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We use global airborne observations of propane (C 3 H 8 ) and ethane (C 2 H 6 ) from the Atmospheric Tomography (ATom) and HIAPER Pole-to-Pole Observations (HIPPO), as well as U.S.-based aircraft and tower observations by NOAA and from the NCAR FRAPPE campaign as tracers for emissions from oil and gas operations. To simulate global mole fraction fields for these gases, we update the default emissions' configuration of C 3 H 8 used by the global chemical transport model, GEOS-Chem v13.0.0, using a scaled C 2 H 6 spatial proxy. With the updated emissions, simulations of both C 3 H 8 and C 2 H 6 using GEOS-Chem are in reasonable agreement with ATom and HIPPO observations, though the updated emission fields underestimate C 3 H 8 accumulation in the arctic wintertime, pointing to additional sources of this gas in the high latitudes (e.g., Europe). Using a Bayesian hierarchical model, we estimate global emissions of C 2 H 6 and C 3 H 8 from fossil fuel production in 2016-2018 to be 13.3 ± 0.7 (95% CI) and 14.7 ± 0.8 (95% CI) Tg/year, respectively. We calculate bottom-up hydrocarbon emission ratios using basin composition measurements weighted by gas production and find their magnitude is higher than expected and is similar to ratios informed by our revised alkane emissions. This suggests that emissions are dominated by pre-processing activities in oil-producing basins.

We use historical and new atmospheric trace gas observations to refine the estimated source of methane (CH(4)) emitted into California's South Coast Air Basin (the larger Los Angeles metropolitan region). Referenced to the California Air Resources Board (CARB) CO emissions inventory, total CH(4) emissions are 0.44 ± 0.15 Tg each year. To investigate the possible contribution of fossil fuel emissions, we use ambient air observations of methane (CH(4)), ethane (C(2)H(6)), and carbon monoxide (CO), together with measured C(2)H(6) to CH(4) enhancement ratios in the Los Angeles natural gas supply. The observed atmospheric C(2)H(6) to CH(4) ratio during the ARCTAS (2008) and CalNex (2010) aircraft campaigns is similar to the ratio of these gases in the natural gas supplied to the basin during both these campaigns. Thus, at the upper limit (assuming that the only major source of atmospheric C(2)H(6) is fugitive emissions from the natural gas infrastructure) these data are consistent with the attribution of most (0.39 ± 0.15 Tg yr(-1)) of the excess CH(4) in the basin to uncombusted losses from the natural gas system (approximately 2.5-6% of natural gas delivered to basin customers). However, there are other sources of C(2)H(6) in the region. In particular, emissions of C(2)H(6) (and CH(4)) from natural gas seeps as well as those associated with petroleum production, both of which are poorly known, will reduce the inferred contribution of the natural gas infrastructure to the total CH(4) emissions, potentially significantly. This study highlights both the value and challenges associated with the use of ethane as a tracer for fugitive emissions from the natural gas production and distribution system.

A laser photoacoustic spectroscopy (LPAS) instrument was developed and used for aircraft measurements of ethene from industrial sources near Houston, Texas. The instrument provided 20 s measurements with a detection limit of less than 0.7 ppbv. Data from this instrument and from the GC-FID analysis of air samples collected in flight agreed within 15% on average. Ethene fluxes from the Mt. Belvieu chemical complex to the northeast of Houston were quantified during 10 different flights. The average flux was 520 +/- 140 kg h(-1) in agreement with independent results from solar occultation flux (SOF) measurements, and roughly an order of magnitude higher than regulatory emission inventories indicate. This study shows that ethene emissions are routinely at levels that qualify as emission upsets, which need to be reported to regional air quality managers.

We use recent aircraft measurements of a comprehensive suite of anthropogenic halocarbons, carbon monoxide (CO), and related tracers to place new constraints on North American halocarbon emissions and quantify their global warming potential. Using a chemical transport model (GEOS-Chem) we find that the ensemble of observations are consistent with our prior best estimate of the U.S. anthropogenic CO source, but suggest a 30% underestimate of Mexican emissions. We develop an optimized CO emission inventory on this basis and quantify halocarbon emissions from their measured enhancements relative to CO. Emissions continue for many compounds restricted under the Montreal Protocol, and we show that halocarbons make up an important fraction of the total greenhouse gas source for both countries: our best estimate is 9% (uncertainty range 6-12%) and 32% (21-52%) of equivalent CO2 emissions for the U.S. and Mexico, respectively, on a 20 year time scale. Performance of bottom-up emission inventories is variable, with underestimates for some compounds and overestimates for others. Ongoing methylchloroform emissions are significant in the U.S. (2.8 Gg/y in 2004-2006), in contrast to bottom-up estimates (< 0.05 Gg), with implications for tropospheric OH calculations. Mexican methylchloroform emissions are minor.

The 1990 Clean Air Act Amendments required the United States Environmental Protection Agency (U.S. EPA) to enact stricter regulations aimed at reducing benzene emissions. In an effort to determine whether these new regulations have been successful in reducing atmospheric benzene concentrations, we have evaluated benzene-to-acetylene ratios from data sets spanning nearlythree decades, collected during several field studies and from the U.S. EPA's Photochemical Assessment Monitoring Station (PAMS) network. The field-study data indicate a decrease in benzene relative to acetylene of approximately 40% from 1994 to 2002. This corresponds to a decrease in benzene alone of approximately 56% over the same period. In contrast, the PAMS data exhibit high interannual variability with no discernible trend. This discrepancy is attributed to measurement problems in the PAMS data sets.