AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
The Correlation between Positive Sampling Artifacts and Organic Aerosol Volatility
ANDREW A. MAY, Albert A. Presto, Allen Robinson, Carnegie Mellon University
Abstract Number: 341 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Collecting organic aerosol on bare quartz filters can often lead to a positive sampling artifact -- organic vapors that adsorb onto the filter. This is particularly true in source tests, which often have high concentrations of low-volatility organic vapors. These adsorbed organic vapors result in over-estimated particulate organic carbon on the quartz filter. The adsorbed vapors can be partially accounted for by collecting samples on quartz-behind-Teflon (QBT) filters in parallel to the bare quartz filters and calculating the difference (Q-QBT). Recent work has indicated that the relative amount of the positive sampling artifact associated with source testing of light-duty gasoline-powered vehicles is related to gas-particle partitioning.$^1 Furthermore, recent work has indicated that the quantity of sampling artifact is not constant across a volatility distribution. This work compares the volatility distribution inferred using thermal desorption-gas chromatography-mass spectrometry$^2 on bare quartz filters and QBT filters for light-duty gasoline-powered vehicles, a gas-turbine engine, and ambient samples collected during the Pittsburgh Air Quality Study. The results indicate that the sampling artifact is closely related to the volatility distribution of the organic aerosol for source testing; it is hypothesized that this relationship will also be observed for ambient sampling. The implications of this study are that accurate positive sampling artifact corrections require knowledge of the volatility distribution of both the sample collected on the bare quartz filter as well as the QBT filter.
References:
1) Lipsky, E.M. and Robinson, A.L. “Effects of Dilution on Fine Particle Mass and Partitioning of Semivolatile Organics in Diesel Exhaust and Wood Smoke.” Environ. Sci. Technol. 40 (2006): 155-162.
2) Presto, A.A., Nguyen, N.T., Ranjan, M., Reeder, A.J., Lipsky, E.M., Hennigan, C.J., Miracolo, M.A., Riemer, D.A., and Robinson, A.L. “Fine particle and organic vapor emissions from staged tests from an in-use aircraft engine.” Atmos. Envion. 45 (2011): 3603-3612.