Impact/Purpose:

1. Carry out smog chamber experiments to generate concentration data bases for developing and evaluating chemical mechanisms for toluene and alpha pinene, hydrocarbons that are emitted into the troposphere in significant quantities.

2. Use new derivative-based gas chromatography-mass spectroscopy methods to determine the concentrations of photochemical oxidation products.

3. Develop improved chemical mechanisms for toluene and alpha pinene based on results of smog chamber experiments.

Description:

The state of science in ozone chemistry was reviewed recently in a series of journal reports published under the auspices of the North American Research Strategy for Tropospheric Ozone (NARSTO) in Atmospheric Environment. Included in the NARSTO reports are research gaps that need to be filled to reduce uncertainties in the atmospheric chemistry of ozone. The purpose of this task is to carry out research to address two critical needs identified in the reports. Research will be conducted to reduce uncertainties in the chemical mechanisms of aromatic and biogenic hydrocarbons in air quality models used to assess their impact on tropospheric ozone concentrations. To date the development of data bases for developing and evaluating chemical mechanisms for high volume aromatic and biogenic hydrocarbons has been limited by the lack of reliable analytical methods for measuring the concentrations of their photochemical oxidation products. Under this task a new derivative-based gas chromatography mass spectroscopy method will be employed to measure the concentrations of the multifunctional gas phase oxidation products in smog chamber hydrocarbon/NOx irradiations. The results will be used to develop improved chemical mechanisms for toluene and alpha pinene.

Record Details:

Record Type:PROJECT

Start Date:10/01/2001

Projected Completion Date:09/01/2005

Record ID: 56075

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Project Information:

Progress :1. The smog chambers in the new EPA building have now been set up and tested. These efforts included installing the supporting instrumentation associated with the chamber - temperature and relative humidity sensors, NOx, O3 and SO2 monitors, and gas chromatographs. In addition the software and hardware need to collect gas-phase data was installed and documented. Characterization studies were carried out to assess performance of the chamber, e.g., series of propylene/NOx irradiations were carried out as control experiments. Once the performance of the chamber was determined to be satisfactory, a set of alpha-pinene experiments were conducted.

2. Investigations of the gas-phase products from "-pinene/NOx has been undertaken. Six irradiations with time-resolved sampling have been undertaken in this series. A high-flow static mode has been developed for this series in order to collect gas phase products onto an 8-channel, 30-cm denuder. Periodic samples were taken along the reaction profile. In addition, one "-pinene/NOx irradiation was been conducted in a dynamic mode to collect high gas-phase volumes using an 8-channel, 60-cm denuder. The denuder extracts have been extracted, derivatized, and analyzed. The mass spectrum of the extracts is currently being interpreted.

3. To supplement the biogenic data base, investigations of the gas-phase products from a second biogenic system, d-limonene/NOx, were also undertaken in a high volume static mode. A single irradiation has been conducted in this series. Periodic samples were taken along the reaction profile using the 8 channel, 30-cm denuder. Samples have been analyzed and are now being interpreted.

4. An investigation of the gas-phase products from a toluene/NOx irradiation have been undertaken in a dynamic mode and high dilution static mode. The gas phase products from the dynamic mode collected using a denuder were discussed in a recent article, "Determination of Secondary Organic Aerosol Products from the Photooxidation of Toluene and their Implications in Ambient PM2.5." The article appeared in the Journal of Atmospheric Chemistry, vol. 47, pp. 79-100. In a separate experiment, samples were taken along the reaction profile in a static mode experiment.using the 8 channel, 30-cm denuder.

5. The initial chemical mechanism has been developed based on SAPRC 99 and CB4 chemical mechanisms with recent rate constant updates. These standard mechanism will be compare to an explicit a-pinene mechanism. The solver found in PKSS is now running. Test runs to determine chamber parameters have been completed.



Relevance :The research will directly address a key area of uncertainty identified in the NARSTO State of Science Reports that limits our ability to predict the contribution of hydrocarbons to photochemical ozone formation. For certain hydrocarbons including aromatic and natural hydrocarbons, the absence of analytical methods for measuring their oxidation products has prevented the development of smog chamber data bases for evaluating and improving chemical mechanisms used to predict their contributions to tropospheric ozone levels. Under the proposed research task a new analytical method will be used to measure concentrations of the oxidation products and a series of smog chamber experiments will be carried out to develop data bases that can be used to develop improved chemical mechanisms for toluene and alpha pinene.

Clients :OAQPS Tom Helms

Project IDs:

ID Code :12043

Project type :OMIS