Version 2 2019-08-09, 18:47Version 2 2019-08-09, 18:47
Version 1 2019-07-08, 15:05Version 1 2019-07-08, 15:05
journal contribution
posted on 2019-08-09, 18:47authored byKristian
D. Hajny, Olivia E. Salmon, Joseph Rudek, David R. Lyon, Andrew A. Stuff, Brian H. Stirm, Robert Kaeser, Cody R. Floerchinger, Stephen Conley, Mackenzie L. Smith, Paul B. Shepson
Current research efforts on the atmospheric
impacts of natural
gas (NG) have focused heavily on the production, storage/transmission,
and processing sectors, with less attention paid to the distribution
and end use sectors. This work discusses 23 flights at 14 natural
gas-fired power plants (NGPPs) using an aircraft-based mass balance
technique and methane/carbon dioxide enhancement ratios (ΔCH4/ΔCO2) measured from stack plumes to quantify
the unburned fuel. By comparing the ΔCH4/ΔCO2 ratio measured in stack plumes to that measured downwind,
we determined that, within uncertainty of the measurement, all observed
CH4 emissions were stack-based, that is, uncombusted NG
from the stack rather than fugitive sources. Measured CH4 emission rates (ER) ranged from 8 (±5) to 135 (±27) kg
CH4/h (±1σ), with the fractional CH4 throughput lost (loss rate) ranging from −0.039% (±0.076%)
to 0.204% (±0.054%). We attribute negative values to partial
combustion of ambient CH4 in the power plant. The average
calculated emission factor (EF) of 5.4 (+10/–5.4) g CH4/million British thermal units (MMBTU) is within uncertainty
of the Environmental Protection Agency (EPA) EFs. However, one facility
measured during startup exhibited substantially larger stack emissions
with an EF of 440 (+660/–440) g CH4/MMBTU and a
loss rate of 2.5% (+3.8/–2.5%).