Smog Chamber Simulation of Los Angeles Pollutant Transport

The body of information presented in this paper is directed to those individuals concerned with the effect of urban pollution on downwind areas. In the absence of any evidence, it has been widely assumed that increasing NO _x emissions have caused oxidant levels to increase downwind of Los Angeles, i.e., Riverside and San Bernardino. This smog chamber study simulated pollutant transport from Los Angeles to the downwind areas by irradiating a typical Los Angeles hydrocarbon/NO _x mixture for extended periods of time. The smog chamber experiments were extended to 22 hours to obtain an integrated light intensity equal to that which occurs in the Los Angeles area. The effects of variations of nitrogen oxide emissions on an aged air mass were examined. The results show that downwind oxidant levels are only slightly affected by large changes in NO _x emissions. However, it is clear that reduced nitrogen oxide emissions will lead to an increase in oxidant in downtown Los Angeles.     

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.     

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.     

Photochemical Pollution at Two Southern California Smog Receptor Sites

A one-year survey of air quality has been carried out at two southern California inland locations, Perris and Palm Springs (90 km E-SE and 120 km E of Los Angeles) to evaluate transport of photochemical smog from the Los Angeles area and to assess population exposure to toxic air pollutants in the Coachella Valley and eastern Riverside County. Air pollutants measured included formaldehyde, acetaldehyde, nitric acid, and peroxyacetyl nitrate (PAN). Acetic acid was also measured as part of the time-integrated method employed to measure PAN. In addition, intensive studies were carried out at both locations and included measurements of aldehydes, nitric acid, PAN, peroxypropionyl nitrate (PPN), methylchloroform and tetrachloroethylene.

Maximum concentrations of HCHO, CH₃CHO, HNO₃, PAN, PPN, CH₃COOH and C₂CI₄ were 26, 21, 4.5, 7.6, 0.42, 6.6 and 0.29 ppb in Palm Springs and 15, 30, 6.3, 9.1, 0.73, 7.8 and 0.43 ppb in Perris. Pollutant concentrations measured in Palm Springs and Perris are compared to those measured in the Los Angeles area, and are discussed in terms of formation and removal during transport.     

Weekday-Weekend Pollutant Studies of the Los Angeles Basin

Pollutant data from the Los Angeles Basin were analyzed for weekday-weekend differences for the smog months of June through September 1972 and 1973. The pollutants investigated were oxidant, NO, NO₂, total hydrocarbons (HC), CO, and particulates. In order to maintain the diurnal variation, the concentration percentiles were calculated for each weekday and weekend hour.     

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.     

Air Pollution and Hospital Admissions for Diseases of the Circulatory System in Three U.S. Metropolitan Areas

ABSTRACT

Generalized additive models were used to analyze the time series of daily hospital admissions for cardiovascular and cerebrovascular diseases over the period of 19871995 in three major metropolitan areas—Cook County, IL; Los Angeles County, CA; and Maricopa County, AZ— in the United States. In Cook and Maricopa Counties, admissions information was only available for the elderly (ages 65 and over), while in Los Angeles County, admissions information was available for all ages. In Cook County, daily monitoring information was available on PM₁₀, CO, SO₂, NO₂, and O₃. In Los Angeles and Maricopa Counties, monitoring information was available daily on the gases, and information on PM₁₀ was available every sixth day. In Los Angeles County, information on PM₂₅ was also available every sixth day. In Cook and Los Angeles Counties, associations were found between each pollutant, with the exception of O₃, and admissions for cardiovascular disease, with the gases showing the strongest associations. In two-pollutant models with PM and one of the gases, the effect of the gases remained stable, while the effect of PM became unstable and insignificant. In Maricopa County, the gases, with the exception of O₃, were weakly associated with hospital admissions for cardiovascular disease, while PM was not. In two-pollutant models with two of CO, SO₂, and NO₂, the pattern of results is heterogeneous in the three counties. In all three counties, only weak evidence of any association between air pollution and cere-brovascular admissions was found.     

summary of the California aerosol characterization experiment

This report gives a brief summary of the experimental plan and the early results of field observations from the California Aerosol Characterization Experiment (ACHEX). The objectives of the program center on questions of the sources and evolution of aerosols in urban air, as they are superimposed on a natural background, particularly as they relate to visibilitydegradation. The project initially nvolved the use of an elaborately instrumented mobile laboratory combined with a fixed station in San Jose, in Pasadena, and in Riverside, and later incorporated several satellite monitoring stations in the Los Angeles Basin. Intensive field observationswere taken from July 1972 to November 1972 in several urban and nonurban locations between the San Francisco Bay area and the South Coast Basin, covering the Los Angeles area. In a second phase of the ACHEX, aerosols accompanying photochemical smog were studied intensively in the Los Angeles Basin during the period between July and October of 1973. The observations cover a wide variety of parameters including physical and chemical properties of aerosols, pollutant gas concentrations, and meteorological variables. The initial results show the great importance of sulfate, nitrate, noncarbonate carbon, and liquid water to the mass concentration of airborne particles and their relation to reduction in visibility. The anthropogenic contribution to atmospheric aerosols is consistently found to be allocated primarily to the submicron or fine particle size range.     

Reducing Air Pollutant Emissions at Airports by Controlling Aircraft Ground Operations

Potential reductions in air pollutant emissions were determined for four strategies to control aircraft ground operations at two case study airports, Los Angeles and San Francisco International Airports. Safety, cost, and fuel savings associated with strategy implementation were examined.

Two strategies, aircraft towing and shutdown of one engine during taxi operations, provided significant emission reductions. However, there are a number of safety problems associated with aircraft towing. The shutdown of one engine while taxiing was found to be the most viable strategy because of substantial emission reductions, cost benefits resulting from fuel savings, and no apparent safety problems.     

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     

Realistic Mixing Depths for Above Ground Aircraft Emissions

Analysis of vertical temperature soundings at Los Angeles International Airport (LAX) shows that a conservative height of the inversion base for pollutant containment purposes is 490 ft (150 m). This altitude is considerably less than the 3000 ft (914 m) pollution containment altitude assumed by the EPA in preparing their emission inventory for the airport. (Figure 1.) After correcting the EPA emission inventory to reflect a real world inversion height, the emission inventory for aircraft at Los Angeles International Airport is estimated to be approximately 50% less. Aircraft thus become a less significant pollution source and consideration should be given to relaxing engine emission control requirements accordingly.

This paper examines current emission control philosophy, which according to the EPA should be based upon the significance of the particular polluting source. The problem of accounting for above ground aircraft emissions is then considered. Daily inversion height data are then used to determine a realistic vertical containment altitude for aircraft emissions. Problems in obtaining good inversion data are described. Finally, aircraft emissions at Los Angeles International Airport are adjusted to reflect real world inversion conditions on those days when the inversion height is low enough to influence significantly air pollution levels. Recommendations are made for additional research leading to possible change to NO_x emission control requirements for aircraft.     

motor vehicle emissions and atmospheric lead concentrations in the los angeles area

This paper is directed to those concerned with the effect of changes in lead consumption by motor vehicles on atmospheric lead concentrations. Atmospheric lead concentrations in the Los Angeles area have been found to be dependent on lead consumption, meteorology, and source-receptor relationships. Mathematical relationships between these variables for selected Los Angeles area sites are derived. Los Angeles County experienced a 50% reduction in annual average atmospheric lead concentrations between 1971 and 1976, which was found to be due to a decrease in vehicular emissions of lead. Seasonal variations in lead concentration were found to be mainly a product of seasonal variations in weather. Projections of atmospheric lead concentrations for the next decade show a continued downtrend, based on regulation of fuel lead content and introduction of additional catalyst equipped vehicles. By the mid-1980's most locations in the Los Angeles area are expected to attain the California and federal ambient air quality standards for lead, 1.5 micrograms per cubic meter, based on a monthly average.     

Source apportionment of secondary organic aerosol during a severe photochemical smog episode

The UCD/CIT air quality model was modified to predict source contributions to secondary organic aerosol (SOA) by expanding the Caltech Atmospheric Chemistry Mechanism to separately track source apportionment information through the chemical reaction system as precursor species react to form condensable products. The model was used to predict source contributions to SOA in Los Angeles from catalyst-equipped gasoline vehicles, non-catalyst equipped gasoline vehicles, diesel vehicles, combustion of high sulfur fuel, other anthropogenic sources, biogenic sources, and initial/boundary conditions during the severe photochemical smog episode that occurred on 9 September 1993. Gasoline engines (catalyst+non-catalyst equipped) were found to be the single-largest anthropogenic source of SOA averaged over the entire model domain. The region-wide 24-h average concentration of SOA produced by gasoline engines was predicted to be 0.34 μg m⁻³ with a maximum 24-h average concentration of 1.81 μg m⁻³ downwind of central Los Angeles. The region-wide 24-h average concentration of SOA produced by diesel engines was predicted to be 0.02 μg m⁻³, with a maximum 24-h average concentration of 0.12 μg m⁻³ downwind of central Los Angeles. Biogenic sources are predicted to produce a region-wide 24-h average SOA value of 0.16 μg m⁻³, with a maximum 24-h average concentration of 1.37 μg m⁻³ in the less-heavily populated regions at the northern and southern edges of the air basin (close to the biogenic emissions sources). SOA concentrations associated with anthropogenic sources were weakly diurnal, with slightly lower concentrations during the day as mixing depth increased. SOA concentrations associated with biogenic sources were strongly diurnal, with higher concentrations of aqueous biogenic SOA at night when relative humidity (RH) peaked and little biogenic SOA formation during the day when RH decreased.     

A Portable Electrical Analyzer for Size Distribution Measurement of Submicron Aerosols

An electrical aerosol analyzer capable of performing rapid, in situ size distribution measurement on aerosols from 0.003 to 1 μm diameter has been described. The instrument is based on the “diffusion charging-mobility analysis” principle first described by Whitby and Clark. The prototype instrument has a total volume of 3.75 ft³ and a total weight of 60 lb, and is sufficiently portable to be used on small airplanes and ground based vehicles for mobile air pollution studies. The paper describes the design, operation, and performance of the instrument. Sample data are presented showing the size distributions of aerosols measured by the instrument on board a small research aircraft over the Los Angeles basin at several different altitudes. In addition, data are presented showing the size distribution of smog chamber aerosols and aerosols produced by a conventional Collison atomizer.     

Lead Concentrations in Detroit,New York,and Los Angeles Air

Lead concentrations in air were measured at 12 sites in Detroit, New York and Los Angeles as part of a program to relate automobile emissions and polynuclear aromatic hydrocarbons in air. The information on lead is reported separately because of the current interest in lead as an air pollutant. Sampling was conducted by means of a large “absolute” filter and equipment contained in a step-van truck. A portion of the filter was macerated in nitric acid and the lead determined spectrographically. The combined annual average lead concentration for four sites in metropolitan Los Angeles was approximately 40% higher than the combined averages of either the five sites in metropolitan New York or the three sites in metropolitan Detroit. Concentrations ranged from 0.4 ug/M³ at Santa Monica, to 18.4 ug/M³ at a Los Angeles Freeway Interchange. Concentrations were generally highest in freeway areas, intermediate in commercial areas, and lowest in residential areas. They were about 40% higher in daytime than at night. Average lead concentrations were highest during autumn in New York and winter in Los Angeles reflecting an inverse relationship with wind speed. Correlation coefficients between lead and carbon monoxide, at all sites, were statistically non-zero with 99% confidence and varied from 0.75 to 0.96. Lead concentrations in this study were higher than concentrations reported by others for Detroit, New York, and Los Angeles, presumably because sampling in this study was closer to traffic. However, concentrations in this study were lower than in-traffic concentrations given in the literature.     

A photochemical model for air quality assessment: Model description and verification

A hybrid Eulerian-Lagrangian, photochemical model has been developed for the assessment and prediction of the impact of large point sources on air quality. This simple model is based on solving the mass conservation equations which include chemical reaction terms in the cells of a two-dimensional crosswind plane which moves with the air parcel. Testing of the model is done in three ways. First, the chemistry is evaluated using results of smog chamber experiments simulating Melbourne's emissions and meteorological conditions. Second, the accuracy of the emissions inventory is tested using aircraft measurements. Finally the overall performance of the model is evaluated using monitoring station data. In general the model gives good agreement with the measurements, with the predictions for O₃ being somewhat better than those for NO₂. This result was also found in the three-dimensional study of McRae and Seinfeld (1983, Atmospheric Environment17, 501–522) for the Los Angeles area.     

Cyclic Trends in Los Angeles Fine Participates

Noontime visibilities in downtown Los Angeles, averaged over the smog season of June through November, show two cycles of general deterioration and improvement. The improvement since 1962 is confirmed by available high volume filter data and conditions in 1974/75 are at least as good as at anytime since observations were begun in 1933. The decrease in frequency of “rule 57” days suggests that the improvement of the last decade and perhaps the cyclic variation of the past 40 years has been primarily of meteorological origin.     

Shade trees reduce building energy use and CO2 emissions from power plants

Urban shade trees offer significant benefits in reducing building air-conditioning demand and improving urban air quality by reducing smog. The savings associated with these benefits vary by climate region and can be up to $200 per tree. The cost of planting trees and maintaining them can vary from $10 to $500 per tree. Tree-planting programs can be designed to have lower costs so that they offer potential savings to communities that plant trees. Our calculations suggest that urban trees play a major role in sequestering CO2 and thereby delay global warming. We estimate that a tree planted in Los Angeles avoids the combustion of 18 kg of carbon annually, even though it sequesters only 4.5-11 kg (as it would if growing in a forest). In this sense, one shade tree in Los Angeles is equivalent to three to five forest trees. In a recent analysis for Baton Rouge, Sacramento, and Salt Lake City, we estimated that planting an average of four shade trees per house (each with a top view cross section of 50 m2) would lead to an annual reduction in carbon emissions from power plants of 16,000, 41,000, and 9000 t, respectively (the per-tree reduction in carbon emissions is about 10-11 kg per year). These reductions only account for the direct reduction in the net cooling- and heating-energy use of buildings. Once the impact of the community cooling is included, these savings are increased by at least 25%.     

Survey of volatile organic compounds associated with automotive emissions in the urban airshed of São Paulo,Brazil

The Metropolitan Region of São Paulo (MRSP), Brazil, is one of the largest metropolitan areas in the world (population 17 million, approx.) and relies heavily on alcohol-based fuels for automobiles. It is estimated that about 40% of the total volume of fuel is ethanol with some vehicles using pure ethanol and others a gasoline/ethanol blend. As such, São Paulo is an excellent example of an oxygenates-dominated airshed of mobile sources and is most likely indicative of the future in heavily populated areas in the US such as Los Angeles where “oxy-fuels” are becoming an important replacement for the conventional pure petroleum-based fuels. In this work, we surveyed the ambient air to identify and quantify the organic compounds associated with the evaporative and exhaust emissions of these fuels and to begin to understand the potential for human exposure. Because this was an initial test without detailed prior knowledge of the airshed of the area, we applied two different air sampling methods for various time periods to assess the ambient concentrations of a variety of polar and nonpolar volatile organic compounds (VOCs). For quality assurance (QA), we collected all the samples in duplicate (whole-air samples in Summa canisters and adsorbent-based samples on Perkin-Elmer Air Toxics tubes) at various flow rates to test performance. All samples were collected over identical time frames, typically for 1-, 2-, and 4-h periods per day at six different locations over a period of 1 week. Overall São Paulo results demonstrate that mean concentrations of single-ring aromatics are 2–3 times higher, volatile aldehydes are 5–10 times higher, and simple alcohols 10–100 times higher as compared to results of a recent study performed by EPA in the Los Angeles basin. C₄–C₁₁ n-alkanes were only slightly elevated in São Paulo.