New insights into atmospherically relevant reaction systems using direct analysis
in real time-mass spectrometry (DART-MS)
Yue Zhao, Michelle C. Fairhurst, Lisa M. Wingen, Véronique Perraud, Michael J. Ezell, and Barbara J. Finlayson-Pitts
Department of Chemistry, University of California, Irvine, CA 92697, USA
Received: 27 Oct 2016 – Accepted for review: 24 Nov 2016 – Discussion started: 29 Nov 2016
Abstract. The application of direct analysis in real time mass spectrometry (DART-MS), which is finding increasing use in atmospheric chemistry, to two different laboratory model systems for airborne particles is investigated: (1) submicron C3-C7 dicarboxylic acid (diacid) particles reacted with gas phase trimethylamine (TMA) or butylamine (BA); (2) secondary organic aerosol (SOA) particles from the ozonolysis of α-cedrene. The diacid particles exhibit a clear odd-even pattern in their chemical reactivity toward TMA and BA, with the odd-carbon diacid particles being substantially more reactive than even ones. The ratio of base to acids in reacted particles, determined using known acid-base mixtures, was compared to that measured by high resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), which vaporizes the whole particle. Results show that DART-MS probes mainly surface layers, consistent with other studies on different systems. For α-cedrene SOA particles, it is shown that varying the temperature of the particle stream as it enters the DART-MS ionization region can distinguish between specific components with the same molecular mass but different vapor pressures. These results demonstrate the utility of DART-MS for (1) examining reactivity of heterogeneous model systems for atmospheric particles and (2) probing components of SOA particles based on volatility.
Zhao, Y., Fairhurst, M. C., Wingen, L. M., Perraud, V., Ezell, M. J., and Finlayson-Pitts, B. J.: New insights into atmospherically relevant reaction systems using direct analysis
in real time-mass spectrometry (DART-MS), Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-357, in review, 2016.