Grantee Research Project Results
2000 Progress Report: A Modeling Investigation of NHx Cycling in the Troposphere and Its Impact on Particulate Matter and Acidic Substances Budgets
EPA Grant Number: R826773Title: A Modeling Investigation of NHx Cycling in the Troposphere and Its Impact on Particulate Matter and Acidic Substances Budgets
Investigators: Mathur, Rohit , Coats, Carlie J. , McHenry, John , Houyoux, Marc , Shankar, Uma
Current Investigators: Mathur, Rohit , Alapaty, Kiran , Shankar, Uma , Houyoux, Marc , Adelman, Zac
Institution: MCNC / North Carolina Supercomputing Center
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1998 through September 30, 2001 (Extended to March 31, 2003)
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $488,744
RFA: Air Pollution Chemistry and Physics (1998) RFA Text | Recipients Lists
Research Category: Air
Objective:
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, and potential eutrophication and nutrient loading effects resulting from their deposition. While significant attention has been devoted towards studying oxidized nitrogen in the atmosphere, little effort has been devoted towards quantifying the budgets of reduced nitrogen species. The overall objective of this 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 comprehensive multipollutant regional models.Progress Summary:
To investigate the processes governing the fate of NHx in a consistent modeling framework, and to develop a preliminary assessment of the adequacy of existing NH3 emissions, a comprehensive gas-aerosol version of the Multiscale Air Quality Simulation Platform (MAQSIP) was used to simulate the regional and local distributions of reduced and oxidized nitrogen and related species. MAQSIP is a comprehensive urban to intercontinental scale atmospheric transport-transformation-deposition model that has served as a prototype for EPA's CMAQ/Models-3 system. Model simulations were performed over two regions using grid nesting: (1) the eastern United States using a grid resolution of 36 km to examine the regional characteristics; and (2) North Carolina and surrounding states to examine local characteristics in vicinity of the high NH3 emissions in eastern North Carolina, using a finer resolution 12 km grid. Meteorological inputs for both domains were created using the MM5. Emission inputs for these simulations were based on the National Emissions Trends (NET) 1996 inventory (now known as the National Emissions Inventory (NEI)), which provides the most current estimates for emissions of ammonia, sulfur, PM2.5, and PM10 in the eastern United States.Model predicted concentrations of various aerosol constituents were rigorously compared against observations from the CASTNet and IMPROVE networks. As an example, Figure 1 shows comparisons of the predicted compositional characteristics of the NH4-SO4-NO3 aerosol against measurements from the CASTNet network and indicate that the model can reasonably well capture the spatial trends in both ambient levels and relative fractional contribution to aerosol mass.
Figure 1: Comparison of modeled and observed compositional characteristics of the NH4-SO4-NO3 aerosol for June 19-30, 1996. (a) ambient concentrations; (b) fractional contributions.
Detailed analyses of model predictions also were performed to assess the model's representation of gas/particle partitioning of both oxidized and reduced nitrogen. Table 1 presents a comparison of modeled NH3/NHx ratio against limited available observations. The Extended RADM simulation results presented in this table are based on updated NH3 emissions from the 1985 NAPAP inventory. A number of preliminary though important conclusions can be drawn from these comparisons: (1) using NH3 emissions estimates from the 1996 NET inventory provide better estimates of NH3/NHx partitioning, (2) finer resolution enables better simulation of the near source (eastern farm site) and downwind (Clinton and Kinston) distributions and partitioning of NH3, and (3) the 1996 NET inventory does appear to provide relatively accurate distribution of NH3 emissions.
Table 1. Comparison of NH3/NHx ratio at different sites.*
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*RTP data for 1989; Bondville data for 1989-90; Kinston, Clinton, Eastern Farm for 1997.
A number of model enhancement activities initiated during the previous year, continued in this reporting period and include: (1) investigation of the use of an alternate thermodynamic aerosol equilibrium module (ISORROPIA by Nenes, et al., 1998) in MAQSIP to include additional inorganic aerosol components; (2) enhancement of the aerosol-cloud processor; and, (3) interfacing the aqueous chemistry calculations with different gas-phase chemical mechanisms.
References:
Nenes A, Plinis C, Pandis S. User's guide for the "ISORROPIA" thermodynamic equilibrium aerosol model. Division of Marine and Atmospheric Chemistry of the Rosenstiel School of Marine and Atmospheric Science, University of Miami, 1998.
Future Activities:
Detailed analysis of budgets of various modeled processes will be performed. In particular, modeled deposition fluxes and the impact of model grid resolution will be assessed. Recently, a number of improvements related to speciation of PM2.5 and PM10 have been made to the NEI inventory. These, along with Continuous Emissions Monitoring (CEM), will be used to further improve emission estimates to the model. We also will investigate improvements in spatial allocation of NH3 sources through the use of a data set containing location of individual livestock farms. Methods to introduce seasonal variation in NH3 emissions will be investigated.The anticipated model enhancements activities include testing and assessment
of alternate aerosol equilibrium modules; interfacing and the multiscale
cloud-chemistry package with the MAQSIP gas-aerosol model; investigation of
potential improvements in dry-deposition velocity estimates for NH3; and,
initiation of the development of an inverse modeling methodology.
Model
simulations with the updated emissions will be conducted to: (1) further study
the sensitivity to grid resolution; (2) determine range of influence of reduced
and oxidized nitrogen; and (3) study impact of potential reductions in NOx and increases in NH3 emissions on PM composition.
Journal Articles:
No journal articles submitted with this report: View all 14 publications for this projectSupplemental Keywords:
air, atmospheric chemistry, chemical transport, regional models, model evaluation, deposition., RFA, Scientific Discipline, Air, Engineering, Ecology, Environmental Chemistry, Engineering, Chemistry, & Physics, tropospheric ozone, aerosol particles, ambient aerosol, particle size, fine particles, human exposure, nitrogen removal, particulate matter, sulfur, troposphere, air pollution models, fate and transport, particulates, eutrophication, ozone, regional scale, ambient air, oxides, air modeling, PM2.5Relevant Websites:
http://www.envpro.ncsc.org/ 
http://www.envpro.ncsc.org/products/maqsip/
http://www.envpro.ncsc.org/products/smoke/SMOKEV1.html#enhance
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.