Off-Site Flux Estimates of Volatile Organic Compounds from Oil and Gas Production Facilities Using Fast-Response Instrumentation

Flux estimates of volatile organic
compounds (VOCs) from oil and
gas (O&G) production facilities are fundamental in understanding
hazardous air pollutant concentrations and ozone formation. Previous
off-site emission estimates derive fluxes by ratioing VOCs measured
in canisters to methane fluxes measured in the field. This study uses
the Environmental Protection Agency’s Other Test Method 33A
(OTM 33A) and a fast-response proton transfer reaction mass spectrometer
to make direct measurements of VOC emissions from O&G facilities
in the Upper Green River Basin, Wyoming. We report the first off-site
direct flux estimates of benzene, toluene, ethylbenzene, and xylenes
from upstream O&G production facilities and find that these estimates
can vary significantly from flux estimates derived using both the
canister ratio technique and from the emission inventory. The 32 OTM
33A flux estimates had arithmetic mean (and 95% CI) as follows: benzene
17.83 (0.22, 98.05) g/h, toluene 34.43 (1.01, 126.76) g/h, C8 aromatics
37.38 (1.06, 225.34) g/h, and methane 2.3 (1.7, 3.1) kg/h. A total
of 20% of facilities measured accounted for ∼67% of total BTEX
emissions. While this heavy tail is less dramatic than previous observations
of methane in other basins, it is more prominent than that predicted
by the emission inventory.