Reaction Kinetics of Green Leaf Volatiles with Sulfate, Hydroxyl, and Nitrate Radicals in Tropospheric Aqueous Phase

Abstract

Green plants exposed to abiotic or biotic stress release C-5 and C-6 unsaturated oxygenated hydrocarbons called Green Leaf Volatiles (GLVs). GLVs partition into tropospheric waters and react to form secondary organic aerosol (SOA). We explored the kinetics of aqueous-phase reactions of 1-penten-3-ol (PENTOL), (Z)-2-hexen-1-ol (HEXOL), and (E)-2-hexen-1-al (HEXAL) with SO₄^•-, ^•OH, and NO₃^•. At 298 K, the rate constants for reactions of PENTOL, HEXOL, and HEXAL with SO₄^•- were, respectively, (9.4 ± 1.0) × 10⁸ L mol^-1 s^-1, (2.5 ± 0.3) × 10⁹ L mol^-1 s^-1, and (4.8 ± 0.2) × 10⁸ L mol^-1 s^-1; with ^•OH - (6.3 ± 0.1) × 10⁹ L mol^-1 s^-1, (6.7 ± 0.3) × 10⁹ L mol^-1 s^-1, and (4.8 ± 0.3) × 10⁹ L mol^-1 s^-1; and with NO₃^• - (1.5 ± 0.15) × 10⁸ L mol^-1 s^-1, (8.4 ± 2.3) × 10⁸ L mol^-1 s^-1, and (3.0 ± 0.7) × 10⁷ L mol^-1 s^-1. The rate constants increased weakly with temperatures ranging from 278 to 318 K. The diffusional limitations of the rate constants appeared significant only for the GLV-^•OH reactions. The aqueous-phase reactions appeared negligible in deliquescent aerosol and haze water but not in clouds and rains. The atmospheric lifetimes of GLVs decreased from many days to hours with increasing liquid water content and radicals' concentration.

Keywords: (E)-2-hexen-1-al; (Z)-2-hexen-1-ol; 1-penten-3-ol; atmospheric lifetime; atmospheric radicals; atmospheric removal rates.