History of Carbon Measurement in Atmospheric Particulate Matter
STEPHEN MCDOW, Barbara Turpin,
U.S. EPA Abstract Number: 137
Working Group: History of Aerosol Science
AbstractA vast literature now documents the health effects of particulate matter (PM), including cardiac effects, aggravated asthma, decreased lung function, and premature mortality. To better understand these effects and effectively control PM sources, the measurement of particular PM components has been a high priority. Parallel efforts have concerned the role of different PM components in effects on visibility, climate, materials, and ecosystems. Carbon containing species account for a large fraction, if not the majority, of PM mass in many U.S. locations. But carbon in PM is distributed among thousands of individual organic compounds with diverse properties, as well as large amorphous structures of nearly pure carbon, commonly referred to as elemental carbon. Early approaches to quantify organic material in PM involved extraction from glass fiber filters with various organic solvents, but these were time consuming and often hindered by poor extraction efficiencies for some compounds. A more convenient approach was to measure carbon dioxide after combustion of PM collected on quartz fiber filters, either directly using infrared spectroscopy or after reduction to methane using flame ionization detection. Added benefits of this method were: 1) the ability to evaluate for carbon mass closure in comparison to molecular-level analyses, and 2) the separation and analysis of both organic and elemental carbon if changes in filter reflectance or absorption during analysis was monitored. This presentation follows the story of thermal/optical carbon analysis: its early development, challenges separating organic and elemental carbon, addressing organic vapor adsorption artifacts on filters, development of high time resolution methods to study atmospheric processes, incorporation into national monitoring networks for PM speciation trends and atmospheric visibility impairment, and standard development and method harmonization for routine analysis.