The Effects of Photochemical Oxidants on Materials

The excessive cracking of rubber products was one of the earliest indicators of the presence of atmospheric photochemical oxidants. It has been demonstrated that this excessive cracking of rubber is caused by atmospheric ozone formed in the photochemical smog formation process. Depending on the formulation of the rubber, cracking under stress can readily be detected within 3/4 hr when atmospheric oxidant levels are as low as 0.03 ppm. Natural and certain synthetic rubbers are particularly vulnerable. These rubbers when stressed show cracking when exposed to 0.02 ppm laboratory ozone for about 1 hr. Other materials known to deteriorate under atmospheric photochemical smog conditions are textiles and certain dyed fabrics, particularly under conditions of high humidity. Loss of tensile strength of cotton textiles when wet or moist, and similar fading of these dyed fabrics, particularly under high humidity, can be also produced by laboratory exposure of these textiles to pure ozone. Ozone effects on asphaltic materials ate also reported.     

Control of Photochemical Smog by Alteration of Initial Reactant Ratios

This paper is an endeavor to show how several experimenters have quite closely equaled the results of the other, and how the results from these various laboratories can, by a change of coordinate system, be related to each other in a systematic manner. Only after demonstrating where the Los Angeles Civic Center atmosphere is in relation to these coordinates and the contours, or gradients, of these various effects, eye irritation and oxidant, is it possible to predict the photochemical effect of a reduction of olefins (hydrocarbons) or the reduction of nitric oxide. In addition, a study of the variation in eye irritation with irradiation time, demonstrates that the time at which eye irritation measurements are taken is important in understanding the entire photochemical mechanism underlying the “smog” problem in the summertime in Los Angeles     

The effect of the increase in urban temperature on the concentration of photochemical oxidants

An atmospheric dispersion model, where the inputs of meteorological field were calculated using a meteorological model, was used to reproduce the observed air pollution conditions for the typical fine day in summer period, especially the concentration of the photochemical oxidants. As well, the effects of an increase in the urban temperature and VOC emissions on the concentration of photochemical oxidants were also considered. The following conclusions were drawn.The observed air pollution levels were well modeled by the atmospheric dispersion model using in this study, although modeled NO levels were slightly lower than the observed levels. An analysis of the temperature data showed that a 1 °C increase in temperature leads to a maximal photochemical oxidant concentration of 5.3 ppb, which is an increase of 11%. Additionally, the effect on the photochemical oxidant concentration due to an increase in the vegetation-derived VOCs was more than double the effect due to an increase in the photochemical reactions. It was found that the temperature and photochemical oxidant concentration were linearly related up to a temperature increase of 3 °C. When the temperature increases up to 3 °C, the concentration of photochemical oxidants increases by 19 ppb. An analysis of the effect of vegetation-derived VOCs on photochemical oxidant concentrations showed that, the concentration of photochemical oxidants was 30 ppb higher in the afternoon by the effect of vegetation-derived VOCs, so even in metropolitan areas with relatively little vegetation, vegetation-derived VOCs have a strong impact on photochemical oxidant concentrations.     

Consideration of Air Quality Standards for Vegetation With Respect to Ozone

Present evidence suggests that ozone is the most damaging of all air pollutants affecting vegetation. It is the principal oxidant in the photochemical smog complex. Concentrations of ozone have exceeded 0.5 part per million (ppm) in the Los Angeles area. One-tenth of this level for 8 hours is known to injure very sensitive tobacco varieties. Many plant species are visibly affected after a few hours exposure at concentrations much lower than 0.5 ppm. There is also some evidence that ozone reduces plant growth. Many factors must be taken into account when considering standards to protect vegetation from ozone damage. These include ozone concentration and methods of measurement, time of exposure, possible additive effects of other pollutants, sensitivity of plant species, their economic value, and the extent of injury which can be tolerated. The response of a species to the pollutant is conditioned by genetic factors and environmental conditions. Lack of specific routine methods for measuring ozone in ambient air is a handicap. California and Colorado established standards for oxidants at 0.15 and 0.10 ppm, respectively, for 1 hour. How these standards relate to the ozone dosage causing acute and chronic injury to various plant species is discussed.     

A Study of Sulfur Dioxide in Photochemical Smog I. Effect of SO2 and Water Vapor Concentration in the 1-Butene/NOx/SO2 System

There is an appreciable chemical interaction between SO₂ and photochemical smog which depends on the concentration of SO₂ and water vapor. The rate of decay of SO₂ concentration is greatly increased in the presence of photochemical smog. With 0.75 ppm SO₂, a light-scattering aerosol is produced in dry systems and systems at 22 and 55% relative humidity (RH). Aerosol is not observed until after the NO₂ peak has been reached and the NO concentration has fallen to a very low value. The formation of aerosol corresponds in time to the region of most rapid decrease in the SO₂ profile. In systems at 65% RH or with smaller amounts of SO₂, no light scattering is observed, but the percentage of SO₂ disappearing is greater. In relatively dry systems the presence of SO₂ results in a general slowing down of the photochemical smog reactions. In systems containing water vapor concentrations comparable to those found in the atmosphere, the inhibiting influence of SO₂ on the smog reaction is less pronounced. However, the maximum concentration of oxidant produced by the photochemical smog reactions is significantly lower when SO₂ is present.     

Ultrastructural Effects Of Air Pollution on Lung Cells

The lungs of exposed mice taken during 2- to 3-hour heavy smog periods (over 0.4 ppm total oxidants) showed various degrees of cytoplasmic damage in the alveolar epithelial cells. The extent of damage was markedly age-dependent. Alveolar wall cells taken during heavy smog from 5-month-old animals contained slightly more lamellar inclusion bodies than corresponding animals kept in clean air. The cytoplasm of alveolar cells of 9-month-old animals sacrificed during heavy smog was severely disorganized; however, animals of this age showed a marked recovery 14 hours following the smog peak. In a group of older mice (21 months), similar cytoplasmic damage was obvious, and those sacrificed 24 hours after the heavy smog peak showed even more cellular disruption, suggesting irreversible damage in the older animals. The effect of synthetic photochemical smog showed a pattern of ultrastructural alterations similar to that of the heavy natural smog. Some permanent changes occurred in alveolar cells of 15-month-old mice. Partial recovery of lining cells took place, but few wall cells and phagocytes remained. If older lung tissue has relatively fewer wall cells as is indicated, recovery is decreased to the point of permanent damage. Coupled with extensive disruption of lining membranes, exposures of this nature may well cause the death of older animals.     

The Effect of Water Vapor on Ozone Synthesis in the Photo-oxidation of Alpha-pinene

A study of the effect of water vapor on the photochemical system NO₂ + alphapinene + hv was conducted. A Hotpack Environmental Room was used as a constant temperature chamber, a bank of ultraviolet and fluorescent lamps as a source of simulated solar radiation, and a 150-liter FEP Teflon bag as a reaction vessel. Representative concentrations of 10 pphm NO₂ and 50 pphm alphapinene were used in a 3 × 2 × 2 factorial design where absolute humidities of 0.0000, 0.0090, 0.01 80 g H₂O/g dry air were varied.

Matheson zero air was passed through a clean air train and used as the diluent. Nitrogen dioxide was added to the reaction mixture by a permeation tube, and water and alpha-pinene by evaporation techniques.

Variables measured as a function of time over a 2-hour irradiation period were total oxidants (Mast Ozone Meter), condensation nuclei (General Electric Small Particle Detector), ozone (Regener Chemiluminescent Ozone Meter), nitrogen dioxide and nitric oxide (Technicon Autoanalyzer), and alpha-pinene (Perkin- Elmer Model 800 gas chromatograph).

Upon irradiation, systems containing nitrogen dioxide and alpha-pinene formed oxidants, ozone, condensation nuclei, and nitric oxide. Based on the differences between simultaneous oxidant and ozone measurements, the formation of peroxide- like compounds may be inferred. During the course of the irradiation, nitrogen dioxide and alpha-pinene were consumed. The concentration-time profiles of all variables were characteristic of those exhibited by typical photochemical smog systems.

An effect of water vapor on the systems studied was demonstrated. Increasing humidity decreased net mean/time oxidant and ozone production and net maximum condensation nuclei production. These effects were significant at a 0.05 confidence level. Effects of water on average mean/time NO₂, NO, and alphapinene concentrations were insignificant at this level. The oxidant to ozone ratio was found to decrease with increasing humidity.

The significant decreases in net oxidant and ozone production and NO₂ consumption with increasing water vapor concentration in systems of nitrogen dioxide alone, suggests that water manifests an effect on pertinent inorganic reactions, and the data also suggest additional water participation in the organic reactions.     

Environmental Appraisal: And Oxides of Nitrogen Oxidants,Hydrocarbons

The relationships between criteria, standards, and control of air pollutants involve complex multidisciplinary interactions. Their over-all impact on the public health and welfare is directly related to the confidence level held by members of government, industry, and universities in the validity of the data upon which these criteria are based. The Environmental Appraisal section of the preliminary draft of the Air Quality Criteria Document “Photochemical Oxidant” prepared by the State of California, Department of Public Health, is reviewed. In general, it is a thoughtful and extensive effort to present the current status of information concerning the physical and chemical aspects of photochemical oxidant. Suggestions as to how it might be extended, revised, or updated are presented along with a brief discussion of two new research areas of possible interest, singlet molecular oxygen as a possible environmental oxidant, and the photochemistry of mixed lead halides in the atmosphere.     

Ambient Oxidant Exposure andHealth Costs in the United States—1973

The body of information presented in this paper is directed to policy makers and administrators involved in the evaluation and assessment of damages caused by oxidant air pollution on human health and welfare and of possible benefits of control.

To provide a comparison of some of the benefits that can be obtained by reducing photochemical oxidant levels, estimated health costs were derived from data relating adverse health effects to hourly oxidant concentrations. Hourly oxidant or ozone concentrations were measured at approximately 400 monitoring stations scattered throughout the U.S. Most of these sites were located in major urban areas or in other areas where high oxidant concentrations prevailed. Estimates of populations at risk and per capita health costs were generated for those areas where oxidant data was available.

During the period 1971-1973, nearly two-thirds of the U.S. population resided in areas where the hourly primary standard for oxidants of 160 µg/m³ was exceeded. The total annual health cost attributable to oxidants was estimated to range from $120 to over $240 million in the U.S.     

Global total ozone dynamics

An overview of the ozone issues is given including the following aspects: 1. The impact of tropospheric ozone on climate as a greenhouse gas (GHG), 2. Solar activity effects on TO and ozone concentration vertical profiles in both the troposphere and stratosphere (in cases of solar radiation absorption by the stratosphere, an unexpected problem arises via a coupling between processes of increased absorption due to “bursts” of solar activity and an enhanced destruction of ozone molecules due to the same increase resulting in weakening UV radiation absorption) and 3. Surface ozone concentration variations under conditions of polluted urban atmospheres which lead to episodes of photochemical smog formation (dangerous for human health).     

The effect of aniline on photochemical reactions in atmospheric and synthetic air samples

The inhibitory effect of aniline in photochemical smog reactions was studied using actual Toronto air samples. An aniline concentration of 0.81 pphm had negligible effect in a light traffic air sample containing negligible NO, whereas 20 pphm in a heavy traffic sample caused a 70% decrease in the oxidant dosage, a 50% decrease in the NO₂ peak and a four-fold increase in the NO half-life. In experiments with propylene in synthetic mixtures, the half-life of propylene was increased from 144 min. to 192 min. by the present of 20 pphm of aniline. In addition, a thirty-fold increase in condensation nuclei was produced following a one hour induction period. A chemical mechanism is proposed which is consistent with these results. Although the condensation nuclei detected may be too small to produce light scattering, they may be retained in the lung. In addition they may grow in size. These consequences do not favour the use of aniline as an inhibitor in photochemical smog.     

Modelling photochemical oxidant formation, transport, deposition and exposure of terrestrial ecosystems

The chemical processes responsible for production of photochemical oxidants within the troposphere have been the subject of laboratory and field study throughout the last three decades. During the same period, models to simulate the atmospheric chemistry, transport and deposition of ozone (O(3)) from individual urban sources and from regions have been developed. The models differ greatly in the complexity of chemical schemes, in the underlying meteorology and in spatial and temporal resolution. Input information from land use, spatial and temporally disaggregated emission inventories and meteorology have all improved considerably in recent years and are not fully implemented in current models. The development of control strategies in both North America and Europe to close the gaps between current exceedances of environmental limits, guide values, critical levels or loads and full compliance with these limits provides the focus for policy makers and the support agencies for the research. The models represent the only method of testing a range of control options in advance of implementation. This paper describes currently applied models of photochemical oxidant production and transport at global and regional scales and their ability to simulate individual episodes as well as photochemical oxidant climatology. The success of current models in quantifying the exposure of terrestrial surfaces and the population to potentially damaging O(3) concentrations (and dose) is examined. The analysis shows the degree to which the underlying processes and their application within the models limit the quality of the model products.     

An historical experiment: Los Angeles smog evolution observed by blimp

Observations of smog over the Los Angeles Basin (LAB) links high oxidant mixing ratios with poor visibility, sometimes <5 km. By the 1970s, investigators recognized that most of the aerosol affecting visibility was from gaseous oxidation products, sulfate, nitrate, and organic carbon. This led to the 1972–1973 Aerosol Characterization Experiment (ACHEX), which included observations at the ground and from aircraft. Part of ACHEX was the measurement of smog by blimp in a Lagrangian-like format. The experiment on September 6, 1973, demonstrated that a blimp could travel with the wind across the LAB, observing ozone (O₃) and precursors, and particles of different size ranges. These included condensation nuclei (CN) concentrations dominated by particles of ≤ 0.1 µm diameter and light scattering coefficient (b_sc) representing mainly particles of 0.1–2.0 µm diameter. The results indicated a pollutant variation similar to that measured at a fixed site. Ozone was produced in an air mass, reaching a maximum of ~400 ppb in the presence of nitrogen oxides (NO_x) and nonmethane hydrocarbons (NMHCs), then declined. Although the photochemistry was developing, b_sc grew with O₃ mixing ratio to a quasi-steady state at ~9–10 × 10^?4 m^?1, decreasing in value much later with decease in O₃. The light scattering coefficient was found to be positively associated with the O₃ mixing ratio, whereas CN concentrations were negatively proportional to O₃ mixing ratio. The blimp experiment was supported with aircraft vertical profiles and ground-level observations from a mobile laboratory. The blimp flight obtained combined gas and particle changes aloft that could not be obtained by ground or fixed-wing aircraft measurements alone. The experiment was partially successful in achieving a true Lagrangian characterization of smog chemistry in a constrained or defined “open” air mass.

Implications: The Los Angeles experiment demonstrated the use of a blimp as a platform for measurement of air pollution traveling with an air mass across an urban area. The method added unique data showing the relationship between photochemical smog chemistry and aerosol dynamics in smog. The method offers an alternative to reliance on smog chamber and modeling observations to designing air quality management strategies for reactive pollutants.     

Effects of oxidant air pollution on Pinus maximartinezii Rzedowski in the México City region

The response of Pinus maximartinezii Rzedowski to photochemical oxidant air pollution was examined using 100 trees, during a 1 year cycle, at Vivero de Coyoacán, a tree nursery located in the south central part of México City, where exposure to polluted air masses has been continuous. The tree response assessment method was based upon documented symptoms of pollutant injury on the foliage. The results showed a homogeneous pattern of health and vigor and only medium sensitivity (based on foliar injury) to photochemical oxidants, although the trees maintained their needles through a three and not the normal 5 year period as at its geographic location of origin (different habitat or environment). Nevertheless, these data suggest that this species of pine could be proposed as good planting material for reforestation in the urban metropolitan area of México city.     

Controlling the Flue-Fed Incinerator

This paper examines various health effects of photochemical air pollution in Japan, primarily through the review of epidemiological studies. Health effects discussed include subjective respiratory symptoms, respiratory function testing, ocular effects, and hospital diagnostic tests. The downward trend in oxidant cautions and paralleled health effects, as reported by the Japanese Environmental Agency, are discussed. The methods determined by Japanese ordinance for measurement of oxidants, SO₂, NO _x , and CO are described.     

Distribution of Light Hydrocarbons in Ambient Air

The diversity of hydrocarbons which are present in ambient polluted air provide a potentially rich source of information concerning the nature of this type of pollution. Measurements of the relative amounts of various hydrocarbons can be correlated with the various possible sources. Since hydrocarbon reactivities vary widely it is also possible to estimate the extent to which various individual hydrocarbons have reacted. Except for samples taken deliberately near sources of hydrocarbon pollution these air samples invariably resemble auto exhaust with an addition of natural gas and of C₃–C₅ paraffins which resemble gasoline vapor. Samples taken in industrial areas and near the smoke plume from a brush fire showed distinctive differences in composition. During the smog season in the fall of 1968 good data were obtained of “typical” or “representative” samples of light, medium and heavy smog. These show the expected depletion of more reactive hydrocarbons in a much more convincing way than before. By comparing these distributions with composition in unreacted samples and by making use of data from bottle irradiations, it was possible to estimate the contribution of the various hydrocarbons in terms of “amount reacted.” The amounts of higher hydrocarbons present and reacted were also estimated from gasoline composition.     

An Evaluation of the Fuel Factor Through Direct Measurement of Photochemical Reactivity of Emissions

Findings in research at the Bureau of Mines Bartlesville Petroleum Research Center show that photochemical reactivities of vehicular emissions are reliably measured in laboratory experiments in which smog manifestations are observed directly. Results of the direct smog-chamber measurements reveal that the photochemical behavior of emissions may differ significantly from the behavior that is predicted from the exhaust composition using reactivity scales. The concept of direct measurement of reactivity was applied to determine differences in characteristics of emissions from 20 passenger vehicles, each tested using 10 different fuels. The primary objective of the fuel study was to assess the over-all effect on vehicle emissions of fuel modifications designed to reduce the photochemical pollution associated with automotive evaporative losses. A similar, brief, comparative study of leaded and nonleaded fuels was also made. Reducing volatility was found to reduce the over-all smog potential of vehicle emissions but involved some penalty by way of increased exhaust emissions. Replacing light olefin with the corresponding paraffin also reduced over-all smog potential and in this case exhaust reactivity was not affected. In general greater smog potential was found to be associated with prototype nonleaded fuels than with leaded fuels typical of products currently marketed.     

Photochemical oxidants: state of the science

Atmospheric photochemical processes resulting in the production of tropospheric ozone (O(3)) and other oxidants are described. The spatial and temporal variabilities in the occurrence of surface level oxidants and their relationships to air pollution meteorology are discussed. Models of photooxidant formation are reviewed in the context of control strategies and comparisons are provided of the air concentrations of O(3) at select geographic locations around the world. This overall oxidant (O(3)) climatology is coupled to human health and ecological effects. The discussion of the effects includes both acute and chronic responses, mechanisms of action, human epidemiological and plant population studies and briefly, efforts to establish cause-effect relationships through numerical modeling. A short synopsis is provided of the interactive effects of O(3) with other abiotic and biotic factors. The overall emphasis of the paper is on identifying the current uncertainties and gaps in our understanding of the state of the science and some suggestions as to how they may be addressed.     

Evaluation of the mutagenic effect of N,N-diethylhydroxylamine in Salmonella typhimurium TA 100

A recent approach suggested to suppress photosmog formation has been the addition of small quantities of N,N-diethylhydroxylamine (DEHA) to the polluted air. Thus knowledge of possible mutagenic properties of the compound became important. DEHA was investigated using the Ames Salmonella/microsome mutagenicity test. Toxicity as well as a mutagenic effect were observed at concentrations much exceeding those proposed for practical application.It is well known that photochemical smog arises via the long chain free radical oxidation of NO to NO₂ in hydrocarbon containing atmospheres¹. Thus one recent approach suggested for alleviating smog formation has been the addition of small quantities of free radical scavengers (“photosmog inhibitors”) locally to the polluted air. Of the substances tested, mainly aromatic compounds and ammonia derivatives^2,3, N,N-diethylhydroxylamine (DEHA) has proven sufficiently active to be selected for field trials⁴. In this context the effect of DEHA exposure on living organisms is obviously of interest. Massie and Williams⁵ have recently reported an insignificant change in life-span of fruit flies after exposure to DEHA at concentrations of up to 89 ppm. In judging the safety of environmental chemicals, however, mutagenic testing is of great importance. We therefore under took the investigations described below employing the Salmonella/microsome test.     

Collaborative Testing of Methods to Measure Air Pollutants

A collaborative test was conducted to determine the precision of the chemiluminescent method which has been specified for measuring ozone, to determine photochemical oxidant. Ten laboratories participated in a test involving the analysis of an urban atmosphere containing a photochemical smog mixture. Ozone generators were used to increase the O₃ level over that naturally occurring, in order to cover an adequate range of concentrations. The range tested was 0 to 0.5 ppm.

A statistical analysis of the data obtained was used to derive equations for within laboratory and between laboratory standard deviations. In order to evaluate sampling data, these equations can be used in various statistical procedures to estimate repeatability, reproducibility, lower detectable limit, and other measures that establish the precision of the method.

Using specific definitions for repeatability and reproducibility, the following approximate estimates were obtained in the range of zero to 0.5 ppm:

Repeatability—0.01 to 0.04 ppm (varies with concentration, linear).

Reproducibility—0.01 to 0.09 ppm (varies with concentration, non-linear).

The lower detectable limit depends on instrumental and other variables, and cannot be specified precisely. Under typical assumptions, this limit can be estimated at between 0.006 and 0.009 ppm.