10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Improved Estimation of Organic Aerosol Volatility Distributions by Combining Thermodenuder and Isothermal Dilution Measurements
KERRIGAN CAIN, Eleni Karnezi, Spyros Pandis, Carnegie Mellon University
Abstract Number: 522 Working Group: Aerosol Transport and Transformation
Abstract Volatility is one of the most important physical properties of organic aerosol (OA), as it determines the partitioning of its components between the gas and particulate phases and eventually, their atmospheric fate. Most studies have estimated the OA volatility distribution using a thermodenuder (TD); however, the resulting distributions were quite uncertain. In this work, we test the hypothesis that the combination of TD and dilution measurements can better constrain OA volatility distributions over a wide range.
In this study, the method of Louvaris et al. (2017) combining TD and isothermal dilution measurements was refined using secondary organic aerosol (SOA) generated from the ozonolysis and reaction with OH radicals of several different precursors. SOA was produced in a smog chamber and sampled with a TD followed by a high-resolution time-of-flight aerosol mass spectrometer (AMS) and a scanning mobility particle sizer (SMPS). Parallel to the TD, a dilution chamber partially filled with clean air was used to isothermally dilute the SOA. The mass fraction remaining as a function of TD temperature and time in the dilution chamber was monitored by the AMS and SMPS. Improved wall loss corrections were used in order to better account for evaporation in the dilution chamber. The thermograms were then used with the algorithm of Karnezi et al. (2014) to estimate the volatility distributions, effective enthalpies of vaporization, and accommodation coefficients of the SOA tested. The results indicated that TD measurements alone overestimate the amount of semi-volatile SOA components. Furthermore, when the dilution measurements were added, the uncertainties of the semi-volatile components and enthalpy of vaporization were reduced.
The combination of TD and dilution measurements shows improvement over current techniques to estimate OA volatility distributions and can be implemented easily into volatility studies already using a TD. The application of this technique to ambient aerosol can provide insight into OA volatility and the results can be used to update chemical transport models accordingly.
References:
Karnezi, E., Riipinen, I., and Pandis, S. N.: Measuring the atmospheric organic aerosol volatility distribution: A theoretical analysis, Atmos. Meas. Tech., 7, 2953-2965, 2014.
Louvaris, E. E., Karnezi, E., Kostenidou, E., Kaltsonoudis, C., and Pandis, S. N.: Estimation of the volatility distribution of organic aerosol combining thermodenuder and isothermal dilution measurements, Atmos. Meas. Tech., 10, 3909-3918, 2017.