Opportunity Title:

Improving Characterization of Atmospheric and Deposited Nitrogen Across Multiple Spatial and Temporal Regimes

Research Area:

Air

EPA Lab/Center/Office:

National Exposure Research Laboratory (NERL)

Location:

Research Triangle Park, NC

Duration:

12 months

Brief Summary:

This internship will utilize air quality modeling and precipitation measurements to improve characterization of atmospheric nitrogen to support the development of national ambient air quality standards (NAAQS).

Opportunity Description:

This opportunity will be used to utilize measurements and atmospheric modeling to improve our characterization of atmospheric nitrogen as nitrogen impacts deposition to sensitive ecosystems and the formation of particulate matter (PM). From a policy perspective, understanding the role of nitrogen deposition is a critically important component of EPA’s review of the oxides of nitrogen and sulfur (NO_x/SO_x) and particulate matter (PM) secondary National Ambient Air Quality Standards (NAAQS). EPA’s current Integrated Science Assessment (ISA) supporting the NO_x/SO_x review points to a strong emphasis on adverse ecosystem effects such as eutrophication associated with nitrogen deposition. All forms of atmospheric nitrogen will be investigated, although the modeling component of this effort will focus on reduced inorganic nitrogen (NH_x, defined as the sum of ammonia gas, NH₃, and particulate ammonium pNH₄).   Improved characterization of NH_x deposition is necessary to estimate the capacity for improvement associated with oxidized forms of nitrogen only. Particulate ammonium is a significant fraction of NH_x, leading to nitrogen deposition, and PM₁₀ and PM_2.5, which are criteria pollutants. Consequently, efforts to improve the characterization of both NH₃ and pNH₄ are critical to secondary NO_X/SO_X and primary and secondary PM NAAQS reviews. In addition to supporting EPA’s NAAQS reviews, this internship directly supports the agency’s multi-office nitrogen and co-pollutants roadmap project.

Research from this internship will elucidate the spatial and temporal (inter- and intra- annually) distribution of ambient ammonia gas (NH₃) and particulate ammonium (pNH₄) across the continental United States (CONUS), as well as the role of these species in contributing to nitrogen deposition to sensitive ecosystems. NH_x now constitutes roughly half of all atmospheric nitrogen, and over the next two decades is predicted to be the dominant component of atmospheric nitrogen. These calculations are necessary to estimate how much pNH₄ contributes to wet deposition, values which currently are not generated by CMAQ.  The anticipated modeling related work includes working with EPA’s Community Multiscale Air Quality (CMAQ) model to develop and implement process analysis algorithms that enable explicit tracking of the generation and loss of pNH₄ at selected time and spatial regimes. Additional modeling efforts could include analyzing the 2002-2014 modeling results to support

• a basic understanding of the factors influencing the broad spatial and temporal patterns of oxidized and reduce nitrogen species,
• examining the vertical profile patterns of these species to assist in improving gaps in the treatment of modeling processes,
• inspection of specific pre- and post-rain events using available observation sets to evaluate scavenging treatment of NH_x in CMAQ, and
• evaluating CMAQ performance using existing observations.

The measurement component of this internship will deploy a time resolved precipitation collector to generate diurnal profiles of a suite of discrete and aggregated nitrogen species, including oxidized and reduced forms of both inorganic and organic components of the nitrogen budget. This research will aid in improving the compositional and temporal characterization of nitrogen deposition and provide insight into both the natural and anthropogenic source contributions to atmospheric nitrogen. In combination with ongoing NERL based research on nitrogen dry deposition, this effort on wet deposition will help reach closure on techniques to assemble a total atmospheric nitrogen deposition budget.

The NERL scientists work in a very collaborative and welcoming culture that values the technical and personal contributions of new members, regardless of how long they become part of this amazing group. 

Opportunities for Professional Development:

The intern will collaborate with a unique mix of internationally renowned atmospheric and ecosystem scientists as well as air quality management professionals that in combination foster a unique science-policy interface. The resulting research portfolio would include experience in cutting edge atmospheric research with direct policy relevance in an era of dramatic changes in atmospheric composition. This rich experience will be broad and substantive and elucidate insight into multiple career paths.

Point of Contact or Mentor:

Donna Schwede (schwede.donna@epa.gov)