe an enhancement in O3 production up to PM2.5 concentrations of 60–70 μg/m3 in smoke, after which we see a reduction in average MDA8 O3 mixing ratios. We use the four highest O3 events during summer 2017 as case studies to examine the highly variable conditions due to the influence of wildfire smoke in an urban area. In two cases, we investigate smoke days that show significant O3 enhancement and moderate PM2.5 concentrations. These cases suggest that ERs, such as ΔPM2.5/ΔCO and ΔNOy/ΔCO, are less useful in determining the influence of wildfire smoke in an urban area on moderate smoke days. Another case shows reduced O3 production during a very high, 3-day smoke event (PM2.5 > 70 μg/m3). After this high smoke period, a 20 ppbv enhancement in MDA8 O3 is observed in moderate smoke. These results indicate that wildfire-influenced O3 enhancements are highly variable in urban areas but generally increase up to around 60 μg/m3 of PM2.5, after which they decrease at very high smoke concentrations. This study also suggests that multiple tracer measurements are needed to fully characterize wildfire plumes in urban areas.

Oxidation processes in the eastern Mediterranean atmosphere: evidence from the modelling of HO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; measurements over Cyprus

Abstract. The Mediterranean is a climatically sensitive region located at the crossroads of air masses from three continents: Europe, Africa, and Asia. The chemical processing of air masses over this region has implications not only for the air quality but also for the long-range transport of air pollution. To obtain a comprehensive understanding of oxidation processes over the Mediterranean, atmospheric concentrations of the hydroxyl radical (OH) and the hydroperoxyl radical (HO2) were measured during an intensive field campaign (CYprus PHotochemistry EXperiment, CYPHEX-2014) in the northwest of Cyprus in the summer of 2014. Very low local anthropogenic and biogenic emissions around the measurement location provided a vantage point to study the contrasts in atmospheric oxidation pathways under highly processed marine air masses and those influenced by relatively fresh emissions from mainland Europe.The CYPHEX measurements were used to evaluate OH and HO2 simulations using a photochemical box model (CAABA/MECCA) constrained with CYPHEX observations of O3, CO, NOx, hydrocarbons, peroxides, and other major HOx (OH + HO2) sources and sinks in a low-NOx environment (&lt; 100 pptv of NO). The model simulations for OH agreed to within 10 % with in situ OH observations. Model simulations for HO2 agreed to within 17 % of the in situ observations. However, the model strongly under-predicted HO2 at high terpene concentrations, this under-prediction reaching up to 38 % at the highest terpene levels. Different schemes to improve the agreement between observed and modelled HO2, including changing the rate coefficients for the reactions of terpene-generated peroxy radicals (RO2) with NO and HO2 as well as the autoxidation of terpene-generated RO2 species, are explored in this work. The main source of OH in Cyprus was its primary production from O3 photolysis during the day and HONO photolysis during early morning. Recycling contributed about one-third of the total OH production, and the maximum recycling efficiency was about 0.7. CO, which was the largest OH sink, was also the largest HO2 source. The lowest HOx production and losses occurred when the air masses had higher residence time over the oceans.

Intra-urban variability of ozone in a tropical city—characterization of local and regional sources and major influencing factors

Tropospheric ozone (O3), a secondary air pollutant, was assessed to evaluate the intra-urban variability of O3, its local and distant sources, and the influence of O3 precursor gases and meteorological variables on seasonal and temporal trends of O3 from 2013 to 2017 in a tropical urban city located in the middle Indo-Gangetic Plains of India. Passive samplers and data from real-time air quality monitoring station were considered. Trajectory statistical models, multivariate statistical methods, and geographic information system were further used to identify spatial-temporal variability and source apportionment. O3 concentrations showed significant intra-urban variability with higher concentrations in suburban or background regions of the city, which were mostly attributed to the transport of O3 at high wind speed from distant and rural areas away from the city, while lower concentrations in traffic and commercial areas were due to titration of O3 by nitric oxide (NO). Variations in meteorological variables (temperature, relative humidity, wind speed) and planetary boundary layer height were responsible for seasonal variations in O3 concentrations. Long-range and regional transport of O3 and its precursors such as volatile organic compounds and NOx from the northwestern and eastern directions of the city significantly influenced O3 variability with distinct seasonal patterns. A negative trend in O3 levels was recorded during the study period which may be due to increase in NOx emission in the city. The observed outcomes suggest significant intra-urban variability of O3 in the city which is influenced by traffic as well as by distant and local sources.

Impact of biogenic emissions on early summer ozone and fine particulate matter exposure in the Seoul Metropolitan Area of Korea

Understanding how ozone (O3) and fine particulate matter (PM) formation respond to the precursor concentrations in the presence of biogenic emissions (BEs) and thereby changes in health effects can be a key step to design effective air quality management plans. This is particularly true in the Seoul Metropolitan Area (SMA), where future significant controls of anthropogenic sources of O3 and PM2.5 precursors are expected. In this paper, we investigate the effects of BEs on O3 and fine PM (PM2.5) concentrations during a strong photochemical air pollution season in the SMA in Korea. O3 and PM2.5 levels are modeled with and without BEs in June 2008. Further, we perform the health impact assessments (HIA) of O3 and PM2.5 concentration changes due to BEs to seek useful implications for air quality management by utilizing the adjusted exposure concentration fields for O3 and PM2.5 with an observation fusing (OBF) method. With BEs, daily maximum 8-h average O3 (maximum 8-h O3) and secondary organic aerosol (SOA) concentrations in the SMA increase by 17 and 474%, respectively. These increments are associated with significant consumption of photochemical oxidants (Ox), such as a ~ 60% reduction in OH∙ radicals. The reduction in Ox, conversely, lowers the production of secondary inorganic aerosols (SIOAs) by 2.7%. Adjusted O3 and PM2.5 exposure metrics and the subsequent HIA reveal that large mean increments of O3, about 8.43 ppb, due to BEs are responsible for approximately 62 all-cause premature mortalities in the SMA in June. However, mean increment of PM2.5 due to BEs is approximately 0.3 μg m−3 and results in negligible impacts on the all-cause mortality. Significant correlations of O3 and mortality rates (MR) with the VOC/NOx ratios across the SMA suggest that controlling volatile organic compounds (VOCs) from anthropogenic sources can be a priority to reduce O3 levels and population health risks in the SMA. Specifically, linear relationships of log [O3] and log [MR] to log [VOC/NOx] ensure that a 10% decrease in the VOC/NOx ratios through the VOC abatements would lead to a 1.5% decrease in the O3 levels and a 4.3% decrease in the MR on average across the SMA.

Structure and Electrical Properties of ZrO2/Al2O3/TiO2 Films Grown Via Atomic Layer Deposition on TiN Electrodes

As the design rule becomes smaller, it becomes increasingly difficult to ensure the storage capacitance of DRAM. At present, ZrO2/Al2O3/ZrO2 (ZAZ) is being used for dielectric film of DRAM capacitor. When the design rule of device becomes < 20nm, the ZAZ film thickness should be too thin to crystalize it. As a result, the dielectric constant of a ZAZ thin film is lower than the expected value, particularly the upper ZrO2 layer [1]. In this regard, TiO2, which has a higher dielectric constant than that of ZrO2 and lower crystallization temperature, could be an alternative to the ZrO2 layer. However, the small band gap of TiO2 (3.4eV) makes it challenging to be used as a single dielectric layer in the structure. Therefore, in this study, the upper ZrO2 layer of the conventional ZAZ structure is replaced by a TiO2 layer, which may result in the lower equivalent oxide thickness (EOT) than that of the original structure without a significant increase in the leakage current. In this study, the electrical and physical properties of ZrO2/Al2O3/TiO2 (ZAT) and ZAZ deposited on TiN substrate using ALD method were evaluated. A traveling-wave-type ALD reactor was used for in-situ ZAT and ZAZ and the oxygen source of O3 and the precursors of TEMAZr, TMA and TTIP were used to deposit ZrO2, Al2O3 and TiO2. Various ratios between upper and lower dielectric layers were evaluated in order to observe any changes in their properties. The capacitance density of ZAT dielectric was higher (Figure 1) even without the rapid thermal annealing (RTA) process, and there was no significant difference in the I-V properties. The capacitance of ZAT device was improved by 50% after the N2 ambient RTA performed at 600oC for 30 seconds, but the higher leakage current was observed. The EOT decreases due to the crystallization of TiO2 and the extent of crystallization was analyzed. A tetragonal phase was observed in ZrO2 after the annealing. With the use of thinner ZAT films, EOT was improved by ~0.5 nm at a given physical thickness of 7nm which is a significant merit over ZAZ.

Scientific assessment of background ozone over the U.S.: Implications for air quality management.

Ozone (O3) is a key air pollutant that is produced from precursor emissions and has adverse impacts on human health and ecosystems. In the U.S., the Clean Air Act (CAA) regulates O3 levels to protect public health and welfare, but unraveling the origins of surface O3 is complicated by the presence of contributions from multiple sources including background sources like stratospheric transport, wildfies, biogenic precursors, and international anthropogenic pollution, in addition to U.S. anthropogenic sources. In this report, we consider more than 100 published studies and assess current knowledge on the spatial and temporal distribution, trends, and sources of background O3 over the continental U.S., and evaluate how it inflattainment of the air quality standards. We conclude that spring and summer seasonal mean U.S. background O3 (USB O3), or O3 formed from natural sources plus anthropogenic sources in countries outside the U.S., is greatest at high elevation locations in the western U.S., with monthly mean maximum daily 8-hour average (MDA8) mole fractions approaching 50 parts per billion (ppb) and annual 4th highest MDA8s exceeding 60 ppb, at some locations. At lower elevation sites, e.g., along the West and East Coasts, seasonal mean MDA8 USB O3 is in the range of 20-40 ppb, with generally smaller contributions on the highest O3 days. The uncertainty in U.S. background O3 is around ±10 ppb for seasonal mean values and higher for individual days. Noncontrollable O3 sources, such as stratospheric intrusions or precursors from wildfires, can make significant contributions to O3 on some days, but it is challenging to quantify accurately these contributions. We recommend enhanced routine observations, focused fi studies, process-oriented modeling studies, and greater emphasis on the complex photochemistry in smoke plumes as key steps to reduce the uncertainty associated with background O3 in the U.S.

Evaluation of Variations in Ground-Level Ozone (O3) Concentrations

ABSTRACTThis article presents the results of measuring the concentrations of ground-level ozone (O3) in ambient air and meteorological parameters (atmospheric pressure, temperature, wind speed, and relative humidity during the year 2008. The measurements were performed at measuring station located near Campo Grande, away from local sources of O3. Fourier analysis, Principal Component Analysis (PCA) and Multiple Linear Regression (MLR) were used as tools for mathematical analysis of the indicated occurrence. The results of Fourier analysis indicate that not only the daily cycles but also the weekly and monthly cycles are visible in all periods as well as the 12-h cycles. The statistical analysis of the obtained data, based on PCA have shown that approximately 60% of the variance in the measured values can be described with two factors. The attempt of O3 distribution modeling, using MLRA, resulted in a linear model whose coefficient of determination was equal to R2 = 0.98. The results of the study indicate that all these methods are useful for understanding the impact of meteorological parameters on variations of ozone concentration over time.