EC-17. Analysis of NOx emission and formaldehyde formation in U.S. oil and gas production regions using satellite data

Abstract
The development of horizontal drilling and hydraulic fracturing has led to a steep increase in the U.S. production of natural gas and crude oil from shale formations since the mid 2000s. Associated with this industrial activity are emissions of ground-level ozone precursors such as nitrogen oxides and VOCs. Here we use NO2 and formaldehyde (HCHO) observations from the OMI and TROPOMI satellite instruments to study these emissions. Multivariate fitting to the long term OMI NO2 series yields source estimates that can be attributed to the drilling of new wells, to oil and gas extraction and to gas flaring. Our top-down source attributions compare well with the bottom-up NOx emission estimates from the Fuel based Oil and Gas emissions inventory (FOG). Current research using the higher spatially resolved TROPOMI NO2 columns aims to separate NOx emissions into areal emissions from well pad fields and emissions from large point sources within those fields, like power or gas plants. We use TROPOMI HCHO and simulated HCHO from the WRF-Chem model to study if HCHO can serve as a proxy for oil and gas related VOC emissions. Correlation of TROPOMI HCHO with production data shows a positive slope between April and September, as increases in photochemical activity yield HCHO amounts that are significantly discernible from space. We observe no correlation in winter indicating a smaller contribution of direct emission sources of HCHO. To investigate if and how much of the observed HCHO is the product of oil and gas related VOC emissions versus the product of other VOC sources, e.g. biogenic emissions, we compare TROPOMI HCHO with WRF-Chem simulations and utilize 0D modeling with the Master Chemical Mechanism to study the involved VOC chemistry in more detail. Finally, we are analyzing data from 2020 to look at the implications of the COVID-19 lockdowns and the downturn in drilling activity on oil and gas emissions.