Formation and reaction of hydroxycarbonyls from the reaction of OH radicals with 1,3-butadiene and isoprene

Abstract

1,3-Butadiene and isoprene (2-methyl-1,3-butadiene) are emitted into the atmosphere in vehicle exhaust and, in the case of isoprene, from vegetation. We have investigated the formation and further reaction of products of their hydroxyl radical-initiated reactions using atmospheric pressure ionization mass spectrometry (API-MS) and solid-phase microextraction fibers precoated with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine for on-fiber derivatization of carbonyl compounds, with subsequent analysis by thermal desorption and gas chromatography with flame ionization detection (SPME/GC-FID) or MS detection. Products attributed as HOCH2CH=CHCHO and HOCH2CH=CHCH2ONO2 (and isomers) from 1,3-butadiene; HOCD2CD=CDCDO and HOCD2CD=CDCD2ONO2 (and isomers) from 1,3-butadiene-d6; HOCH2C(CH3)=CHCHO and/or HOCH2CH=C(CH3)CHO, and HOCH2C(CH3)=CHCH2ONO2 (and isomers) from isoprene; and HOCD2C(CD3)=CDCDO and/or HOCD2CD=C(CD3)CDO, and HOCD2C(CD3)=CDCD2ONO2 (and isomers) from isoprene-d8 were observed as their NO2- adducts in the API-MS analyses. The hydroxycarbonyls were observed from SPME/GC-FID analyses of the 1,3-butadiene and isoprene reactions as their oximes, together with acrolein, glycolaldehyde, and glyoxal from the 1,3-butadiene reaction. A rate constant for the reaction of OH radicals with 4-hydroxy-2-butenal of (5.7 +/- 1.4) x 10(-11) cm3 molecule(-1) s(-1) at 298 +/- 2 K was derived, and formation yields of acrolein and 4-hydroxy-2-butenal from the 1,3-butadiene reaction of 58 +/- 10% and 25 (+15/-10)%, respectively, were determined. Analogous experiments showed that the two C5-hydroxycarbonyls formed from isoprene have rate constants for their reactions with OH radicals of (1.0 +/- 0.3) x 10(-10) cm3 molecule(-1) s(-1) and (4 +/- 2) x 10(-11) cm3 molecule(-1) s(-1) and a combined yield of approximately 15%, although isomer-specific identification of the hydroxycarbonyls was not achieved.