The ozone source–receptor model – A tool for UK ozone policy

The Ozone Source–Receptor Model (OSRM) is a Lagrangian trajectory model developed to describe photochemical ozone production in the UK. The OSRM builds on existing boundary layer trajectory models used previously for assisting the development of UK ozone policy, but has a number of notable differences. A novel feature of the OSRM is a surface conversion module to represent the vertical gradient in ozone arising from chemical loss and deposition to the surface. This has significantly improved the performance of the model, especially in urban areas. In this paper, the modelling system is described and its performance against measured ozone concentrations and metrics and other UK ozone models is discussed. The model has been used to calculate future ozone concentrations in the UK and thus to assess a number of possible control measures developed for the UK Air Quality Strategy.     

GARCH modelling in association with FFT–ARIMA to forecast ozone episodes

In operational forecasting of the surface O₃ by statistical modelling, it is customary to assume the O₃ time series to be generated through a homoskedastic process. In the present work, we’ve taken heteroskedasticity of the O₃ time series explicitly into account and have shown how it resulted in O₃ forecasts with improved forecast confidence intervals. Moreover, it also enabled us to make more accurate probability forecasts of ozone episodes in the urban areas. The study has been conducted on daily maximum O₃ time series for four urban sites of two major European cities, Brussels and London. The sites are: Brussels (Molenbeek) (B1), Brussels (PARL.EUROPE) (B2), London (Brent) (L1) and London (Bloomsbury) (L2). Fast Fourier Transform (FFT) has been used to model the periodicities (annual periodicity is especially distinct) exhibited by the time series. The residuals of “actual data subtracted with their corresponding FFT component” exhibited stationarity and have been modelled using ARIMA (Autoregressive Integrated Moving Average) process. The MAPEs (Mean absolute percentage errors) using FFT–ARIMA for one day ahead 100 out of sample forecasts, were obtained as follows: 20%, 17.8%, 19.7% and 23.6% at the sites B1, B2, L1 and L2. The residuals obtained through FFT–ARIMA have been modelled using GARCH (Generalized Autoregressive Conditional Heteroskedastic) process. The conditional standard deviations obtained using GARCH have been used to estimate the improved forecast confidence intervals and to make probability forecasts of ozone episodes. At the sites B1, B2, L1 and L2, 91.3%, 90%, 70.6% and 53.8% of the times probability forecasts of ozone episodes (for one day ahead 30 out of sample) have correctly been made using GARCH as against 82.6%, 80%, 58.8% and 38.4% without GARCH. The incorporation of GARCH also significantly reduced the no. of false alarms raised by the models.     

Weekday/weekend ozone differences: what can we learn from them?

A national analysis of weekday/weekend ozone (O3) differences demonstrates significant variation across the country. Weekend 1-hr or 8-hr maximum O3 varies from 15% lower than weekday levels to 30% higher. The weekend O3 increases are primarily found in and around large coastal cities in California and large cities in the Midwest and Northeast Corridor. Both the average and the 95th percentile of the daily 1-hr and 8-hr maxima exhibit the same general pattern. Many sites that have elevated O3 also have higher O3 on weekends even though traffic and O3 precursor levels are substantially reduced on weekends. Detailed studies of this phenomenon indicate that the primary cause of the higher O3 on weekends is the reduction in oxides of nitrogen (NOx) emissions on weekends in a volatile organic compound (VOC)-limited chemical regime. In contrast, the lower O3 on weekends in other locations is probably a result of NOx reductions in a NOx-limited regime. The NOx reduction explanation is supported by a wide range of ambient analyses and several photochemical modeling studies. Changes in the timing and location of emissions and meteorological factors play smaller roles in weekend O3 behavior. Weekday/weekend temperature differences do not explain the weekend effect but may modify it.     

HNO3 analyzer by scrubber difference and the NO–ozone chemiluminescence method

A fast response analyzer for HNO₃ in highly polluted air is described. The time resolution attainable was 12 s. The method is based on the difference in a technique for HNO₃-scrubbed and non-scrubbed air and the reduction of HNO₃ to NO with the use of a line of catalytic converters and a method for the subsequent NO-ozone chemiluminescence. A sample air stream, in which particulates are removed with a Teflon filter, is divided into two channels. CH-1 is directly connected to the converter line, and CH-2 contains a HNO₃ scrubber packed with a nylon fiber that goes to another converter line. Each converter line is composed of a hot quartz-bead converter (QBC) and a molybdenum converter (MC) in a series. A QBC reduces HNO₃ to (NO+NO₂), which is called NO_x. The MC reduces the NO_x to NO.For CH-1, the analyzer detects most compounds that typically comprise NO_y (J. Geophys. Res. 91 (1986) 9781). These CH-1 compounds are called NO_y′ hereafter (NO_y-particulate nitrate) because the particulates are removed by the filter. A difference in the detector signal for the two channels indicates HNO₃. For a blank test, atmospheric air in which HNO₃ was pre-scrubbed by an extra nylon fiber was introduced to the analyzer. Variations in the blank value were 0.38±0.42 and 0.34±0.55 ppb during the high readings (NO_y′-HNO₃ ) (called NO_y^* hereafter) (111±12 ppb, N=180), and low NO_y^* readings (62±8 ppb, N=180), respectively, indicating that the lowest detection limit of the analyzer is 1.1 ppb (2σ). When the data obtained with the analyzer is compared to the data using the denuder method, a linear correlation with the regression of Y=0.973X+0.077 (r²=0.916 (N=20)) in the range of 0–6.5 ppb HNO₃ is obtained, which is an excellent agreement. Atmospheric monitoring was carried out at Kobe. Although the average concentration of HNO₃ was 2.6±1.3 ppb, ca.10 ppb for a HNO₃ concentration was occasionally observed when the NO_y^* concentration was high, i.e., more than 100 ppb.     

Corrosion on cultural heritage buildings in Italy: A role for ozone?

Because of climatic reasons and of reduced concentrations of SO₂, ground-level ozone (O₃) is one of the main air pollutants in Southern Europe. Ozone levels are very high both in rural and urban locations. In the cities, O₃ can affect human health and materials. Regarding materials, most relevant is the exposure to pollutants of cultural heritage buildings. In particular, monuments registered on UNESCO's list of the world heritage require special monitoring. In Italy 34% and 97% of the territory is exposed to corrosion risk higher than the tolerable level for limestone and copper, respectively. The tolerable corrosion level for limestone and copper was also exceeded in the central area of Milan. In this area the tolerable O₃ concentration for copper was calculated. These concentrations (ranging between 30 and 40 μg/m³) cannot be exceeded at unchanged concentration of other pollutants to maintain corrosion levels below the tolerable ones.     

Variability of total ozone over India and its adjoining regions during 1997–2008

Total Ozone Concentration (TOC) data over nineteen stations around India (fifteen stations) and its adjoining regions (three stations in Pakistan and one station in Bangladesh) are investigated in the present analysis. The overpass satellite data for these nineteen stations, distributed in the latitude range from 8.48°N to 35.83°N and altitude range from 6 m to 2718 m are available from FTP Site. TOC data pertaining to the last twelve years from 1997 to 2008 were obtained from two different instruments: Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instrument (OMI) on Earth Probe and AURA satellites respectively. The analysis is divided into two phases, each of six years duration; from 1997 to 2002 and from 2003 to 2008. Seasonal average values of TOC are calculated for the two phases and compared to study the spatial distribution (latitude, longitude and station altitude) and the trends of TOC variation. In general a decreasing tendency in ozone concentration was found everywhere. The average yearly rate of the TOC decrease was ?0.363 DU over the entire region during the period 1997–2008. The trends in the TOC distribution and its decrease with latitude were found parabolic, with a deep near 14.7°N and 12.1°N for the two phases respectively. The decrease was maximum at lower latitude (?1.87%) and minimum (?0.25%) at higher latitude. Weak oscillatory trends in the TOC distribution and its decrease with longitude were found. A deep in the longitudinal variation was observed in each phase, at 77.4°E during 1997–2002 and at 78.2°E during 2003–2008. The minimum centre of the ozone distribution is therefore shifted from 14.7°N, 77.4°E to 12.1°N, 78.2°E over the last twelve years, and in general a meridional line near 78°E appears to divide symmetrically the TOC distribution over this region. Strong oscillatory trends in the seasonal average of TOC distribution and its decrease with station altitude are observed during the two phases. The inversion of high correlation coefficients between the seasonal average TOC and station altitude in the range 6 m to 2718 m indicate the existence of four transition layers aloft, near 200, 740, 1670, and 2400 m in the lower troposphere. Emission of precursor pollutants together with complex wind pattern around the marine boundary appears to have strong potentials to modulate tropospheric ozone and the observed spatial distribution of TOC may be expected.     

Evaluating the performance of regional-scale photochemical modeling systems: Part II—ozone predictions

In this paper, the concept of scale analysis is applied to evaluate ozone predictions from two regional-scale air quality models. To this end, seasonal time series of observations and predictions from the RAMS3b/UAM-V and MM5/MAQSIP (SMRAQ) modeling systems for ozone were spectrally decomposed into fluctuations operating on the intra-day, diurnal, synoptic and longer-term time scales. Traditional model evaluation statistics are also presented to illustrate how the scale analysis approach can help improve our understanding of the models’ performance. The results indicate that UAM-V underestimates the total variance (energy) of the ozone time series when compared with observations, but shows a higher mean value than the observations. On the other hand, MAQSIP is able to better reproduce the average energy and mean concentration of the observations. However, both modeling systems do not capture the amount of variability present on the intra-day time scale primarily due to the grid resolution used in the models. For both modeling systems, the correlations between the predictions and observations are insignificant for the intra-day component, high for the diurnal component because of the inherent diurnal cycle but low for the amplitude of the diurnal component, and highest for the synoptic and baseline components. This better model performance on longer time scales suggests that current regional-scale models are most skillful in characterizing average patterns over extended periods, rather than in predicting concentrations at specific locations, during 1–2 day episodic events. In addition, we discuss the implications of these results to using the model-predicted daily maximum ozone concentrations in the regulatory framework in light of the uncertainties introduced by the models’ poor performance on the intra-day and diurnal time scales.     

Evaluation of pre-industrial surface ozone measurements made using Schönbein’s method

Ozone measurements made using Schönbein’s method during the late nineteenth and early twentieth centuries have been examined and converted to modern units using a method originally developed by Linvill et al. (1980). Monthly Weather Review 108, 1880–1891 and Anfossi et al. (1991). Journal of Geophysics Research 96, 17,349–17,352. New data are presented here from sites in Europe, Asia, Africa, Australia, and South America. The values obtained lie in the range 5–15 ppb for all sites. A negative correlation between ozone and humidity is observed, which may be consistent with photochemical loss of ozone in the presence of water vapour. However, uncertainties in the humidity correction to the Schönbein reading will lead to considerable inaccuracies in the seasonal cycle established by this method.     

A synoptic climatology for surface ozone concentrations in Southern Ontario, 1976–1981

The synoptic climatology of ozone (O₃) for S Ontario has shown that, over the 1976–1981 period, average summer O₃ concentrations follow a relationship similar to that reported for event analysis during periods of high O₃ concentration. Highest average concentrations, 36 parts per billion (ppb), occur with ‘back of the high’ situations while lowest average concentrations (20 ppb) occur with ‘front of the high’ situations.With similar weather events in the winter, the pattern is reversed with highest average O₃ concentrations on the ‘front of the high’ (19 ppb) and lowest average concentrations on the ‘back of the high’ (13 ppb). Concentration of O₃ in the ‘front of the high’ sector is due in part to the intrusion of O₃ in the vicinity of storms from the stratosphere. The seasonal variation of average concentrations in these situations is low, ranging from 14 to 26 ppb.The very low average concentration during the winter and fall for the ‘back of the high’ situation may be the result of scavenging by NO_x from the urban/industrial areas around the Great Lakes. During the spring and summer, solar energy and warm temperatures cause the photochemical production of O₃ from NO_x and HCs precursors. In the fall and winter, photochemical production of O₃ is either very low or absent, and the NO_x consume O₃ rather than produce it. Thus, average O₃ concentrations for winter ‘back of the high’ situations are one-third of those in the summer months.The synoptic climatology of events during the months from May to September with maximum O₃ concentrations in excess of 80 ppb indicates that 78 % of these events occur under synoptic weather classes generally indicative of back or centre of the high situations.     

Analyses of ozone in urban and rural sites in Málaga (Spain)

Ozone concentrations were measured at two (urban and a rural) sites near the city of Málaga (Spain). The aim of this study was to determine the daily, monthly and seasonal variation patterns of ozone concentrations at both sites and to study the possible regional influences. The daily variations mostly have the usual features with the afternoon maximum and the night minimum being more pronounced in the urban area. The average monthly concentrations throughout the year start to increase in March reaching their maximum values in July for the urban site. However, in the rural area, the monthly variations are smaller reaching their maximum value in June. The hourly evolution of the ozone concentrations in both sampling sites is well defined in spring and summer and not so well defined in autumn and winter. Taking into account the four seasons, the rural concentrations are higher than the urban ones. Summer is the season when there are similar concentrations at both sampling sites. Average hourly summer afternoon ozone for the hours 12:00-20:00 LST exceeded the 110 microg m(-3) European Union guidelines for human health for 8 h ozone exposure at the urban and rural sites.     

Photochemical air pollutant levels and ozone phytotoxicity in the region of Mesogia–Attica, Greece

The levels of photochemical air pollutants: O₃, NO and NO₂, were monitored in Athens and in the neighbouring region of the Mesogia plain (Spata, Artemis and Markopoulo) from 1 May–31 August 2000. Phytodetection of ozone was also conducted using bioindicator plants of Bel-W3 and Zichnomirodata (KK6/5) tobacco varieties. The average maximum daily O3 concentration was 60–75 ppb, while the 24 hour average ranged from 40–65 ppb. The AOT40 (ppb hours) index was very high in Athens (16 679 over 121 days), Spata (16 325 over 110 days), Artemis (8093 over 22 days) and Markopoulo (18 646 over 113 days), suggesting potentially phytotoxic ozone levels. The ozone bioindicator plants of Bel-W3 and KK6/5 tobacco varieties were highly injured in all regions confirming the phytotoxicity of those ozone levels. The levels of NO and NO₂ recorded at the three stations, in the Mesogia plain, were considerably lower than those occurring in Athens. The data presented here provide important background information concerning pollution levels in the Mesogia plain shortly before the operation of the new international airport 'Eleftherios Venizelos' in this region (March 2001).     

Formation of strong airway irritants in a model mixture of (+)-α-pinene/ozone

The airway irritation of (+)-α-pinene, ozone, mixtures thereof, and formaldehyde was evaluated by a mouse bioassay, in which sensory irritation, bronchoconstriction, and pulmonary irritation were measured. The effects are distinguished by analysis of the respiratory parameters. Significant sensory irritation (assessed from reduction of mean respiratory rate) was observed by dynamic exposure of the mice, over a period of 30 min, to a ca. 22 s old reaction mixture of ozone and (+)-α-pinene from a Teflon flow tube. The starting concentrations were 6 ppm and 80 ppm, respectively, which were diluted and let into the exposure chamber. About 10% ozone remained unreacted (0.4 ppm), <0.2 ppm formaldehyde, <0.4 ppm pinonaldehyde, <2 ppm formic acid, and <1 ppm acetic acid were formed. These concentrations, as well as that of the unreacted (+)-α-pinene (51 ppm), were below established no effect levels. The mean reduction of the respiratory rate (30%) was significantly different (p≪0.001) from clean air, as well as from exposure of (+)-α-pinene, ozone, and formaldehyde themselves at the concentrations measured. Addition of the effects of the measured residual reactants and products cannot explain the observed sensory irritation effect. This suggests that one or more strong airway irritants have been formed. Therefore, oxidation reactions of common naturally occurring unsaturated compounds (e.g., terpenes) may be relevant for indoor air quality.     

An assessment of source contributions to the ozone concentrations in southern Ontario, 1979–1985

Source contributions to the surface O₃ concentrations in southern Ontario were assessed for the 1979–1985 period. Ozone episode analyses indicate a frequency of about nine episodes per year (15 episode-days). These occur primarily in the summer months and are generally manifestations of the northern extent of the O₃ problem in eastern North America. Widespread elevated O₃ levels tend to occur under weather classes indicative of back or centre of the high pressure situations and associated flow/trajectory from areas south/southwest of the lower Great Lakes. These episodes vary considerably from year-to-year. Local impacts on O₃ levels are generally small.A study of O₃ levels during cloud-free summer days for the period 1981–1985 gave local ‘background’ O₃ levels of about 20–30 ppb daily and 30–50 ppb hourly maxima. The O₃ contributions from the U.S. to southern Canada (assuming local ‘background’ O₃ levels to be independent of wind direction) were estimated to be 30–35 ppb daily and 30–50 ppb hourly maxima. These results indicate an overall O₃ contribution of about 50–60% from the U.S. to southern Ontario. For episode-days, the U.S. contribution is even more significant.     

Newly characterized products and composition of secondary aerosols from the reaction of α-pinene with ozone

Secondary aerosols from the reaction of α-pinene with ozone were generated in a 190 m³ outdoor Teflon chamber, and products of these aerosols were characterized. Products were separated by gas chromatography and detected with electron-impact mass spectrometry, chemical-impact mass spectrometry, and Fourier transform infrared spectrometry. Because products from the reaction of α-pinene with ozone contain oxidized functional groups such as carboxylic acids and carbonyls, these products are poorly resolved by standard gas chromatography. To use standard chromatographic techniques, derivatization of oxidized functional groups was necessary. Carbonyl products were derivatized with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride and carboxylic acids with pentafluorobenzyl bromide. The major identified products were nor-pinonic acid, pinonic acid, 2,2-dimethylcyclobutane-1,3-dicarboxylic acid, pinic acid, and pinonaldehyde. Dicarboxylic acids have lower vapor pressures than either their corresponding di-aldehydes or mono-acids, and have only recently been identified in α-pinene–ozone aerosols. Given their comparatively low vapor pressures, diacids contribute significantly to the aerosol formation process from the reaction of α-pinene with ozone. The composition of these secondary aerosols is strongly influenced by temperature. During the summer experiments, the aerosol composition is dominated by diacids. During the cooler winter experiments, the di-carbonyl and carbonyl-acid products also contributed to the aerosol composition.     

A comparison of North American and Asian exposure–response data for ozone effects on crop yields

Modelling-based studies to assess the extent and magnitude of ozone (O₃) risk to agriculture in Asia suggest that yield losses of 5–20% for important crops may be common in areas experiencing elevated O₃ concentrations. These assessments have relied on European and North American dose–response relationships and hence assumed an equivalent Asian crop response to O₃ for local cultivars, pollutant conditions and climate. To test this assumption we collated comparable dose–response data derived from fumigation, filtration and EDU experiments conducted in Asia on wheat, rice and leguminous crop species. These data are pooled and compared with equivalent North American dose–response relationships. The Asian data show that at ambient O₃ concentrations found at the study sites (which vary between ～35–75 ppb 4–8 h growing season mean), yield losses for wheat, rice and legumes range between 5–48, 3–47 and 10–65%, respectively. The results indicate that Asian grown wheat and rice cultivars are more sensitive to O₃ than the North American dose–response relationships would suggest. For legumes the scatter in the data makes it difficult to reach any equivalent conclusion in relative sensitivities. As such, existing modelling-based risk assessments may have substantially underestimated the scale of the problem in Asia through use of North American derived dose–response relationships.     

Scientometric analysis: identification of research trends for ozone as an air pollutant for 2011–2019

Environmental Science and Pollution Research - Ground level ozone is a major air pollutant with known toxic effects on humans. The research field is well established with many scientists from...     

Does living in elevated CO2 ameliorate tree response to ozone? A review on stomatal responses

Short-term elevated O3 reduces photosynthesis, which reduces stomatal conductance (g(s)) in response to increased substomatal CO2 concentration (Ci). Further exposure causes stomata to become sluggish in response to environmental stimuli. Exposure to elevated CO2 stimulates rapid stomata closure in response to increased Ci. This reduction in g(s) may not be sustained over time as photosynthesis down-regulates and with it, g(s). The relationship between g(s) and photosynthesis may not be constant because stomata respond more slowly to environmental changes than photosynthesis, and because elevated CO2 may alter guard cell sensitivity to other signals. Also, reduced stomatal density (and g(s)) in response to long-term CO2 enrichment suggests sustained reduction in g(s). Elevated CO2 is believed to ameliorate the deleterious O3 effects by reducing g(s) and thus the potential O3 flux into leaves. Confirmation that g(s) acclimation to CO2 enrichment does not lessen over time is critical for developing meaningful O3 flux scenarios.