Vicken Etyemezian

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.

Overview of Real-World Emission Characterization Methods

Abstract Real-world emissions do not necessarily correspond with those derived from certification tests, owing to changes in equipment, fuels, and operating cycles. Therefore, emission rates from sources that affect ambient air quality are needed to drive air quality models and to provide accountability for air quality management strategies. Since the early 1960s, source characterization methods have been established that quantify emission rates to certify sources and determine their compliance over time. However, these certification and compliance methods have not been adapted to changes in emission processes and controls nor have they incorporated advances in measurement technology. This results in source tests that are incompatible with each other and with ambient measurement methods. Source characterization methods need to be improved to better represent real-world hardware, operating conditions, and feedstocks and to obtain more information at lower costs. Hot-ducted exhaust can be cooled to ambient temperatures prior to measurement to better approximate emissions as they appear in the atmosphere. Engine exhaust can be characterized in situ with portable monitoring systems. A portable wind tunnel can characterize fugitive dust threshold suspension velocities, reservoir sizes, particle size distributions, and chemical profiles.

A New Technique for Characterizing the Efficacy of Fugitive Dust Suppressants

Abstract The Portable In-Situ Wind Erosion Laboratory (PI-SWERL) instrument was evaluated for testing the effectiveness of dust suppressants for a range of native and constructed soils. The PM10 (particles with diameter ≤10 µm) emissions from dust suppressant-treated and untreated soil surfaces were measured periodically over 14 months. No statistically significant differences were found among soil surfaces treated with three dilution mixtures of the dust suppressant. The temporal variation of PM10 emissions from treated and untreated plots for native and constructed soil textures indicated that: (1) reductions of PM10 emissions by the dust suppressant were significant within 2–3 months after the application and diminished substantially thereafter, (2) decomposition of the protective treated layer resulted in high PM10 emissions for longer environmental exposure times, and (3) emissions from untreated soil surfaces declined over time because of the formation of a natural crust. These results demonstrated that the PI-SWERL can provide qualitative and quantitative information on PM10 emissions for a range of soil textures and can be used to estimate the effectiveness of dust suppressants exposed to actual environmental (i.e., weather and solar radiation) conditions over long periods of time.

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.

Soil humic-like organic compounds in prescribed fire emissions using nuclear magnetic resonance spectroscopy.

Here we present the chemical characterization of the water-soluble organic carbon fraction of atmospheric aerosol collected during a prescribed fire burn in relation to soil organic matter and biomass combustion. Using nuclear magnetic resonance spectroscopy, we observed that humic-like substances in fire emissions have been associated with soil organic matter rather than biomass. Using a chemical mass balance model, we estimated that soil organic matter may contribute up to 41% of organic hydrogen and up to 27% of water-soluble organic carbon in fire emissions. Dust particles, when mixed with fresh combustion emissions, substantially enhances the atmospheric oxidative capacity, particle formation and microphysical properties of clouds influencing the climatic responses of atmospheric aeroso. Owing to the large emissions of combustion aerosol during fires, the release of dust particles from soil surfaces that are subjected to intense heating and shear stress has, so far, been lacking.

Fugitive Dust Emissions from Paved Road Travel in the Lake Tahoe Basin

Abstract The clarity of water in Lake Tahoe has declined substantially over the past 40 yr. Causes of the degradation include nitrogen and phosphorous fertilization of the lake waters and increasing amounts of inorganic fine sediment that can scatter light. Atmospheric deposition is a major source of fine sediment. A year-round monitoring study of road dust emissions around the lake was completed in 2007 using the Testing Re-entrained Aerosol Kinetic Emissions from Roads (TRAKER) system developed at the Desert Research Institute (DRI). Results of this study found that, compared with the summer season, road dust emissions increased by a factor of 5 in winter, on average, and about a factor of 10 when traction control material was applied to the roads after snow events. For winter and summer, road dust emission factors (grams coarse particulate matter [PM10] per vehicle kilometer traveled [g/vkt]) showed a decreasing trend with the travel speed of the road. The highest emission factors were observed on very low traffic volume roads on the west side of the lake. These roads were composed of either a 3/8-in. gravel material or had degraded asphalt. The principle factors influencing road dust emissions in the basin are season, vehicle speed (or road type), road condition, road grade, and proximity to other high-emitting roads. Combined with a traffic volume model, an analysis of the total emissions from the road sections surveyed indicated that urban areas (in particular South Lake Tahoe) had the highest emitting roads in the basin.

Effect of Soil Type and Momentum on Unpaved Road Particulate Matter Emissions from Wheeled and Tracked Vehicles

Excluding windblown dust, unpaved road dust PM 10 emissions in the US EPAs 2002 National Emission Inventory account for more than half of all PM 10 emissions in the arid states of the western U.S. (i.e., CA, AZ, NV, NM, and TX). Despite the large size of the source, substantial uncertainty is associated with both the vehicle activity (i.e., number of kilometers traveled at a particular speed) and the emission factors (i.e., grams of PM 10 per kilometer traveled). In this study, emission factors were measured using the flux tower method for both tracked and wheeled military vehicles at three military bases in the Western U.S. Test vehicle weights ranged from 2400 kg to 60,000 kg. Results from both previously published and unpublished field studies are combined to link emission factors to three related variables: soil type, vehicle momentum, and tred type (i.e., tire or track). Current emission factor models in US EPAs AP-42 Emission Factor Compendium do not factor both speed and weight into unpaved road emission factor calculations. Tracked vehicle emission factors from Ft. Carson, CO, and Ft. Bliss, TX were related to vehicle momentum (speed * mass) with ratios ranging from 0.004–0.006 (g-PM vkt− 1)/(kg m s− 1). For similar vehicle momentum, wheeled vehicles emitted approximately 2 to 4 times more PM 10 than tracked vehicles. At Yakima, WA, tracked vehicle PM 10 emission factors were substantially higher (0.38 (g-PM vkt− 1)/(kg m s− 1)) due to the unique volcanic ash soil characteristics (48% silt). Results from PI-SWERL, a portable wind tunnel surrogate, are presented to assess its utility to predict unpaved road dust emissions without the deployment of flux tower systems. PI-SWERL showed only a factor of 6 variation between sites in comparison with the 60-fold variation as measured by the flux towers.

Particulate Emissions from U.S. Department of Defense Artillery Backblast Testing

Abstract There is a dearth of information on dust emissions from sources that are unique to the U.S. Department of Defense testing and training activities. However, accurate emissions factors are needed for these sources so that military installations can prepare accurate particulate matter (PM) emission inventories. One such source, coarse and fine PM (PM10 and PM2.5) emissions from artillery backblast testing on improved gun positions, was characterized at the Yuma Proving Ground near Yuma, AZ, in October 2005. Fugitive emissions are created by the shockwave from artillery pieces, which ejects dust from the surface on which the artillery is resting. Other contributions of PM can be attributed to the combustion of the propellants. For a 155–mm howitzer firing a range of propellant charges or zones, amounts of emitted PM10 ranged from ∼19 g of PM10 per firing event for a zone 1 charge to 92 g of PM10 per firing event for a zone 5. The corresponding rates for PM2.5 were ∼9 g of PM2.5 and 49 g of PM2.5 per firing. The average measured emission rates for PM10 and PM2.5 appear to scale with the zone charge value. The measurements show that the estimated annual contributions of PM10 (52.2 t) and PM2.5 (28.5 t) from artillery backblast are insignificant in the context of the 2002 U.S. Environment Protection Agency (EPA) PM emission inventory. Using national–level activity data for artillery fire, the most conservative estimate is that backblast would contribute the equivalent of 5 x 10–4% and 1.6 x 10–3% of the annual total PM10 and PM2.5 fugitive dust contributions, respectively, based on 2002 EPA inventory data.

Spatial Variability of Unpaved Road Dust PM10 Emission Factors near El Paso, Texas

Abstract The testing re-entrained aerosol kinetic emissions from roads technique is compared with distance-based emission factors (EFs; g/VKT) measured downwind of a dirt road by using towers instrumented with real-time meteorological and particle sensors at multiple heights. The emission potential (EP), defined as the EF divided by the vehicle speed (m/sec), and weight index permits the inter-comparison of emissions from multiple roadways surveyed by the TRAKER vehicle. A survey of 72 km of un-paved roads on the Ft. Bliss Military Base near El Paso, Texas, indicated that 60% of all measured EPs fell between 6.7 (g/VKT)/(m/sec) and 9.6 (g/VKT)/(m/sec). The EP measured across the base was ~50% lower than those collected in the vicinity of the instrumented towers. This implies that EFs measured for other vehicles on the same test section should be reduced by 50% to more accurately represent EFs for the entire military base. Using geographic information system-based soil maps, the inferred EFs are related to differences in soil types over the survey area. Variations among five different soil types accounted for <10% of variation in EP. Individual measurements using the testing re-entrained aerosol kinetic emissions from roads technique did show larger spatial variations in EP; however, these were not effectively captured by the soil classifications, partly because of the comparatively coarse spatial classification used in the soil survey data.

Scattering Cross-Section Emission Factors for Visibility and Radiative Transfer Applications: Military Vehicles Traveling on Unpaved Roads

Abstract Emission factors for particulate matter (PM) are generally reported as mass emission factors (PM mass emitted per time or activity) as appropriate for air quality standards based on mass concentration. However, for visibility and radiative transfer applications, scattering, absorption, and extinction coefficients are the parameters of interest, with visibility standards based on extinction coefficients. These coefficients (dimension of inverse distance) equal cross‐section concentrations, and, therefore, cross‐section emission factors are appropriate. Scattering cross‐section emission factors were determined for dust entrainment by nine vehicles, ranging from light passenger vehicles to heavy military vehicles, traveling on an unpaved road. Each vehicle made multiple passes at multiple speeds while scattering and absorption coefficients, wind velocity and dust plume profiles, and additional parameters were measured downwind of the road. Light absorption of the entrained PM was negligible, and the light extinction was primarily caused by scattering. The resulting scattering cross‐section emission factors per vehicle kilometer traveled (vkt) range from 12.5 m2/vkt for a slow (16 km/ hr), light (1176 kg) vehicle to 3724 m2/vkt for a fast (64 km/hr), heavy (17,727 kg) vehicle and generally increase with vehicle speed and mass. The increase is approximately linear with speed, yielding emission factors per vkt and speed ranging from 4.2 m2/(vkt km/hr) to 53 m2/(vkt km/hr). These emission factors depend approximately linearly on vehicle mass within the groups of light (vehicle mass ≤3100 kg) and heavy (vehicle mass >8000 kg) vehicles yielding emission factors per vkt, speed, and mass of 0.0056 m2/(vkt km/hr kg) and 0.0024 m2/(vkt km/hr kg), respectively. Comparison of the scattering cross‐section and PM mass emission factors yields average mass scattering efficiencies of 1.5 m2/g for the light vehicles and of 0.8 m2/g for the heavy vehicles indicating that the heavy vehicles entrain larger particles than the light vehicles.