William C. Malm

Revised Algorithm for Estimating Light Extinction from IMPROVE Particle Speciation Data

Abstract The Interagency Monitoring of Protected Visual Environments (IMPROVE) particle monitoring network consists of approximately 160 sites at which fine particulate matter (PM2.5) mass and major species concentrations and course particulate matter (PM10) mass concentrations are determined by analysis of 24-hr duration sampling conducted on a 1-day-in-3 schedule. A simple algorithm to estimate light extinction from the measured species concentrations was incorporated in the 1999 Regional Haze Rule as the basis for the haze metric used to track haze trends. A revised algorithm was developed that is more consistent with the recent atmospheric aerosol literature and reduces bias for high and low light extinction extremes. The revised algorithm differs from the original algorithm in having a term for estimating sea salt light scattering from Cl - ion data, using 1.8 instead of 1.4 for the mean ratio of organic mass to measured organic carbon, using site-specific Rayleigh scattering based on site elevation and mean temperature, employing a split component extinction efficiency associated with large and small size mode sulfate, nitrate and organic mass species, and adding a term for nitrogen dioxide (NO2) absorption for sites with NO2 concentration information. Light scattering estimates using the original and the revised algorithms are compared with nephelometer measurements at 21 IMPROVE monitoring sites. The revised algorithm reduces the underprediction of high haze periods and the overprediction of low haze periods compared with the performance of the original algorithm. This is most apparent at the hazier monitoring sites in the eastern United States. For each site, the PM10 composition for days selected as the best 20% and the worst 20% haze condition days are nearly identical regardless of whether the basis of selection was light scattering from the original or revised algorithms, or from nephelometer-measured light scattering.

Linear trend analysis: a comparison of methods

In this paper, we present an overview of statistical approaches available for detecting and estimating linear trends in environmental data. We evaluate seven methods of trend detection and make recommendations based on a simulation study. We also illustrate the methods using real data.

Chemical Smoke Marker Emissions During Flaming and Smoldering Phases of Laboratory Open Burning of Wildland Fuels

Smoke emitted by prescribed and wild fires can make a substantial contribution to ambient aerosol (McMeeking et al. 2006; Park et al. 2007; Spracklen et al. 2007). Approaches to investigate these contributions have used a variety of different chemical smoke markers, including levoglucosan, produced by thermal degradation of cellulose, and water-soluble potassium (Andreae 1983; Engling et al. 2006; Hays et al. 2002; Simoneit 2002;Ward et al. 2006). Filter sampling is commonly employed to measure smoke markers in ambient and source samples; however, these time-integrated measurements limit knowledge about variability of smoke marker emissions, especially between flaming and smoldering fire phases.

Examination of the effects of sulfate acidity and relative humidity on light scattering at Shenandoah National Park

Abstract Sulfate aerosols in the eastern United States of America are known to be acidic, at least on an episodic basis. Intensive particle and optical measurements made during a special study at Shenandoah National Park in the summer of 1991 are used to examine the acidity and how it influences light scattering. Reconstructed fine mass, calculated by summing the constituents, matches measured mass quite well if water associated with sulfates is included. However, reconstructed scattering is much lower than measured even when acidity-dependent mass and scattering efficiencies are used for sulfates. It is hypothesized that the mass of organic particles may be underestimated and/or organics may be hygroscopic. Uncertainty in relative humidity is also fairly large. Reduction of this uncertainty may allow closer agreement between reconstructed and measured scattering in future studies. Sulfates were found to be about 1 2 neutralized on average during this study.

Indirect Measurement of Hydrocarbon Aerosols Across the United States by Nonsulfate Hydrogen-Remaining Gravimetric Mass Correlations

In order to determine the levels of fine organic aerosols at remote sites, two methods were devised to calculate organic concentration from data collected on chemically inert teflon filters by the 34-site National Park Service (NPS) Fine Particle Network from 1982 to 1986. The remaining mass method is based on the difference between the measured gravimetric mass and the sum of the ammonium sulfate, soil, and soot carbon components, derived from measured parameters. This remaining mass is between 53% and 67% organic matter, based on two studies measuring organic carbon directly in the arid west. The nonsulfate hydrogen method is based on the concentration of particulate hydrogen, which has been measured on NPS samples since 1984, using techniques developed at Davis, CA. After removing the contribution associated with ammonium sulfate, the remaining nonsulfate hydrogen is predominantly due to organic matter. The two methods are in good agreement, with a sample to sample correlation of 0.76. For each western...

On the potential of regional-scale emissions zoning as an air quality management tool for the grand canyon

Abstract 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.

One– and Three–Hour PM2.5 Characterization, Speciation, and Source Apportionment Using Continuous and Integrated Samplers

Ammonium nitrate and semivolatile organic compounds (SVOC) are significant components of fine particles in many urban atmospheres. These components, however, are not properly measured by current EPA accepted methods, such as the R&P TEOM monitor, due to loss of semivolatile material (SVM) from particles in the heated environment of the filter during sampling. The accurate determination of semivolatile material is important due to the possible effects of these species on human health, visibility, and global climate change. The concentration and composition of fine particulate material were determined using a combination of continuous and integrated samplers at the Brigham Young University–EPA Environmental Monitoring for Public Access and Community Tracking (BYU–EPA EMPACT) monitoring site in Salt Lake City, Utah over a six–day sampling period (30 January to 4 February) during the winter of 2001. Continuous samples were collected using a RAMS (total PM2.5 mass), a TEOM monitor (nonvolatile PM2.5 mass), an Aethalometer (elemental carbon), a TSI CPC (particle count), and a Nephelometer (light scattering by particles, bsp). Fine particle composition and mass were determined on a three–hour basis using the PC–BOSS diffusion denuder sampler. Total PM2.5 mass–determined with the RAMS agreed with constructed mass determined from the chemical composition measured in collocated PC–BOSS–integrated samples. Results from this study indicate that semivolatile material (ammonium nitrate and semivolatile organic compounds) is a significant component of fine particle mass. Semivolatile organic compounds were the major contributor to light scattering during the six–day sampling period. Semivolatile nitrate, but not organic material, was suggested to be hygroscopic by the nephelometric data. The majority of the SVM observed appeared to be secondary material formed from photochemical reactions of the organic and NOx emissions from mobile sources and wood smoke combustion.

Visibility Measurements lo National Parks In the Western United States

The Nationl Park Service (NPS)in cooperation with the Environmental Protection Agency, Environmental Monitoring Systems Laboratory, has operated a regional (western US) visibility monitoring network since the fall of 1978. At each of the 27 monitoring sites NPS personnel record sky-target contrast three times a day using a multiwavelength teleradiometer. After each measurement, operators also photograph the vista to pictorially record the appearance of the target when the measurement was made. This paper discusses teleradiometer data reduction and editing techniques as well as temporal and spatial visibility trends in the western US. Throughout the West, winter months correspond to highest visibility, while summer months have the lowest overall air quality. Visibilities which were highest in 1978 decreased until 1981; 1982 showed a slight increase in visibility. Examination of visibilities throughout the West in summer of 1982 shows that visibilities are highest in northern Nevada, northern Utah and southern Idaho. The Colorado Plateau, the geographic area containing Grand Canyon, Bryce, Zion and Canyonlands National Parks as well as a number of national monuments, has the second highest visibility. Other areas of the west have intermediate visibilities with the coastal areas of California having the lowest visual air quality.

Optical characteristics of fine and coarse particulates at Grand Canyon, Arizona

Abstract The relationship between airborne particulate matter and atmospheric light extinction was examined using the multivariate techniques of principal component analysis and multiple linear regression on data gathered at the Grand Canyon, Arizona, from December 1979 to November 1981. Results showed that, on the average, fine sulfates were most strongly associated with light attenuation in the atmosphere. Other fine mass (nitrates, organics, soot and carbonaceous material) and coarse mass (primarily windblown dust) were much less associated with atmospheric extinction. Fine sulfate mass at the Grand Canyon was responsible for 63% of atmospheric light extinction while other fine mass and coarse mass were responsible for 17 and 20% of atmospheric extinction, respectively.

Impact of Impaired Visibility on Visitor Enjoyment of the Grand Canyon A Test of an Ordered Logit Utility Model

An ordered logit probability model of the impact of visibility impairment on visitor enjoyment of the Grand Canyon was examined. Ninety male and female undergraduates rank ordered the six alternatives of a stimulus set. Each alternative consisted of one of three levels of visibility at each of three vistas, a driving time to the vistas, and a waiting time to get into an archaeological site. Results indicated that a wide range of driving times (0-2.5 hours) and waiting times (0-1 hour) yielded a significant coefficient for each of the five attributes in the alternatives. Examination of trade-off ratios indicated that subjects were willing to spend about an hour more in driving time or half an hour more in waiting time for a one-unit increase in visibility of the San Francisco Peaks. Differential vista sensitivities to changes in visibility were also demonstrated. Additional questions to be explored with the model are discussed.