Carbonaceous and Ionic Components of Atmospheric Fine Particles in Beijing and Their Impact on Atmospheric Visibility

Ground-based observation of fine particulate matter (PM2.5) in Beijing was carried out continuously in 2006. The carbonaceous and ionic components, as well as their distribution characteristics and seasonal variation, were obtained. The annual mean mass concentration of PM2.5 was 176.6 +/- 100.3 mu g/m(3). Long-range transport dust and local dust raised by strong wind during the spring made a considerable contribution to PM2.5 mass concentration. There was significant seasonal variation in carbonaceous and water-soluble ionic components associated with diverse emission sources, varying meteorological conditions during different seasons, and different mechanisms of formation for secondary aerosol ions. Comparing studies under different synoptic conditions suggested that PM2.5 pollution was mainly caused by transportation of particulates from remote sources, whereas hazy synoptic conditions are caused by local pollution. PM2.5 and visibility were negatively correlated, and the relationship between the concentrations of NH4+, SO42-, and NO3- with PM2.5 concentration during winter can be described using power function fitting.</p

Source apportionment of atmospheric particulate carbon in Las Vegas, Nevada, USA

A study was conducted to quantify wintertime contributions of source types to carbonaceous PM2.5 at four urban sites in the Las Vegas Valley, one of the most rapidly growing urban areas in the southwestern United States. Twenty-four hour average ambient samples were collected for mass, ions, elements, organic carbon (OC), elemental carbon (EC), and trace organic markers analysis. Additional measurements were made to determine diurnal patterns in light-absorbing black carbon (BC) as a marker for combustion sources. Carbonaceous PM sources of on-road gasoline vehicles, on-road diesel vehicles, and off-road diesel engines were characterized with their chemical profiles, as well as fuel-based emission factors, using an In-Plume Sampling System. The Effective Variance Chemical Mass Balance (EV-CMB) source apportionment model was applied to the ambient samples collected, using source profiles developed in this study as well as profiles from other relevant studies. Four main sources contributed to PM2.5 carbon within the Las Vegas Valley: (1) paved road dust, (2) on-road gasoline vehicles, (3) residential wood combustion, and (4) on-road diesel vehicles. CMB estimated that on-road mixed fleet gasoline vehicles are the largest source for OC and EC at all the sites. The contribution of paved road dust to both OC and EC was 5-10% at the four sites. On-road diesel vehicles contribute 22% of the OC and 34% of the EC at a site near the city center, which is located immediately downwind of a major freeway. Residential wood combustion is a more important source than on-road diesel vehicles for two residential neighborhood sites. These results are consistent with our conceptual model, and the research methodology may be applied to studying other urban areas.</p

Aerosol and Air Toxics Exposure in El Paso, Texas: A Pilot Study

The Paso del Norte (PdN) region is one of the largest metropolitan areas along the U.S.-Mexico border. Different emission regulations between the two countries, particularly with respect to on-road vehicle and domestic burning, have impacted the regional concentration and human exposure of air toxics (e. g., metals, polycyclic aromatic hydrocarbons [PAHs], and carbonyls). Comprehensive air quality measurements were conducted using a mobile monitoring system at two urban-scale sites within El Paso, Texas in December 2008 as a pilot study to understand aerosol and air toxics exposure and sources in the PdN region. The measurements show clear diurnal variations due to traffic emissions and a major pollution episode likely caused by both motor vehicles and domestic burning. Wind analysis further confirms the importance of cross-border transport on elevated pollutant concentrations at the monitoring sites. The traffic-dominated periods are characterized by high fractions of black carbon, particle-bound PAHs (p-PAHs), and carbonyls in comparison with dust-related periods. During the particular pollution episode, high levels of elemental chlorine and vinyl chloride were observed that might relate to unregulated domestic burning of polyvinyl chloride (PVC) products. Although most pollution indicators show a substantial improvement in air quality over the last decade, short-term exposure to some p-PAHs, e.g., benzo[a] pyrene, is still close to the health effects screening level. Bi-national efforts are required to further reduce air toxics emissions.</p

Wind erosion potential for fugitive dust sources in the Athabasca OilSands Region

This study characterized the generation of windblown dust from various sources in the Athabasca Oil Sands Region (AOSR) in Alberta, Canada. The Portable In-Situ Wind Erosion Laboratory (PI-SWERL) equipped with two real-time dust monitors and nine-channel filter packs was used to simulate wind-driven erosion and measure emissions. Sixty four sites were measured, including oil sands mining facilities, quarry operations, and roadways in the vicinity of Ft. McMurray and Ft. McKay. Key parameters related to windblown dust generation were characterized including: threshold friction velocity, reservoir type, and particle size-segregated emission potential. The threshold wind speed for particle suspension varies from 11 to 21.5 km/h (u10 + ; measured at 10 m above ground level), and saltation occurs at higher speeds of u10 + &gt;32 km/h. All surfaces have limited dust supplies at lower wind speeds of &lt;27 km/h, but have unlimited dust supplies at the highest wind speed tested (56 km/h). Unpaved roads, parking lots, or bare land with high abundances of loose clay and silt materials along with frequent mechanical disturbances are the highest dust emitting surfaces. Paved roads, stabilized or treated (e.g., watered) surfaces with limited loose dust materials are the lowest emitting surfaces. Surface watering proved effective in reducing dust emissions, with potential emission reductions of 50&ndash;99%. Surface disturbances by traffic or other activities were found to increase PM10 emission potentials 9&ndash;160 times. These data will improve the accuracy of emission inventories, dust dispersion, transport, and source apportionment models, and help design and evaluate dust control strategies.</p

Characterization and seasonal variations oflevoglucosan in fine particulate matter in Xi’an, China

PM2.5 (particulate matter with an aerodynamic diameter &lt;2.5 mm) samples (n &frac14; 58) collected every sixth day in Xi&rsquo;an, China, from 5 July 2008 to 27 June 2009 are analyzed for levoglucosan (1,6-anhydro-b-D-glucopyranose) to evaluate the impacts of biomass combustion on ambient concentrations. Twenty-four-hour levoglucosan concentrations displayed clear summer minima and winter maxima that ranged from 46 to 1889 ng m 3, with an average of 428 399 ng m 3. Besides agricultural burning, biomass/biofuel combustion for household heating with straws and branches appears to be of regional importance during the heating season in northwestern China. Good correlations (0.70 &lt; R &lt; 0.91) were found between levoglucosan relative to watersoluble K&thorn;, Cl , organic carbon (OC), elemental carbon (EC), and glyoxal. The highest levoglucosan/OC ratio of 2.3% was found in winter, followed by autumn (1.5%). Biomass burning contributed to 5.1&ndash;43.8% of OC (with an average of 17.6 8.4%).</p

Biases in ketone measurements using DNPH-coated solid sorbent cartridges

Biases associated with carbonyl measurement using active air sampling through a 2,4-dinitrophenylhydrazine (DNPH)-coated solid sorbent cartridge following the U.S. EPA Method TO-11A are known but have not been fully investigated. Ketones are less reactive than aldehydes in the derivatization with DNPH, resulting in poor collection efficiency. Field studies and laboratory experiments demonstrate the uncertainties associated with two ketones (i.e., acetone and methyl ethyl ketone [MEK]). Ketone collection efficiencies are inversely related to relative humidity (RH), sample flow rate, and sample duration. Since water is a product in the bidirectional derivatization of carbonyls, the reverse reaction competes with the forward reaction as RH increases. Laboratory experiments demonstrate that similar to 35-80% of the ketones can be lost for RH &gt; 50% with a single DNPH cartridge at a temperature of 22 +/- 2 degrees C. Optimal sampling flow rates and sampling durations under high RH need to be determined in various environments to ensure tolerable collection efficiencies.</p

Winter and Summer PM2.5 Chemical Compositions in Fourteen Chinese Cities

PM2.5 in 14 of China&#39;s large cities achieves high concentrations in both winter and summer with averages &gt; 100 mu g m(-3) being common occurrences. A grand average of 115 mu g m(-3) was found for all cities, with a minimum of 27 mu g m(-3) measured at Qingdao during summer and a maximum of 356 mu g m(-3) at Xi&#39;an during winter. Both primary and secondary PM2.5 are important contributors at all of the cities and during both winter and summer. While ammonium sulfate is a large contributor during both seasons, ammonium nitrate contributions are much larger during winter. Lead levels are still high in several cities, reaching an average of 1.68 mu g m(-3) in Xi&#39;an. High correlations of lead with arsenic and sulfate concentrations indicate that much of it derives from coal combustion, rather than leaded fuels, which were phased out by calendar year 2000. Although limited fugitive dust markers were available, scaling of iron by its ratios in source profiles shows similar to 20% of PM2.5 deriving from fugitive dust in most of the cities. Multipollutant control strategies will be needed that address incomplete combustion of coal and biomass, engine exhaust, and fugitive dust, as well as sulfur dioxide, oxides of nitrogen, and ammonia gaseous precursors for ammonium sulfate and ammonium nitrate.</p

Impacts of aerosol compositions on visibility impairment in Xi'an, China

Daily particle light scattering coefficient, PM2.5 mass and chemical composition were measured in Xi&#39;an from February to December 2009. Visibility was strongly affected by anthropogenic air pollution sources, resulting in an average visual range (VR) of 6.4 &plusmn; 4.5 km. The threshold PM2.5 mass concentration, corresponding to VR &lt;10 km, was &sim;88 &mu;g m&minus;3. The revised IMPROVE equation was applied to estimate chemical extinction (bext), which on average was &sim;15% lower than measured bext. PM2.5 ammonium sulfate was the largest contributor, accounting for &sim;40% of bext, followed by organic matter (&sim;24%), ammonium nitrate (&sim;23%), and elemental carbon (&sim;9%), with minor contributions from soil dust (&sim;3%), and NO2 (&sim;1%). High secondary inorganic aerosol contributions (i.e., SO42&minus; and NO3&minus;) were the main contributors for VR &lt;5 km. A Positive Matrix Factorization (PMF) solution to the Chemical Mass Balance (CMB) receptor model showed that coal combustion was the dominant factor, accounting for &sim;52% of the dry particle light scattering coefficient, followed by the engine exhaust factor (&sim;31%). Other factors included biomass burning (&sim;12%) and fugitive dust (&sim;5%).</p