Multiple regression has been widely used to apportion particle light scattering among distinct chemical species. The resulting scattering budgets are shown here to be unbiased estimates under certain theoretical conditions. The theory allows species’ particle size distributions and water uptakes to vary from sample to sample, as they are known to do in reality. The sole constraint is that variations in each species’ characteristics be statistically independent of all species’ concentrations. Individual violations of this condition cause identifiable biases, and multiple violations can offset each other to yield regression estimates that are accurate by accident. Detailed and summary accountings of statistical errors are illustrated using a mechanistic model derived from measurements in southern California.

Emissions from distant source areas are often imagined to provide a steady background to the emissions of whatever local sources are being studied. As part of Project MOHAVE in summer 1992, several air mass markers and an injected stack tracer were measured hourly near the Grand Canyon. Observed haze events generally coincided with transients in methylchloroform and water vapor, which we interpret as endemic tags for air from southern California and the subtropics. The results depict a dynamic regional background.

Particle size distributions are sometimes conveniently described in terms of their integral moments. It is known that the details of a size distribution cannot always be recovered from its moments, but it has also been shown that an aerosol's optical properties can be insensitive to these details. This paper explores the limits of the correspondence between optics and moments, exhibiting size distributions with identical moments but dissimilar optical properties, and dissimilar moments but similar optical properties. The examples involve multimodal size distributions of the type observed in continental ambient air.

Air trajectory and particle scattering data (bsp) for the period 1984-1989 are used to determine the relationship between atmospheric transport and visual air quality at the Grand Canyon National Park. Using cluster analysis, 72-hour back-trajectories arriving four times per day were grouped into distinct transport patterns. Northwesterly and southerly/southwesterly flow dominate in the winter and summer seasons, respectively. Comparisons of bsp values accompanying different transport patterns showed a clear relationship between air flow pathway and light scattering due to small particles during the non-summer months only. An index is defined which describes the percentage of annual trajectories belonging to specific transport routes delivering predominantly clear air to the GCNP.

A spatial calibration for conditional frequency analysis, the inversion technique applied to routine back trajectories to study the association between geographical regions and conditions at a receptor, is discussed for trajectories arriving at Hopi Point, Arizona. Several 0.5° × 0.5° cells were selected at three different distances from Hopi Point. These cells were used to mimic sources, with air residing over them considered contaminated by imaginary emissions. The distribution of back trajectory segment endpoints over a latitude‐longitude grid was then examined as a function of the trajectories sojourn over each imaginary source cell on their way to the receptor. The areal extent of significant associations, evaluated for different seasons and the various ideal source positions, suggests that this inversion technique can resolve the direction of potential sources but has limited resolution for their radial distance from the receptor.

Dust particles in the 2.5 µm to 15 µm diameter range contribute to regional haze that sometimes impairs visibility at the Grand Canyon and other National Parks in the southwestern U.S. The proportion of airborne dust that is attributable to land modification is unknown, but can be expected to increase as a consequence of the region's rapid population growth. This note examines the upwind histories of air masses bringing high coarse‐particle concentrations to the Grand Canyon over a five‐year monitoring period. Although arid and semi‐arid lands extend in all directions, and the fastest airflows generally have a northerly component, high dust concentrations are most common in air arriving from the southwest, where development has been concentrated. This empirical association suggests that the expansion of suburban and agricultural lands is raising dust levels at the Grand Canyon.

The potential of routine back trajectory analyses to locate sources of contaminants in air at Grand Canyon is investigated with data on methylchloroform (CH3CCl3) concentrations collected during the Subregional Cooperative Electric Utility, Department of Defense, National Park Service, and Environmental Protection Agency Study(SCENES). Following a now-standard approach, the distribution of back trajectory segment endpoints over a latitude-longitude grid is examined as a function of measured concentrations at the fixed monitoring site. Grid cells in which segment endpoints are preferentially associated with high concentrations are then identified as candidate emissions sources. The method correctly identifies southern California as a source of CH3CCl3. An objective rationale is developed for screening out chance associations, attributable to statistical fluctuations, and the results are evaluated for real and hypothetical tracers with known, simple distributions.

The observed composition of visibility-reducing aerosols in the Grand Canyon region is summarized in climatological terms. Observations are from SCENES, a measurement program extending from 1984 to 1989. Results are presented as average mass balances stratified by various factors.Aerosols were found to exhibit substantial seasonal variation, but little systematic diurnal variation. Crustal material was a dynamic component, and peaked during springtime. Aerosol composition, but not total concentration, depended strongly on ambient relative humidity, with crustal material augmented at low humidities and sulfates augmented at high humidities. Total fine-particle concentrations correlated strongly with light scattering, as expected; however, little association between chemical composition and light scattering was observed.

Measurements are reported from integrating nephelometers modified to sample alternately from a fine-particle (D(aero) < 2.5 mum) cyclone and an unrestricted inlet. These nephelometers were successfully operated at two sites in the southwest U.S.A. as part of the SCENES program in the spring and summer of 1989. One of the nephelometers was collocated with a transmissometer monitoring total extinction. Fine- and total-particle samples were collected at each site for determination of mass and light absorption.Intercomparisons of the collocated daytime scattering, absorption, and total extinction measurements indicate that the nephelometer reported somewhat less than half the actual scattering by coarse particles. When this under-response is corrected for, the nephelometer and transmissometer show good agreement. The corrected data indicate that coarse particles were responsible from one-quarter to one-third of the total particle scattering. Predominantly coarse-particle dusts are estimated to have contributed one-third to one-half of the total-particle scattering.

Air arriving at the Grand Canyon of the Colorado River during 1988–1989 is attributed to one of four geographic quadrants—NE, SE, SW, NW—on the basis of routinely calculated back-trajectories. Most of the haze observed at the Canyon is attributed to the SW quadrant, which contains the populous and industrialized areas of southern California. Air from either northern quadrant tends to be significantly clearer than air from either southern quadrant. Clear northern air is most common during the winter, and is rarely observed during the summer tourist season, when steady flow from the southwest is the norm. Various possible interpretations of these empirical results are discussed, with varying implications for emissions management policy.

Many potential applications of the chemical mass balance involve more sources than species, or sources whose emissions vary with time. This paper demonstrates how standard methodology can be extended to accomodate such situations. Procedures are illustrated with data from a unique study in southern California which characterized fine particle composition in distinct polluted airsheds (sources) and the high desert (receptor). The sample apportionments are consistent with observed meteorological patterns, and identify the San Joaquin Valley as a major contributor to fine particle loadings in the high desert.

The halocarbons CFCl3, CH3CCl3, CCl4, and C2Cl4 have been monitored at four locations in southern California, southern Nevada, and northwestern Arizona. Summertime concentrations of CH3CCl3 and C2Cl4 at the Nevada and Arizona sites exhibit strong weekly cycles that lag similar cycles observed in the Los Angeles Basin by 1–2 days. The observed patterns imply a nearly complete weekend shutdown of emissions, and remarkably consistent long‐range (300–400 km) transport through complex terrain. The average amplitude of the summertime CH3CCl3 cycle is about 1200 ppt in air leaving the Los Angeles Basin, 80 ppt at the mountain‐top Nevada observatory, and 40 ppt at the level‐terrain Arizona observatory.

A two-year record of hourly concentrations of halocarbon tracers (methylchloroform and perchloroethylene) and hourly averages of particle light scattering (Bsp) has been analyzed In an effort to understand the sources of haze In the U.S. southwestern deserts and mountains. Measurements were taken on top of Spirit Mountain in southern Nevada. In conjunction with photographs used to interpret visual quality, haze episodes at Spirit Mountain were usually coincident with elevated concentrations of tracers originating from urban sources. Haze obscured an 88-km-distant mountain 17 percent of the total observation time. Of those Incidents, 69 percent were associated with long-range transport of haze from the Los Angeles Basin.

In rural areas of the western United States, atmospheric mass concentrations of participate organic carbon are comparable to those of sulfate. At the low humidities characteristic of this region, atmospheric light-scattering coefficients are empirically as sensitive to carbon concentrations as they are to sulfate concentrations. The abundance and scattering effectiveness of organic particles imply that they are major contributors to the impairment of scenic views.

As part of the Western Regional Air Quality Study (WRAQS), Teflon particle filters and Nylon backup filters were used to sample fine-particle nitrate and gaseous HNO3 over the course of 1 year at rural sites in nine western states. Observed nitrate concentrations were generally low in the southern part of the network, even when allowances are made for possible losses of particulate nitrate in sampling and analysis. Particulate nitrate concentrations were substantially higher in the northern portion of the network, both in absolute terms and relative to sulfate concentrations. Measured HNO3 concentrations, which were inflated over ambient levels by any volatilization of particulate nitrate during sampling, never exceeded 0.5 μg m−3 at the majority of sites. Occasional episodes of very high particulate nitrate concentrations were recorded; almost 15 % of the total particulate nitrate measured during the year was contributed by the five samples, out of the nearly 1500 analyzed, in which concentrations exceeded 1.5 μg m−3. These episodes manifested themselves not only in elevated nitrate concentrations, but in extinction coefficients and particulate mass concentrations which could not be accounted for by other measured chemical species.

Gas chromatography/methane chemical ionization mass spectrometry was used to determine the amount of methyl and linear C/sub 24/-C/sub 30/ alkanes in ambient and source aerosols. Vehicle exhaust was found to be the dominant source of C/sub 24/-C/sub 30/ alkanes in St. Louis. Most of the C/sub 24/-C/sub 39/ alkane in vehicle exhaust was synthesized during combustion; thus, alkane composition of particulate exhaust depends on the type of vehicle. Vehicle alkane signatures hold the promise of being useful vehicle tracers for source apportionment studies.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTContribution of fine particle sulfates to light scattering in St. Louis summer aerosolTeri L. Vossler and Edward S. MaciasCite this: Environ. Sci. Technol. 1986, 20, 12, 1235–1243Publication Date (Print):December 1, 1986Publication History Published online1 May 2002Published inissue 1 December 1986https://pubs.acs.org/doi/10.1021/es00154a007https://doi.org/10.1021/es00154a007research-articleACS PublicationsRequest reuse permissionsArticle Views42Altmetric-Citations6LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Airborne measurements were made in and near the plumes of the following mid western coal-fired power plants in 1981: Kincaid in central Illinois in February, La Cygne near Kansas City in March and Labadie near St. Louis in August and September. One objective of these measurements was to obtain data (reported elsewhere) to be used for the evaluation of plume visibility models. The results of the chemical and aerosol measurements are reported here. Good agreement was obtained from different measurement methods for SO2 and sulfate, but not for two different nitrate measurement methods. No more than a few per cent of the NOx emitted by these plants was NO2, and NO2 formation in the plumes could be accounted for by the ozone loss at the observed distances (up to 100 km in winter and 40 km in summer). Sulfate formation rates were in agreement with prior data, and there was no evidence of increased sulfate formation rates in a scrubbed plume (La Cygne). Both aerosol size distributions and sulfur particle size distributions were measured and showed reasonable agreement. The amount of light scattering by particles in the plume was quite variable, in pan because of variations in their mean particle size. The summer measurements were conducted during a rainy and hazy period when the Labadie plume typically could be seen from the ground only within a few km of the source. During this time, the visual impact of the plume was minimal.