Urban emissions remain an underexamined part of the methane budget. Here we present and interpret aircraft observations of six old and leak‐prone major cities along the East Coast of the United States. We use direct observations of methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), ethane (C2H6), and their correlations to quantify CH4 emissions and attribute to natural gas. We find the five largest cities emit 0.85 (0.63, 1.12) Tg CH4/year, of which 0.75 (0.49, 1.10) Tg CH4/year is attributed to natural gas. Our estimates, which include all thermogenic methane sources including end use, are more than twice that reported in the most recent gridded EPA inventory, which does not include end‐use emissions. These results highlight that current urban inventory estimates of natural gas emissions are substantially low, either due to underestimates of leakage, lack of inclusion of end‐use emissions, or some combination thereof.
Flaring is widely used by the fossil fuel industry to dispose of natural gas. Industry and governments generally assume that flares remain lit and destroy methane, the predominant component of natural gas, with 98% efficiency. Neither assumption, however, is based on real-world observations. We calculate flare efficiency using airborne sampling across three basins responsible for >80% of US flaring and combine these observations with unlit flare prevalence surveys. We find that both unlit flares and inefficient combustion contribute comparably to ineffective methane destruction, with flares effectively destroying only 91.1% (90.2, 91.8; 95% confidence interval) of methane. This represents a fivefold increase in methane emissions above present assumptions and constitutes 4 to 10% of total US oil and gas methane emissions, highlighting a previously underappreciated methane source and mitigation opportunity.
We demonstrate an all-fiber supercontinuum source that generates a continuous spectrum from 1.6 μm to >11 μm with 417 mW on-time average power at 33% duty cycle. By utilizing a master oscillator power amplifier pump with three amplification stages and concatenating solid core ZBLAN, arsenic sulfide, and arsenic selenide fibers, we shift 1550 nm light to ∼4.5 μm, ∼6.5 μm, and >11 μm, respectively. With 69 mW past 7.5 μm, this source provides both high power and broad spectral expansion, while outputting a single fundamental mode.
Abstract. We apply airborne measurements across three seasons
(summer, winter and spring 2017–2018) in a multi-inversion framework to
quantify methane emissions from the US Corn Belt and Upper Midwest, a key
agricultural and wetland source region. Combing our seasonal results with
prior fall values we find that wetlands are the largest regional methane
source (32 %, 20 [16–23] Gg/d), while livestock (enteric/manure; 25 %,
15 [14–17] Gg/d) are the largest anthropogenic source. Natural
gas/petroleum, waste/landfills, and coal mines collectively make up the
remainder. Optimized fluxes improve model agreement with independent
datasets within and beyond the study timeframe. Inversions reveal coherent
and seasonally dependent spatial errors in the WetCHARTs ensemble mean
wetland emissions, with an underestimate for the Prairie Pothole region but
an overestimate for Great Lakes coastal wetlands. Wetland extent and
emission temperature dependence have the largest influence on prediction
accuracy; better representation of coupled soil temperature–hydrology
effects is therefore needed. Our optimized regional livestock emissions
agree well with the Gridded EPA estimates during spring (to within 7 %) but
are ∼ 25 % higher during summer and winter. Spatial analysis
further shows good top-down and bottom-up agreement for beef facilities (with
mainly enteric emissions) but larger (∼ 30 %) seasonal
discrepancies for dairies and hog farms (with > 40 % manure
emissions). Findings thus support bottom-up enteric emission estimates but
suggest errors for manure; we propose that the latter reflects inadequate
treatment of management factors including field application. Overall, our
results confirm the importance of intensive animal agriculture for regional
methane emissions, implying substantial mitigation opportunities through
improved management.
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