6 research outputs found
Methane Emissions from United States Natural Gas Gathering and Processing
New
facility-level methane (CH<sub>4</sub>) emissions measurements
obtained from 114 natural gas gathering facilities and 16 processing
plants in 13 U.S. states were combined with facility counts obtained
from state and national databases in a Monte Carlo simulation to estimate
CH<sub>4</sub> emissions from U.S. natural gas gathering and processing
operations. Total annual CH<sub>4</sub> emissions of 2421 (+245/–237)
Gg were estimated for all U.S. gathering and processing operations,
which represents a CH<sub>4</sub> loss rate of 0.47% (±0.05%)
when normalized by 2012 CH<sub>4</sub> production. Over 90% of those
emissions were attributed to normal operation of gathering facilities
(1697 +189/–185 Gg) and processing plants (506 +55/-52 Gg),
with the balance attributed to gathering pipelines and processing
plant routine maintenance and upsets. The median CH<sub>4</sub> emissions
estimate for processing plants is a factor of 1.7 lower than the 2012
EPA Greenhouse Gas Inventory (GHGI) estimate, with the difference
due largely to fewer reciprocating compressors, and a factor of 3.0
higher than that reported under the EPA Greenhouse Gas Reporting Program.
Since gathering operations are currently embedded within the production
segment of the EPA GHGI, direct comparison to our results is complicated.
However, the study results suggest that CH<sub>4</sub> emissions from
gathering are substantially higher than the current EPA GHGI estimate
and are equivalent to 30% of the total net CH<sub>4</sub> emissions
in the natural gas systems GHGI. Because CH<sub>4</sub> emissions
from most gathering facilities are not reported under the current
rule and not all source categories are reported for processing plants,
the total CH<sub>4</sub> emissions from gathering and processing reported
under the EPA GHGRP (180 Gg) represents only 14% of that tabulated
in the EPA GHGI and 7% of that predicted from this study
Methane Emissions from United States Natural Gas Gathering and Processing
New
facility-level methane (CH<sub>4</sub>) emissions measurements
obtained from 114 natural gas gathering facilities and 16 processing
plants in 13 U.S. states were combined with facility counts obtained
from state and national databases in a Monte Carlo simulation to estimate
CH<sub>4</sub> emissions from U.S. natural gas gathering and processing
operations. Total annual CH<sub>4</sub> emissions of 2421 (+245/–237)
Gg were estimated for all U.S. gathering and processing operations,
which represents a CH<sub>4</sub> loss rate of 0.47% (±0.05%)
when normalized by 2012 CH<sub>4</sub> production. Over 90% of those
emissions were attributed to normal operation of gathering facilities
(1697 +189/–185 Gg) and processing plants (506 +55/-52 Gg),
with the balance attributed to gathering pipelines and processing
plant routine maintenance and upsets. The median CH<sub>4</sub> emissions
estimate for processing plants is a factor of 1.7 lower than the 2012
EPA Greenhouse Gas Inventory (GHGI) estimate, with the difference
due largely to fewer reciprocating compressors, and a factor of 3.0
higher than that reported under the EPA Greenhouse Gas Reporting Program.
Since gathering operations are currently embedded within the production
segment of the EPA GHGI, direct comparison to our results is complicated.
However, the study results suggest that CH<sub>4</sub> emissions from
gathering are substantially higher than the current EPA GHGI estimate
and are equivalent to 30% of the total net CH<sub>4</sub> emissions
in the natural gas systems GHGI. Because CH<sub>4</sub> emissions
from most gathering facilities are not reported under the current
rule and not all source categories are reported for processing plants,
the total CH<sub>4</sub> emissions from gathering and processing reported
under the EPA GHGRP (180 Gg) represents only 14% of that tabulated
in the EPA GHGI and 7% of that predicted from this study
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
Primary Gas- and Particle-Phase Emissions and Secondary Organic Aerosol Production from Gasoline and Diesel Off-Road Engines
Dilution
and smog chamber experiments were performed to characterize
the primary emissions and secondary organic aerosol (SOA) formation
from gasoline and diesel small off-road engines (SOREs). These engines
are high emitters of primary gas- and particle-phase pollutants relative
to their fuel consumption. Two- and 4-stroke gasoline SOREs emit much
more (up to 3 orders of magnitude more) nonmethane organic gases (NMOGs),
primary PM and organic carbon than newer on-road gasoline vehicles
(per kg of fuel burned). The primary emissions from a diesel transportation
refrigeration unit were similar to those of older, uncontrolled diesel
engines used in on-road vehicles (e.g., premodel year 2007 heavy-duty
diesel trucks). Two-strokes emitted the largest fractional (and absolute)
amount of SOA precursors compared to diesel and 4-stroke gasoline
SOREs; however, 35–80% of the NMOG emissions from the engines
could not be speciated using traditional gas chromatography or high-performance
liquid chromatography. After 3 h of photo-oxidation in a smog chamber,
dilute emissions from both 2- and 4-stroke gasoline SOREs produced
large amounts of semivolatile SOA. The effective SOA yield (defined
as the ratio of SOA mass to estimated mass of reacted precursors)
was 2–4% for 2- and 4-stroke SOREs, which is comparable to
yields from dilute exhaust from older passenger cars and unburned
gasoline. This suggests that much of the SOA production was due to
unburned fuel and/or lubrication oil. The total PM contribution of
different mobile source categories to the ambient PM burden was calculated
by combining primary emission, SOA production and fuel consumption
data. Relative to their fuel consumption, SOREs are disproportionately
high total PM sources; however, the vastly greater fuel consumption
of on-road vehicles renders them (on-road vehicles) the dominant mobile
source of ambient PM in the Los Angeles area
Correction to Measurements of Methane Emissions from Natural Gas Gathering Facilities and Processing Plants: Measurement Results
Correction to Measurements
of Methane Emissions from Natural Gas
Gathering Facilities and Processing Plants: Measurement Result