Atmospheric aqueous phase radical chemistry of the isoprene oxidation products methacrolein, methyl vinyl ketone, methacrylic acid and acrylic acid – kinetics and product studies

Abstract

Kinetic and mechanistic studies were conducted on the isoprene oxidation products methacrolein, methyl vinyl ketone, methacrylic and acrylic acid reacting with hydroxyl and nitrate radicals and sulfate radical anions in aqueous solution by use of the laser flash photolysis technique and a reversed-rate method for kinetics. High-performance liquid chromatography/mass spectrometry was applied for product analysis. The kinetic investigations show the highest reactivity of the hydroxyl radical followed by sulfate and nitrate radicals. For methacrolein and methyl vinyl ketone the following rate constants have been determined at 298 K: k(OH+methacrolein) = (9.4 ± 0.7) × 10(9) M(-1) s(-1), k(OH+methyl vinyl ketone) = (7.3 ± 0.5) × 10(9) M(-1) s(-1), k(NO3+methacrolein) = (4.0 ± 1.0) × 10(7) M(-1) s(-1), k(NO3+methyl vinyl ketone) = (9.7 ± 3.4) × 10(6) M(-1) s(-1), k(SO4(-)+methacrolein) = (9.9 ± 4.9) × 10(7) M(-1) s(-1) and k(SO4(-)+methyl vinyl ketone) = (1.0 ± 0.2) × 10(8) M(-1) s(-1). Temperature and pH dependencies of the reactions of OH, NO3 and SO4(-) with methacrolein, methyl vinyl ketone, methacrylic and acrylic acid as well as Arrhenius parameters have been obtained and discussed. Product studies were performed on the OH radical induced oxidation of methacrolein and methyl vinyl ketone. In the reaction of methacrolein + OH methylglyoxal and hydroxyacetone were identified as first oxidation products with yields of 0.099 and 0.162. Methylglyoxal was primarily produced in the oxidation of methyl vinyl ketone with a yield of 0.052. For both precursor compounds the formation of glycolaldehyde was observed for the first time with yields of 0.051 and 0.111 in the oxidation of methacrolein and methyl vinyl ketone, respectively. Furthermore, highly functionalised C4 compounds were determined from the oxidation of both precursor compounds, but for the first time for methyl vinyl ketone. Reaction schemes were developed based on known peroxyl radical reaction mechanisms. The aqueous phase conversion of the first generation isoprene oxidation products can potentially contribute to tropospheric aqueous phase budgets of important carbonyl and dicarbonyl components which are expected to be conducive to the formation of aqSOA.

CLEPS 1.0: A new protocol for cloud aqueous phase oxidation of VOC mechanisms

“…One hour after the start of aqueous phase chemistry, O / C in the aqueous phase has remained around 1.0 and n C has decreased to 2.8 after a sharp initial increase to 2.9, thus showing that fragmentation is a major process. This result is in good agreement with other aqueous phase studies (Brégonzio-Rozier et al, 2016;Epstein and Nizkorodov, 2012;Epstein et al, 2013) and other models (Schrödner et al, 2014), but is in disagreement with field studies, probably due to a lack of descriptions of high molecular weight substances, and of their reactivity, as well as oligomerization processes. The higher O / C ratios obtained by Schrödner et al (2014) after the cloud event (1.8 for their rural case) can be due to important oxalic acid concentrations dissolved into the aqueous phase in their model, when the cloud is being formed.…”

Molecular Characterization of Organosulfates in Highly Polluted Atmosphere Using Ultra‐High‐Resolution Mass Spectrometry

“…The photooxidation of isoprene could produce isoprene epoxydiols (IEPOX C 5 H 10 O 3 ), methacrylic acid epoxide (MAE C 4 H 6 O 3 ) or hydroxymethyl‐methyl‐α‐lactone (HMML C 4 H 6 O 3 ), and MVK (C 4 H 6 O) or MACR (C 4 H 6 O) (Schoene et al, 2014; Worton et al, 2013). Among these oxidation products, IEPOX and MAE/HMML have been identified as two key gas‐phase intermediates to isoprene‐derived OSs formation under low‐NO x (i.e., hydroperoxyl (HO 2 ) channel) and high‐NO x (i.e., nitrogen oxides (NO/NO 2 ) channel) conditions, respectively (Lin et al, 2013; Paulot et al, 2009).…”

Efficient Nighttime Biogenic SOA Formation in a Polluted Residual Layer

“…The predicted final isoprene mixing ratios account for losses due to gas‐phase reactions with simulated NO 3 , O 3 , and OH along the cyan trajectory. The model does not include aqueous‐phase chemistry of isoprene oxidation products with NO 3 radical (Schöne et al, 2014). Figure 14 shows the estimated SOA mass yields range from 0 to 0.55 as a function of newly formed SOA mass, calculated by dividing the observed SOA masses by the corresponding modeled amounts of isoprene mass reacted with NO 3 .…”