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

Abstract

[1] 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 g MO = 1.12 (±0.36) Â 10 À3 with 2-methyl-2-butene as the gas-phase reference. This value compares favorably with our previously published value of 1.23 Â 10 À3 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 g BES = 1.8 ( À0.3 +0.8 ) and g BES = 2.0 ( À0.1 +0.6 ) with Cl and OH, respectively. These fast rates of reaction (g BES > 1) imply that secondary reactions, perhaps involving radical chain mechanisms, could impact the rate at which organic particles are oxidized in the atmosphere. Citation: Hearn, J. D., and G. D. Smith (2006), A mixed-phase relative rates technique for measuring aerosol reaction kinetics, Geophys. Res. Lett., 33, L17805,

Heterogeneous oxidation of saturated organic aerosols by hydroxyl radicals: uptake kinetics, condensed-phase products, and particle size change

“…In contrast, the latter case may lead to γ values that are greater than unity when secondary condensed-phase chemistry is an important loss mechanism for condensed-phase species. For example, Hearn and Smith (2006) measured γ 0 =2.0 for OH oxidation of BES particles, which is somewhat larger than our value. From their results, Hearn and Smith (2006) suggested that OH-initiated secondary chemistry lead to additional loss of BES.…”

“…Laboratory research has concentrated on the reaction of O 3 with condensed-phase unsaturated organic compounds, e.g., oleic acid, as a proxy for chemical aging of organic aerosol (e.g., Morris et al, 2002;Hearn and Smith, 2004;Katrib et al, 2004;Thornberry and Abbatt, 2004;Hearn and Smith, 2005;Katrib et al, 2005;Knopf et al, 2005;Ziemann, 2005). Fewer studies have been conducted to investigate the chemical aging of condensed-phase saturated organics by atmospheric radicals (e.g., Bertram et al, 2001;Moise and Rudich, 2001;Eliason et al, 2004;Molina et al, 2004;Hearn and Smith, 2006;Knopf et al, 2006;Hearn et al, 2007;Lambe et al, 2007).…”

Oxidation of a model alkane aerosol by OH radical: the emergent nature of reactive uptake

“…Typical values for the uptake of OH by saturated organic compounds are 0.3-1.0. 11,12,16,20,21 Because the primary reaction between OH and a hydrocarbon is the abstraction of an H atom, a very fast process, γ in this chemical system has been interpreted to mean that OH accommodates efficiently, i.e. nearly every OH collision results in an oxidation reaction, and therefore γ represents the overall accommodation process directly.…”

Detailed heterogeneous chemistry in an urban plume box model: reversible co-adsorption of O<sub>3</sub>, NO<sub>2</sub>, and H<sub>2</sub>O on soot coated with benzo[a]pyrene

“…Other trace gases, such as OH and NO 3 , are also involved in important heterogeneous reactions (e.g. Bertram et al, 2001;Molina et al, 2004;Hearn and Smith, 2006;Knopf et al, 2006;Gross and Bertram, 2008;Park et al, 2008;Gross and Bertram, 2009), but have not been shown to adhere to Langmuir adsorption kinetics with subsequent surface reactions (Langmuir-Hinshelwood type reactions) and are therefore not the subject of this study. Although we attempt to use realistic values characteristic of an urban plume scenario as input parameters, our purpose is not to make exact atmospheric predictions.…”