Contribution of Oil and Gas Production to Nitrogen Deposition and Critical Load Exceedance in Class 1&2 Areas in the Western US

Nitrogen deposition has become a major concern for protected ecosystems in the Western US. A “critical load” value for an individual pollutant is defined as the amount of that pollutant an ecosystem can absorb before detrimental changes occur to that ecosystem. Researchers have found that many areas in the Western US have surpassed their critical load for nitrogen deposition. Here we utilize the Comprehensive Air quality Model with Extensions (CAMx) with two year-long modeling episodes representing 2008 and 2011, meteorology and emissions. The model inputs for the 2008 and 2011 episodes were generated as part of the West-wide Jump-start Air Quality Modeling Study (WestJumpAQMS) and Three State Air Quality Study (3SAQS) respectively. Both studies included a detailed assessment of oil and gas (O&G) emissions in Western States for the respective years. We compare modeled nitrogen deposition to critical load values for sensitive lichen species, finding that 73% of class 1&2 areas in the Western US have modeled annual nitrogen deposition totals above these conservative critical load values in 2008. Oil and gas production in the Western US has increased considerably in the past 5 to 10 years, often in remote areas near class 1&2 sensitive ecosystems. We also quantify the modeled contribution of emissions associated with oil and gas production to nitrogen deposition by comparing each years modeling run, without oil and gas emissions, to the respective basecase modeling run with full emissions. We report the contributions of oil and gas to nitrogen deposition in all class 1&2 areas in the Western US in the context of their critical load values for each modeling episode and we report the impacts of increasing oil and gas activity on total nitrogen deposition.