Wood smoke contribution to ambient aerosol in Fresno during winter 2003-2004

Includes bibliographical references.Sponsored by San Joaquin Valley-Wide Air Pollution Study Agency NSF ATM-0222607

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

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

Characterization of carbonaceous aerosol during the Big Bend Regional Aerosol and Visibility Observational study

December 2001.Includes bibliographical references.The Big Bend Regional Aerosol and Visibility Observational (BRAVO) study was a four month field campaign (July-October 1999) to investigate aerosol particle properties, sources, and impacts on regional visibility in Big Bend National Park, Texas. Daily PM2.5 aerosol samples were collected on pre-fired quartz fiber filters for detailed molecular analysis of the aerosol organic carbon fraction. Aerosol black carbon concentrations during BRAVO were measured with an aethalometer. The molecular characterization of the organic carbon fraction of aerosol present during the BRAVO study was performed using gas chromatography - mass spectroscopy (GC-MS). Organic carbon concentrations on individual days were too low for a detailed analysis by GC-MS. Therefore, multi-day composite samples, selected based on common air mass trajectories and temporal proximity, were extracted and analyzed for numerous compounds, including n-alkanes, polycyclic aromatic hydrocarbons (PAH), and alkanoic acids. Low alkane Carbon Preference Indices (CPIs) during July through September reflect similar concentrations of n-alkanes containing odd and even numbers of carbon atoms and indicate that anthropogenic emissions were important contributors to carbonaceous aerosol during this period, when air masses generally were advected from the east over Texas and Mexico. In October, CPIs increased, reflecting increased influence of odd carbon numbered alkanes and suggesting a predominant biogenic aerosol influence with air masses arriving from the north and the south. Plant wax contributions to odd carbon number alkanes (C25-C33) were estimated to range between 26% and 78%, with the highest contributions occurring in October with air masses arriving from the north and south. Periods with transport from eastern Texas and northeastern Mexico had much smaller plant wax contributions. Alkanoic acids were the most abundant compound class, with CPIs that were high throughout the study. The high acid CPI suggests that the alkanoic acids may be largely biogenic in origin, a finding consistent with other studies. Caution is required in interpreting the acid CPI, however, as alkanoic acids can also be formed as secondary products of atmospheric reactions. Polycyclic aromatic hydrocarbons (P AH) were usually not found in abundance, suggesting that upwind combustion emissions were not important contributors to carbonaceous aerosol or that P AH were removed by reaction or deposition in transit. Higher P AH concentrations during one period indicated a more significant contribution from fresh combustion emissions. Molecular source tracer (hopanes for vehicle emissions, levoglucosan for wood combustion, cholesterol for meat cooking) concentrations were generally not detected. Based on analytical detection limits for these species, it was estimated that wood smoke contributed no more than 1% of the total Organic Carbon (OC) present, vehicle exhaust contributed no more than 4%, and smoke from meat cooking contributed less than 13%. The presence of other wood smoke tracer molecules, however, suggests a possibly greater influence from wood combustion and possible chemical instability of levoglucosan during multi-day transport in an acidic atmosphere. Several observations suggest that secondary production contributed significantly to BRAVO carbonaceous aerosol. Examination of ratios of aerosol organic carbon to elemental carbon indicates that secondary organic aerosol may have contributed between 45% and 90% of the total BRAVO aerosol organic carbon. High ratios of saturated/unsaturated C18 acids, an abundance of nonanoic acid, and high concentrations of 6,10,14 trimethylpentadecan-2-one (an indicator of secondary aerosol production from vegetation emissions) all support the conclusion that secondary aerosol formation was important in the region. Total black carbon (BC) concentrations ranged from below detection limit (71 ng/m3) to 267 ng/m3, averaging 129 ng/m3. Fine (< 1 μm) aerosol BC concentrations averaged 114 ng/m3, and comprised 89% of the total BC. BC concentrations correlated reasonably well with aerosol sulfate concentrations, suggesting similar source regions for these species.Funding agency: National Park Service #CA2350-97-001 T098-07, #CA2380-99-001 T001-52

Chemical characterization of organic particulate matter from on-road traffic in Sao Paulo, Brazil

This study reports emission of organic particulate matter by light-duty vehicles (LDVs) and heavy-duty vehicles (HDVs) in the city of São Paulo, Brazil, where vehicles run on three different fuel types: gasoline with 25 % ethanol (called gasohol, E25), hydrated ethanol (E100), and diesel (with 5 % biodiesel). The experiments were performed at two tunnels: Jânio Quadros (TJQ), where 99 % of the vehicles are LDVs, and RodoAnel Mário Covas (TRA), where up to 30 % of the fleet are HDVs. Fine particulate matter (PM2.5) samples were collected on quartz filters in May and July 2011 at TJQ and TRA, respectively. The samples were analyzed by thermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) and by thermal–optical transmittance (TOT). Emission factors (EFs) for organic aerosol (OA) and organic carbon (OC) were calculated for the HDV and the LDV fleet. We found that HDVs emitted more PM2.5 than LDVs, with OC EFs of 108 and 523 mg kg−1 burned fuel for LDVs and HDVs, respectively. More than 700 ions were identified by TD-PTR-MS and the EF profiles obtained from HDVs and LDVs exhibited distinct features. Unique organic tracers for gasoline, biodiesel, and tire wear have been tentatively identified. nitrogen-containing compounds contributed around 20 % to the EF values for both types of vehicles, possibly associated with incomplete fuel burning or fast secondary production. Additionally, 70 and 65 % of the emitted mass (i.e. the OA) originates from oxygenated compounds from LDVs and HDVs, respectively. This may be a consequence of the high oxygen content of the fuel. On the other hand, additional oxygenation may occur during fuel combustion. The high fractions of nitrogen- and oxygen-containing compounds show that chemical processing close to the engine / tailpipe region is an important factor influencing primary OA emission. The thermal-desorption analysis showed that HDVs emitted compounds with higher volatility, and with mainly oxygenated and longer chain hydrocarbons than LDVs

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

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

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

Levoglucosan and phenols in Antarctic marine, coastal and plateau aerosols

Due to its isolated location, Antarctica is a natural laboratory for studying atmospheric aerosols and pollution in remote areas. Here, we determined levoglucosan and phenolic compounds (PCs) at diverse Antarctic sites: on the plateau, a coastal station and during an oceanographic cruise. Levoglucosan and PCs reached the Antarctic plateau where they were observed in accumulation mode aerosols (with median levoglucosan concentrations of 6.4 pgm(-3) and 4.1 pgm(-3), and median PC concentrations of 15.0 pgm(-3) and 7.3 pgm(-3)). Aged aerosols arrived at the coastal site through katabatic circulation with the majority of the levoglucosan mass distributed on larger particulates (24.8 pgm(-3)), while PCs were present in fine particles (34.0 pgm(-3)). The low levoglucosan/PC ratios in Antarctic aerosols suggest that biomass burning aerosols only had regional, rather than local, sources. General acid/aldehyde ratios were lower at the coastal site than on the plateau. Levoglucosan and PCs determined during the oceanographic cruise were 37.6 pgm(-3) and 58.5 pgm(-3) respectively. Unlike levoglucosan, which can only be produced by biomass burning, PCs have both biomass burning and other sources. Our comparisons of these two types of compounds across a range of Antarctic marine, coastal, and plateau sites demonstrate that local marine sources dominate Antarctic PC concentrations. (C) 2015 Elsevier B.V. All rights reserved

A new comprehensive approach to characterizing carbonaceous aerosol with an application to wintertime Fresno, California PM_2.5

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