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SAMPLING DURATION DEPENDENCE OF SEMI-CONTINUOUS ORGANIC CARBON MEASUREMENTS ON STEADY STATE SECONDARY ORGANIC AEROSOLS
Citation:
Offenberg, J, M Lewandowski, T E. Kleindienst, E O. Edney, M. Jaoui, AND E. W. Corse. SAMPLING DURATION DEPENDENCE OF SEMI-CONTINUOUS ORGANIC CARBON MEASUREMENTS ON STEADY STATE SECONDARY ORGANIC AEROSOLS. Presented at American Association for Aerosol Research 2004 Annual Conference, Atlanta, GA, October 4-8, 2004.
Impact/Purpose:
1. Using laboratory and field study data generated during FY99-FY04, develop a science version of a PM chemistry model for predicting ambient concentrations of water, inorganics, and organics in PM2.5 samples. The model will include the Aerosol Inorganic Model for predicting concentrations of inorganic compounds and a computational chemistry-based method for predicting concentrations of organic compounds.
2. Identify and evaluate methods for analyzing the polar fraction of PM2.5 samples.
3. Carry out short term field studies in Research Triangle Park, North Carolina in the summer and the winter to determine the composition of the organic fraction of ambient PM2.5 samples, with special emphasis placed on identifying and determining ambient concentrations of polar compounds.
4. Conduct laboratory studies to establish the chemical composition of secondary organic aerosol (SOA) and to determine source signatures for aromatic and biogenic SOA.
5. Conduct laboratory and theoretical investigations of thermodynamic properties of polar organic compounds.
6. Evaluate the science version of the PM chemistry model using laboratory and field data generated under this task as well as other available data in the literature.
7. Conduct PM chemistry-related special studies for OAQPS
Description:
Semi-continuous organic carbon concentrations were measured through several experiments of statically generated secondary organic aerosol formed by hydrocarbon + NOx irradiations. Repeated, randomized measurements of these steady state aerosols reveal decreases in the observed concentration with increasing sampling time for a given sampling flow rate. More pronounced changes are observed when a gas phase denuder is not upstream of the semi-continuous instrument. Initial results indicate that longer sampling integrations times will minimize the influence of the apparent sampling artifacts. Furthermore, these experiments indicate that reported organic carbon concentrations collected using one set of sampling time/flow rate parameters may not be comparable to other sampling protocols, especially when protocols involve short duration sampling, or when integrations periods are most dissimilar. Extrapolation of these results to ambient measurements of organic carbon also suggests that comparison of concentrations measured via differing instrumental protocols may lead to results which are not directly comparable.
This work has been funded wholly or in part by the United States Environmental Protection Agency under Contract 68-D-00-206 to ManTech Environmental Technology, Inc. Although this work was reviewed by the EPA and approved for publication, it may not necessarily reflect official Agency policy.