Articles | Volume 10, issue 4
Research article
11 Apr 2017
Research article |  | 11 Apr 2017

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

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) and (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 diacid in reacted particles, determined using known diacid–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  ∼  30 nm of the surface layer, 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.

Short summary
Two model systems are studied: dicarboxylic acid particles with gaseous amines and α-cedrene ozonolysis particles. Measurements by direct analysis in real-time mass spectrometry and high-resolution time-of-flight aerosol mass spectrometry show that the reaction of the amines with the acid particles is restricted to the surface layer, with an odd–even alternating pattern. Furthermore, in the α-cedrene study, DART-MS is able to differentiate isomers based on their volatility.