A mixed‐phase relative rates technique for measuring aerosol reaction kinetics

A mixed‐phase relative rates approach for measuring rates of reaction in aerosols is presented. Using this method the rate of reaction of methyl oleate (MO) particles, normalized to the gas‐particle collision rate, was measured to be γMO = 1.12 (±0.36) × 10−3 with 2‐methyl‐2‐butene as the gas‐phase reference. This value compares favorably with our previously published value of 1.23 × 10−3 measured using an absolute technique. Reaction of bis(2‐ethylhexyl) sebacate (BES) particles with Cl and OH radicals was also studied using acetone and hexanal, respectively, as the gas‐phase references. The rates of reaction of BES, normalized to the gas‐particle collision rate, were measured to be γBES = 1.8 (−0.3+0.8) and γBES = 2.0 (−0.1+0.6) with Cl and OH, respectively. These fast rates of reaction (γBES > 1) imply that secondary reactions, perhaps involving radical chain mechanisms, could impact the rate at which organic particles are oxidized in the atmosphere.