American Association for Aerosol Research - Abstract Submission

AAAR 38th Annual Conference
October 5 - October 9, 2020

Virtual Conference

Abstract View


Atmospheric Significance of the Aqueous-Phase Reactions of Green Leaf Volatiles: 1-Penten-3-ol, (Z)-2-Hexen-1-ol, and (E)-2-Hexen-1-al With Atmospheric Radicals

KUMAR SARANG, Tobias Otto, Krzysztof Rudzinski, Irena Grgić, Nestorowicz Klara, Hartmut Herrmann, Rafal Szmigielski, ICHF PAS, Warsaw, Poland

     Abstract Number: 353
     Working Group: Aerosol Chemistry

Abstract
Atmospheric particulate matter mostly consists of organic aerosols (OA), of which up to 90% exists as secondary organic aerosol (SOA). The incomplete knowledge of SOA precursors has led to the discrepancies between field measurements and the computer-modeled SOA budget. One of such potentially important, but missing sources of SOA is a class of compounds known as green leaf volatiles (GLVs). GLVs are C6-C5 unsaturated alcohols, aldehydes, or esters, which are released when a plant undergoes stress or mechanical wounding, such as cutting, freezing, or drying. The estimated annual global emission of C6 GLVs can alone give rise to 1-5 Tg C/yr SOA, i.e., at least one-third of that isoprene.

We investigated the temperature-dependent aqueous-phase kinetics of three GLVs: 1-penten-3-ol, (Z)-2-hexen-1-ol, and (E)-2-hexen-1-al with SO4•ꟷ, and •OH radicals. The second-order rate constants determined, range from 108-109 L mol-1s-1 for GLV+SO4•ꟷ, and from 109 to 1010 L mol-1s-1 for GLV+•OH kinetics. Various thermodynamic parameters, such as activation energy (EA), molar enthalpy of activation (ΔH‡), molar entropy of activation (ΔS‡), and Gibb’s free energy of activation (ΔG‡) were calculated. The activation energies of less than 20 kJ mol-1 indicated the weak temperature dependence of the reactions. The second-order rate constants, especially of the order 109 L mol-1s-1, are diffusion-controlled, and therefore, we investigated them for the diffusion limitation; and diffusion-corrected rate constants were obtained. To explain the atmospheric significance of these aqueous-phase reactions, we calculated the aqueous-phase lifetime and the relative removal rate of GLVs by the overall gas- and aqueous-phase to the aqueous-phase reactions. The calculations demonstrated the dominance of aqueous-phase reactions of GLVs in cloud and rain waters under certain specific conditions for available radical concentrations.