AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Linking Chemical Composition and Volatility to the Oxidative Potential of Diesel Exhaust Aerosols
SHANTANU JATHAR, Cody Vanderheyden, Abril Galang, Liam Lewane, Kevin Klunder, Charles Henry, John Volckens, Colorado State University
Abstract Number: 522 Working Group: Linking Aerosol Oxidative Potential with Chemical Composition and Biological Endpoints
Abstract The aerosol oxidative potential is emerging as an important aerosol property that could help identify the chemical mechanisms by which aerosols affect human health. While certain chemical constituents (e.g., semi-volatile organic compounds, transition metals, elemental carbon) have been shown to correlate strongly with the measured oxidative potential, it is unclear how each of these chemical compounds contribute individually to the total oxidative potential. Furthermore, the aerosol chemical composition varies significantly with atmospheric mixing as semi-volatile organic compounds evaporate with dilution, affecting the aerosol oxidative potential. To systematically probe chemical composition and volatility, we conducted experiments with a non-road diesel engine for two different fuels (conventional diesel and soy-based biodiesel) and two different engine loads (idle and 50% load) at 8 to 10 different dilution ratios on a combination of bare quartz, Teflon, and quartz behind Teflon filters. The aerosol was mostly composed of organic aerosol and elemental carbon (~95%) with trace amounts of inorganic ions and metals (<1%). The organic aerosol at all fuel-load combinations was found to be strongly semi-volatile where more than three-quarters of the particle mass in the tailpipe was found to evaporate when diluted to urban-like concentrations. The aerosol chemical composition and volatility was nearly identical for diesel and biodiesel exhaust implying that the aerosol properties were only loosely linked to the fuel type. The oxidative potential, expressed as the rate of DTT consumption per unit aerosol mass, was higher (factor of ~2) for diesel exhaust compared to biodiesel exhaust and higher (factor of ~3) at 50% engine load than at idle. The oxidative potential per unit aerosol mass was found to be significantly lower for the semi-volatile vapors in equilibrium with the organic aerosol suggesting that the oxidative potential was more closely associated with the non-volatile and possibly insoluble aerosol components. Ongoing work is focused on performing a multilinear regression to shed further light on the relationship between the measured aerosol properties (composition and volatility) and the oxidative potential.