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A very compact, transportable differential absorption lidar (DIAL) for ozone and aerosol profiling in the lower troposphere (from near surface to about 3 km) has been developed at the National Oceanic and Atmospheric Administration's Environmental Technology Laboratory. The ozone lidar has been employed in two field experiments in California. The first was an intercomparison experiment of the lidar and an airborne ozone analyzer carried out in the Sacramento valley of northern California during July 1993. The second field experiment involving the ozone lidar was the Free Radical Study, carried out in the Los Angeles basin during September 1993, where the highest ozone episode of the year was observed during the experiment. The system will be described and examples of ozone profiles taken during the high ozone episode in inland Los Angeles will be shown.

In the alpine region as well as in other European areas the ozone concentration appears to be increasing (Warmbt, 1977). During this century the ozone levels in the atmospheric boundary layer have been almost doubled (Volz and Kley, 1988). After Puxbaum et al. (1991) the ozone concentration in the Zillertal (a small valley in the Austrian Alps) has been increased by a factor of 3 since 1950. Beside this long term trend high ozone values of 100 ppb and more are increasingly observed during pollution episodes. These episodes are associated with high pressure systems, when the meteorological condition, in particular warm temperatures, clear skies and low wind speeds, encourage the photochemical formation of ozone. Calms and inversions causing reduced ventilation occur more frequently in mountain valleys than over flat terrain (Dreiseitl and Weber, 1991). Therefore the meteorological conditions in the Alps conduce the ozone production.

During the summer of 1990 several high ozone events have taken place in Rheinland-Pfalz (Western Germany), accompanied by warm and dry anticyclonic weather conditions. In those periods, winds from the east have transported air masses contaminated by anthropogenic sources from urban areas near the river Rhine to rural and forest regions, which are located in the western and northern part of the country. In order to test the assumption, that anthropogenic air pollutants are responsible for high ozone concentrations measured in remote areas, a mathematical model has been developed, which uses urban NOX, NMHC, CO and O3 data measured in the morning as input parameters and calculates the diurnal formation of oxidants, especially of ozone, during transportation. the calculation results show an excellent agreement of NOx and O3 concentrations with measured data at stations which may have been crossed by the calculated air mass. Anthropogenic NOx and NMHC concentrations will be dispersed and chemically destroyed to the detection limit during transportation by forming that amount of ozone which remains stable even at night in an aged air mass. Because of this contrary diurnal variation of air pollutants during photosmog periods, the daily average of the sum of NO2 and O3 shows similar values over the land with no spatial differences.

The four highest measured ozone peaks in the Vienna area were analysed with respect to temperature and wind field with the help of the OZIPR computer model (Gery et al. 1990), a box model with hourly emission and meteorological input, in conjunction with the CBM-IV-mechanism (Gery et al. 1989). Calculated peak ozone values for a receptor point 10 km downwind of Vienna matched measured values within −3 % to + 16 % and have been identified as effects of high temperature (approx. 60 % of local o3 formation) and low wind speed (approx. 40 % respectively) under constant precursor emissions.

Photochemical smog often enshrouds metropolitan areas throughout the Northeastern United States during the summer. Ozone levels exceeding the level of the National Ambient Air Quality Standard (NAAQS), 120 ppb, occur during such smog episodes. Ambient monitoring data indicate that high ozone levels persist despite efforts to reduce ozone precursor emissions from automobiles and industrial sources. Also, field studies have shown that ozone pollution often spreads over several States to impact areas across hundreds of miles. The Environmental Protection Agency has responded to the need to understand this complex problem of long-range ozone transport in part by sponsoring the development of the Regional Oxidant Model (ROM). The purpose of this video is to display ozone concentrations predicted by ROM in a manner which graphically depicts the formation and transport of ozone within the Northeast. As shown in the video, patterns of interurban and interstate transport of moderate to high ozone levels are clearly evident across this region.

The use of pesticides in California’s agricultural industry plays a role in air quality with emissions of organic compounds thought to contribute to the formation of ground level ozone. Ozone levels in many regions of California exceed the prescribed Federal and State standards every year. The actual contribution from pesticide applications (as well as other agricultural sources) is largely unknown, and relies on assumptions of reactivity and tendency to evaporate. Progress on accurate determinations of either parameter is limited by many factors, including the proprietary nature of formulations. We have developed an approach which can measure the ozone formation potential of many agricultural sources, in the field. This approach was previously validated and described during a recently completed and published study of emissions from dairy cattle, their feed, as well as their fresh waste. With accompanying measurements of the most abundant volatile organic compounds (VOCs) involved there, we showed agreement between laboratory studies, field measurements, and a computer model of atmospheric photochemical reactions that improves upon past efforts, which were limited to urban/industrial VOCs. Our goal is to reach the same level of understanding for VOCs contained in pesticide formulations. Two sets of field experiments were performed to assess the ozone formation potential of pesticide solvents using a set of transportable smog chambers in the summer of 2007. The first set of experiments were conducted for a solvent-based emulsifiable concentrate (EC) base-spray on a one-acre bare field, and the second set of experiments were conducted for an agricultural application of Lorsban 4E in a three-acre citrus orchard. By comparing the upwind and downwind measurements, the experiments indicated that the emission of pesticide solvent after field application led to increased ozone formation. After a 180 min UV exposure, the ozone formation potential measured at the downwind side averaged 14 ppb higher than that of upwind air, while the average difference was around 3 ppb for background levels on both the day before and the day after pesticide spray. Laboratory experiments were also conducted for different doses of EC base with various levels of nitrogen oxides using the transportable smog chambers. The experimental isopleth demonstrates that VOCs emitted from the EC base could result in high ozone formation. Future work will provide full VOC speciation and application of the results in a regional photochemical model to predict ozone impacts.

In this paper, we present a validation study for oxidants and secondary inorganic aerosols using the new regional Chemistry Transport Model (CTM) Long Term Ozone Simulation (LOTOS) European Operational Smog (EUROS). The model is the product of the integration of the Netherlands Organisation for Applied Scientific Research (TNO) LOTOS model and the National Institute for Public Health and the Environment (RIVM) EUROS model. In addition to a model description, we present an overview of a validation of the model. The new model is able to capture the variability of ozone well, especially in summer. However, the exchange between the mixing layer and the free troposphere was assessed to be too low resulting in too high ozone levels at days with low ozone. Sulphate levels are underestimated, whereas the concentrations of nitrate and ammonium are in line with measured data. The performance of LOTOS-EUROS is similar to other regional models in Europe. Examples of new applications of the model are presented. These include the modelling of sea salt and heavy metals.

Spatial distribution of hydrogen peroxide and of some other atmospheric trace gases (NO, NO2, NOy, O3, SO2) was measured from an aircraft over the northeastern U.S. during an extended field campaign in August and September 1988. Hydrogen peroxide was measured with an improved instrument based on the enzyme catalyzed fluorometric technique.

Ozone in the atmosphere has many useful functions. Most of it is in the stratosphere (above 10 to 20 km) and only ten per cent is in the troposphere (the region down to ground level), where it helps to remove undesirable emissions. The two regions are usually separated, dynamically, by the tropopause, but new measurements taken on airliners show that pockets of extremely high ozone concentration are somehow getting from the stratosphere into the troposphere over the tropical Atlantic.

The objective of this work is to investigate the sensitivity of an Eulerian Chemical Tranport Model to the reconstruction of the wind field. In the framework of City-Delta exercise, three 14-day simulations have been performed, using the same model (CAMx) and different meteorological inputs; these were built combining large-scale analysis, local observations and the output of a high resolution meteorological model (Aladin). When Aladin output is used, stronger surface winds lead to enhanced nighttime mixing, resulting in higher ozone and lower PM10 concentrations in urban areas; on the other hand, the stronger advection associated with Aladin wind seems to help the model reproduce high ozone concentrations during day. The use of local wind observations appears beneficial to model performance.

This paper presents a study to determine the areas that could most probably be affected by high ozone levels in the centre of the Iberian Peninsula. Considering the years 1992 and 1995, cluster analysis was applied to some variables to group those days with similar meteorological states. Three different meteorological cluster groups were identified and their main features analysed. Additionally, wind direction was used to set up representative subclusters. Finally, representatives to the mean state of every subcluster scenarios were selected. Among these, several days were chosen to represent meteorological conditions that could most probably be associated to photochemical episodes and simulations with the TVM meteorological model coupled to a transport-chemistry module were carried out. Results show very high ozone production levels for some days. Thus, four impact areas could be identified, located both tens of kilometres away far from the city (in N, NW and E directions) or affecting the whole community of Madrid.

An optimum-dielectric-constant material with a fixed size was experimentally obtained for high ozone generation in a parallel-plate barrier discharge. The ozone production rate as a function of dielectric constant was found to depend strongly on discharge voltage. The ozone production rate for strontium titanium oxide (SrTiO3) with high dielectric constant of approximately 300 was the highest among various existing dielectric materials under low discharge voltage (root-mean-square value) of 1.2 kV, while for titanium oxide (TiO2) with dielectric constant of about 100, the highest ozone production efficiency was obtained at a wide range of discharge power and/or ozone concentration.

Hourly measurements of ozone concentration in the urban atmosphere of Istanbul were carried out from February 1998 to July 1999. An assessment of the annual variations and relationships of ozone concentrations and meteorological variables was made. Annual variations were first examined without considering meteorological variables, and meteorological influences on ozone seasonal values were then examined. Furthermore, a typical ozone threshold period was analysed by considering meteorological variables for a case study. Meteorological conditions favourable for high ozone concentrations appeared when Istanbul and its surrounding region were dominated by an anticyclonic pressure system. During conducive ozone days, southerly and southwesterly winds with low speeds (daytime mean value

High ozone levels detected over large inland areas in Israel triggered an analysis of air mass back-trajectory, which pointed to the coastal Tel-Aviv metropolitan transportation system as the origin of the ozone's precursors. In order to link the transportation emissions to ozone formation interdisciplinary modelling systems were utilized and integrated. The transportation-to-ozone formation simulation interfaced transportation, emission factor, atmospheric and transport/diffusion models. The modelling results elucidated the spatial and temporal overlap between the ozone precursors and ozone production. The model simulations indicated an eastward transport accompanied with a 3-D expansion of the pollution cloud. The results agreed well with observed spatial and temporal ozone levels.

The consequences of the long-range transport of highway-related emissions are discussed. Three areas are addressed (1) the direct deposition of nitrogen compounds in precipitation, (2) the influence of emissions from motor vehicles on the wet deposition of sulphate and (3) their role in the formation of regional episodes of high ozone. Though there are many unknowns, much can be gained by establishing the value of key time-scales in each problem.

The occasional high ozone levels measured in Jerusalem could not be attributed solely to local sources such as vehicular traffic or industry. A satellite monitoring station was set up outside the city limits to explore the possibility of transport and transformation of air pollutants from the highly populated and industrialized coastal area of Israel to the inland hilly region. This study revealed that the high ozone levels were always associated with a parallel increase of SO 2 and that power plants and/or vehicles operating in the coastal region are a major source for the nitrogen oxides which undergo photochemical transformation to form ozone during inland travel of the air parcel under conditions of intense sunlight.

Elevated ozone concentrations, in excess of accepted background levels, were frequently measured at night in Jerusalem and Tel-Aviv. High ozone at night is connected with persisting low level inversions, under which the photochemically generated ozone is trapped during the day. With the gradual descent of the inversion towards evening and cessation of traffic, ozone levels rise, reaching peak values about 4 h after midnight. The onset of early morning traffic with increasing NO and other pollutants then decreases the ozone concentrations, which reach a minimum level at about 7–8 h local time.

Results from an ozono monitoring programme in Oslo (60°N) show that high ozone concentrations, up to 218 μg m −3 (109 ppb) occurred, mainly during high-pressure situations. An assessment of the local meteorological conditions together with air trajectory analyses seems to indicate that the local and mesoscale formation and transport were more important than transport from distant sources.

The relationship of high ozone (ozone in excess of the National Ambient Air Quality Standards—NAAQS) with high pressure systems was examined using data collected in the summer of 1973, 1974 and 1975. It was found that high surface ozone occurred most often when a high pressure system was near a reporting station. Long periods of high ozone were associated with long-term buildups of high pressure greater than 20 days. High ozone occurred most often on the back side of the high pressure system in air that had large residence times in the system. This suggested that time was required to develop large or critical concentrations of ozone precursors. It was shown that high ozone occurred most often when the high pressure system was in the eastern portions of the United States. The evidence indicated that as the high pressure system moved from west to east, the air in the high had larger concentrations of ozone precursors and destructive agents when it was in the east. This suggested an injection of these constituents in the east. Furthermore, there appeared to be a change in the role of synthesis and destruction of ozone between 1973 and 1974 or 1975.

The diurnal variations during summer and winter of the concentrations of NO, NO 2 , O 3 and hydrocarbons downwind from a polluting source in pristine areas are calculated using a chemically oriented expanding box model. It is found that during the summer high ozone levels could be expected in the afternoon, particularly from a mixture originally emitted between 6 and 10 a.m. Under identical conditions high ozone levels are not predicted at any time of the day during the winter. HO 2 NO 2 is predicted to be present at higher levels than PAN during the winter, whereas during summer the reverse situation obtains.

Long-range transport of ozone across the midwestern and eastern U.S. was investigated by analyzing daily ozone isopleth maps and comparing them to meteorological maps and air parcel trajectories for the period April 12–23, 1976. This period was characterized by the presence of a large high pressure system which produced widespread ozone concentrations of greater than 0.08 ppm as well as record-breaking maximum springtime temperatures over much of the study area. Daily maximum ozone values from the state networks were used to produce the daily ozone maps. Movement of areas of high ozone concentrations corresponded to the movement of the high pressure system. Actual transport across these areas is supported by trajectory analysis. Daily visibility maps were also prepared and they suggest that areas of low visibility generally coincide with areas of elevated ozone under certain conditions.

Two-year-old seedlings of Sitka spruce [Picea sitchensis (Bong) Cart.] were exposed to < 5, 70, 120 and 170 nl l−1 O3 for 7 h day−1 in large ventilated glasshouses during the summer of 1986. Relative growth rates (RGR) were calculated at intervals throughout the summer and autumn using a non-destructive technique in which measurements of stem height and diameter were used to estimate above-ground biomass. No statistically significant effects of the ozone on growth were apparent during or after the period of fumigation, and growth of the seedlings had largely been completed by the end of August. The winter hardiness of these plants was subsequently tested on 10 November and 8 December by subjecting detached shoots to a range of carefully regulated freezing temperatures in controlled environment chambers. The results for the samples taken on the earlier date suggested that plants exposed to ozone were more sensitive to frost than the controls, and that this effect was dependent on the concentration of the pollutant. In the samples taken later, all the shoots appeared to have hardened equally to freezing temperatures in excess of about –20 °C. The results suggest that early autumn frosts might be damaging to Sitka spruce after exposure to high ozone concentrations in summer.

PAN and ozone or oxidant measurements were made at four different sites. Three of these sites were urban locations, the other was rural. PAN and corresponding ozone and oxidant measurements were compared. The maximum O/sub 3//PAN or O/sub x//PAN ratios varied at each sampling site thus preventing the prediction of PAN concentrations estimates from ambient ozone concentration alone. Generally high ozone concentrations were observed when corresponding high PAN concentrations were measured. However, high ozone was observed when PAN concentrations were low. These observations concur with simulated chamber irradiations and modeling predictions of ozone and PAN concentrations.

A graphical technique is presented which enhances the information on scatterplots by plotting three smooth cluves of movie statistics which slunmarize the change in the distribution of Y given X. The three curves involve the tue of the midmean ithe average of all observations betweell the qluxtiles), and two new statistics: the lower semi-midmean (the midmenn of all observations below the median), and the upper semi-midmean (the midmean of all observations above the mediate). The technique is used in the analysis of air pollutiou data to show that emissions of primary pollrltnnts in the Camden-Philadelphia urban complex are partly responsible for high ozone concentratiotls 37 km tO the southeast in Ancora, New Jersey, a nonluban area, where concentrations of primary pollutants are low, but where ozone daily maxima freqltently exceed the Federal Standard.

Precursor concentration distributions and the derived relationships which characterize the spatial distribution of emission sources in the Sydney airshed in 1975/6/7 are compared with precursor data obtained during the 1981/2 summer. The 1981/2 data shows that: 1. (i) NMHC point sources no longer dominate the character of Sydney's moring time urban air parcels and 2. (ii) morning time meteorology and/or overall 6:00–10:00 a.m. mass emission rates have changed, resulting in an increase in the frequency of occurrrence of moderate to high NHMC and NO x concentration events. The absence of dominant morning time NMHC point sources balances the increased precursor concentrations and gives rise to a predicted ozone concentration distribution for 1981/2 which is similar to that reported elsewhere for 1975/6/7. The marked reduction in the monitored frequency of occurrence of high ozone events since 1975/6/7 cannot be explained by changes in the characteristics of morningtime air parcels and it is suggested that the observed reduction may be due to a change in the midday (10:00 a.m.–4:00 p.m.) meteorology since 1975/6/7.

As a result of the 1975 Moodus Conference, a task force was established to analyze the ozone data from the 19 Moodus states and to assess the importance of ozone transport across the Midwestern and Northeastern United States. Data from daily ozone maps, aerial ozone measurements, and trajectory analysis are used in this paper to describe the typical summertime ozone episode in the Moodus study area. The results indicate that ozone concentrations in a high pressure system as it moves out of Canada into the Midwest are typically 30–50 ppb. Higher concentrations first develop over the areas of high anthropogenic percursor emissions. As the high pressure moves eastward, the areas of high ozone increase in size and concentration and eventually merge together. Verticle ozone profiles conducted on consecutive days and nights suggest an ozone half‐life of 46.8 h above the nocturnal inversion layer. Using the corresponding dark phase rate of ozone decay in conjunction with air parcel trajectories, it was ...

A quasi-equilibrium theory is presented for the mixing of nitric-oxide rich emissions with ozone-containing background air. Average concentrations of species are obtained by weighting with the probability density function of a mixing parameter, experimental information on which is reviewed. Results show that the photostationary state parameter, \ gl = k 3 [NO] [O 3 ]/(k 1 [NO 2 ] ), can be much greater than unity when average concentrations are used even though the parameter is taken as unity on an instantaneous pointwise basis. Considerations of the rates of molecular mixing of the reactants show that these must be comparable to the chemical kinetic rate of reactant consumption under many situations of interest, thus indicating that quasi-equilibrium breaks down and the photostationary state parameter is not unity even on a pointwise instantaneous basis. High values of \ gl are favoured by low u.v. light intensity, intermittent and high intensity turbulent fluctuations, and background smog of high ozone and low NOx, concentration.

The EPA, in cooperation with the U.S. Forest Service, has established a network of air monitoring stations designed to measure levels of ozone in remote areas within the contiguous 48 states. There are currently 8 sites, at various National Forests, which measure ozone, wind speed and direction, temperature, relative humidity, and solar radiation. This is a review of the network data collected during 1979, the year for which the most complete meteorological and ozone records were available. The mean ozone level for 1979 at these sites fell within the range of 0.025- 0.04 ppM. At most sites, there were several days in 1979 when hourly concentrations of ozone exceeded 0.08 ppM. The maximum 1 h ozone concentration observed was 0.125 ppM. The report provides analyses of the statistical distributions of the ozone data from these remote sites, their relationships with local meteorological data, and the possible impact of air parcel history upon ozone concentration. Examination of several individual days in 1979 with relatively high ozone levels using a back trajectory model showed that in almost all of these cases, the air had passed over large urban areas within the previous 3 days. The hypothesis is presented that high levels ofmore » ozone at remote sites may be due in part to the long range transport of ozone and/or its precursors. 1 figure, 4 tables.« less

A large number of radioactive and non-radioactive airborne constituents are being measured continually at our Coastal Air Reference Station located in Northwestern Washington State. Important correlations have been observed between many of these materials. There are also apparent relationships between changing concentrations and meteorological parameters. Interesting fluctuations in the ozone levels observed by workers elsewhere. Positive correlations between certain known high altitude source region particulate radionuclides and ozone on a daily basis point to the upper level origin of the high ozone concentrations observed at this site. This view is reinforced by the more usual negative correlations observed between general particulate levels at Quillayute and ozone concentrations when measured on a continuous monitoring basis.

The spatial and temporal distributions of ozone in the eastern two-thirds of the U.S. during three typical ozone episodes that occurred in July 1978 are examined. In all three cases, a distinct area of high ozone concentrations was observed flowing northeastward in an aerial ''''river'' extending from the southwest Gulf Coast to New England. The formation, size, and characteristics of this ''''river'' are discussed. (12 maps, 9 references)

The penetration of stratospheric air into the troposphere, revealed by high ozone concentrations measured both by an aircraft (Electra) and at a mountain station (Mt. Cimone) during a lee cyclogenesis event (April 24–25, 1982), is investigated. A detailed analysis of the meteorological fields and the application of the isentropic-trajectory method allowed us to reveal the dynamical processes responsible for the ozone transport into the troposphere. We show that the two episodes of high ozone concentrations have to be attributed to the evolution of two distinct upper vortexes, only one of which was associated with surface lee cyclone development.

A modified iodometric procedure using an absorbing solution of 2% NBKI with a known amount of As(III) is described for 10 ml aqueous samples. Ozone contents from 0.5 to 65 mg O3/I were determined. High ozone concentrations can also be measured for generator calibration. This method gives results which are not significantly different than a boric acid method but are for a modified standard methods procedure. Volatility of iodine has been completely eliminated. Stabilized samples do not make the time between sampling and final titration critical.

An examination of exceptionally high ozone values (138–228 ppb) recorded at the ground level in Regina, Saskatchewan suggested that they were due to downward transport from the stratosphere. The occurrence of high O3 concentrations, in excess of 120 ppb near the ground, due to stratospheric intrusion appears to be an uncommon local phenomenon even with the frequent passages of upper troughs and the prevalence of jet streams, etc. Characteristically, such O3 episodes are observed to last only 1–3 h.

As part of the Environmental Protection Agency's Regional Air Pollution Study (RAPS) a network of 25 stations continuously recorded aeromatic data in the Greater St. Louis area. Various photochemical pollutants (O 3 , NO, NO 2 and total hydrocarbons) and some selected meteorological variables (wind speed, temperature, and solar radiation) were analyzed with respect to the day of the week using 11 months of data collected during the warm months of the year — periods during which high ozone concentrations were common in St. Louis. The results reveal that the sign (±) of the workday to Sunday differences in the concentration of ozone depends to a large extent on the distance of the measurement from the major emission area of the metropolitan area of St. Louis. The data suggest that this is due to the impact of nitric oxide on the ambient ozone concentrations. This appears to offer at least a partial explanation for some of the contrasting results reported by various investigators regarding the differences in ozone concentrations between weekends and weekdays.

The effect of changes in NO/sub x/ emissions on downwind regions of the California south coast air basin was investigated with th elstar trajectory model. Smog formation was simulated in air parcels which originated near Los Angeles in the early morning, passes through the San Gabriel Valley, and arrived at or near San Bernardino in the mid to late afternoon on days of moderate to high ozone. With nonvehicular emissions held fixed at the 1973 levels, the planned reduction in motor vehicle emissions is predicted to result in reduced atmospheric concentrations of CO, NO, NO/sub 2/, O/sub 3/, pan, and HNO/sub 3/ along the air parcel trajectories. However, when the hydrocarbon emissions are held fixed at a projected future level, a decrease in NO/sub x/ emissions will result in a decrease in NO/sub 2/ concentrations, but an increase in O/sub 3/ and pan concentrations at all positions along the trajectories.

Carbathiin (2,3-dihydro-5-carboxanilido-6-methyl-1,4-oxathiin) or its sulfoxide analog, carbathiin-monoxide sprayed at a rate of 2.2 kg/ha gave appreciable control of ozone injury on white beans (Phaseolus vulgaris L.). When either of the two chemicals was applied to white bean plots on 2 August 1973, 2 days before a major ozone eipsode, the amount of premature leaf drop was reduced and yields increased as compared to unsprayed checks. Spraying the chemicals after the ozone episode was ineffective in reducing ozone injury. Pyracarbolid, a related oxathiin analog, did not protect white beans from ozone injury in field trials. Benomyl sprays gave a slight reduction in premature leaf drop but did not increase yields significantly when applied just before the ozone episode in early August. None of the chemicals was effective when applied after the incident of high ozone levels. A cost benefit analysis indicated that a single carbathiin spray applied prior to high ozone levels was effective and economical for the control of bronzing of white beans.

Five years of observations of the ozone concentration in the surface air at Aspendale, Victoria, are presented. On some occasions the concentrations of ozone (or oxidant) reach 0.1 ppm v v . Such high ozone concentrations are associated with high air temperatures and reduced intensity of ultra-violet radiation observed at the earth's surface. On such occasions it appears that there is local production of ozone near the earth's surface.

The paper contains a summary of the results of the height distribution of ozone in the atmosphere obtained at Motmt. Abu with a Dobson Speetrophotometer during the period October 1951 to April 1952, when western disturbances affect North Indian weather. The observations show that there is very little ozone in the atmosphere below 18 km., that the ozone amount above 27 km. show very little systematic change with total amount, and that most of the changes take place in the layer 18 to 27 km. These results are compared with those obtained at Delhi, Kodaikanal, New Mexico (with V2 rockets), Arosa (in Switzerland) and Tromsϕ (Norway). In middle and high latitudes, there are substantial amounts of ozone below 18 km., and the larger the total amount, the larger is the proportion in the lower levels. For high ozone amounts in high latitudes, nearly hall the total amount may be below 20 km.

A convenient rubber cracking test for ozone is described. This method serves not only as a rapid, positive means of identifying ozone in complex gas mixtures but also gives close approximation to the quantity present. Application of the method in determining ozone in heavy smog atmosphere is shown. The high ozone concentration in these tests is attributed to ozone formation under the catalytic action of nitrogen oxides and sunlight.

Damage to tobacco plants, known as “weather fleck”, is now recognized as being due to ozone. Over the northern shores of Lake Erie ozone is believed to be mainly generated by photo-chemical processes from oxides of nitrogen and hydrocarbons emitted in industrial areas to the south. However, thunderstorm activity and stratospheric ozone might at times contribute to total ozone concentration, although only in small quantities. Indications are that on most occasions of high ozone concentration, lake breeze surges, and meso-scale systems forming as a result of the physiographical features of the Great Lakes area, dominated the weather picture and were the key mechanism by which ozone was advected and brought down to the surface. Severe flecking generally occurred with a particular combination of amounts of ozone dose and evapotranspiration. When the hourly ozone concentrations were modified by a coefficient of evapotranspiration derived from a simple form of the mass transfer equation, a much improved correlation between flecking severity and modified ozone dose was obtained, and several hitherto obscure results could be explained.

The reaction of dyes with atmospheric contaminants, including ozone and oxides of nitrogen, is shown to be an important factor in light-fastness testing. Ozone, present to the extent of 0·05 to 0·2 p.p.m., is responsible for fading in exposures away from sunlight. Oxides of nitrogen also contribute to anomalous fading in industrial areas when present in concentrations up to 0·3 p.p.m. Fading has been observed on cotton dyed with certain vat, direct, sulphur, and reactive dyes, and on nylon and acetate dyed with typical dyes. Fading is greater in areas of high humidity, including sunlight exposure stations. Ozone fading is discussed in terms of occurrence, vulnerable dyes, chemical reaction, and effect of humidity. The experimental results are used to explain certain variations in light-fastness results obtained by the AATCC in exposures at a constant number of Lacg'eys, equivalent temperatures and humidity, but in different localities. Data on various dyes and fibres are presented for three-month exposures protected from sunlight in Los Angeles, California (an area of high NO2, very low SO2, and high ozone contents), Chicago, Illinois (moderate NO2, high SO2, and low ozone), Phoenix, Arizona (a sunlight testing station of moderate ozone, no NO2 or SO2, but low humidity) and Sarasota, Florida (a sunlight testing station of moderate ozone, no NO2 or SO2, but high humidity). Laboratory test methods for fading clue to oxides of nitrogen and ozone are correlated with the actual service-exposure results. Exposure to irradiated car-exhaust fumes in a laboratory chamber representing a combination of NO2 and ozone duplicates the Los Angeles exposure results. It is concluded that consideration should be given to the combined effects of atmospheric contaminants and sunlight on dyed fibres.

A survey was made to (1) measure ozone concentrations in CAR 4b jet aircraft cabins and cockpits on flights above 25,000 ft to obtain a 12-month evaluation with emphasis on seasonal and meteorological correlation and (2) locate and chart ozone-enriched air masses to obtain further correlations and to find any abnormal conditions that result in high ozone concentration. The data obtained by monitoring jets showed: (1) External ozone enters via the pressurization system. (2) Ozone concentration varies with altitude, latitude, and season. (3) Pressurization systems of various aircraft do not differ in ozone-decomposing efficiency. (4) Internal ozone concentration is negligible on flights made below the tropopause.

The results of the Ordnance Corps Pasadena exposure tests may be summarized as follows: 1. The ozone resistance of synthetic elastomers, particularly SBR, can be substantially improved by the addition of suitable antiozonants and waxes to the rubber compound. 2. The one to two years protection at Pasadena appears to be equivalent to 3–5 years protection in other areas where ozone concentrations are low. 3. Butyl and neoprene rubbers which have inherent high ozone resistance become less effective when plasticized to meet the military's low temperature requirements and require the addition of suitable antiozonants and careful compounding in order to regain their ozone resistance. 4. Polyurethane rubbers promise to play an important role in the manufacture of many end items used on military vehicles when it becomes economically available. 5. For storage purposes a surface coating with a 50/50 mixture of dioctyl-p-phenylenediamine and acetone promises to impart good ozone resistance to tires that were not protected against ozone during manufacture.

This paper discusses meteorological conditions associated with high ozone concentrations in the New York Metropolitan area. To this end, ambient air quality measurements from the states of New Jersey, New York and Connecticut were examined for a six-year period from 1978 to 1983. High ozone days were selected from the available data. The defining criterion was a maximum hourly reading of greater than or equal to 200 ppb in the New York metropolitan area, New Jersey, and/or at two sites in Connecticut.

The development and application of a photochemical model capable of simulating regional transport of ozone and its precursors are the focus of an extensive program now in progress at the U.S. Environmental Protection Agency (EPA). This model, the Regional Oxidant Model (ROM) is designed for use in evaluating the effectiveness of various emission control strategies on a regional (1000 km) scale. The first model application will be for the Northeast U.S. where various studies have demonstrated the occurrence of widespread episodes of high ozone concentrations.1,2 The purposes of this paper are to describe the basis and structure of the ROM including design and implementation considerations and to present some preliminary model results.

Hourly concentrations of ozone were measured by the chemiluminescence method during the summer of 1971 in the vicinity of 33 cities. A listing was made of the percent of time the National Air Quality Standard for photochemical oxidants was violated. At 4 selected cities the daytime and nighttime average concentrations were related to wind directions showing the direction to source areas. Another set of tables and graphs was used to show the source directions for high concentrations (equal to or above 120 µg/m3) and disregarding the times of more usual or background concentrations. Numerous occasions of high ozone concentrations occurred when wind directions were apparently from areas with low concentrations of the known precursors. Because of this, other sources of ozone were considered such as thunderstorms and the transport of ozone for long distances. Examples of ozone concentrations during thunderstorms or related to long distance transport are cited.

The impact of precursor emissions on oxidant formation in the atmosphere may in principle be assessed on the basis of emission inventories. In the assessment, a correlation must be found between emission rates and ambient air concentrations of precursors, which depend on transport, dispersion, and chemical conversion of the precursors in the atmosphere.

During the past decade there has been a marked shift in emphasis on air pollution problems. Instead of focusing on short or episodic problems of a local nature, significant interest has recently been directed toward the degradation of regional air quality and related problems caused by the transport of atmospheric pollutants from upwind emission sources over long distances. Even the phenomenon of photochemical smog, in the past considered an urban problem, has taken on a regional character. High ozone concentrations exceeding air quality standards have been observed over widespread rural areas located downwind of major metropolitan centers in the eastern United States, according to several reports (e.g., Wolff et al., 1977). Such occurrences have been observed in other areas of the United States and in western Europe (e.g., Fehsenfeld et al., 1983; Hov, Isaksen, and Hesstvedt, 1978).