Simulation of flow and shear stress distribution on the Oceano Dunes,implications for saltation and dust emissions

Environmental Fluid Mechanics - Wind-driven shear stresses drive saltation and dust emissions over sand dunes. However, the complex topography of coastal dunes and practical difficulties in...     

Dust emissions created by low-level rotary-winged aircraft flight over desert surfaces

There is a dearth of information on dust emissions from sources that are unique to U.S. Department of Defense testing and training activities. Dust emissions of PM₁₀ and PM_2.5 from low-level rotary-winged aircraft travelling (rotor-blade ≈7 m above ground level) over two types of desert surfaces (i.e., relatively undisturbed desert pavement and disturbed desert soil surface) were characterized at the Yuma Proving Ground (Yuma, AZ) in May 2007. Fugitive emissions are created by the shear stress of the outflow of high speed air created by the rotor-blade. The strength of the emissions was observed to scale primarily as a function of forward travel speed of the aircraft. Speed affects dust emissions in two ways: 1) as speed increases, peak shear stress at the soil surface was observed to decline proportionally, and 2) as the helicopter's forward speed increases its residence time over any location on the surface diminishes, so the time the downward rotor-generated flow is acting upon that surface must also decrease. The state of the surface over which the travel occurs also affects the scale of the emissions. The disturbed desert test surface produced approximately an order of magnitude greater emission than the undisturbed surface. Based on the measured emission rates for the test aircraft and the established scaling relationships, a rotary-winged aircraft similar to the test aircraft traveling 30 km h^?1 over the disturbed surface would need to travel 4 km to produce emissions equivalent to one kilometer of travel by a light wheeled military vehicle also traveling at 30 km h^?1 on an unpaved road. As rotary-winged aircraft activity is substantially less than that of off-road vehicle military testing and training activities it is likely that this source is small compared to emissions created by ground-based vehicle movements.     

Results from a pilot-scale air quality study in Addis Ababa, Ethiopia

Twenty-one samples were collected during the dry season (26 January–28 February 2004) at 12 sites in and around Addis Ababa, Ethiopia and analyzed for particulate matter with aerodynamic diameter <10 μm (PM₁₀) mass and composition. Teflon-membrane filters were analyzed for PM₁₀ mass and concentrations of 40 elements. Quartz-fiber filters were analyzed for chloride, sulfate, nitrate, and ammonium ions as well as elemental carbon (EC) and organic carbon (OC) content. Measured 24-h PM₁₀ mass concentrations were <100 and 40 μg m⁻³ at urban and suburban sites, respectively. PM₁₀ lead concentrations were <0.1 μg m⁻³ for all samples collected, an important finding because the government of Ethiopia had stopped the distribution of leaded gasoline a few months prior to this study. Mass concentrations reconstructed from chemical composition indicated that 34–66% of the PM₁₀ mass was due to geologically derived material, probably owing to the widespread presence of unpaved roads and road shoulders. At urban sites, EC and OC compounds contributed between 31% and 60% of the measured PM₁₀ while at suburban sites carbon compounds contributed between 24% and 26%. Secondary sulfate aerosols were responsible for <10% of the reconstructed mass in urban areas but as much as 15% in suburban sites, where PM₁₀ mass concentrations were lower. Non-volatile particulate nitrate, a lower limit for atmospheric nitrate, constituted <5% and 7% of PM₁₀ at the urban and suburban sites, respectively. At seven of the 12 sites, real-time PM₁₀ mass, real-time carbon monoxide (CO), and instantaneous ozone (O₃) concentrations were measured with portable nephelometers, electrochemical analyzers, and indicator test sticks, respectively. Both PM₁₀ and CO concentrations exhibited daily maxima around 7:00 and secondary peaks in the late afternoon and evening, suggesting that those pollutants were emitted during periods associated with motor-vehicle traffic, food preparation, and heating of homes. The morning concentration maxima were likely accentuated by stable atmospheric conditions associated with overnight surface temperature inversions. Ozone concentrations were measured near mid-day on filter sample collection days and were in all cases <45 parts per billion.     

Particulate emissions from U.S. Department of Defense artillery backblast testing

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 approximately 9 g of PM2.5 and 49 g of PM2.5 per firing. The average measured emission rates for PM1o 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.