Impact/Purpose:

The objective of this research is to develop chemical mechanisms that accurately represent the complex atmospheric chemistry involved in the formation of ozone and other, related, photochemically- produced pollutants such as secondary air toxics and organic aerosol precursors. This task will produce updated, state-of-the-art photochemical mechanisms, support the evaluation of these mechanisms with experimental data, and apply these mechanisms for regulatory and research purposes in emissions and observations-based models. The application of the models to provide scientific support for VOC-reactivity based ozone control policies will be a major focus of this task. The dissemination of results of model applications in this area (both ours and those from outside agencies) via the US German workshop agreement, are also supported as a small portion of this task. While this task primarily focuses on ozone-related issues, our mechanism development and evaluation will consider that these mechanisms should also be able to adequately predict the concentrations of other related photochemical species. This task is being performed in close collaboration with Task 12043, "Reducing Uncertainty in the Chemical Mechanisms of Aromatic and Biogenic Hydrocarbons" and Task 20461, "FY05 CMAQ Release."

Description:

Air quality models that realistically describe the formation of ozone, air toxics, and other pollutants are needed by EPA and state agencies to predict current and future concentrations of these pollutants and develop ways to decrease their concentrations below harmful levels. The atmospheric chemistry of photochemically-produced pollutants is complex, involving the interactions of tens of thousands of different chemical reactions. This task supports the development and application of improved chemical mechanisms which are accurate as well as computationally-efficient for predicting the production of secondary gas-phase photochemical pollutants in the atmosphere. We will improve, evaluate and analyze new and existing chemical mechanisms, and apply them in air quality models to study ozone production and mitigation strategies such as VOC-reactivity based strategies. The mechanisms to be tested include the Carbon Bond, the Statewide Air Pollution Research Center (SAPRC) and the RACM mechanisms. Without a justifiable and comprehensive description of this complex chemistry, EPA cannot adequately predict the concentrations of criteria pollutants in non-urban areas or the production of secondary organic aerosols. We will coordinate atmospheric chemistry research with German researchers, through the US-German whorksops.

Record Details:

Record Type:PROJECT

Start Date:10/01/2003

Completion Date:09/01/2005

OMB Category:Other

Record ID: 56076

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Project Information:

Progress :Work was begun during FY04 on the updating, ehancement and extension of the Carbon Bond mechanism, which is scheduled for delivery to EPA in early FY05.

During FY04, we also implemented a version of CMAQ with automated sensitivity calculations using the Direct Decoupled Method (DDM). This model will be used to study the sensitivity of ozone to emissions reductions of individual VOC species - information which is necessary in order to calculate Maximum Incremental Reactivity metrics for use in potential VOC-reactivity based regulations. The tool was implemented and tested, and used to simulate an ozone episode in July, 1999. The reactivity metrics developed from this episode can be used to identify the largest VOC contributors to ozone formation and develop more efficient ozone control strategies.

During FY04, we continued the study to empirically examine the performance of observation-based indicators, which are used to determine whether ozone formation is VOC or NOx sensitive. While these indicators have been used for several years to predict ozone sensitivity, they have only been derived from model simulations. This project was the first to systematically examine whether the model-predicted sensitivity is actually consistent with what is determined experimentally. In order to examine some of the more informative integrated indicators, such as the OH chain length, this study also measured the concentrations of OH and HO2 within the carefully controlled smog chamber conditions. This was also the first time that a comprehensive measurement set, including these radicals, was made under controlled conditions.



Relevance :

This research is critical towards meeting the Long-Term goal of producing advanced and accurate monitoring and modeling tools that can be used by the Agency to support the implementation of current ozone standards and to improve the science used in reviewing these standards. Accurate and defensible chemical mechanisms are a key component of the regulatory and research air quality models used to develop State Implementation Plans (SIPs) for demonstrating compliance with the Ozone NAAQS. Better predictions of the concentrations of secondary pollutants and the atmospheric degradation of VOCs will help EPA and States develop more scientifically sound approaches for assessing and characterizing environmental exposure and risk, and developing strategies for reducing concentrations of harmful pollutants. OAQPS will benefit from improvements in the scientific basis by which they evaluate air pollutant control strategies. External groups impacted by the research performed under this task include the NARSTO program, a public-private consortium for ozone and particulate pollution research, and the Reactivity Research Working Group, a working group consisting of government, industry, and academic representatives.

Clients :Helms (OAQPS/AQSSD), Jang (OAQPS/EMAD), Tong (EPA Region 9), RRWG, NARSTO

Project IDs:

ID Code :12044

Project type :OMIS