25 research outputs found
SOA formation from the atmospheric oxidation of 2-methyl-3-buten-2-ol and its implications for PM<sub>2.5</sub>
The formation of secondary organic aerosol (SOA) generated by irradiating 2-methyl-3-buten-2-ol (MBO) in the presence and/or absence of NO<sub>x</sub>, H<sub>2</sub>O<sub>2</sub>, and/or SO<sub>2</sub> was examined. Experiments were conducted in smog chambers operated in either dynamic or static mode. A filter/denuder sampling system was used for simultaneously collecting gas- and particle-phase products. The structural characterization of gas and particulate products was investigated using BSTFA, BSTFA + PFBHA, and DNPH derivatization techniques followed by GC-MS and liquid chromatography analysis. This analysis showed the occurrence of more than 68 oxygenated organic compounds in the gas and particle phases, 28 of which were tentatively identified. The major components observed include 2,3-dihydroxyisopentanol (DHIP), 2-hydroxy-2-oxoisopentanol, 2,3-dihydroxy-3-methylbutanal, 2,3-dihydroxy-2-methylsuccinic acid, 2-hydroxy-2-methylpropanedioic acid, acetone, glyoxal, methylglyoxal, glycolaldehyde, and formaldehyde. Most of these oxygenated compounds were detected for the first time in this study. <br><br> While measurements of the gas-phase photooxidation products have been made, the focus of this work has been an examination of the particle phase. SOA from some experiments was analyzed for the organic mass to organic carbon ratio (OM/OC), the effective enthalpy of vaporization (ΔH<sub>vap</sub><sup>eff</sup>), and the aerosol yield. Additionally, aerosol size, volume, and number concentrations were measured by a Scanning Mobility Particle Sizer coupled to a Condensation Particle Counter system. The OM/OC ratio was 2.1 in the MBO/H<sub>2</sub>O<sub>2</sub> system. The ΔH<sub>vap</sub><sup>eff</sup> was 41 kJ mol<sup>−1</sup>, a value similar to that of isoprene SOA. The laboratory SOA yield measured in this study was 0.7% in MBO/H<sub>2</sub>O<sub>2</sub> for an aerosol mass of 33 μg m<sup>−3</sup>. Secondary organic aerosol was found to be negligible under conditions with oxides of nitrogen (NO<sub>x</sub>) present. Time profiles and proposed reaction schemes are provided for selected compounds. <br><br> The contribution of SOA products from MBO oxidation to ambient PM<sub>2.5</sub> was investigated by analyzing a series of ambient PM<sub>2.5</sub> samples collected in several places around the United States. In addition to the occurrence of several organic compounds in both field and laboratory samples, DHIP was found to originate only from the oxidation of MBO, and therefore this compound could potentially serve as a tracer for MBO SOA. Initial attempts have been made to quantify the concentrations of DHIP and other compounds based on surrogate compound calibrations. The average concentrations of DHIP in ambient PM<sub>2.5</sub> samples from Duke Forest in North Carolina ranged from zero during cold seasons to approximately 1 ng m<sup>−3</sup> during warm seasons. This appears to be the first time that DHIP has been detected in ambient PM<sub>2.5</sub> samples. The occurrence of several other compounds in both laboratory and field samples suggests that SOA originating from MBO can contribute under selected ambient conditions to the ambient aerosol mainly in areas where MBO emissions are high
Airborne Emissions from 1961 to 2004 of Benzo[a]pyrene from U.S. Vehicles per km of Travel Based on Tunnel Studies
We identified 13 historical measurements of polycyclic aromatic hydrocarbons (PAHs) in U.S. vehicular traffic tunnels that were either directly presented as tailpipe emission factors in μg per vehicle-kilometer or convertible to such a form. Tunnel measurements capture fleet cruise emissions. Emission factors for benzo[a]pyrene (BaP) for a tunnel fleet operating under cruise conditions were highest prior to the 1980s and fell from more than 30-μg per vehicle-km to approximately 2-μg/km in the 1990s, an approximately 15-fold decline. Total annual U.S. (cruise) emissions of BaP dropped by a lesser factor, because total annual km driven increased by a factor of 2.7 during the period. Other PAH compounds measured in tunnels over the 40-year period (e.g., benzo[ghi]perylene, coronene) showed comparable reduction factors in emissions. PAH declines were comparable to those measured in tunnels for carbon monoxide, volatile organic compounds, and particulate organic carbon. The historical PAH “source terms” determined from the data are relevant to quantifying the benefits of emissions control technology and can be used in epidemiological studies evaluating the health effects of exposure, such as those undertaken with breast cancer in New York State
Emissions of organic carbon and methane from petroleum and dairy operations in California's San Joaquin Valley
Petroleum and dairy operations are prominent sources of gas-phase organic compounds in California's San Joaquin Valley. It is essential to understand the emissions and air quality impacts of these relatively understudied sources, especially for oil/gas operations in light of increasing US production. Ground site measurements in Bakersfield and regional aircraft measurements of reactive gas-phase organic compounds and methane were part of the CalNex (California Research at the Nexus of Air Quality and Climate Change) project to determine the sources contributing to regional gas-phase organic carbon emissions. Using a combination of near-source and downwind data, we assess the composition and magnitude of emissions, and provide average source profiles. To examine the spatial distribution of emissions in the San Joaquin Valley, we developed a statistical modeling method using ground-based data and the FLEXPART-WRF transport and meteorological model. We present evidence for large sources of paraffinic hydrocarbons from petroleum operations and oxygenated compounds from dairy (and other cattle) operations. In addition to the small straight-chain alkanes typically associated with petroleum operations, we observed a wide range of branched and cyclic alkanes, most of which have limited previous in situ measurements or characterization in petroleum operation emissions. Observed dairy emissions were dominated by ethanol, methanol, acetic acid, and methane. Dairy operations were responsible for the vast majority of methane emissions in the San Joaquin Valley; observations of methane were well correlated with non-vehicular ethanol, and multiple assessments of the spatial distribution of emissions in the San Joaquin Valley highlight the dominance of dairy operations for methane emissions. The petroleum operations source profile was developed using the composition of non-methane hydrocarbons in unrefined natural gas associated with crude oil. The observed source profile is consistent with fugitive emissions of condensate during storage or processing of associated gas following extraction and methane separation. Aircraft observations of concentration hotspots near oil wells and dairies are consistent with the statistical source footprint determined via our FLEXPART-WRF-based modeling method and ground-based data. We quantitatively compared our observations at Bakersfield to the California Air Resources Board emission inventory and find consistency for relative emission rates of reactive organic gases between the aforementioned sources and motor vehicles in the region. We estimate that petroleum and dairy operations each comprised 22% of anthropogenic non-methane organic carbon at Bakersfield and were each responsible for 8–13% of potential precursors to ozone. Yet, their direct impacts as potential secondary organic aerosol (SOA) precursors were estimated to be minor for the source profiles observed in the San Joaquin Valley
Modeling the concentrations of gas-phase toxic organic air pollutants: direct emissions and atmospheric formation
Separation of fine particulate matter emitted from gasoline and diesel vehicles using chemical mass balancing techniques
Separation of Fine Particulate Matter Emitted from Gasoline and Diesel Vehicles Using Chemical Mass Balancing Techniques
Emissions of organic carbon and methane from petroleum and dairy operations in California's San Joaquin Valley
Petroleum and dairy operations are prominent sources of gas-phase organic
compounds in California's San Joaquin Valley. It is essential to understand
the emissions and air quality impacts of these relatively understudied
sources, especially for oil/gas operations in light of increasing US
production. Ground site measurements in Bakersfield and regional aircraft
measurements of reactive gas-phase organic compounds and methane were part
of the CalNex (California Research at the Nexus of Air Quality and Climate
Change) project to determine the sources contributing to regional gas-phase
organic carbon emissions. Using a combination of near-source and downwind
data, we assess the composition and magnitude of emissions, and provide
average source profiles. To examine the spatial distribution of emissions in
the San Joaquin Valley, we developed a statistical modeling method using ground-based data and the
FLEXPART-WRF transport and meteorological model. We
present evidence for large sources of paraffinic hydrocarbons from petroleum
operations and oxygenated compounds from dairy (and other cattle)
operations. In addition to the small straight-chain alkanes typically
associated with petroleum operations, we observed a wide range of branched
and cyclic alkanes, most of which have limited previous in situ measurements
or characterization in petroleum operation emissions. Observed dairy
emissions were dominated by ethanol, methanol, acetic acid, and methane.
Dairy operations were responsible for the vast majority of methane emissions
in the San Joaquin Valley; observations of methane were well correlated with
non-vehicular ethanol, and multiple assessments of the spatial distribution
of emissions in the San Joaquin Valley highlight the dominance of dairy
operations for methane emissions. The petroleum operations source profile
was developed using the composition of non-methane hydrocarbons in unrefined
natural gas associated with crude oil. The observed source profile is
consistent with fugitive emissions of condensate during storage or
processing of associated gas following extraction and methane separation.
Aircraft observations of concentration hotspots near oil wells and dairies
are consistent with the statistical source footprint determined via our
FLEXPART-WRF-based modeling method and ground-based data. We quantitatively
compared our observations at Bakersfield to the California Air Resources
Board emission inventory and find consistency for relative emission rates of
reactive organic gases between the aforementioned sources and motor vehicles
in the region. We estimate that petroleum and dairy operations each
comprised 22% of anthropogenic non-methane organic carbon at Bakersfield
and were each responsible for 8–13% of potential precursors to ozone.
Yet, their direct impacts as potential secondary organic aerosol (SOA)
precursors were estimated to be minor for the source profiles observed in
the San Joaquin Valley