Seasonally Resolved Excess Urban Methane Emissions from the Baltimore/Washington, DC Metropolitan Region

Abstract

Urban areas are increasingly recognized as an important source of methane (CH4), but we have limited seasonally resolved observations of these regions. In this study, we quantify seasonal and annual urban CH4 emissions over the Baltimore, Maryland, and Washington, DC metropolitan regions. We use CH4 atmospheric observations from four tall tower stations and a Lagrangian particle dispersion model to simulate CH4 concentrations at these stations. We directly compare these simulations with observations and use a geostatistical inversion method to determine optimal emissions to match our observations. We use observations spanning four seasons and employ an ensemble approach considering multiple meteorological representations, emission inventories, and upwind CH4 values. Forward simulations in winter, spring, and fall underestimate observed atmospheric CH4 while in summer, simulations overestimate observations because of excess modeled wetland emissions. With ensemble geostatistical inversions, the optimized annual emissions in DC/Baltimore are 39 ± 9 Gg/month (1 δ), 2.0 ± 0.4 times higher than the ensemble mean of bottom-up emission inventories. We find a modest seasonal variability of urban CH4 emissions not captured in current inventories, with optimized summer emissions ∼41% lower than winter, broadly consistent with expectations if emissions are dominated by fugitive natural gas sources that correlate with natural gas usage.

Majority of US urban natural gas emissions unaccounted for in inventories

“…Among these studies, loss rates from NG infrastructure were calculated in different ways; for comparison, we recalculated loss rates for some studies according to our method ( SI Appendix , Table S3 ). These studies produce loss rates of 1.1 to 2.1% for Washington, DC ( 8 , 32 ) and 2 to 2.3% for Los Angeles ( 9 , 35 ), comparable to the 2.5% shown here for Boston.…”

“…Seasonal changes in urban methane emissions have previously been found by Huang et al ( 32 ) in Washington, DC (summer CH 4 emissions were 41% lower than winter emissions) and He et al ( 10 ), Wong et al ( 10 ), and Yadav et al ( 33 ) in Los Angeles (summer emissions were 26%, 22%, and 40% lower than winter emissions, respectively). However, the fraction of NG was not determined in these studies, which assessed total methane emissions only.…”

“… ( Left ) Per capita NG emissions from top-down studies in six US cities. Boston: (a) This work, (b) McKain ( 4 ), (c) This work, (d) Plant ( 5 ), Indianapolis: (e) Lamb ( 6 ), (f) Lamb ( 6 ), (g) Balashov ( 11 ), (h) Lamb ( 6 ), (i) Cambaliza ( 34 ), DC/Baltimore: (j) EPA ( 8 ), (k) Huang ( 32 ), (l) Ren ( 8 ), (m) Plant ( 5 ), Los Angeles: (n) CARB ( 35 ), (o) EPA ( 33 ), (p) Yadav ( 33 ), (q) Cui ( 36 ), (r) Peischl ( 35 ), (s) Wunch ( 7 ), (t) Wong ( 10 ), New York City: (u) EPA ( 5 ), (v) Plant ( 5 ), Philadelphia: (w) EPA ( 5 ), and (x) Plant ( 5 ). ( Right ) Boston bottom-up inventory NG emissions by sector compared to top-down emissions.…”

Biogenic link to the recent increase in atmospheric methane over India

“…The organic soil amendments have been reported to modify the microbial community structure/physiological functions and thus, influence soil emissions (e.g., Gorovtsov et al, 2020;Mackelprang et al, 2018). However, comparatively stable carbon alternatives of organic fertilizers, e.g., biochar-based, are reported as an effective tool to reduce CH 4 emissions and improve the soil carbon status (Huang et al, 2019). The major apprehension in the case of biochar fertilizers might be the reduction in grain yield in the case of paddy (e.g., Ali et al, 2020;El-Naggar et al, 2019).…”

Greenhouse gas observations from the Northeast Corridor tower network

“…First, high-resolution meteorological modeling (using the Weather Research and Forecast (WRF) model) is being conducted ( Lopez-Coto et al, 2020b ), with output coupled to Lagrangian dispersion models such as STILT ( Lin et al, 2003 ; Nehrkorn et al, 2010 ) and HYSPLIT ( Stein et al, 2015 ). These transport and dispersion models are used to interpret observations from both aircraft and tower stations and in atmospheric inverse analyses to estimate fluxes of CO 2 and CH 4 from the cities of Washington, DC, and Baltimore, MD ( Lopez-Coto et al, 2020a ; Huang et al, 2019 ). A high-resolution fossil fuel CO 2 inventory, Hestia, is also being developed for this project ( Gurney et al, 2012 , 2019 ).…”