Mark C. Green

Middle- and neighborhood-scale variations of PM10 source contributions in Las Vegas, Nevada

The Las Vegas Valley PM10 Study was conducted during 1995 to determine the contributions to PM10 aerosol from fugitive dust, motor vehicle exhaust, residential wood combustion, and secondary aerosol sources. Twenty-four-hr PM10 samples were collected at two neighborhood-scale sites every sixth day for 13 months. Five week-long intensive studies were conducted over a middle-scale sub-region at 29 locations that contained many construction projects emitting fugitive dust. The study found that the zone of influence around individual emitters was less than 1 km. Most of the sampling sites in residential and commercial areas yielded equivalent PM10 concentrations in the neighborhood region, even though they were more distant from each other than they were from the nearby construction sources. Based on chemical mass balance (CMB) receptor modeling, fugitive dust accounted for 80-90% of the PM10, and motor vehicle exhaust accounted for 3-9% of the PM10 in the Las Vegas Valley.

Comparison of GOES and MODIS Aerosol Optical Depth (AOD) to Aerosol Robotic Network (AERONET) AOD and IMPROVE PM2.5 Mass at Bondville, Illinois

Abstract Collocated Interagency Monitoring of Protected Visual Environments (IMPROVE) particulate matter (PM) less than 2.5 μm in aerodynamic diameter (PM2.5) chemically speciated data, mass of PM less than 10 μm in aerodynamic diameter (PM10), and Aerosol Robotic Network (AERONET) aerosol optical depth (AOD) and size distribution at Bondville, IL, were compared with satellite-derived AOD. This was done to evaluate the quality of the Geostationary Operational Environmental Satellite (GOES) and Moderate Resolution Imaging Spectroradiometer (MODIS) AOD data and their potential to predict surface PM2.5 concentrations. MODIS AOD correlated better to ERONET AOD (r = 0.835) than did GOES AOD (r = 0.523). MODIS and GOES AOD compared better to AERONET AOD when the particle size distribution was dominated by fine mode. For all three AOD methods, correlation between AOD and PM2.5 concentration was highest in autumn and lowest in winter. The AERONET AOD-PM2.5 relationship was strongest with moderate relative humidity (RH). At low RH, AOD attributable to coarse mass degrades the relationship; at high RH, added AOD from water growth appears to mask the relationship. For locations such as many in the central and western United States with substantial coarse mass, coarse mass contributions to AOD may make predictions of PM2.5 from AOD data problematic. Seasonal and diurnal variations in particle size distributions, RH, and seasonal changes in boundary layer height need to be accounted for to use satellite AOD to predict surface PM2.5.

The Treasure Valley secondary aerosol study I: measurements and equilibrium modeling of inorganic secondary aerosols and precursors for southwestern Idaho

Abstract The SCAPE2 aerosol equilibrium model was applied to measured concentrations of PM2.5 aerosol and precursor gases. Ambient measurements in the Treasure Valley, Idaho were collected during stagnation episodes between December 1999 and March 2000 when conditions were favorable for the formation of secondary inorganic aerosol. SCAPE2 results agreed well with measurements for the episodes tested; Monte Carlo simulation using the uncertainties of the model input variables indicated that discrepancies between measured and modeled results were within the range of analytical precision. Air pollution control strategies were evaluated by perturbing the model input concentrations of total sulfate, nitrate, and ammonium. The largest reductions in secondary aerosol concentrations occurred when total nitrate was reduced, indicating that the formation of ammonium nitrate was limited by the availability of nitrate.

The project MOHAVE tracer study : study design, data quality, and overview of results

In the winter and summer of 1992, atmospheric tracer studies were conducted in support of project MOHAVE, a visibility study in the southwestern United States. The primary goal of project MOHAVE is to determine the effects of the Mohave power plant and other sources upon visibility at Grand Canyon National Park. Perfluorocarbon tracers (PFTs) were released from the Mohave power plant and other locations and monitored at about 30 sites. The tracer data are being used for source attribution analysis and for evaluation of transport and dispersion models and receptor models. Collocated measurements showed the tracer data to be of high quality and suitable for source attribution analysis and model evaluation. The results showed strong influences of channeling by the Colorado River canyon during both winter and summer. Flow from the Mohave power plant was usually to the south, away from the Grand Canyon in winter and to the northeast, toward the Grand Canyon in summer. Tracer released at Lake Powell in winter was found to often travel downstream through the entire length of the Grand Canyon. Data from summer tracer releases in southern California demonstrated the existence of a convergence zone in the western Mohave Desert.

The relationship of the extinction coefficient distribution to wind field patterns in southern California

Abstract The averaged distribution of the extinction coefficient, including its diurnal variation, in southern California is shown for commonly occurring winter and summer wind field patterns. The wind field patterns were generated by an objectively based method using empirical orthogonal function (EOF) analysis of the vector wind, similarity criteria and cluster analysis. For the days assigned to each pattern, averaged extinction coefficient fields were calculated for six diurnal periods. Three main winter and three main summer patterns were identified. Associated with the wind field patterns were distinctly differing extinction coefficient patterns. Transport of visibility reducing aerosols can be inferred by comparing the wind and extinction fields and their diurnal variation. Transport of visibility reducing pollutants from the Los Angeles Basin and San Joaquin Valley into the Mojave Desert and the south-western U.S. was shown to be highly persistent in summer, while only sporadic in winter. The San Joaquin Valley was identified as having a significant potential for additional visibility impacts in the southwest with higher emissions of visibility affecting pollutants associated with the increasing urbanization of the valley. The analysis illustrated a technique for organizing large wind data sets into a reasonable number of patterns. The clear and consistent relationship between the extinction and wind fields demonstrates the usefulness of this technique in air pollution analysis.

Application of the Tracer-Aerosol Gradient Interpretive Technique to Sulfur Attribution for the Big Bend Regional Aerosol and Visibility Observational Study

Abstract A simple data analysis method called the Tracer-Aerosol Gradient Interpretive Technique (TAGIT) is used to attribute particulate S and SO2 at Big Bend National Park in Texas and nearby areas to local and regional sources. Particulate S at Big Bend is of concern because of its effects on atmospheric visibility. The analysis used particulate S, SO2 , and perfluorocarbon tracer data from six 6-hr sampling sites in and near Big Bend National Park. The data were collected in support of the Big Bend Regional Aerosol and Visibility Observational (BRAVO) Study; the field portion was conducted from July through October 1999. Perfluorocarbon tracer was released continuously from a tower at Eagle Pass, TX, approximately 25 km northeast of two large coal-fired power plants (Carbon I and II) in Coahuila, Mexico, and approximately 270 km east-southeast of Big Bend National Park. The perfluorocarbon tracer did not properly represent the location of the emissions from the Carbon power plants for individual 6-hr sampling periods and attributed only 3% of the particulate S and 27% of the SO2 at the 6-hr sites in and near Big Bend to sources represented by the tracer. An alternative approach using SO2 to tag “local” sources such as the Carbon plants attributed 10% of the particulate S and 75% of the SO2 at the 6-hr sites to local sources. Based on these two approaches, most of the regional (65–86%) and a small fraction (19–31%) of the local SO2 was converted to particulate S. The analysis implies that substantial reductions in particulate S at Big Bend National Park cannot be achieved by only reducing emissions from the Carbon power plants; reduction of emissions from many sources over a regional area would be necessary.

The Treasure Valley secondary aerosol study II: modeling of the formation of inorganic secondary aerosols and precursors for southwestern Idaho

Abstract Many locations with very high mixing ratios of ammonia, nitrogen oxides and relatively low sulfate mixing ratios are found in urban areas of the western United States during the wintertime. These urban areas may also experience episodes with high humidity with high levels of secondary inorganic ammonium nitrate particles. Photochemical simulations of the formation of secondary sulfate and ammonium nitrate aerosol were made to investigate possible secondary particle control strategies for Treasure Valley, Idaho. The simulation conditions were based on the field study of Kuhns et al. (Atmos. Environ. 2002, this issue). It was found that under these conditions that almost all of the sulfate and approximately 95% of the nitric acid would be found in the particulate phase. Reductions in the emission rates of volatile organic compounds were found to be most effective in reducing secondary inorganic aerosol concentrations while reductions in nitrogen oxide emission rates would be expected to increase aerosol concentrations. This response of aerosol formation rates is due to the effects of the nitrogen oxide and volatile organic compound emission rates on the concentration of hydroxyl radical mixing ratios.

Effects of Snow Cover and Atmospheric Stability on Winter PM2.5Concentrations in Western U.S. Valleys

AbstractMany populated valleys in the western United States experience increased concentrations of particulate matter with diameter of less than 2.5 μm (PM2.5) during winter stagnation conditions. Further study into the chemical components composing wintertime PM2.5 and how the composition and level of wintertime PM2.5 are related to meteorological conditions can lead to a better understanding of the causes of high PM2.5 and aid in development and application of emission controls. The results can also aid in short-term air-pollution forecasting and implementation of periodic emission controls such as burning bans. This study examines relationships between PM2.5 concentrations and wintertime atmospheric stability (defined by heat deficit) during snow-covered and snow-free conditions from 2000 to 2013 for five western U.S. urbanizations: Salt Lake City, Utah; Reno, Nevada; Boise, Idaho; Missoula, Montana; and Spokane, Washington. Radiosonde data were used where available to calculate daily heat deficit, whi...

Filter Light Attenuation as a Surrogate for Elemental Carbon

Abstract Light attenuation (b att) measured from filter light transmission is compared with elemental carbon (EC) measurements for more than 180,000 collocated PM2.5 (particulate matter [PM] ≤ 2.5 µm in aerodynamic diameter) and PM10 (PM ≤ 10 µm in aerodynamic diameter) samples from nearly 200 U.S. locations during the past 2 decades. Although there are theoretical reasons for expecting highly variable relationships between batt and EC (such as the effects of “brown carbon” and iron oxides in PM2.5), reasonable correlations are found. These correlations are not a strong function of season or location (e.g., rural vs. urban). Median EC concentrations can be predicted from filter transmittance measurements to within ±15–30%. Although EC predicted from batt shows larger uncertainties (30–60%), especially at concentrations less than 0.3 µg/m3, the consistent mass absorption efficiency (σatt) derived from the regression analysis demonstrates the feasibility of using b att as a surrogate for EC. This study demonstrates that a constant factor of 0.1 g/m2 (equivalent to the 10 m2/g σatt used in the Interagency Monitoring of Protected Visual Environments chemical extinction formula) can be used to estimate EC concentrations from batt through a Teflon-membrane filter sample. Greater accuracy is achieved with site-specific σatt derived from a period with collocated EC measurements.

Characterization of regional transport and dispersion using Project MOHAVE tracer data.

ABSTRACT Perfluorocarbon tracers were released continuously from several surface locations and one power plant stack location during the winter (30 days) and summer (50 days) intensive studies as part of Project MOHAVE. Tracers were released in winter from the Mohave Power Plant (MPP) and Dangling Rope, UT, located on the shore of Lake Powell near Page, AZ; and in summer from MPP, the Tehachapi Pass between the Mojave Desert and the Central Valley in California, and El Centro, CA, on the California-Mexico border. At the Tehachapi tracer release site six-hour pulses of a separately identifiable perfluorocarbon tracer were released every four days in order to assess the time for the tracer to clear the monitoring network. Daily 24-hr integrated samples were collected at about 30 sites in four states. Limited tracer concentration data with higher time resolution is also available. Graphical displays and analyses identify several regional transport paths, including a convergence zone in the Mojave Desert, the importance of terrain channeling, especially in winter, and a relationship between 24-hr maximum influence function and distance that may prove useful as a scoping tool and to test regional scale air quality models. In winter, Dangling Rope tracer was routinely transported through the entire length of the Grand Canyon, while in summer, MPP tracer was routinely transported over most of Lake Mead.