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.     

Sulphur dioxide,oxides of nitrogen and ozone measured continuously for 2 years at a rural site

Continuous specific measurements of sulphur dioxide, nitric oxide, nitrogen dioxide and ozone have been made for over 2y at Bottesford, a rural site in central England, 20 km away from town and industry sources and 1 km from traffic sources. Statistics of hourly, daily, monthly, seasonal and yearly values are given.On an annual basis, there was 50% more oxides of nitrogen (nitric oxide plus nitrogen dioxide) than sulphur dioxide, and more ozone than either. The nitric oxide and nitrogen dioxide were approximately equal. No other published annual values of nitric oxide, nitrogen dioxide and ozone at U.K. rural sites are known. The summer nitric oxide values were greater at this site than at three other rural sites in the British Isles for which summer nitric oxide values have been reported, but so was the sulphur dioxide, and the amounts of both these gases probably reflect the size and distance of combustion sources.Diurnal variations of the four gases during summer months at Bottesford were similar to those published for a site in southern England. The diurnal variations for winter months at Bottesford were somewhat different, especially for nitrogen dioxide. No other published winter patterns are known.Usually nitrogen dioxide and ozone concentrations were in opposition, both short and long term, but on rare occasions, for example in relatively clean winter air, the ozone concentration rose and fell directly with the nitrogen dioxide. Hourly ozone values exceeded 50 ppb (10⁻⁹, by volume) for several hours a month in 22 months out of 24. The World Health Organisation guideline for public health exposure limits is given as 50–100 ppb h⁻¹, not to be exceeded more than once per month.     

Photochemical oxidant pollution and vegetation: effects of mixtures of gases, fog and particles

Photochemical 'smog' contains mixtures of gases (e.g. ozone, nitrogen dioxide), and dry particles (e.g. nitrates). Intermittent fog in the same geographical area can be acidic with high concentrations of nitric acid. Results from recent field studies in the Los Angeles Basin have emphasized the relative toxicity of these components of photochemical air pollution. Studies have focused on gaseous+fog or gaseous+dry particulate effects on conifers, gaseous+fog effects on crops, and the effects of trace pollutants produced during generation of ozone on crops. Data from these studies indicate that direct alterations in growth and physiological responses were observed only with gaseous pollutants (primarily ozone), or repeated applications of highly acidic fogs (pH < 2.7). Direct particle dry deposition effects are unclear. Few interactions have been found between gaseous pollutants and acidic fog. Charcoal-filtered open-top chambers are highly effective in removing pollutants in the following order: fog (100%) > peroxyacetyl nitrate > ozone > nitrogen dioxide > sulfur dioxide > nitrate ion > ammonium ion > sulfate ion. However, nitric oxide concentrations are higher in charcoal-filtered chambers than in ambient air. The studies point out the importance of considering other components of photochemical pollution in addition to ozone, especially when investigating subtle, long-term effects on vegetation.     

Calculating Air Quality and Its Control

Air quality is shown as a function of averaging times of five minutes to one year for carbon monoxide, hydrocarbons, nitric oxide, nitrogen dioxide, nitrogen oxides, oxidant, and sulfur dioxide in Chicago, Cincinnati, Los Angeles, New Orleans, Philadelphia, San Francisco, and Washington, D. C. Concentrations are approximately lognormally distributed for all pollutants in all cities for all averaging times. Maximum concentration is inversely proportional to averaging time to an exponent. The exponent is a function of the standard geometric deviation. General air quality and control parameters are derived and shown for one example, nitrogen oxides in Washington, D. C. These values are compared to one air quality standard.     

Photochemical ozone and nitric oxide formation in air-nitrogen dioxide mixtures containing sulfur dioxide or chlorine

Experiments were performed to investigate the effects of sulfur dioxide (0–10 ppm) and chlorine (0–15 ppm) on ozone and nitric oxide concentrations in irradiated mixtures of nitrogen dioxide (1–5 ppm) and air. The mixtures were irradiated by ultraviolet fluorescent lamps while flowing at a steady speed through a 9m long, 15.2cm i.d. Pyrex tube. The presence of sulfur dioxide produced no measurable change in the ozone and nitric oxide concentrations. The addition of small quantities of chlorine increased the ozone concentration in much the same manner as the addition of a hydrocarbon. A reaction model was developed for the chlorine-nitrogen dioxide-air mixtures. The observed increase in ozone concentration could only be predicted if the following two reactions were included : ClOO + NO → NO₂ + ClO and ClOO + NO → ClNO + O₂. Significant quantities of unexpected condensation nuclei were also observed in the chlorine-nitrogen dioxide-air mixtures.     

Air Quality Criteria—Toxicological Appraisal for Oxidants,Nitrogen Oxides,and Hydrocarbons

The ultimate aim of toxicological studies is to determine the effects of pollutants on the health and welfare of human beings. To get this it is essential to conduct animal studies to evaluate the potential toxicity of different pollutants. Toxicological appraisal of the photochemical oxidant type of air pollution shows: (1) The effects are primarily on the lungs and the senses. (2) There is impairment of pulmonary function in humans at concentrations found in polluted air. (3) Both ozone and nitrogen dioxide tend to oxidize in animals the lung tissue for a time. This process creates agents which have the potential for cross-linking structural proteins, and this process initiates inflammation which accelerates cell turnover rates. Both crosslinking and cell turnover rates are factors in aging, which may thus be accelerated by years of repeated exposure to oxidants. (4) Long-term exposure to low levels of nitrogen dioxide can produce pre-emphasematous lesions in the lungs of rats and mice. Studies with other species are needed. (5) Ozone, nitrogen dioxide, and dilute irradiated car exhausts increase susceptibility to respiratory infection.

The constant search for more sophisticated and sensitive techniques to detect subtle changes indicative of pre-disease conditions should not be relaxed. Such techniques will provide chronic disease predictors of great relevance as air quality criteria.     

Non-Methane Hydrocarbon Air Quality Measurements

It is important in the implementation of the air quality standard for ozone/oxidants and non-methane hydrocarbons to develop quantitative relationships between these pollutants in air quality regions. Analyses for ambient air non-methane hydrocarbon give a direct measure of the progress in control of hydrocarbon emissions and in the reduction of oxidant/ozone concentration levels. Total hydrocarbon concentrations are much more available than non-hydrocarbon levels. An empirical relationship between total hydrocarbons and non-methane hydrocarbons has been obtained from measurements at both west and east coast sites in the U. S. The comparability of measurements from flame ionization analyzers and gas chromatography has been demonstrated. Either analytical technique can be applied to samples collected at monitoring sites to provide the 6-9 A.M. non-methane hydrocarbon aerometric results specified in the air quality standards.     

Detection and Measurement of Air Pollutants by Absorptions of Infrared Radiation

A technique of detecting gaseous air pollutants by means of absorption of laser radiation is under development at the NASA Electronics Research Center. The iodine infrared laser and the carbon dioxide infrared laser are forced to emit spectral lines which fall on the infrared absorption bands of atmospheric pollutants. The attenuation of a laser line when passed through an air sample is the measure of the pollutant concentration. The narrow spectral width of the laser emission permits sensitive detection, minimizes interference between pollutants, and allows penetration of atmospheric water bands. The collimation and high power outputs available from lasers permit transmission of the radiation over long straight paths through the atmosphere and over long folded paths in multiple-pass absorption cells. A sample of absorbing gas placed within the laser cavity forces the emission of the selected wavelengths. With a one-half kilometer path to a retro-reflector and back, it is predicted that the following concentrations of air pollutants will be detected by means of the indicated laser lines: carbon monoxide at 2 parts per million in air (ppm), using the 4.86 micron iodine line; nitric oxide at 1 ppm, using the 5.5 micron iodine line; ethylene at 0.1 ppm, using the 10.53 micron carbon dioxide line; sulfur dioxide at 1.5 ppm, using the 9.08 micron carbon dioxide line; and ozone at 0.15 ppm, using the 9.52 micron carbon dioxide line. It seems feasible to extend the technique to other gaseous pollutants such as nitrogen dioxide, methane, butane, and peroxy acetyl nitrate. Continuing effort is being devoted to development and construction of the laser transmitting and receiving equipment. Field testing is planned for the near future.     

A chemical model for urban plumes: Test for ozone and particulate sulfur formation in St. Louis urban plume

A chemical model with anthropogenic sources of nitrogen oxides and hydrocarbons is applied to simulate the chemical behaviour of pollutants in the St. Louis urban plume. It is suggested that a substantial increase in peroxy radical concentrations (HO₂,RO₂) in the polluted air mass outside its source region leads to an effective formation of secondary pollutants like ozone and sulfate particles. The model indicates characteristic time for ozone generation in the plume of a few hours. Maximum ozone mixing ratio of 115 ppb is predicted after 4 h transport time outside the source region. Conversion rates of SO₂ to H₂SO₄ through gas phase reactions with hydroxyl and peroxy radicals are estimated to be 1–5%h⁻¹. This leads to an approx 25% conversion of SO₂ to paniculate sulfur in the plume during the day. Agreement with measured ozone concentrations and flow rates of ozone and participate sulfur in the St. Louis plume on 18 July 1975 can be taken as strong indications that ozone and sulfate particle formation in the plume proceeds through the suggested mechanisms.     

Analysis of Los Angeles Photochemical Smog Data: A Statistical Overview

A research project has been under way to investigate air pollution problems in Los Angeles County with the help of the data supplied by the Los Angeles County Air Pollution Control District. These data consist of measurements of primary pollutants such as nitric oxide, hydrocarbons, carbon monoxide, sulfur dioxide and particu-lates, and secondary pollutants such as ozone and nitrogen dioxide, recorded hourly at a number of different stations in Los Angeles County over the past seventeen years. This present discussion deals in a preliminary way with a particular aspect of this analysis, namely, the occurrence of photochemical smog in Los Angeles. The paper is divided into two main sections. The first is intended to provide a brief survey of the problem of photochemical smog in Los Angeles as presently understood in relation to the available field data and also in relation to chamber experiments which have been run in various laboratories. The second part of the paper discusses a class of intervention problems that arise in studying the data. It is noted that parallel problems occur in the study of other ecological material and elsewhere. Statistical methods for dealing with this class of problems are illustrated with some of the Los Angeles data.     

Gas Dilution Apparatus for Preparing Reproducible Dynamic Gas Mixtures in any Desired Concentration and Complexity

A portable gas dilution apparatus has been constructed by which reproducible known mixtures of the common air pollutants added to carbon filtered air can be prepared in any desired quantity, complexity, and concentration. Sulfur dioxide mixtures with and without the addition of nitrogen dioxide and/or ozone have been analyzed by the conductimetric, titrimetric, turbidimetric, and colorimetric methods. Excellent analytical agreement with the concentrations obtained from the volumes of sulfur dioxide, nitrogen dioxide, hydrogen sulflde, and air that are mixed has been shown by all these methods when an efficient absorber is used though the titrimetric method tended to give slightly low results. Some common absorbers show reduced efficiency in absorbing some of the gases. Nitrogen dioxide determinations by the Saltzman method are not significantly affected by the addition of sulfur dioxide to the nitrogen dioxide-air mixtures. A modification of the Saltzman reagent, due to Lyshkow, was tested. It accelerates the rate of color development and should be useful in the automatic nitrogen dioxide analyzer. The determination of hydrogen sulfide is not affected by the presence of nitrogen dioxide in the gas mixture but sulfur dioxide increases the sulfide reading by about 5-15% while ozone decreases the reading.     

Absorption of Gaseous Air Pollutants By a Standardized Plant Canopy

Concentration profiles for hydrogen fluoride(HF), sulfur dioxide(SO₂), ozone (O₃), nitrogen dioxide(NO₂), and nitric oxide(NO) generated in a standardized alfalfa canopy are presented. Wind, light, temperature, and carbon dioxide(CO₂) profiles, canopy pollutant uptake rates, and canopy structural data are also given. Canopy pollutant concentration profile characteristics were studied to evaluate the relative potentials for major air pollutants to penetrate into canopies. The study was conducted in an environmental growth chamber equipped to control automatically environmental conditions and monitor continuously gas exchange rates. HF, SO₂, and NO₂ profiles suggested that these gases were removed efficiently by the upper portion of the canopy as well as by the immediate subsurface vegetation. The steady state HF profile showed the greatest displacement within the canopy. The NO profile was displaced the least. The uptake rate of NO by plants was apparently too slow in comparison with gas transport and mixing within the canopy to affect the internal profile substantially. O₃ appeared to be readily deposited on the surface tissues, but the deeper tissues in the canopy had less effect on the concentration profile. Data are also presented to show the relationship between NO₂ concentration within the canopy and changes in the air concentration above the vegetation. The results indicated that gas transport between the atmosphere and canopy interior was rapid. The data presented should be of current interest to agriculturists, researchers, administrators, and environmental planners concerned with effects of air pollutants on plants and on the fate of pollutants in the microenvironment.     

The role of nitrogen oxides in nonurban ozone formation in the planetary boundary layer over n America,w europe and adjacent areas of ocean

The status of knowledge on photochemical ozone formation and the effects of nitrogen oxides and peroxyacyl nitrates on such formation have been evaluated. The literature is reviewed on

• 1.(a) nonurban ozone and nitrogen oxide concentration distributions,(b) ozone lifetimes,(c) nitrogen oxide lifetimes, and(d) ozone formation in plumes as related to nitrogen oxide.

The modeling approaches applied to ozone formation

• 1.(a) with urban plumes,
• 2.(b) power plant plumes,
• 3.(c) high pressure systems, and
• 4.(d) during longerrange transport of ozone are discussed. In addition, models concerned with the contributions to ozone formation associated with reactions of natural hydrocarbons and nitrogen oxide near ground level and photochemical ozone formation associated with reactions of carbon monoxide and of more persistent organic species with nitrogen oxides in the free troposphere are considered.

It is concluded that urban plumes are major contributors to elevated ozone concentrations measured at nonurban locations, particularly during the passage of high pressure systems. Ozone can survive at significant concentration levels for more than one day of transport. However, the evidence for multiday ozone transport is to a large extent associated with transport over water.Ozone formation during the first day of transport does not appear to be limited by the availability of nitrogen oxides. However, it is likely that multiday formation and transport of ozone within the boundary layer is limited in duration because of the relatively short lifetimes of nitrogen oxides and peroxyacyl nitrates. Photochemical formation of ozone in the free troposphere may be an important contributor to longer-time average ozone concentrations in rural areas. These free tropospheric processes depend in part on anthropogenic sources of precursors and are especially sensitive to the vertical distribution of nitrogen oxides in the atmosphere.     

Traffic pollution in a downtown site of Buenos Aires City

It has recently been recognized that air and noise pollution constitutes an extended problem over the densely populated city of Buenos Aires. Traffic emissions are of paramount concern, especially along narrow and main traffic arteries. In spite of these considerations, few systematic studies have been undertaken to evaluate the air quality in the metropolitan area of the city. In 1996, concentrations of carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO₂) and ozone (O₃) were simultaneously measured for the first time using a continuous monitoring station. This station was placed in a building at Belgrano Avenue, which is a heavy traffic street in the downtown area of the city (Bogo et al., Atmospheric Environment 33 (1999) 2587. In this work, we analyze the dependence of the measured primary pollutants, CO and the mixture of nitrogen oxides (NO_x), with meteorological conditions, traffic emissions and monitoring location. We compare the registered values with the results obtained from modeling the dispersion of the pollutants emitted from mobile and area sources. We also discuss the relevance of street canyon effects compared with background concentrations of these pollutants.     

The Characterization of Ozone,Sulfur Dioxide,and Nitrogen Dioxide for Selected Monitoring Sites in the Federal Republic of Germany

Ambient ozone, sulfur dioxide, and nitrogen dioxide data collected at 11 rural gaseous air pollution monitoring stations located throughout the Federal Republic of Germany (FRG) were characterized to provide a basis for investigating the effect these air pollutants may have on forest decline. For any given year, with the exception of the Waldhof site, the ozone monitoring sites did not experience more than 50 occurrences of hourly mean concentrations equal to or above 0.10 ppm. In most cases, the number of occurrences equal to or above 0.10 ppm at the FRG ozone monitoring sites was below the number experienced at a rural forested site located at Whiteface Mountain, New York. Several of the FRG monitoring sites experienced a large number of occurrences of hourly mean ozone concentrations between 0.08 and 0.10 ppm. Hof, Selb, Arzberg, and Waldhof experienced several occurrences of elevated levels of sulfur dioxide concentrations. The nitrogen dioxide 24-h mean concentrations were low for all sites. Because the 24-h mean data may mask the occurrence of a few high concentration events, it is not known if any of the sites that monitored nitrogen dioxide experienced short-term elevated concentrations. To gain further insight into the possible effect of pollutant mixtures on vegetation, future efforts should involve characterizing the timing of multi-pollutant exposures.     

Vegetation: A Sink for Atmospheric Pollutants

The possibility of vegetation being an important sink for gaseous air pollutants was investigated. Plant pollutant uptake measurements were made utilizing a typical vegetation canopy and chambers that were designed specifically for gaseous exchange studies. The data indicate that an alfalfa canopy removed gases from the atmosphere in the following order: hydrogen fluoride (HF) > sulfur dioxide (SO₂) > chlorine (Cl₂) > nitrogen dioxide (NO₂) > ozone (O₃) > peroxyacetyl nitrate (PAN) > nitric oxide (NO) > carbon monoxide (CO). The absorption rate of NO was low, and no absorption of CO could be detected with the methods used. In the typical ambient concentration range uptake increased linearly with increasing concentration except for O₃ and Cl₂ which caused partial stomatal closure at the higher concentrations. Wind velocity above the plants, height of the canopy, and light intensity were shown to affect the pollutant removal rate. A relationship between the absorption rate and solubility of the pollutant in water was also shown. It was concluded that vegetation may be an important sink for many gaseous air pollutants.     

Nitrogen Trioxide: Key Intermediate in the Chemistry of Polluted Air?

It is proposed that peroxyacetyl nitrate and its homologues are formed in polluted air via hydrogen abstraction from the corresponding aldehyde by nitrogen trioxide, followed by (a relatively fast) combination of the resulting acyl radical with oxygen and NO₂. This mechanism provides a simple explanation for the formation of nitric acid, HNO3, as well. Nitrogen trioxide should be able to abstract hydrogen atoms from hydrocarbons, since the H-ONO₂ bond strength is about 100 kcal/mole.