The Inhibition of Photochemical Smog

Additional inhibitors for the conversion of NO to NO₂ in C3H6—NO—0₂ irradiated mixtures have been tested at 25°C. These mixtures initially contained 16 mTorr C₃H₆, 8 mTorr NO, 0.012 mTorr NO₂, additive, and enough O₂ to bring the total pressure to 100 Torr. The NO₂ pressure was monitored photometrically. In the absence of additive, the NO₂ pressure first increases with irradiation time reaching a maximum conversion at about 15 minutes. As the irradiation time increases beyond 15 min, the NO₂ pressure drops. Before adding the inhibitors, runs were done with 10 Torr of CO added, and in these runs the conversion was speeded so that the maximum in NO₂ pressure occurred at 10 min. This enhancement in conversion rate is considered to be diagnostic for the presence of HO radicals. Next 10-min irradiations were done with various amounts of hexafluorobenzene (C₆F₆), nitrobenzene (C₆H₅NO₂), or naphtha lene (C₁₀H₈) added. The NO₂ pressure was reduced to one-half its value in the absence of inhibitor with 270 mTorr C₆F₆’, 220 mTorr C₆H₅N0₂, or 4 mTorr C₁₀Hg. The C₁₀H₈ is a very efficient inhibitor, but additions of up to 1 8.5 mTorr C₁₀H₈ did not reduce the N0₂ pressure to zero. Studies of the percent conversion of NO to NO₂ vs. irradiation time were done with either 4.2 mTorr C₁₀H₈ or 40 mTorr 2,6-di-ferf-butyl-4-methylphenol (Ph) added. In the former case the peak conversion was delayed from 15 to 22 min, while in the latter case no delay occurred. However, with the Ph added, there appeared to be some reduction in the maximum value of percent conversion.     

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 Fate of Aromatic Hydrocarbons in Photochemical Smog Systems: Toluene

The economic impact of various ozone concentrations on California agriculture is examined using an economic model of crop production that accounts for interdependence among crops. Such interdependence recognizes that net economic effects are determined not only by yield sensitivity to ozone but also by market conditions that affect relative crop prices and profitability. Changes in crop yields due to alternations in ambient ozone concentrations are used to drive the economic model. The predicted yield changes are derived from NCLAN data under a range of assumptions concerning functional form and yield effects. The results indicate that the economic effects of ozone are substantial for 13 included crops. The economic estimates display varying sensitivity to the functional form of the response relationship. The need for additional experimental data to more precisely define the relationship depends on the range of policy actions being considered.     

Mathematical Modeling of Photochemical Smog Using the PICK Method

A new method for solving the turbulent atmospheric diffusion equation has been developed based on Lagrangian mass points, or particles moving through an Eulerian grid. The method is one of a family of Particle-/n-Cell techniques but is a unique extension to incorporate the effects of turbulent diffusion based on K-theory; thus the acronym PICK.

In the three-dimensional computer-aided model, NEXUS (Numerical EXamination of Urban Smog), this method has been applied to simulation of carbon monoxide (CO) in Los Angeles. For CO the NEXUS simulation was within 20% of observed day-averaged concentrations at 12 stations and the hour-averages were also in good agreement. This model was extended to include the effects of photochemical smog in Los Angeles. The results of the photochemical simulation were also qualitatively correct due to rapid NO to NO₂ conversion in the simulation.     

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.     

Assessment of the Contribution of Chemical Species to The Eye Irritation Potential of Photochemical Smog

Eye irritation measurements are available from smog chamber solar Irradiations of selected hydrocarbon-nitrogen oxide mixtures. These results have been used to compute eye irritation intensity parameters for formaldehyde, acrolein, peroxyacetyl nitrate, and peroxypropionyl nitrate. Peroxypropionyl nitrate is the most irritating of these four substances. The relative contribution of various pairs of eye Irritants in ambient air mixtures to eye irritation has been calculated from the ambient air concentrations and the eye irritation intensity parameters. The relative contribution of the four eye irritants to a "typical" ambient air mixture has been computed. Formaldehyde appears to be the single most significant eye irritant. Other potential ambient air eye irritants are discussed. The relationships between the hydrocarbon control strategies and eye irritation are considered.     

抑制测酚过程中的苯胺类杂质干扰

水样中如含苯胺类，往往使测定挥发酚的浓度偏高。因此，比较了在pH〉12和pH〈0．5两种条件下，蒸馏预处理以抑制苯胺类杂质干扰的方法，得出两法对苯胺类杂质干扰均有明显的抑制作用，而且后者操作简便、省时、省力。     

Analysis of Ozone and Nitric Oxide by a Chemiluminescent Method in Laboratory and Atmospheric Studies of Photochemical Smog

A prototype instrument monitoring ozone or nitric oxide has been used for photochemical smog studies in the laboratory and the atmosphere. The principle of the detector is based on the chemiluminescent reaction     

Effect of Hydrocarbon and NO x on Photochemical Smog Formation under Simulated Transport Conditions

The body of information presented in this paper is directed to those individuals concerned with the effect of urban pollution on downwind areas. Concern has been expressed over the appropriate hydrocarbon and NO _x control strategy to be used in minimizing the effects of ozone and NO₂ on urban population centers and their downwind environs. O₃ and NO₂ formation were studied in smog chamber irradiations as a function of the initial NO _x concentration at three hydrocarbon concentrations. By carrying out the irradiations for a period of time equivalent to one solar day in a continuously diluting system, smog formation in a chemically reacting pollutant system under transport was simulated. The results of this experimental simulation suggest that hydrocarbon reduction reduces O₃ in urban as well as downwind areas while NO _x reduction increases O₃ in the urban area and has little effect on O₃ in downwind areas. Both hydrocarbon and NO _x reduction will reduce atmospheric NO₂ levels, with the effect of NO _x reduction generally being more pronounced.     

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.     

Photochemical Smog Modeling for Assessment of Potential Impacts of Different Management Strategies on Air Quality of the Bangkok Metropolitan Region,Thailand

Abstract

A photochemical smog model system, the Variable-Grid Urban Airshed Model/Systems Applications International Mesoscale Model (UAM-V/SAIMM), was used to investigate photochemical pollution in the Bangkok Metropolitan Region (BMR). The model system was first applied to simulate a historical photochemical smog episode of two days (January 13-14, 1997) using the 1997 anthropogenic emission database available at the Pollution Control Department and an estimated biogenic emission. The output 1-hr ozone (O₃) for BMR, however, did not meet the U.S. Environmental Protection Agency suggested performance criteria. The simulated minimum and maximum O₃ values in the domain were much higher than the observations. Multiple model runs with different precursor emission reduction scenarios showed that the best model performance with the simulated 1-hr O₃ meeting all the criteria was obtained when the volatile organic compound (VOC) and oxides of nitrogen (NO_x) emission from mobile source reduced by 50% and carbon monoxide by 20% from the original database. Various combinations of anthropogenic and biogenic emissions in Bangkok and surrounding provinces were simulated to assess the contribution of different sources to O₃ pollution in the city. O₃ formation in Bangkok was found to be more VOC-sensitive than NO_x-sensitive. To attain the Thailand ambient air quality standard for 1-hr O₃ of 100 ppb, VOC emission in BMR should be reduced by 50-60%. Management strategies considered in the scenario study consist of Stage I, Stage II vapor control, replacement of two-stroke by four-stroke motorcycles, 100% compressed natural gas bus, 100% natural gas-fired power plants, and replacement of methyltertiarybutylether by ethanol as an additive for gasoline.     

Phenol photonitration upon UV irradiation of nitrite in aqueous solution I: effects of oxygen and 2-propanol.

Nitrophenols are formed in aqueous solution upon UV irradiation of phenol and nitrite. The formation of nitrophenols is enhanced by dissolved oxygen and inhibited by the addition of 2-propanol. The mechanism of phenol photonitration involves both .NO2 (or N2O4, reacting with phenol, and 4-nitrosophenol, which is oxidised to 4-nitrophenol. A reaction scheme is proposed based on experimental results.     

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.     

Photochemical formation of hydroxyl radicals catalyzed by montmorillonite

In this work, the photooxidation of benzene and the formation of phenol in aqueous suspensions of the iron-rich montmorillonite under irradiation of a 250W metal halide lamp (lambda> or = 365nm) were investigated. We confirmed that hydroxyl radicals (()OH) were produced by illuminating montmorillonite and was responsible for the photooxidation of benzene in aqueous suspensions of montmorillonite. Low pH value facilitated the formation of hydroxyl radicals in the pH range of 2.0-10.0. The ()OH concentration increased with increasing the concentration of montmorillonite in aqueous solutions in the range of 0-20.0gl(-1). Higher concentration like 25.0gl(-1) montmorillonite inhibited the ()OH production. Iron, predominantly free iron in the clays, is believed to be one of the most important factors determining ()OH formation. Structural irons in montmorillonite have contributions to ()OH formation, especially in the presence of carboxylate ions. The formation of ()OH from montmorillonite under irradiation of near UV and visible light indicates that clays might play important role not only in transfer through adsorption but also in transformation through oxidation of organic compounds on the surface of clay particles in air, water, soil or even top sediments.     

Fenton试剂氧化苯酚的影响因素与过程研究

考察了H2O2与Fe^2＋剂量、反应时间、初始pH值、无机离子（Cl^-、SO4^2-）和进料方式对Fenton氧化降解苯酚效率的影响,测定了Fenton试剂氧化苯酚过程中的Fe^2＋和高锰酸钾消耗量。实验结果表明,在H2O2与Fe^2＋剂量分别为20和2mmol／L、初始pH为4．00、反应30min的条件下,酚去除率约为97％,COD去除率约为87％。并获得了在初始pH值为4．00时的COD去除率最高;Cl^-的存在将显著降低COD的去除率;SO4^2-对COD去除无显著影响;分批次加入药剂对COD去除效果明显优于一次性加入。在Fenton发生反应的第1min,Fe^2＋浓度可降低到初始浓度的65％左右,大约在20minFe^2＋浓度降到最小值（H2O2接近耗尽）,然后随着反应的继续再增大,这说明了中间产物还原Fe^3＋作用的存在。     

Photochemical formation and transport of ozone in Athens,Greece

An evaluation of the diurnal variation of the hourly ozone concentrations measured at five sites in Greater Athens from June until early September 1984 indicates that photosmog episodes in Greater Athens are associated with the sea breeze circulation. Due to local air circulation in the Athens basin, precursors of O₃ are transported to and accumulated in the Saronikos Bay during the morning hours while the land breeze is blowing. At noon, when the sea breeze sets in, the O₃ formed over the sea is brought back to the coast and to central Athens where it increases the local O₃ concentration by a factor of 3–5 within a few hours. The O₃ levels often remain high throughout the night. During the photochemical smog episodes, all of them accompanied by well-developed sea breezes, the U.S. Air Quality Standard of 120 ppb O₃ was exceeded for 4–7 h day⁻¹. Peak O₃ concentrations up to nearly 200 ppb were recorded in the smog episodes.Relatively high O₃ concentrations were measured on the island of Aegina. They tend to remain high during the night and can be attributed only to primary pollutant transport from Greater Athens advected by the land breeze. The O₃ values obtained at Mount Immitos (1000 m above MSL) suggest that, first, the sea breeze inhibits the influence of vertical thermal convection up to heights above 600 m, and second, no O₃ is noticeable from above the tropopause to ground level or from long-range transport.