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Volatile organic compounds (VOCs) and nitrogen oxides (NOx) play a key role in tropospheric chemistry. A typical urban scenario, under VOC-controlled conditions (low VOC/NOx ratios), is discussed with emphasis on the kinetic conditions leading to high ozone concentrations for an urban area of Brazil. As a base case, kinetic and mechanistic reactivities of individual VOCs, were evaluated in the district of Iraja (Rio de Janeiro, Brazil), which receives air masses originating from an industrial area. Aromatic compounds contributed with 41.1% of total mass. They were the most reactive species, representing 48.8% of the total kinetic reactivity and 71.0, 61.0 and 55.9% of the mechanistic reactivity, in MIR, MOIR and EBIR scales, respectively. Results showed that high ozone concentrations are due to a combination of conditions, mainly, relatively low NOx levels and a relatively high reactive VOC mix, primarily originating from an industrial area. Average ozone forming potential for the samples were calculated as 3.57, 1.39 and 0.74 for the MIR, MOIR and EBIR scales, respectively.

The trends per 5th percentile interval of European surface ozone concentrations over urban, suburban and rural sites in the period 1995–2012 have been estimated based on observational data from the European Environment Agency air quality database. Consistent with previous study results, we find a rapid decline of relatively high ozone concentrations after the year 1995, especially of rural summertime ozone. However, the decreasing rate has slowed, and even reversed, of low-level ozone, especially in the urban environment for all seasons. Although the ozone air pollution problem has been declared to be effectively resolved by achieving European air quality goals, our results indicate that ozone remains to be difficult to control for a long time into the future. Global and regional models poorly reproduce the measured differences in ozone and trends in different levels and regions. Thus policy guidelines from the model should be considered with care.

Ozone was investigated as a potential alternative to control phosphine resistant strains of the lesser grain borer, Rhyzopertha dominica (F.). The efficacy of 0.21 and 0.42 g/m3 concentrations of ozone against one phosphine-susceptible laboratory and two phosphine-resistant field strains of R. dominica was evaluated. Vials holding 20 adults with 0 and 10 g of wheat were exposed to each ozone concentration for up to 24 h to estimate lethal doses required for 50 (LD50) and 99% (LD99) mortality. After ozone exposure, mortality was assessed 5 d later. There were no significant differences between LD50 values of the samples exposed to 0.21 and 0.42 g/m3, regardless of strains and presence or absence of wheat. The small amount of wheat (10 g) affected efficacy at 0.21 g/m3, but showed a non-significant effect at 0.42 g/m3. Ozone tends to react with active sites on the surface of wheat kernels prior to reaching an effective lethal concentration for insects. High ozone concentration in the supply air reduced the time to saturate all active sites and ensured that lethal levels of free ozone were available to kill insects. Ozone successfully suppressed the adult progeny production for all tested strains. Emergence of adults from eggs of all three strains was reduced by 96.3–100% only after 72 h exposure to an ozone concentration of 0.42 g/m3. At the same ozone concentration, emergence of adults from young and old larvae was reduced by 97.1–99.7% after a 24 to 34 h exposure. However, reduction in emergence of adults from ozone exposed pupae at 10 h varied among the strains and ranged from 32.8 to 96.6%. After 2 and 6 h of exposure the reduction in emergence of adults from pupae ranged from 19.6 to 76.5%.

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.

Background Studies that seek to link the impact of ozone with mortality display a number of uncertainties. This study sought to ascertain the functional relationship between ozone and mortality, and analyse its short-term impact on daily natural-, respiratory- and circulatory-cause mortality in Spain. Methods We analysed data on daily natural- (ICD 10: A00-R99), respiratory- (ICD 10: J00-J99) and circulatory-cause mortality (ICD 10: I00-I99) for each of Spain's 52 provinces across the period 2000–2009. We calculated the impact of ozone on mortality by reference to relative risks (RRs) using generalised linear models, and performed an overall meta-analysis. Attributable mortality was calculated on the basis of RRs. Results A quadratic relationship was observed and the existence of a threshold value identified in 33 of the 46 monitoring stations judged to be valid for ozone data, this threshold value was located above the 80th percentile. The overall RRs for 10 μg/m3 increases in concentrations of the O3 threshold value were as follows: 1.033 (95%CI: 1.023–1.044) for natural causes; 1.089 (95%CI: 1.058–1.120) for respiratory causes; and 1.025 (95%CI: 1.018–1.033) for mortality circulatory causes. The annual total of natural-cause ozone-attributable deaths was 499 (95%CI: 277–717), 126 of which (95%CI: 54–194) were due to respiratory causes and 167 (95%CI: 39–293) to circulatory causes. Conclusions High ozone concentrations display a quadratic relationship with daily mortality. While this effect is more pronounced in respiratory causes, there is also a short-term effect on natural- and circulatory-cause mortality.

High emissions of volatile organic compounds (VOCs) from the petrochemical industry and vehicle exhaust may contribute to high ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP). In this study, the vertical profiles of VOCs were created for the southern Taiwan industrial city of Kaohsiung. Vertical air samples were collected up to 1000 m using an unmanned aerial vehicle (UAV). In Renwu District, VOC distribution was affected by the inversion layer up to 200 m height. Total VOCs (36–327 ppbv), OFP (66–831 ppbv) and SOAFP (0.12–5.55 ppbv) stratified by height were the highest values at 300 m. The VOCs originated from both local and long-distance transport sources. These findings can be integrated into Kaohsiung's future air quality improvement plans and serve as a reference for other industrialized areas worldwide.

Long-term ozone lidar routine measurements are sparse in China. In this study, we used one year of continuous ozone lidar measurements to systematically investigate the effects of synoptic patterns on the vertical structure of ozone during high ozone episodes in Hong Kong. The height of the near-surface ozone layer was identified and compared with that of the mixing layer. The results showed that Hong Kong was greatly affected by ozone transport from the Pearl River Delta region when a tropical cyclone (“C” pattern) or a trough (“T” pattern) existed. When a high-pressure center was located to the north (“H” pattern) or when both a high-pressure system and a tropical cyclone existed (“CH” pattern), Hong Kong was affected by ozone transport from southeastern or southern China. Substantial amounts of ozone were transported within a layer near the ground with an average height of 0.83, 0.75, 0.94, and 0.85 km under the C, H, CH, and T synoptic patterns, respectively. Variation in the near-surface ozone layer height was consistent with that of the mixing layer height. Weak vertical mixing resulted in a shallow near-surface ozone layer under the C and H synoptic patterns. Due to the combined effect of near-surface transport and suppressed vertical mixing, the ozone concentrations were extremely high near the ground but rapidly declined with height under the C synoptic pattern. Our investigations of the vertical structure of ozone contribute to filling the knowledge gap between synoptic patterns and the evolution of high surface ozone episodes.

The present study focused on investigating the possible atmospheric conditions influencing the high ozone episodes over a semi-urban site (27.16° N, 78.08° E) in Agra, India during July 2014–June 2016. During the study period, average concentration of ozone was 32.3 ± 22.7 ppb, and concentrations of its precursors viz carbon monoxide (CO), nitrogen oxide (NO) and total nitrogen oxides (NO x ⁎ ) were 527.3 ± 482.7 ppb, 6.5 ± 8.2 ppb, and 12.1 ± 7.8 ppb, respectively. The maximum monthly average ozone concentration was observed in June (48.2 ± 31.0 ppb) and it was nearly three times higher than the minimum levels observed in December (16.7 ± 10.5 ppb). Considering high ozone episodes, 78 days exceed hourly ozone limit of 90 ppb specified by National Air Quality Standards (NAAQS, CPCB, 2009) for India while 75 days exceed the daily maximum 8 hourly ozone limit of 70 ppb or above (NAAQS, EPA, 2015). Trajstat model was used for air-mass cluster analysis during episodic days; five clusters of air-masses were identified and among them, the cluster from northwest direction had the maximum frequency (35.4%). During the study period, four different types of high ozone episodes were identified and explained using prevailing meteorology. The episodes were attributed to local photochemistry and/or transport.

In several previous studies emission of ozone (O3) during fireworks has been reported, which was attributed to either photolysis of molecular oxygen (O2) or nitrogen dioxide (NO2) by short/near UV radiation emitted during the high-temperature combustion of fireworks. In contrast, in the present study no O3 formation was observed using a selective O3-LOPAP instrument during the combustion of pyrotechnical material in the laboratory, while a standard O3 monitor using UV absorption showed extremely high O3 signals. The artificial O3 response of the standard O3 monitor was caused by known interferences associated with high levels of co-emitted VOCs and could also be confirmed in field measurements during New Year's Eve in the city of Wuppertal, Germany. The present results help to explain unreasonably high ozone levels documented during ambient fireworks, which are in contradiction to the fast titration of O3 by nitrogen monoxide (NO) in the night-time atmosphere.

Secondary organic aerosols (SOA) are products of the reaction of reactive organic gases (ROGs) and ozone. Most SOA are in the nanometer or submicron range, and thus SOA may be harmful to human health. Concentrations of ROGs may be high in newly decorated rooms, which may result in high SOA concentrations, especially during seasons with high ozone concentration. The objective of this study was to investigate the concentrations of SOA and the extent to which SOA contribute to indoor PM2.5 concentrations in newly decorated residential buildings. We measured concentrations of ROGs in 24 rooms of eight newly decorated (within the preceding three months) residential buildings in Beijing, China. Using previously measured indoor ozone decay rates, air change rates, and corresponding monitored ozone concentrations, we estimated the indoor ozone concentrations for the newly decorated rooms. Subsequently SOA concentrations were calculated using an aerosol mass fraction (AMF) model. We further estimated the fractions of SOA concentrations in indoor PM2.5. The SOA concentrations in 18 of the rooms ranged from 0.88 to 18.18 μg/m3, contributing to between 3.77% and 78.57% of indoor PM2.5 concentrations. The other six rooms had much lower SOA concentrations, less than 0.1 μg/m3, contributing to less than 0.39% of indoor PM2.5 concentrations. The results indicate that the concentrations and contribution of SOA in most newly decorated residential rooms are much higher than those in rooms with long-term occupancy, while some newly decorated rooms can still have low SOA concentrations.

To gain a better understanding of the state of the art of surface ozone in Korea, the trends of several indicators were presented based on the extensive surface ozone monitoring data in 16 administrative districts and Baekryeong island, a background area. Important indicators such as the annual mean of hourly mean surface ozone (AVG1), the daily maximum 8-h values (MDA8), and the AVG1 during daytime (D-AVG1) were high in background areas while low in urban areas including the Seoul Metropolitan Area (SMA). It implies that regional background level largely determines the ozone characteristics in Korea while local photochemical reactions affect the ozone levels in individual district. This hypothesis was validated by the frequency of the high ozone episodes by district. Spatial and temporal heterogeneity of surface ozone in Korea were high, thus, there should be control policy district by district based on the target indicator(s).

Weather Research and Forecast model coupled with Chemistry (WRF-Chem) coupled with CLM4.5 lake model is used to understand the impacts of lake-atmosphere exchange on ozone concentration in the Lake Taihu region during a high temperature and high ozone concentration event. About 8 °C bias in lake surface temperature simulated by different lake schemes significantly change the structure and evolution of the lake-land breeze system. As a result, the vertical and horizontal advection directly impacts distribution of ozone around and over the lake in early morning, the difference in ozone concentration is 20–60 μg m−3. Location of the lake breeze front and development of the thermal inner boundary layer around midday are also highly sensitive to the lake-atmosphere exchange. In addition, difference in the local circulation patterns leads to distinct spatial distributions of NOx, an ozone precursor, in regions downwind of their emission sources, especially along the Yangtze River. In response, ozone concentration in this region is drastically changed (about 80 μg m−3) due to the combined actions of transport and chemical reactions. Overall, this study highlights that in regions with spatially extensive shallow lakes with megacities, it is important to accurately represent the lake-atmosphere exchange for ozone pollution simulations, especially under high-temperature and light-wind conditions, in which ozone high concentration events occur frequently and effects of the local lake breeze are expected to dominate.

Atmospheric volatile organic compounds (VOCs) are not only harmful to human health, but also lead to ozone (O3) formation. From July 3 to August 1 of 2018, online measurements of atmospheric VOCs were conducted in Nanjing City, in order to investigate the source apportionments to VOCs since the Empirical Kinetic Modelling Approach (EKMA) suggested that O3 formation was VOC-limited at the receptor site. Using positive matrix factorization (PMF) model, we quantified eight sources of VOCs, including vehicle exhausts (23%), industrial source (18%), fuel evaporation (17%), petrochemical industry (12%), solvent usage (12%), biogenic emission (8%) and liquefied petroleum gas (7%) along with gasoline additive (3%). The diurnal distributions showed that the contributions of traffic-related sources maximized during the traffic rush hours. In contrast, biogenic sources had the highest contribution at noontime. Backward trajectory results showed that local traffic emissions were the main sources of VOC in Nanjing. Our results revealed that strict control of VOC emissions from local vehicle exhaust might be an important way to decrease high VOC pollution in Nanjing.

Seventeen years (2001–2017) of surface observations and spatial synoptic classification (SSC) data are used to analyze the characteristics of surface ozone concentration according to synoptic weather patterns. While weather conditions are known to play an important role in regional air quality, the extent to which synoptic weather patterns affect the production of high ground-level ozone concentrations has not yet been fully quantified. Using thermal characteristics and geographic origins, the SSC method classifies air masses into six types: dry polar (DP), dry moderate (DM), dry tropical (DT), moist polar (MP), moist moderate (MM), and moist tropical (MT). We link daily maximum 8-h ozone concentrations (MDA8 O3) from 306 monitoring sites to the closest SSC classifications at 17 airport sites and then analyze their association. We find that DM, DT, and MT are commonly associated with high ozone, whereas DT produces ozone with the greatest efficiency, especially high levels of concentration. This finding implies a potentially strong connection between surface ozone and climate change because the occurrence of DT weather has increased by more than three times over the past 50 years in South Korea. Sensitivity tests reveal that mean MDA8 ozone may increase by 3.5% (7.5%) as the DT frequency increases by 200% (300%). The impacts are larger for higher levels of concentration, with 31.7% (63.3%) or more prevalence of the >80 ppb range with the same increased DT frequency. We conclude that synoptic weather and its long-term trends play important roles in the increased surface ozone recently seen in South Korea.

This study investigates the relationship between ground-level ozone variability and synoptic weather conditions in the Chicago area in the summertime over the period 1990–2014. It shows that the occurrence of dry tropical (DT) weather conditions is most likely to lead to high ozone concentrations. Both the 95th percentile of summertime daily maximum 8-hour-average ozone concentrations and the number of days > 70 ppb are shown to have a greater and more significant correlation with DT weather in recent years (2004–2014) than in the preceding period (1990–2003), indicating an increased dependence of ozone on DT weather. The DT weather is shown to be associated with increased geopotential height, warmer temperature, and slower eastward wind at 500 hPa and also with warmer temperature and increased northward wind near the surface. The results have implications for the likely effect of future climate change on ozone as a result of modified synoptic weather conditions. More frequent episodes of high ozone concentrations can be expected, leading to worsened effects on public health and the environment. It will also make it increasingly challenging for Chicago to attain the National Ambient Air Quality Standard for ozone, which has recently been tightened by the U.S. Environmental Protection Agency.

A simple urban air quality model [MODelo de Dispersion Atmosf erica Ubana e Generic Reaction Set (DAUMOD-GRS)] was recently developed. One-hour peak O3 concentrations in the Metropolitan Area of Buenos Aires (MABA) during the summer estimated with the DAUMOD-GRS model have shown values lower than 20 ppb (the regional background concentration) in the urban area and levels greater than 40 ppb in its surroundings. Due to the lack of measurements outside the MABA, these relatively high ozone modelled concentrations constitute the only estimate for the area. In this work, a methodology based on the Monte Carlo analysis is implemented to evaluate the uncertainty in these modelled concentrations associated to possible errors of the model input data. Results show that the larger 1-h peak O3 levels in the MABA during the summer present larger uncertainties (up to 47 ppb). On the other hand, multiple linear regression analysis is applied at selected receptors in order to identify the variables explaining most of the obtained variance. Although their relative contributions vary spatially, the uncertainty of the regional background O3 concentration dominates at all the analysed receptors (34.4 e97.6%), indicating that their estimations could be improved to enhance the ability of the model to simulate peak O3 concentrations in the MABA. Fil: Pineda Rojas, Andrea Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmosfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmosfera; Argentina Fil: Venegas, Laura Esperanza. Universidad Tecnológica Nacional. Facultad Regional Avellaneda; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Mazzeo, Nicolas Antonio. Universidad Tecnológica Nacional. Facultad Regional Avellaneda; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Ozone (O3) concentrations measured at Pinnacle State Park (PSPNY), very close to the southern border of New York State, are used to estimate concentrations in air flowing into New York. On 20% of the ozone season (April–September) afternoons from 2004 to 2015, mid-afternoon 500-m back trajectories calculated from PSPNY cross New York border from the south and spend less than three hours in New York State, in this area of negligible local pollution emissions. One-hour (2p.m.–3p.m.) O3 concentrations during these inflowing conditions were 46 ± 13 ppb, and ranged from a minimum of 15 ppb to a maximum of 84 ppb. On average during 2004–2015, each year experienced 11.8 days with inflowing 1-hr O3 concentrations exceeding 50 ppb, 4.3 days with O3 > 60 ppb, and 1.5 days had O3 > 70 ppb. During the same period, 8-hr average concentrations (10a.m. to 6p.m.) exceeded 50 ppb on 10.0 days per season, while 3.9 days exceeded 60 ppb, and 70 ppb was exceeded 1.2 days per season. Two afternoons of minimal in-state emission influences with high ozone concentrations were analyzed in more detail. Synoptic and back trajectory analysis, including comparison with upwind ozone concentrations, indicated that the two periods were characterized as photo-chemically aged air containing high inflowing O3 concentrations most likely heavily influenced by pollution emissions from states upwind of New York including Pennsylvania, Tennessee, West Virginia, and Ohio. These results suggest that New York state-level attempts to comply with National Ambient Air Quality Standards by regulating in-state O3 precursor NOx and organic emissions would be very difficult, since air frequently enters New York State very close to or in excess of Federal Air Quality Standards.

Airshed modeling to determine photochemical ozone creation potentials (POCPs) provides a means of ranking regional emission contributions of individual volatile organic compounds (VOC) to O3 formation. Here POCPs are determined for Perth, Western Australia and compared with those from other Continents; Europe (UK), America (USA) and Asia (The Pearl River Delta and Hong Kong). Considering only the commonality of VOC across the top 50 ranked VOC by POCP and top 15 ranked VOC by POCP-weighted emission, indicates a group of 27 alkane, alkene, aromatic and oxygenated VOC that should be considered as useful targets in emission limitation and reduction strategies. This target group includes; ethene, propene, the butenes (6 VOC) and pentenes (3 VOC), trimethyl benzenes (2 VOC), xylenes (3 VOC), toluene, ethyl benzene, m-ethyl toluene, butanes (2 VOC), pentanes (2 VOC) and 2-methyl heptane, as well as methanal, ethanal and methyl-i-butyl ketone. The top 50 ranked VOC by POCP (from >130 VOC) also highlights those more reactive VOC that should be taken note of, as potential high ozone contributors, should emissions increase. POCPs are determined for Perth, Western Australia & compared with those from other Continents.VOC are ranked by POCP & POCP-weighted emission across high and low air pollution regions.Some common VOC contributing to high O3 are identified across 4 Continents.These common VOC are a group of 27 alkane, alkene, aromatic and oxygenated compounds.Overall analysis identifies potential target VOC for further emission control studies.

The north and east Pearl River Delta (PRD) is usually a clean, upwind area in autumn. Serious ozone pollution there in mid-late October 2008 was first discovered and then analyzed. Trajectory analysis, process analysis, ozone source apportionment technology, and sensitivity analysis were used to study this episode. Under the influence of a weak south wind, the precursors emitted in Guangzhou and Foshan were transported to the north and northeast PRD and formed ozone there, which resulted in high ozone concentration (>100 ppb). As the wind direction later transited to northerly, the precursors in the northeast PRD that originated from the central and west PRD were transported to the south, and caused severe ozone pollution in the southeast PRD. The ozone contributed by chemical processes reached >20 ppb/h in Jinguowan. More than 40 ppb ozone was contributed by the precursor emission in the central and west PRD during the episode. The ozone concentration was highly sensitive to the precursor emission in the PRD region in the high-ozone situations. This episode showed the complexity of regional pollution in the PRD. When the PRD is controlled by a low air pressure system and then cold air moves from northern China to the south, the risk of ozone pollution in the north and southeast PRD increases.

An observational field campaign was carried out from 20 June to July 31, 2016 at Raoyang, a rural site in the North China Plain (NCP). In-situ measurements of O3 and related gases were obtained and analyzed in this work. Heavy photochemical pollution episodes lasting for a few days were observed in the campaign. The episodes could be divided into two categories, with one being influenced by plume from northeast (NE) via Beijing-Tianjin cities and the other from southeast (SE) via Shandong province. The SE episodes were more frequent with higher O3 concentrations and lagged daily peaks of O3 despite of lower concentrations of precursors. Such episodes could last for several days or even a week. In contrast, the NE episode was associated with relatively lower O3 levels and earlier daily O3 peaks though the levels of precursors were higher. The WRF-Chem model was used to study the differences between typical SE and NE episodes in regional distributions of O3 concentrations, chemical regimes of O3 formation, ozone production efficiency (OPE), photochemical age of plume, and evolution of O3 concentration within the boundary layer. Our results suggest that the O3 production regimes were different for the Raoyang site, with the NE episode being VOCs-sensitive and the SE episode in the VOC-sensitive to NOx-sensitive transition regime. In both episodes, a major part of the NCP was under the VOCs-sensitive regime. Plumes in the SE episodes were more aged than those in the NE episode. The OPE values were higher in more aged SE plumes, resulting in higher O3 concentrations despite of lower precursor concentrations. Our results also indicate that downward mixing of O3 in the nocturnal residual layer played an important role in rapid buildup of surface O3 in the next morning in both NE and SE episodes. The formation of photochemical smog seems to be particularly effective in the SE episode since O3 is rapidly produced during daytime, stored aloft at night, and mixed downward to the ground-level, and the process can circulate for several consecutive days. Our study highlights the complicated role of chemical reaction, transport and boundary layer processes in the formation of severe photochemical smog in the region.

The abatement of several emerging contaminants (ECs) in groundwater by conventional ozonation and three ozone-based advanced oxidation processes (AOPs) - catalytic ozonation with manganese dioxide (MnO2), conventional peroxone (O3/H2O2), and electro-peroxone (EP) - was compared in this study. The addition of MnO2, H2O2, or electro-generation of H2O2 during ozonation enhanced ozone transformation to hydroxyl radicals to different extent. These changes did not considerably influence the abatement of ECs with moderate to high ozone reactivities ( k O 3 ≥500 M -1 s -1 ), whose abatements were similar with >90 % during all four processes. In comparison, the abatements of ozone-refractory ECs ( k O3 M -1 s -1 ) were lower during conventional ozonation (∼40–85 % abatement), but could be enhanced by ∼10–40 % during the three ozone-based AOPs. Besides enhancing ozone-refractory EC abatement, the three AOPs, especially the O3/H2O2 and EP processes, reduced considerably bromate formation compared to conventional ozonation. These results demonstrate that the EP process performs similarly as catalytic ozonation and O3/H2O2 processes in terms of EC abatement and bromate control. Considering its more convenient, flexible, and safer way of operation, the EP process may provide an attractive alternative to the two more traditional AOPs for water treatment.

High spatial- and temporal-resolution ozone lidar profiles, in conjunction with ozonesonde and satellite observations, are well suited to characterize short-term ozone variations due to different physical and chemical processes, such as the impact of lightning-generated NOx (LNOx) on tropospheric ozone. This work presents the hourly variation of tropospheric-ozone profiles measured by an ozone lidar at the University of Alabama in Huntsville, on July 14, 18, and 27, 2011. These ozone lidar data are compared with two WRF/Chem simulations, one with lightning NO (LNO) emissions and the other without. On July 14, 2011, the ozone lidar observed an ozone laminar structure with elevated ozone concentrations of 65∼80 ppbv below 2 km, low ozone (50∼65) ppbv between 2 and 5 km, and high ozone up to 165 ppbv between 5 and 12 km AGL. WRF/Chem simulations, in conjunction with backward trajectory analysis, suggest that lightning events occurring within upwind regions resulted in an ozone enhancement of 28 ppbv at 7.5 km AGL over Huntsville. On July 27, LNO emissions were transported to Huntsville from upwind and account for 75% of NOx and an 8.3 ppbv of ozone enhancement at ∼10 km; the model overestimates ozone between 2.5 and 5 km AGL.

Building materials (BMs) are major contributors to indoor emission sources of volatile organic compounds (VOCs). In this study, 8 kinds of BMs (including conventional and green) for ceiling, cabinetry, and flooring commonly used indoors were tested in a 216 L chamber. Primary emissions of carbonyls (C 1 to C 8 aldehydes and ketones) at 48 h were 75–673 μg m −2 h −1 from conventional BMs, and 62–151 μg m −2 h −1 from green BMs. Primary emissions of BTEX at 48 h were 59–264 μg m −2 h −1 from conventional BMs, and 37–56 μg m −2 h −1 from green BMs. Ozone initiated molar yields of carbonyls were 0.10–2.36 from conventional BMs, and 0.13–0.86 from green BMs. Secondary emissions of carbonyls were 7–150 μg m −2 h −1 from conventional BMs, and 4–73 μg m −2 h −1 from green BMs. Green BMs had lower emissions than conventional analogs, especially for wooden flooring and gypsum board. BMs with mineral content are the most promising materials in this study, given moderately high ozone deposition velocity but generating the least byproducts. Secondary emissions determined in this study demonstrate that moderate indoor ozone concentrations may lead to increased concentrations of carbonyls, especially formaldehyde and acetaldehyde that potentially increase adverse chronic health effects.

Fourteen years of regulated air pollutants concentrations were analyzed in order to characterize the benefits of Brazil's emission control policies on air quality conditions and to evaluate the temporal patterns between 1996 and 2009 over the Metropolitan Area of Sao Paulo (MASP). MASP includes one of the largest cities in the world (Sao Paulo) and its light-duty vehicular fleet has a very important characteristic in that it uses, on a large scale, fuels such as ethanol derived from sugar cane and compressed natural gas. Nowadays, ethanol makes up more than 50% of the fuel used in Brazil. The frequent episodes with high ozone and PM 10 concentration values in the MASP are mostly associated with vehicular emissions – primary emission of particles and gases enrolled in ozone photochemical production and formation of secondary fine particles. Although the fleet has increased at a substantial rate, annual mean values show a diminishing tendency for all pollutants except for ozone, which presents no significant tendency. This diminishing tendency in the analyzed period is due to the vehicular emission control program established by the Brazilian Government in 1986, called PROCONVE (Program for the Control of Vehicular Emission). Monthly mean values, as expected, show higher concentrations of all pollutants except for ozone during wintertime. The diurnal cycle of the pollutants in most of the stations shows two peaks, associated with rush hours, except for ozone, whose peak follows the maximum radiation incidence. Secondary (nocturnal) ozone concentration maxima were sometimes verified around three and four LST. Average values for weekdays and weekends showed that the different air quality stations showed different patterns for the pollutants. For ozone the concentrations were higher during the weekend when compared to weekdays.

Surface ozone concentrations are high throughout Joshua Tree National Park (JOTR), as demonstrated by direct monitoring at multiple sites within JOTR. Multiple years of data from continuous ozone monitors and passive samplers indicate that the highest ozone concentrations occur in the northwest corner of JOTR, and decrease as one moves to the south and east. Analysis of long-term (1994–2010) hourly data from the Black Rock monitoring station indicates that average summertime ozone concentrations have remained essentially constant, with a concurrent decrease in the number, and magnitude, of high ozone events. Calculation of ozone exposure indices suggests that ozone concentrations may be high enough to adversely affect local flora, especially in the northwestern region of the park. Back-trajectory analysis using the HYSPLIT model suggests that most of the ozone measured in JOTR is transported into the park from a high source area (Los Angeles and surrounding suburbs) to the west.

This study investigated the effects of preozonation on disinfection by-products (DBPs) formation during chlorination and chloramination of the water collected from Tai Lake. Results showed that the high ozone dose (0.6–1.0 mg O3/mg DOC) pretreatment reduced the yields of trihaloacetic acids (reduced 62–63% in chlorination), dihaloacetonitriles (reduced 53–55% and 14–26% in chlorination and chloramination, respectively) and trihaomethanes (reduced 19% in chloramination), but markedly increased the formation of halonitromethanes (increased 4.7–5.6 times in chlorination and 2.1–2.7 times in chloramination), haloketones (increased 4.8–7.1 times in chlorination and 2.5–2.9 times in chloramination) and dihaloacetic acids (increased 1.5–2.4 times in chlorination and 0.3–0.6 times in chloramination). Thus the high ozone dose pretreatment should be avoided during chlorination/chloramination of Tai Lake water. Also, chloramination (with and without preozonation) produced much lower DBPs yields as compared with chlorination (with and without preozonation), indicating that chloramine was a better choice to control the DBPs yields. Further analysis also revealed that the bromine substitution factors (BSFs) of DBPs varied with disinfection mode. In chlorinamination, the BSFs generally showed a decrease trend with the ozone dose, yet in chlorination, the BSFs mostly exhibited first an increase and then a decrease trend. Moreover, the BSFs of DBPs in chloramination (with or without preozonation) were dominantly lower than those in chlorination (with or without preozonation).

The impacts of interstate transport of anthropogenic nitrogen oxides (NOx) and volatile organic compound (VOC) emissions on peak ozone formation in four nonattainment areas (i.e., Baltimore, Philadelphia-Wilmington-Atlantic City, Pittsburgh-Beaver Valley and Washington, DC) in the Mid-Atlantic U.S. were quantified in this study. Regional air quality and sensitivities of ground-level ozone to emissions from four regions in the eastern U.S. were simulated for three summer months (June, July and August) in 2007 using the U.S. EPA's Community Multiscale Air Quality model with the decoupled direct method 3D. The emissions inventory used in this study was the 2007 Mid-Atlantic Regional Air Management Association Level 2 inventory, developed for State Implementation Plan screening modeling for the Ozone Transport Commission region. The modeling results show that responses of peak ozone levels at specific locations to emissions from EGU (i.e., electric generating unit) and non-EGU sources could be different. Therefore, emissions from EGU and non-EGU sources should be considered as two different control categories when developing regional air pollution mitigation strategies. Based on the emission inventories used in this study, reductions in anthropogenic NOx emissions (including those from EGU and non-EGU sources) from the Great Lake region as well as northeastern and southeastern U.S. would be effective for decreasing area-mean peak ozone concentrations during the summer of 2007 in the Mid-Atlantic ozone air quality nonattainment areas. The results also show that reductions in anthropogenic VOC emissions from the northeastern U.S. would also be effective for decreasing area-mean peak ozone concentrations over the Mid-Atlantic U.S. In some cases, reductions in anthropogenic NOx emissions from the Great Lake and northeastern U.S. could slightly increase area-mean peak ozone concentrations at some ozone monitors in the Pittsburgh-Beaver Valley and Washington, DC areas. However, the disbenefit of the slight increase in ozone concentrations attributed to the NOx emission controls was far outweighed by the overall ozone air quality benefits over the Mid-Atlantic region.

The sensitivity of ozone production to increasing temperature and a decreasing concentration of precursors, namely nitrogen oxides and non-methane hydrocarbon, has been estimated with probability theory using observation data for 2004–2015 for the Kanto region, Japan. The sensitivity of ozone, in terms of the number of high ozone concentration days, to temperature was higher at the beginning of the observation period when precursor concentrations were high but lower in more recent years when the precursor concentrations were lower. Analysis of the high ozone concentration days showed that a 10-percent reduction of both precursor concentrations yields a reduction in the number of high concentration ozone days of approximately 4 days per year, whereas a 0.2 °C temperature increase leads to less than a 1-day increase per year. This indicates that precursor concentration is more important than temperature for determining ozone concentration.

A top-down approach to evaluate high ozone (O3) formation, attributed to different emission sources, is developed for anti-cyclonic conditions in a region of Hong Kong influenced by meso-scale circulations. A near-explicit photochemical model coupled with the Master Chemical Mechanism (MCMv3.2) is used to investigate the chemical characteristics in the region. Important features have been enhanced in this model including the photolysis rates, simulated by the National Center for Atmospheric Research (NCAR) Tropospheric Ultraviolet and Visible (TUV) Radiation Model, as well as hourly variation of Volatile Organic Compound (VOC) concentration input from on-site sampling. In general, the combined model gives a reasonably good representation of high O3 levels in the region. The model successfully captured a multi-day O3 event in the autumn of 2010. Source apportionment via Positive Matrix Factorization (PMF) was carried out on the sampled VOC data, to determine the major sources in the region. Based on the outcomes of the PMF source apportionment, a sensitivity analysis using the developed photochemical model was conducted and used to estimate O3 reduction under different source removal regimes. Results indicate that vehicular emissions are the dominant VOC source contributing to O3 formation. This study has demonstrated a potentially efficient secondary pollutants control methodology, using a combined field measurements and modelling approach.

A three-dimensional photochemistry model is applied to analyze three unusual high O 3 episodes that occurred continuously in Taiwan from May 1 to 11, 2007. During this period, the first high ozone episode was observed in northern and central western Taiwan on May 4. Following this episode, the second episode was observed throughout Taiwan on May 7, and continued for several days until May 10, when the third episode was observed in central western and southwestern Taiwan. This was the worst O 3 period in Taiwan over the past two decades. During this period, 70% of the local air quality station reported an O 3 concentration of over 120 ppb, and a maximum O 3 concentration of 175 ppb was observed in background Taiwan. Based on model analyses, the sources of the three high O 3 episodes differ. The high O 3 concentration observed during the first episode is mainly attributed to the northeastward transport of O 3 precursors and concentrations from northern and central western Taiwan under southwesterlies prior to frontal passage, chemically producing O 3 over 30 ppb h −1 in northern Taiwan. During the second episode, horizontal advection of Asian outflow during the passage of an anticyclone and front contributes a maximum of 25 ppb h −1 in both northern and southern tip of Taiwan, respectively, increasing to more than 75 ppb h −1 in southwestern Taiwan because of the combination with the local source. During the third episode when the prevailing easterlies associated with a departing anticyclone to the east of Taiwan is blocked by the high central mountain, local O 3 chemical production and horizontal transport contribute a maximum of 25 ppb h −1 and 35 ppb h −1 in central and southwestern Taiwan, respectively, under a calm and high background O 3 condition. Source from Taiwan contributes more than half of the high O 3 concentration over northwestern Taiwan prior to frontal passage during the first episode, but decreases to mostly below 40% over western Taiwan during the second episode when Asian outflow occurs, and increases to more than 60% over central and southwestern Taiwan due to pollution accumulation under an anticyclonic departure.

We use a global chemical transport model (GEOS-Chem) driven by the GISS GCM to investigate the effect on China’s surface ozone from 2000 to 2050 global changes in climate and anthropogenic emissions as projected by the IPCC A1B scenario, with a focus on the different response between East and West China where present-day anthropogenic emissions, natural conditions, and ozone source attributions differ significantly. Over East China, climate change will increase both surface ozone and the possibility of high ozone episodes, implying a significant ‘climate change penalty’ that can be attributed mainly to increasing biogenic emissions of volatile organic compounds (VOCs). Over West China on the other hand, climate change will decrease mean surface ozone as a result of an increased ozone destruction rate in low-NOx regimes, assuming constant stratosphereetroposphere exchange (STE) of ozone. Chinese emissions change in 2050 will enlarge the EasteWest ozone difference in China, but emissions change from the rest of the world (excluding China) will decrease it. Driven by climate change and emissions change in combination, nation-mean surface ozone will increase, whereas EasteWest ozone contrast will decrease. In the future climate, the sensitivity of surface ozone to a given change in Chinese emissions will decrease over West China due to the accelerated ozone destruction rate and reduced transport from East China, but increase over East China as a result of the coupling effect between anthropogenic NOx and biogenic VOCs. The latter result suggests that the emission controls over East China need to be more aggressive in future climate.

The Lagrangian tropospheric ozone model ELMO-v2 (Edinburgh Lancaster Model for Ozone) is applied to the intense 2003 ozone episode in SE England. When using model parameters representative of typical episodes, ELMO-v2 was found to underestimate ozone levels substantially during peak ozone days, but, by increasing three parameters (temperature, biogenic and anthropogenic VOC emission rates) to levels close to those observed, good agreement between modelled and observed ozone was achieved. Using attribution techniques possible with a Lagrangian model, the episode was divided into five phases with each exhibiting different geographical origins for ozone precursor emissions. Anthropogenic VOCs, primarily of European (non-UK) origin, made the biggest contribution to modelled ozone levels. European biogenic VOC emissions significantly contributed to ozone levels on some days, whereas the contribution from UK biogenic VOC emissions was comparatively small throughout. The VOC:NO x ratio was also shown to change during the episode, with high ozone days being less VOC-sensitive. The implications of both variable NO x /VOC sensitivity and the possibility of more frequent heatwaves due to climate change need to be taken into account in planning effective future emissions reductions to control ground-level ozone in the UK.

The aim of this paper is to study the levels and variability of surface ozone in the lower Ebre Valley and to estimate whether this surface ozone has its origin in local photochemical processes or in long–range transport. Surface ozone data series of twelve years (1994–2005) have been used from a rural area (Ebre Observatory) together with three years (2003–2005) data of nitrogen dioxide (NO 2 ). Ozone trends over the whole seasonal period, weekly and daily variations and exceedances of the legal threshold have been investigated. Furthermore, a representative ozone event has been studied in detail. Using ozone data from the twelve–year period resulted in a positive trend with an increase of 2.18 μg m –3 year –1 and 0.64 μg m –3 year –1 in summer and winter, respectively. The seasonal evolution of ozone gives a minimum value in winter and a maximum higher than 75 μg m –3 associated with the minimum values of NO 2 . Ozone– NO 2 variation shows a weak ozone increase on weekdays and a small decrease in NO 2 concentrations at the weekends. Hence, a weekend effect is not observed. Ozone and NO 2 concentrations show a diurnal pattern with NO 2 peaks both in the early morning and in the evening, and maximum ozone concentrations, higher than 90–100 μg m –3 , from 12:00 to 18:00 UTC in the warmer seasons. The threshold for the protection of human health has been exceeded from March to September each year, with a mean of 33 times per year. An event with high ozone levels originated by transport processes from the Mediterranean area was also analysed. The results suggest that high ozone could be caused mainly by transport mechanisms, and the Ebre valley could be considered to be a natural communication channel between the western Mediterranean basin and the Atlantic Ocean.

Due to several regional–scale high ozone episodes that impacted the urban areas in south and central Texas over the past decade, the Texas Commission on Environmental Quality (TCEQ) has designated several urban regions as near non–attainment areas. A regional photochemical modeling experiment was set up to simulate a high ozone episode of September 11–14, 2002 in order to evaluate the impact of various anthropogenic emissions sources on ozone concentrations. The base case simulation showed reasonable model performance by capturing the peaks and the diurnal variability of observed ozone concentrations within the modeling domain. A comprehensive impact assessment of anthropogenic emissions from various source categories to the 8–hour ozone concentration was evaluated for each of the urban areas within the study region. Through a source apportionment analysis of emissions influencing the 8– hour ozone concentrations, NOx and VOC limited areas were identified. The model results showed that the net effect of all anthropogenic emissions was approximately 8.4 ppb in Victoria, 8.8 ppb in Corpus Christi, and 31.2 and 34.1 ppb in Austin and San Antonio, respectively. Impact of major emissions source categories differed regionally with ozone concentrations in Austin and San Antonio mainly influenced by mobile sources, while Corpus Christi and Victoria were largely impacted by long–range transport of ozone. On a local scale, Corpus Christi was also impacted by non–road sources, while Victoria was influenced by point sources. Ozone sensitivity analysis showed higher sensitivity towards VOC within the urban cores of Austin, San Antonio, and Corpus Christi, while the overall modeling regions showed higher NOx sensitivity. This would indicate that both NOx and VOC emissions reduction plans need to be developed and implemented for the mitigation of regional and urban ozone. The results also revealed that biogenic emissions played an important role in the urban regions of south and central Texas.

The O-3 uptake in 17 adult trees of six urban species was evaluated by the sap flow-based approach under free atmospheric conditions. The results showed very large species differences in ground area scaled whole-tree ozone uptake (F-O3), with estimates ranging from 0.61 +/- 0.07 nmol m(-2) s(-1) in Robinia pseudoacacia to 4.80 +/- 1.04 nmol m(-2) s(-1) in Magnolia liliiflora. However, average F-O3 by deciduous foliages was not significantly higher than that by evergreen ones (3.13 vs 2.21 nmol m(-2) p = 0.160). Species of high canopy conductance for 03 (G(O3)) took up more 03 than those of low G(O3), but that their sensitivity to vapour pressure deficit (D) were also higher, and their F-O3 decreased faster with increasing D, regardless of species. The responses of F-O3 to D and total radiation led to the relative high flux of O-3 uptake, indicating high ozone risk for urban tree species. (C) 2011 Elsevier Ltd. All rights reserved.

This paper presents results of measuring episodes of extremely high ozone concentrations in urban area of the town of Bor in Serbia. The measured ozone concentration of 3000 μgm −3 in two episodes, which lasted 3–5 days in November 2010, has not been recorded in the literature in this field. Sensitivity of generated ozone to the NOx was determined, since the concentrations of NOx in the same period were also high. In the morning when working hours start, episodes of increased NOx concentrations appear after several hours, leading to episodes of increased ozone concentrations reaching up to twenty times more than the threshold value, defined as harmful to vegetation and human health.

The main objective of this study was to investigate the causes as well as the temporal and spatial dynamics of ozone pollution during three high ozone episodes in the northeastern Mediterranean Basin using surface measurements and WRF/Chem model simulations. The simulation results revealed that the analyzed episodes were mainly caused by the impact of accumulation of pollution rich in ozone over the northern Adriatic. Two mechanisms were simulated: (1) the accumulated pollutants occasionally encroaching and retreating, impacting the coastal areas; and (2) broad advection impacting areas further inland in the northeastern Mediterranean Basin including Slovenia. The simulations also show that in some specific conditions the elevated ozone levels over continental Slovenia can be separated from the direct Mediterranean influences by the Alpine-Dinaric mountain ridge. The simulations show a trend of underestimating maximum and overestimating minimum ozone concentrations, but the overall statistics agree fairly well with the statistics of the measured ozone concentrations.

Each summer period extremely high ozone levels are registered at the rural background station of Lamas d'Olo, located in the Northeast of Portugal. In average, 30% of the total alert threshold registered in Portugal is detected at this site. The main purpose of this study is to characterize the atmospheric conditions that lead to the ozone-rich episodes at this site. Synoptic patterns anomalies and back trajectories cluster analysis were performed, for the period between 2004 and 2007, considering 76 days when ozone maximum hourly concentrations were above 200 μg m−3. The obtained atmospheric anomaly fields suggested that a positive temperature anomaly is visible above the Iberian Peninsula. A strong wind flow pattern from NE is observable in the North of Portugal and Galicia, in Spain. These two features may lead to an enhancement of the photochemical production and to the transport of pollutants from Spain to Portugal. In addition, the 3D mean back trajectories associated to the ozone episode days were analysed. A clustering method has been applied to the obtained back trajectories. Four main clusters of ozone-rich episodes were identified, with different frequencies of occurrence: north-westerly flows (11%); north-easterly flows (45%), southern flow (4%) and westerly flows (40%). Both analyses highlight the NE flow as a dominant pattern over the North of Portugal during summer. The analysis of the ozone concentrations for each selected cluster indicates that this northeast circulation pattern, together with the southern flow, are responsible for the highest ozone peak episodes. This also suggests that long-range transport of atmospheric pollutants is the main contributor to the ozone levels registered at Lamas d'Olo. This is also highlighted by the correlation of the ozone time-series with the meteorological parameters analysed in the frequency domain.

The city of Santiago, Chile experiences frequent high pollution episodes and as a consequence very high ozone concentrations, which are associated with health problems including increasing daily mortality and hospital admissions for respiratory illnesses. The development of ozone abatement strategies requires the determination of the potential of each pollutant to produce ozone, taking into account known mechanisms and chemical kinetics in addition to ambient atmospheric conditions. In this study, the photochemical formation of ozone during a summer campaign carried out from March 8–20, 2005 has been investigated using an urban photochemical box model based on the Master Chemical Mechanism (MCMv3.1). The MCM box model has been constrained with 10 min averages of simultaneous measurements of HONO, HCHO, CO, NO, j(O1D), j(NO2), 31 volatile organic compounds (VOCs) and meteorological parameters. The O3–NOx–VOC sensitivities have been determined by simulating ozone formation at different VOC and NOx concentrations. Ozone sensitivity analyses showed that photochemical ozone formation is VOC-limited under average summertime conditions in Santiago. The results of the model simulations have been compared with a set of potential empirical indicator relationships including H2O2/HNO3, HCHO/NOy and O3/NOz. The ozone forming potential of each measured VOC has been determined using the MCM box model. The impacts of the above study on possible summertime ozone control strategies in Santiago are discussed.

The halocarbons studied here are chemicals controlled in the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer and its Amendments, which have both high ozone depleting potentials (ODPs) and high global warming potentials (GWPs). These halocarbons are mainly used for refrigeration, air-conditioning, foam blowing, tobacco expansion, aerosol propulsion, solvent cleaning, and fire fighting. China ratified the Montreal Protocol in 1991 and has been implementing the phase-out of halocarbons since then. In this paper, the emissions of halocarbons from China were estimated for 1995–2024 based on the historical consumption, the country program for complying with the Montreal Protocol, and the sector plans for phasing out halocarbons. The results show that China's compliance with the Montreal Protocol contributes greatly to both ozone protection and climate protection.

The purpose of this paper is to identify the atmospheric conditions associated with elevated ground-level ozone concentrations during June–August of 2000–2007 at 11 ozone-monitoring stations in the Atlanta, GA, USA metropolitan statistical area (MSA). Analyses were confined to high-ozone days (HODs), which had a daily maximum 8-h average ozone concentration in the 95th percentile of all June–August values. Therefore, each station had 36 HODs. The southeastern and far northern portions of the MSA had HODs with the highest and lowest ozone concentrations, respectively. HODs at nearly all Atlanta MSA ozonemonitoring stations were enabled by migratory anticyclones. HODs for most stations were hot, dry, and calm with low morning mixing heights and high afternoon mixing heights. All sets of HODs had daily mean relative humidities and afternoon mixing heights that, respectively, were significantly less than and significantly greater than mean values for the remaining days. Urbanized Atlanta typically was upwind of an ozone-monitoring station on its HODs; therefore, wind direction on HODs varied considerably among the stations. HODs may have been caused partially by NO x emissions from electricutility power plants: HODs in the southern portion of the MSA were linked to air-parcel trajectories intersecting a power plant slightly northwest of Atlanta and plants in the Ohio River Valley, while HODs in the northern portion of the MSA were linked to air-parcel trajectories intersecting two large power plants slightly southeast of the Atlanta MSA. Results from this study suggest that future research in the Atlanta MSA should focus on power-plant contributions to ground-level ozone concentrations as well as the identification of non-monitored locations with potentially high ozone concentrations.

This study focuses on a new emissions model, Numerical Emissions Model for Air Quality (MNEQA), to be used in photochemical simulations and emission control strategies relating to tropospheric ozone pollutants. MNEQA processes available local information from external files and is easily adaptable to any desired spatial resolution. Top-down and bottom-up methodologies are combined to calculate emissions at the required resolution for photochemical simulations. It was used in conjunction with the MM5-CMAQ air quality modelling system and was applied to an episode of high ozone levels in June 2003. Emission results are widely analysed showing a difference of −8.8% with EMEP NOx emissions, and −18.7% with EMEP VOC emissions. Related to ozone simulations, comparative results between measurements and simulations indicated good behaviour of the model in reproducing diurnal ozone concentrations, as statistical values fall within the EPA and EU regulatory frameworks.

The impact of climate changes on the pollution levels in Denmark is the major topic of this paper. Variations of the Danish air pollution levels that are caused by climatic changes are studied together with variations caused by other factors (emissions, inter-annual variability of meteorological conditions, etc.). The Unified Danish Eulerian Model (UNI-DEM) was run on a fine, 10 km × 10 km, grid over a space domain covering all of Europe to minimize the influence of the boundary conditions on the Danish pollution levels. This study is based on four categories of scenarios: (i) traditional scenarios, (ii) climatic scenarios, (iii) scenarios with variations of the human-made (anthropogenic) emissions and (iv) scenarios in which the biogenic emissions were varied. The total number of applied scenarios was 14, and a time-period of 16 years was used. The results show clearly that although the concentrations of the major pollutants do not depend too much on the climatic changes, some quantities, in particular quantities related to high ozone levels, might be increased significantly as a result of the warming trends in the future climate. The reason for this phenomenon is explained.

Surface O3 air quality in Jakarta, Indonesia, was analyzed using hourly monitoring data during January 2002–March 2004 from the five automatic monitoring stations with the aim to provide the first insight into the ozone formation and accumulation leading to the high ozone levels over the city. The city location near the equator with the intensive emission sources is of especial interest in this regard. The surface O3 levels in Jakarta were high which frequently exceeded the hourly national ambient air quality standard (120 ppb), i.e. over 450 hourly measurements in 2002 and 2003 or 0.7% over 66,000 hourly ozone measurements at the five stations during 2002–2003. The monthly average of O3 was maximum in October and minimum in February. Selected days of episodic high O3 in April, May, and October, and low ozone days in February were comparatively analyzed in relation to local and synoptic meteorological conditions. The high ozone days were characterized by more intense solar radiation, higher temperature, and lighter surface wind which are favorable for photochemical production of O3. Low pressure gradients on synoptic charts of the high ozone days linked to the low wind and more stagnant air that are favorable for ozone build-up over the city. Further studies, including photochemical modeling, are required to understand better the conditions leading to high ozone in the city in order to formulate the ozone management strategies.

Ambient observations have indicated that high concentrations of ozone observed in the Houston/Galveston area are associated with plumes of highly reactive hydrocarbons, mixed with NOx, from industrial facilities. Ambient observations and industrial process data, such as mass flow rates for industrial flares, indicate that the VOCs associated with these industrial emissions can have significant temporal variability. To characterize the effect of this variability in emissions on ozone formation in Houston, data were collected on the temporal variability of industrial emissions or emission surrogates (e.g., mass flow rates to flares). The observed emissions variability was then used to construct regionwide emission inventories with variable industrial emissions, and the impacts of the variability on ozone formation were examined for two types of meteorological conditions, both of which lead to high ozone concentrations in Houston. The air quality simulations indicate that variability in industrial emissions has the potential to cause increases and decreases of 10–52 ppb (13–316%), or more, in ozone concentration. The largest of these differences are restricted to regions of 10–20 km2, but the variability also has the potential to increase regionwide maxima in ozone concentrations by up to 12 ppb.

High ozone concentrations are observed more and more frequently in the lower troposphere. The development of such polluted episodes is linked to a complex set of chemical, physical and dynamical parameters that interact with each other. To improve air quality, it is necessary to understand and quantify the role of all these processes on the intensity of ozone formation. The ESCOMPTE program, especially dedicated to the numerical simulation of photochemical episodes, offers an ideal frame to investigate details of the roles of many of these processes through 3D modeling. This paper presents the analysis, with a 3D eulerian model, of a severe and local episode of ozone pollution that occurred on the 21st of March 2001 in the ESCOMPTE region. This episode is particularly interesting due to the intensity of the observed ozone peaks (450 μg/m 3 during 15 mn) but also because it did not occur in summer but at the beginning of spring. As part of the premodeling work of the ESCOMPTE program, this study focuses on the sensitivity of the simulated ozone peaks to various chemical and physical phenomena (long-range transport, industrial emissions, local dynamic phenomena…) to determine their influence on the rise of high local photooxidant concentrations and to better picture the photochemistry of the ESCOMPTE region. Through sensitivity tests to dynamical calculation resolution and emissions, this paper shows how the combination of sea and pond breezes with emissions of reactive VOCs can generate local intense ozone peaks.

The weekend effect on ozone, a phenomenon with high ozone concentration at weekend, was analyzed using the data measured at 7 photochemical assessment monitoring stations (PAMS), (1) volatile organic compounds (VOCs) monitoring station and (2) routine ambient air quality monitoring stations in southern California during ozone season from 1995 to 2001. Weekend/weekday differences of ozone, ozone precursors and PM10 concentrations and the light scatter, composition and reactivity of VOCs in morning traffic rush time and afternoon peak ozone time were compared. The possible causes for the weekend effect were discussed. The significant weekend effect was observed in southern California except in areas close to beach and far downwind direction from L.A. Downtown. On average, the peak O3 and max 8 h average O3 concentrations at weekend were 20% and 22%, respectively, higher than those on weekday while the concentrations of O3 precursors and PM10 and the light scatter were lower at weekday in southern California. In morning traffic rush time, the average concentrations of NOx, CO, NMOC and PM10 and the light scatter at weekend were about 37%, 18%, 15%, 14% and 9%, respectively, lower than those on weekday. In afternoon peak ozone time, the average concentrations of NOx, CO, NMOC and PM10 and the light scatter at weekend were about 29%, 13%, 24%, 17% and 17%, respectively, lower than those on weekday. The reactivities of VOCs in morning traffic rush time and afternoon peak ozone time at weekend were 17% and 26%, respectively, lower than those on weekday. VOCs sensitivity for ozone formation and a decrease NOx emissions at weekend can well explain the weekend effect in southern California. Less scatter of sunlight due to lower fine particle concentration at weekend results in enhanced ozone formation might be another possible cause for the weekend effect.

The results obtained during several campaigns conducted at various places in Southern Europe and focused on ozone deposition on vegetation are analyzed and interpreted with the main scope of determining the relative contribution of stomatal uptake to the total ozone flux. The stomatal ozone fluxes are calculated using the analogy with water vapour fluxes inside the stomata. By integrating stomatal fluxes over time, ozone doses received by the plants are calculated. At most sites, the stomatal ozone flux accounts

Biogenic sources contribute a large portion of emissions of volatile organic compounds (VOCs), a precursor to tropospheric ozone (O 3 ). These emissions are difficult to control and are affected by land-use and climate. A sensitivity analysis was performed using an emissions scenario with a 100% increase in biogenic emissions and another scenario with an additional 100% increase in motor vehicle emissions. Meteorological and air pollution models were used to generate hourly ozone estimates for a case study high ozone episode. Resulting concentration estimates correspond to the total effect of changes from emissions, incorporating the interaction between anthropogenic and biogenic emissions. Biogenic VOCs had a greater impact than a comparable percent increase in motor vehicle emissions of ozone precursors, in this case study. The 100% increase in biogenic VOC emissions raised ozone levels, with an estimated maximum 1-h concentration 30% higher than that of the baseline scenario. The additional emissions of ozone precursors from motor vehicles raised the maximum 1-h concentration 40% over that of the baseline. The largest increases in ozone concentrations occurred near peak values. Urban areas had larger increases in ozone levels than rural regions. Both adjusted emissions scenarios resulted in ozone concentrations lower than that of the baseline for some estimates. These reductions occurred near low ozone levels however and were generally small. This research demonstrates the importance of biogenic VOC emissions in ozone formation for this region and of biogenic emissions inventories. Results also imply that climate change-induced increases in biogenic VOC emissions could significantly impact ozone concentrations.

A comparison study has been performed with neural networks (NNs) and multiple linear regression models to forecast the next day's maximum hourly ozone concentration in the Athens basin at four representative monitoring stations that show very different behavior. All models use 11 predictors (eight meteorological and three persistence variables) and are developed and validated between April and October from 1992 to 1999. Performance results based on a wide set of forecast quality measures indicate that the NNs provide better estimates of ozone concentrations at the monitoring sites, whilst the more often used linear models are less efficient at accurately forecasting high ozone concentrations. The violation of the European information threshold of 180 microg/m(3) is successfully predicted by the NN in 72% of the cases on average. Results at all stations are consistent with similar ozone forecast studies using NNs in other European cities.