Emissions from oil and gas operations in the United States and their air quality implications

摘要

The 46th Annual A&WMA Critical Review (CR) "Emissions From Oil and Gas Operations in the United States and Their Air Quality Implications" (Allen, 2016) examines air quality impacts that result from changes in energy supplies and use, with an emphasis on changes in greenhouse gas, criteria air pollutants, and air toxics emissions from oil and gas production activities. National emission inventories indicate that VOC and NOx emissions from oil and gas supply chains in the United States have been increasing significantly; however, some national emission inventories for greenhouse gases showed slight declines over the past decade. The review points out that there are discrepancies in the concentrations reported for greenhouse gases based on whether the assessment is "top-down" or "bottom up." Bottom-up emission inventory estimates are based on national scale counts of equipment and operational activities (activity factors), multiplied by average emission factors, and therefore these trends are subject to uncertainties in activity and emission factors. While uncertainties associated with activity data and missing emission source types can be significant in some situations, multiple recent measurement studies indicate that the greatest uncertainties are associated with emission factors. Top-down estimates atmospheric concentrations of pollutants using measurements acquired from ground, aircraft, and satellite platforms that can be used to infer (using atmospheric models and assumptions) emissions in a region in a process. The CR provides information indicating that some of the discrepancies between the estimation methods could be attributed to unaccounted-for differences in source emission factors. For example, in many source categories, small groups of devices or sites contribute a large fraction of emissions. Collectively, these sources have been referred to as "super-emitters." When super-emitters are accounted for, multiple measurement approaches, at multiple scales, can produce similar results for estimated emissions. Overall, this review was timely, and especially with the recent issues relating to large accidental releases of CH_4, the importance of super-emitters was especially relevant. This review dealt with potential health effects as a peripheral issue and did not go into this in depth. It should be noted that unprocessed natural gas contains low concentrations of many contaminants that are known to be toxic and carcinogenic. Contaminants such as benzene, toluene, ethyl benzene, xylene, and radon have been reported (Hildebrand et al, 2016; Mitchell et al., 2016). The effects of chronic exposures to low levels of these compounds to human health represent an area that should receive greater consideration.