10 research outputs found
BTEX exposures in an area impacted by industrial and mobile sources: Source attribution and impact of averaging time
<p>The impacts of emissions plumes from major industrial sources on black carbon (BC) and BTEX (benzene, toluene, ethyl benzene, xylene isomers) exposures in communities located >10 km from the industrial source areas were identified with a combination of stationary measurements, source identification using positive matrix factorization (PMF), and dispersion modeling. The industrial emissions create multihour plume events of BC and BTEX at the measurement sites. PMF source apportionment, along with wind patterns, indicates that the observed pollutant plumes are the result of transport of industrial emissions under conditions of low boundary layer height. PMF indicates that industrial emissions contribute >50% of outdoor exposures of BC and BTEX species at the receptor sites. Dispersion modeling of BTEX emissions from known industrial sources predicts numerous overnight plumes and overall qualitative agreement with PMF analysis, but predicts industrial impacts at the measurement sites a factor of 10 lower than PMF. Nonetheless, exposures associated with pollutant plumes occur mostly at night, when residents are expected to be home but are perhaps unaware of the elevated exposure. Averaging data samples over long times typical of public health interventions (e.g., weekly or biweekly passive sampling) misapportions the exposure, reducing the impact of industrial plumes at the expense of traffic emissions, because the longer samples cannot resolve subdaily plumes. Suggestions are made for ways for future distributed pollutant mapping or intervention studies to incorporate high time resolution tools to better understand the potential impacts of industrial plumes.</p> <p><i>Implications</i>: Emissions from industrial or other stationary sources can dominate air toxics exposures in communities both near the source and in downwind areas in the form of multihour plume events. Common measurement strategies that use highly aggregated samples, such as weekly or biweekly averages, are insensitive to such plume events and can lead to significant under apportionment of exposures from these sources.</p
Urban Organic Aerosol Exposure: Spatial Variations in Composition and Source Impacts
We
conducted a mobile sampling campaign in a historically industrialized
terrain (Pittsburgh, PA) targeting spatial heterogeneity of organic
aerosol. Thirty-six sampling sites were chosen based on stratification
of traffic, industrial source density, and elevation. We collected
organic carbon (OC) on quartz filters, quantified different OC components
with thermal-optical analysis, and grouped them based on volatility
in decreasing order (OC1, OC2, OC3, OC4, and pyrolyzed carbon (PC)).
We compared our ambient OC concentrations (both gas and particle phase)
to similar measurements from vehicle dynamometer tests, cooking emissions,
biomass burning emissions, and a highway traffic tunnel. OC2 and OC3
loading on ambient filters showed a strong correlation with primary
emissions while OC4 and PC were more spatially homogeneous. While
we tested our hypothesis of OC2 and OC3 as markers of fresh source
exposure for Pittsburgh, the relationship seemed to hold at a national
level. Land use regression (LUR) models were developed for the OC
fractions, and models had an average <i>R</i><sup>2</sup> of 0.64 (SD = 0.09). The paper demonstrates that OC2 and OC3 can
be useful markers for fresh emissions, OC4 is a secondary OC indicator,
and PC represents both biomass burning and secondary aerosol. People
with higher OC exposure are likely inhaling more fresh OC2 and OC3,
since secondary OC4 and PC varies much less drastically in space or
with local primary sources
Estimating ambient particulate organic carbon concentrations and partitioning using thermal optical measurements and the volatility basis set
<p>We introduce a new method to estimate the mass concentration of particulate organic carbon (POC) collected on quartz filters, demonstrating it using quartz-filter samples collected in greater Pittsburgh. This method combines thermal-optical organic carbon and elemental carbon (OC/EC) analysis and the volatility basis set (VBS) to quantify the mass concentration of semi-volatile POC on the filters. The dataset includes ambient samples collected at a number of sites in both summer and winter as well as samples from a highway tunnel. As a reference we use the two-filter bare-Quartz minus Quartz-Behind-Teflon (Q-QBT) approach to estimate the adsorbed gaseous fraction of organic carbon (OC), finding a substantial fraction in both the gas and particle phases under all conditions. In the new method we use OC fractions measured during different temperature stages of the OC/EC analysis for the single bare-quartz (BQ) filter in combination with partitioning theory to predict the volatility distributions of the measured OC, which we describe with the VBS. The effective volatility bins are consistent for data from both ambient samples and primary organic aerosol (POA)-enriched tunnel samples. Consequently, with the VBS model and total OC fractions measured over different heating stages, particulate OC can be determined by using the BQ filter alone. This method can thus be applied to all quartz filter-based OC/EC analyses to estimate the POC concentration without using backup filters.</p> <p>© 2016 American Association for Aerosol Research</p
Effects of Particle Filters and Selective Catalytic Reduction on Heavy-Duty Diesel Drayage Truck Emissions at the Port of Oakland
Effects
of fleet modernization and use of diesel particle filters
(DPF) and selective catalytic reduction (SCR) on heavy-duty diesel
truck emissions were studied at the Port of Oakland in California.
Nitrogen oxides (NO<sub><i>x</i></sub>), black carbon (BC),
particle number (PN), and size distributions were measured in the
exhaust plumes of ∼1400 drayage trucks. Average NO<sub><i>x</i></sub>, BC, and PN emission factors for newer engines (2010–2013
model years) equipped with both DPF and SCR were 69 ± 15%, 92
± 32%, and 66 ± 35% lower, respectively, than 2004–2006
engines without these technologies. Intentional oxidation of NO to
NO<sub>2</sub> for DPF regeneration increased tailpipe NO<sub>2</sub> emissions, especially from older (1994–2006) engines with
retrofit DPFs. Increased deployment of advanced controls has further
skewed emission factor distributions; a small number of trucks emit
a disproportionately large fraction of total BC and NO<sub><i>x</i></sub>. The fraction of DPF-equipped drayage trucks increased
from 2 to 99% and the median engine age decreased from 11 to 6 years
between 2009 and 2013. Over this period, fleet-average BC and NO<sub><i>x</i></sub> emission factors decreased by 76 ±
22% and 53 ± 8%, respectively. Emission changes occurred rapidly
compared to what would have been observed due to natural (i.e., unforced)
turnover of the Port truck fleet. These results provide a preview
of more widespread emission changes expected statewide and nationally
in the coming years
Effects of Particle Filters and Selective Catalytic Reduction on Heavy-Duty Diesel Drayage Truck Emissions at the Port of Oakland
Effects
of fleet modernization and use of diesel particle filters
(DPF) and selective catalytic reduction (SCR) on heavy-duty diesel
truck emissions were studied at the Port of Oakland in California.
Nitrogen oxides (NO<sub><i>x</i></sub>), black carbon (BC),
particle number (PN), and size distributions were measured in the
exhaust plumes of ∼1400 drayage trucks. Average NO<sub><i>x</i></sub>, BC, and PN emission factors for newer engines (2010–2013
model years) equipped with both DPF and SCR were 69 ± 15%, 92
± 32%, and 66 ± 35% lower, respectively, than 2004–2006
engines without these technologies. Intentional oxidation of NO to
NO<sub>2</sub> for DPF regeneration increased tailpipe NO<sub>2</sub> emissions, especially from older (1994–2006) engines with
retrofit DPFs. Increased deployment of advanced controls has further
skewed emission factor distributions; a small number of trucks emit
a disproportionately large fraction of total BC and NO<sub><i>x</i></sub>. The fraction of DPF-equipped drayage trucks increased
from 2 to 99% and the median engine age decreased from 11 to 6 years
between 2009 and 2013. Over this period, fleet-average BC and NO<sub><i>x</i></sub> emission factors decreased by 76 ±
22% and 53 ± 8%, respectively. Emission changes occurred rapidly
compared to what would have been observed due to natural (i.e., unforced)
turnover of the Port truck fleet. These results provide a preview
of more widespread emission changes expected statewide and nationally
in the coming years
Gas-Particle Partitioning of Vehicle Emitted Primary Organic Aerosol Measured in a Traffic Tunnel
We
measured the gas-particle partitioning of vehicle emitted primary
organic aerosol (POA) in a traffic tunnel with three independent methods:
artifact corrected bare-quartz filters, thermodenuder (TD) measurements,
and thermal-desorption gas-chromatography mass-spectrometry (TD-GC-MS).
Results from all methods consistently show that vehicle emitted POA
measured in the traffic tunnel is semivolatile under a wide range
of fleet compositions and ambient conditions. We compared the gas-particle
partitioning of POA measured in both tunnel and dynamometer studies
and found that volatility distributions measured in the traffic tunnel
are similar to volatility distributions measured in the dynamometer
studies, and predict similar gas-particle partitioning in the TD.
These results suggest that the POA volatility distribution measured
in the dynamometer studies can be applied to describe gas-particle
partitioning of ambient POA emissions. The POA volatility distribution
measured in the tunnel does not have significant diurnal or seasonal
variations, which indicate that a single volatility distribution is
adequate to describe the gas-particle partitioning of vehicle emitted
POA in the urban environment
Chemical Composition of Gas-Phase Organic Carbon Emissions from Motor Vehicles and Implications for Ozone Production
Motor vehicles are
major sources of gas-phase organic carbon, which includes volatile
organic compounds (VOCs) and other compounds with lower vapor pressures.
These emissions react in the atmosphere, leading to the formation
of ozone and secondary organic aerosol (SOA). With more chemical detail
than previous studies, we report emission factors for over 230 compounds
from gasoline and diesel vehicles via two methods. First we use speciated
measurements of exhaust emissions from on-road vehicles in summer
2010. Second, we use a fuel composition-based approach to quantify
uncombusted fuel components in exhaust using the emission factor for
total uncombusted fuel in exhaust together with detailed chemical
characterization of liquid fuel samples. There is good agreement between
the two methods except for products of incomplete combustion, which
are not present in uncombusted fuels and comprise 32 ± 2% of
gasoline exhaust and 26 ± 1% of diesel exhaust by mass. We calculate
and compare ozone production potentials of diesel exhaust, gasoline
exhaust, and nontailpipe gasoline emissions. Per mass emitted, the
gas-phase organic compounds in gasoline exhaust have the largest potential
impact on ozone production with over half of the ozone formation due
to products of incomplete combustion (e.g., alkenes and oxygenated
VOCs). When combined with data on gasoline and diesel fuel sales in
the U.S., these results indicate that gasoline sources are responsible
for 69–96% of emissions and 79–97% of the ozone formation
potential from gas-phase organic carbon emitted by motor vehicles
Ethylene Glycol Emissions from On-road Vehicles
Ethylene glycol (HOCH<sub>2</sub>CH<sub>2</sub>OH), used as engine
coolant for most on-road vehicles, is an intermediate volatility organic
compound (IVOC) with a high Henry’s law coefficient. We present
measurements of ethylene glycol (EG) vapor in the Caldecott Tunnel
near San Francisco, using a proton transfer reaction mass spectrometer
(PTR-MS). Ethylene glycol was detected at mass-to-charge ratio 45,
usually interpreted as solely coming from acetaldehyde. EG concentrations
in bore 1 of the Caldecott Tunnel, which has a 4% uphill grade, were
characterized by infrequent (approximately once per day) events with
concentrations exceeding 10 times the average concentration, likely
from vehicles with malfunctioning engine coolant systems. Limited
measurements in tunnels near Houston and Boston are not conclusive
regarding the presence of EG in sampled air. Previous PTR-MS measurements
in urban areas may have overestimated acetaldehyde concentrations
at times due to this interference by ethylene glycol. Estimates of
EG emission rates from the Caldecott Tunnel data are unrealistically
high, suggesting that the Caldecott data are not representative of
emissions on a national or global scale. EG emissions are potentially
important because they can lead to the formation of secondary organic
aerosol following oxidation in the atmospheric aqueous phase
Methane Emissions from Natural Gas Compressor Stations in the Transmission and Storage Sector: Measurements and Comparisons with the EPA Greenhouse Gas Reporting Program Protocol
Equipment-
and site-level methane emissions from 45 compressor
stations in the transmission and storage (T&S) sector of the US
natural gas system were measured, including 25 sites required to report
under the EPA greenhouse gas reporting program (GHGRP). Direct measurements
of fugitive and vented sources were combined with AP-42-based exhaust
emission factors (for operating reciprocating engines and turbines)
to produce a study onsite estimate. Site-level methane emissions were
also concurrently measured with downwind-tracer-flux techniques. At
most sites, these two independent estimates agreed within experimental
uncertainty. Site-level methane emissions varied from 2–880
SCFM. Compressor vents, leaky isolation valves, reciprocating engine
exhaust, and equipment leaks were major sources, and substantial emissions
were observed at both operating and standby compressor stations. The
site-level methane emission rates were highly skewed; the highest
emitting 10% of sites (including two superemitters) contributed 50%
of the aggregate methane emissions, while the lowest emitting 50%
of sites contributed less than 10% of the aggregate emissions. Excluding
the two superemitters, study-average methane emissions from compressor
housings and noncompressor sources are comparable to or lower than
the corresponding effective emission factors used in the EPA greenhouse
gas inventory. If the two superemitters are included in the analysis,
then the average emission factors based on this study could exceed
the EPA greenhouse gas inventory emission factors, which highlights
the potentially important contribution of superemitters to national
emissions. However, quantification of their influence requires knowledge
of the magnitude and frequency of superemitters across the entire
T&S sector. Only 38% of the methane emissions measured by the
comprehensive onsite measurements were reportable under the new EPA
GHGRP because of a combination of inaccurate emission factors for
leakers and exhaust methane, and various exclusions. The bias is
even larger if one accounts for the superemitters, which were not
captured by the onsite measurements. The magnitude of the bias varied
from site to site by site type and operating state. Therefore, while
the GHGRP is a valuable new source of emissions information, care
must be taken when incorporating these data into emission inventories.
The value of the GHGRP can be increased by requiring more direct measurements
of emissions (as opposed to using counts and emission factors), eliminating
exclusions such as rod-packing vents on pressurized reciprocating
compressors in standby mode under Subpart-W, and using more appropriate
emission factors for exhaust methane from reciprocating engines under
Subpart-C
Methane Emissions from Natural Gas Compressor Stations in the Transmission and Storage Sector: Measurements and Comparisons with the EPA Greenhouse Gas Reporting Program Protocol
Equipment-
and site-level methane emissions from 45 compressor
stations in the transmission and storage (T&S) sector of the US
natural gas system were measured, including 25 sites required to report
under the EPA greenhouse gas reporting program (GHGRP). Direct measurements
of fugitive and vented sources were combined with AP-42-based exhaust
emission factors (for operating reciprocating engines and turbines)
to produce a study onsite estimate. Site-level methane emissions were
also concurrently measured with downwind-tracer-flux techniques. At
most sites, these two independent estimates agreed within experimental
uncertainty. Site-level methane emissions varied from 2–880
SCFM. Compressor vents, leaky isolation valves, reciprocating engine
exhaust, and equipment leaks were major sources, and substantial emissions
were observed at both operating and standby compressor stations. The
site-level methane emission rates were highly skewed; the highest
emitting 10% of sites (including two superemitters) contributed 50%
of the aggregate methane emissions, while the lowest emitting 50%
of sites contributed less than 10% of the aggregate emissions. Excluding
the two superemitters, study-average methane emissions from compressor
housings and noncompressor sources are comparable to or lower than
the corresponding effective emission factors used in the EPA greenhouse
gas inventory. If the two superemitters are included in the analysis,
then the average emission factors based on this study could exceed
the EPA greenhouse gas inventory emission factors, which highlights
the potentially important contribution of superemitters to national
emissions. However, quantification of their influence requires knowledge
of the magnitude and frequency of superemitters across the entire
T&S sector. Only 38% of the methane emissions measured by the
comprehensive onsite measurements were reportable under the new EPA
GHGRP because of a combination of inaccurate emission factors for
leakers and exhaust methane, and various exclusions. The bias is
even larger if one accounts for the superemitters, which were not
captured by the onsite measurements. The magnitude of the bias varied
from site to site by site type and operating state. Therefore, while
the GHGRP is a valuable new source of emissions information, care
must be taken when incorporating these data into emission inventories.
The value of the GHGRP can be increased by requiring more direct measurements
of emissions (as opposed to using counts and emission factors), eliminating
exclusions such as rod-packing vents on pressurized reciprocating
compressors in standby mode under Subpart-W, and using more appropriate
emission factors for exhaust methane from reciprocating engines under
Subpart-C