A new study published in the journal Atmospheric Chemistry and Physics by researchers at the Lamont-Doherty Earth Observatory, part of the Columbia Climate School, measured and analyzed atmospheric methane concentrations and emissions sources around New York City. They found that incomplete combustion in appliances like furnaces and natural gas heat pumps,
According to Phys.org:
“The researchers estimate that methane emissions
associated with natural gas were approximately 1.7% of all gas delivered
through the system. These emissions represent a substantial amount of fuel NYC
consumers are paying for but not fully using, equivalent to nearly $300 million
of natural gas, based on 2023 and 2024 retail prices.”
The researchers were able to
distinguish between non-combustion emissions, either from leaks in underground
utility pipes or from building appliances, and inefficiently burned gas from
heating and cooling systems. The two-year study covering 2023 and 2024 involved
hourly methane measurements from the Mineola Tower, a National Institute of
Standards and Technology monitoring site on Long Island. They sampled air
flowing out of Manhattan and western Long Island during westerly winds. They
set out to capture seasonal patterns. Along with methane, they sampled ethane
and carbon monoxide at similarly frequent rates.
According to Phys.org:
“The measurements revealed a distinct seasonal cycle:
Methane emissions peaked during the winter heating season, declined through
spring and rose again during the summer cooling season before increasing
further during the following heating season. Natural gas accounted for 99% of
total methane emissions in February and 98% in May, and 85% to 88% during the
summer cooling months.”
Biogenic sources from wetlands, wastewater treatment plants, and landfills were not present in high concentrations in this region. The summer peaks were not expected, and some may be attributable to natural gas cooling systems. Ethane emissions are a signature of thermogenic subsurface natural gas sources. Carbon monoxide (CO) is produced during the incomplete combustion of any carbon-based fuel and is a signature of it in the data. Ratios and other correlations between the three gases can distinguish natural gas pre-meter leaks, post-combustion emissions, and microbial activities.
Incomplete combustion was found to be the main methane
source in the heating and cooling seasons.
“Only 6% of the identified natural gas plumes in winter
and 7% in summer showed no combustion signature, indicating that pipeline leaks
were detected less frequently at the tower than methane associated with
incomplete combustion.”
Methane increases closely followed
methane deliveries in the heating and cooling seasons, and lack of them in the
shoulder seasons of spring and fall when demand is low, matching combustion
source availability. The methane increases from end-use appliances show why
methane inventory estimates were lower than these and other field measurements
for the NYC area.
“Despite efforts to fix pipeline leaks, methane
emissions in cities have remained higher than expected, suggesting that
important sources were being overlooked. The authors say inefficient use of
natural gas, including incomplete combustion, accounts for much of the missing
methane and should be incorporated into future calculations.”
Higher combustion rates on end-use
appliances should also be sought. Post-meter combustion is now known as a
dominant rather than a negligible source of urban methane. This was unexpected and has implications. Comparisons with
other cities are given in a section of the conclusion below. Note that some
cities spent a lot of money digging up and replacing very old, often cast-iron,
distribution lines only to find barely any change in urban methane levels.
“Source attribution analysis reveals that the incomplete
combustion of natural gas (post-meter emissions from the inefficient burning of
natural gas in any appliance or power unit) dominates methane emissions in the
city, regardless of season. There is no natural gas methane loss rate currently
included in national or global inventories (Crippa et al., 2024; Maasakkers et
al., 2023), but the local NYCMA inventory (Pitt et al., 2024) has included a
beyond-the-meter loss rate of 0.5 %
(Fischer et al., 2018). However, we calculated a consumption-driven loss rate
for the NYCMA that is a factor of three times greater than these previous
studies of appliance emissions. These largely overlooked combustion-related
post-meter methane emissions can help explain the persistent missing
thermogenic methane sources reported by previous studies.”
“The observed loss rate of 1.7 ± 0.6 % is
within the range observed for other cities. It is less than the 2.5 ± 0.5 %
(Sargent et al., 2021) and 2.7 ± 0.6 %
(McKain et al., 2015) reported for the Boston area, but greater than the lower
limit of the 1.3 %–2.3 %
reported for Los Angeles (He et al., 2019; Sargent et al., 2021) and the 1.3 %
reported for the Baltimore/DC area (Huang et al., 2019).”
“Many cities, including Boston, have dedicated millions
of dollars to upgrading street-level natural gas infrastructure, without seeing
any substantial change in methane emissions (Sargent et al., 2021). At the
monthly retail prices of natural gas for 2023 and 2024, a 1.7 % loss
rate is close to 300×106 USD yr−1 of
natural gas purchased, but unused, by consumers in NYCMA.”
“Our results highlight the three-dimensional nature of
urban methane emissions: the largest methane emissions are observed from
rooftops and not from the pipelines beneath the streets below. Our findings
emphasize the urgent need to incorporate emissions from post-meter natural gas
combustion into methane inventories and emphasize emissions reductions from
natural gas end-use sectors as a means to reduce urban methane emissions.”
References:
Unused
natural gas behind NYC's $300 million waste of a potent greenhouse gas. Rebecca
Fowler. Phys.org. September 14, 2026. Unused natural gas behind NYC's $300
million waste of a potent greenhouse gas
Inefficient
consumption of natural gas drives methane emissions from a megacity. Yuwei
Zhao, Andrew Hallward-Driemeier, Luke D. Schiferl, Trey Maddaleno, Michael P.
Vermeuel, Dylan B. Millet, Delphine Farmer, and Róisín Commane. Atmospheric
Chemistry and Physics. Volume 26, issue 17. ACP, 26, 12911–12924, 2026. ACP - Inefficient consumption of
natural gas drives methane emissions from a megacity
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