46 research outputs found

    Black Carbon Concentrations and Sources in the Marine Boundary Layer of the Tropical Atlantic Ocean using Four Methodologies

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    Combustion-derived aerosols in the marine boundary layer have been poorly studied, especially in remote environments such as the open Atlantic Ocean. The tropical Atlantic has the potential to contain a high concentration of aerosols, such as black carbon, due to the African emission plume of biomass and agricultural burning products. Atmospheric particulate matter samples across the tropical Atlantic boundary layer were collected in the summer of 2010 during the southern hemispheric dry season when open fire events were frequent in Africa and South America. The highest black carbon concentrations were detected in the Caribbean Sea and within the African plume, with a regional average of 0.6 μg m−3 for both. The lowest average concentrations were measured off the coast of South America at 0.2 to 0.3 μg m−3. Samples were quantified for black carbon using multiple methods to provide insights into the form and stability of the carbonaceous aerosols (i.e., thermally unstable organic carbon, soot like, and charcoal like). Soot-like aerosols composed up to 45% of the carbonaceous aerosols in the Caribbean Sea to as little as 4% within the African plume. Charcoal-like aerosols composed up to 29% of the carbonaceous aerosols over the oligotrophic Sargasso Sea, suggesting that non-soot-like particles could be present in significant concentrations in remote environments. To better apportion concentrations and forms of black carbon, multiple detection methods should be used, particularly in regions impacted by biomass burning emissions

    Physical–chemical characterisation of the particulate matter inside\ud two road tunnels in the São Paulo Metropolitan Area

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    The notable increase in biofuel usage by the road\ud transportation sector in Brazil during recent years has significantly\ud altered the vehicular fuel composition. Consequently,\ud many uncertainties are currently found in particulate\ud matter vehicular emission profiles. In an effort to better\ud characterise the emitted particulate matter, measurements\ud of aerosol physical and chemical properties were undertaken\ud inside two tunnels located in the São Paulo Metropolitan\ud Area (SPMA). The tunnels show very distinct fleet profiles:\ud in the Jânio Quadros (JQ) tunnel, the vast majority\ud of the circulating fleet are light duty vehicles (LDVs), fuelled\ud on average with the same amount of ethanol as gasoline.\ud In the Rodoanel (RA) tunnel, the particulate emission\ud is dominated by heavy duty vehicles (HDVs) fuelled with\ud diesel (5% biodiesel). In the JQ tunnel, PM2.5 concentration\ud was on average 52 μgm−3, with the largest contribution\ud of organic mass (OM, 42 %), followed by elemental carbon\ud (EC, 17 %) and crustal elements (13 %). Sulphate accounted\ud for 7% of PM2.5 and the sum of other trace elements\ud was 10%. In the RA tunnel, PM2.5 was on average\ud 233 μgm−3, mostly composed of EC (52 %) and OM\ud (39 %). Sulphate, crustal and the trace elements showed a\ud minor contribution with 5 %, 1 %, and 1 %, respectively. The\ud average OC: EC ratio in the JQ tunnel was 1.59±0.09, indicating\ud an important contribution of EC despite the high\ud ethanol fraction in the fuel composition. In the RA tunnel,\ud the OC: EC ratio was 0.49±0.12, consistent with previous\ud measurements of diesel-fuelled HDVs. Besides bulk carbonaceous\ud aerosol measurement, polycyclic aromatic hydrocarbons\ud (PAHs) were quantified. The sum of the PAHs concentration\ud was 56±5 ngm−3 and 45±9 ngm−3 in the RA\ud and JQ tunnel, respectively. In the JQ tunnel, benzo(a)pyrene\ud (BaP) ranged from 0.9 to 6.7 ngm−3 (0.02–0. 1‰of PM2.5)\ud whereas in the RA tunnel BaP ranged from 0.9 to 4.9 ngm−3\ud (0.004–0. 02‰ of PM2.5), indicating an important relative\ud contribution of LDVs emission to atmospheric BaP.\ud Real-time measurements performed in both tunnels provided\ud aerosol size distributions and optical properties. The\ud average particle count yielded 73 000 cm−3 in the JQ tunnel\ud and 366 000 cm−3 in the RA tunnel, with an average diameter\ud of 48 nm in the former and 39 nm in the latter. Aerosol single\ud scattering albedo, calculated from scattering and absorption\ud observations in the JQ tunnel, indicates a value of 0.5 associated\ud with LDVs. Such single scattering albedo is 20–50%\ud higher than observed in previous tunnel studies, possibly as a\ud result of the large biofuel usage. Given the exceedingly high\ud equivalent black carbon loadings in the RA tunnel, real time\ud light absorption measurements were possible only in the JQ\ud tunnel. Nevertheless, using EC measured from the filters, a\ud single scattering albedo of 0.31 for the RA tunnel has been\ud estimated. The results presented here characterise particulate\ud matter emitted from nearly 1 million vehicles fuelled with a\ud considerable amount of biofuel, providing a unique experimental\ud site worldwideFAPESP - 2008/58104-8CNPq - 402383/2009-

    Efficient control of atmospheric sulfate production based on three formation regimes

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    The formation of sulfate (SO₄²⁻) in the atmosphere is linked chemically to its direct precursor, sulfur dioxide (SO₂), through several key oxidation paths for which nitrogen oxides or NO_x (NO and NO₂) play essential roles. Here we present a coherent description of the dependence of SO₄²⁻ formation on SO₂ and NO_x under haze-fog conditions, in which fog events are accompanied by high aerosol loadings and fog-water pH in the range of 4.7–6.9. Three SO₄²⁻ formation regimes emerge as defined by the role played by NO_x. In the low-NO_x regime, NO_x act as catalyst for HO_x, which is a major oxidant for SO₂, whereas in the high-NO_x regime, NO₂ is a sink for HO_x. Moreover, at highly elevated NO_x levels, a so-called NO₂-oxidant regime exists in which aqueous NO₂ serves as the dominant oxidant of SO₂. This regime also exists under clean fog conditions but is less prominent. Sensitivity calculations using an emission-driven box model show that the reduction of SO₄²⁻ is comparably sensitive to the reduction of SO₂ and NO_x emissions in the NO₂-oxidant regime, suggesting a co-reduction strategy. Formation of SO₄²⁻ is relatively insensitive to NO_x reduction in the low-NO_x regime, whereas reduction of NO_x actually leads to increased SO₄²⁻ production in the intermediate high-NO_x regime

    A new comprehensive approach to characterizing carbonaceous aerosol with an application to wintertime Fresno, California PM<sub>2.5</sub>

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    International audienceFine particulate matter (PM2.5) samples were collected during a three week winter period in Fresno (CA). A composite sample was characterized by isolating several distinct fractions and characterizing them by infrared and nuclear magnetic resonance (NMR) spectroscopy. More than 80% of the organic matter in the aerosol samples was recovered and characterized. Only 35% of the organic matter was water soluble with another third soluble in dichloromethane and the remainder insoluble. Within the isolated water soluble material, hydrophobic acid and hydrophilic acids plus neutrals fractions contained the largest amounts of carbon. The hydrophobic acids fraction appears to contain significant amounts of lignin type structures, spectra of the hydrophilic acids plus neutrals fraction are indicative of carbohydrates and secondary organic material. The dichloromethane soluble fraction contains a variety of organic compound families typical of many previous studies of organic aerosol speciation, including alkanes, alkanols, alkanals and alkanoic acids. Finally the water and solvent insoluble fraction exhibits a strong aromaticity as one would expect from black or elemental carbon like material; however, these spectra also show a substantial amount of aliphaticity consistent with linear side chains on the aromatic structures

    Chemical mass balance source apportionment of fine and PM<sub>10</sub> in the Desert Southwest, USA

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    The Desert Southwest Coarse Particulate Matter Study was undertaken in Pinal County, Arizona, to better understand the origin and impact of sources of fine and coarse particulate matter (PM) in rural, arid regions of the U.S. southwestern desert. The desert southwest experiences some of the highest PM10 mass concentrations in the country. To augment previously reported results, 6-week aggregated organic speciation data that included ambient concentrations of n-alkanes, polycyclic aromatic hydrocarbons, organic acids, and saccharides were used in chemical mass balance modeling (CMB). A set of re-suspended soil samples were analyzed for specific marker species to provide locally-appropriate source profiles for the CMB analysis. These profiles, as well as previously collected plant and fungal spore profiles from the region, were combined with published source profiles for other relevant sources and used in the CMB analysis. The six new region-specific source profiles included both organic and inorganic species for four crustal material sources, one plant detritus source, and one fungal spore source.Results indicate that up to half of the ambient PM2.5 was apportioned to motor vehicles with the highest regional contribution observed in the small urban center of Casa Grande. Daily levels of apportioned crustal material accounted for up to 50% of PM2.5 mass with the highest contributions observed at the sites closest to active agricultural areas. Apportioned secondary PM, biomass burning, and road dust typically contributed less than 35% as a group to the apportioned PM2.5 mass. Crustal material was the primary source apportioned to PM10 and accounted for between 50–90% of the apportioned mass. Of the other sources apportioned to PM10, motor vehicles and road dust were the largest contributors at the urban and one of the rural sites, whereas road dust and meat cooking operations were the largest contributors at the other rural site
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