You are here:
NONLINEARITIES IN THE SULFATE SECONDARY FINE PARTICULATE RESPONSE TO NOX EMISSIONS REDUCTIONS AS MODELED BY THE REGIONAL ACID DEPOSITION MODEL
Citation:
Dennis, R L., G. S. Tonnesen, AND R. Mathur. NONLINEARITIES IN THE SULFATE SECONDARY FINE PARTICULATE RESPONSE TO NOX EMISSIONS REDUCTIONS AS MODELED BY THE REGIONAL ACID DEPOSITION MODEL. Presented at Millennium NATO/CCMS International Technical Meeting on Air Pollution Modeling and Its Application, Boulder, CO, May 15-19, 2000.
Impact/Purpose:
The goal of this task is to thoroughly characterize the performance of the emissions, meteorological and chemical/transport modeling components of the Models-3 system, with an emphasis on the chemical/transport model, CMAQ. Emissions-based models are composed of highly complex scientific hypotheses concerning natural processes that can be evaluated through comparison with observations, but not validated. Both performance and diagnostic evaluation together with sensitivity analyses are needed to establish credibility and build confidence within the client and scientific community in the simulations results for policy and scientific applications. The characterization of the performance of Models-3/CMAQ is also a tool for the model developers to identify aspects of the modeling system that require further improvement.
Description:
Attention is increasingly being devoted to the health effects of fine particulates. In regions that have a large production of sulfate, sulfuric acid and nitric acid compete for the available ammonia to form aerosols. In addition, the available nitric acid is the result of urban and regional photochemical production, as are the oxidant fields involved in the oxidation of SO2 to sulfate. To create an integrated modeling capability to investigate the particulate cycling, the Regional Acid Deposition Model (RADM) was enhanced by adding several modules to dynamically represent the physical and chemical processes involved in the geochemical cycling of sulfate and reduced and oxidized forms of nitrogen. The modules are based on those of the Regional Particulate Model (RPM); the resulting version of the model is referred to as the Extended RADM. The Extended RADM is used to investigate the connection between oxidant production and secondary particulate production resulting from NOx-SOx-NHx interactions.
The reduction of regional NOx emissions from major point sources has been proposed as a means to reduce levels of regional and urban ozone. Many thought the overall level of sulfate and nitrate fine particulate, and the associated ammonium, would decrease for these emissions reductions. The effect on secondary fine particulate levels resulting from a reduction in regional NOx emissions for the eastern United States was investigated with the Extended RADM. It was found that in parts of the domain, but not everywhere, the fine particulate mass increased due to increases in sulfate. In different parts the reason for the increase was different. Around a few cities the increase in OH associated with the NOx - Ozone disbenefit was the cause. In western Pennsylvania, the increase in hydrogen peroxide due to increased radical termination was the cause. The nonlinear increase in fine particle mass due to a reduction in NOx emissions is explainable through the examination of the response in different chemical regimes.