A Modeling Investigation of NHx Cycling in the Troposphere and Its Impact on Particulate Matter and Acidic Substances Budgets

EPA Grant Number: R826773
Title: A Modeling Investigation of NHx Cycling in the Troposphere and Its Impact on Particulate Matter and Acidic Substances Budgets
Investigators: Mathur, Rohit , Houyoux, Marc , McHenry, John , Shankar, Uma
Current Investigators: Mathur, Rohit , Adelman, Zac , Alapaty, Kiran , Houyoux, Marc , Shankar, Uma
Institution: MCNC / North Carolina Supercomputing Center
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1998 through September 30, 2001 (Extended to March 31, 2003)
Project Amount: $488,744
RFA: Air Pollution Chemistry and Physics (1998) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air , Engineering and Environmental Chemistry


The fate of nitrogen-containing species in the atmosphere is of considerable interest given their role in the formation of acidic substances, particulate matter, and tropospheric ozone. Further, deposition of nitrogen compounds can contribute significantly to eutrophication and other nutrient loading effects. While much attention has been devoted to studying the role of oxides of nitrogen in the atmosphere and towards reducing their emissions, there has been little focus on the cycling of reduced nitrogen compounds in the atmosphere and their role in determining budgets of tropospheric acids and particulate matter. The overall objective of the proposed research is to improve current understanding of the cycling of reduced nitrogen compounds in the atmosphere and to investigate the coupling of such compounds with atmospheric aerosols and other criteria pollutants responsible for the acidifying atmospheric load, through development, enhancement, and continuous evaluation of a comprehensive multipollutant regional model.


The modeling of NHx cycling in the atmosphere is a relatively unexplored area of research. The research approach outlined in this proposal is motivated by the need to improve the current level of understanding and quantification of the sources, sinks, and processes governing atmospheric NHx cycling and its coupling with the chemistry of oxides of sulfur and nitrogen. The modeling system chosen for this research is a comprehensive regional scale tropospheric gas- aerosol model. Our research approach includes: (1) synthesizing the current knowledge of the processes governing the fate of NHx in a consistent modeling framework; (2) developing specific model enhancements and conducting a series of process-based simulations to improve our understanding of the coupling of various atmospheric process involved in atmospheric NHx cycling; (3) reducing the uncertainty in emission estimates through development and application of model inversion techniques; and (4) the complimentary analysis of model prediction and measurements of aerosol composition and deposition amounts to evaluate the model.

Expected Results:

The proposed research would help reduce uncertainties associated with the sources, sinks, and processes and pathways associated with reduced nitrogen atmospheric cycling. Through a detailed examination of the NHx cycling in the troposphere it will result in significant advances in our understanding of the coupling between reduced and oxidized nitrogen compounds, the coupling between O3 and particulate matter in the fine particle size range (PM2.5), and consequently contribute to design of multi-pollutant control strategies. The improved estimates of aerosol composition and distributions over regional scales, obtained through model enhancement activities, will contribute to improving regional assessment of aerosol radiative and visibility effects. Further, the quantification of the relative contribution of oxidized and reduced nitrogen compounds to total atmospheric nitrogen deposition will contribute to risk assessment and risk management studies concerned with critical load exceedances to natural ecosystems. Finally, improved estimates of the distributions and levels of particulate matter resulting from the proposed research can be linked with exposure assessment studies and help better quantify the health risks resulting from anthropogenic influences.

Publications and Presentations:

Publications have been submitted on this project: View all 14 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 3 journal articles for this project

Supplemental Keywords:

RFA, Scientific Discipline, Air, Ecology, Environmental Chemistry, tropospheric ozone, Engineering, Engineering, Chemistry, & Physics, ambient aerosol, fate and transport, particle size, particulate matter, particulates, eutrophication, fine particles, aerosol particles, ambient air, ozone, air modeling, sulfur, air pollution models, human exposure, regional scale, PM2.5, troposphere, nitrogen removal, oxides

Relevant Websites:


Progress and Final Reports:

  • 1999 Progress Report
  • 2000 Progress Report
  • 2001 Progress Report
  • 2002 Progress Report
  • Final Report