Unique products of the reaction of isoprene with atomic chlorine: Potential markers of chlorine atom chemistry

Abstract

Abstract. The contribution of atomic chlorine to the chemistry of marine regions as well as the Arctic at ground level at polar sunrise is the subject of a number of recent studies. However, identifying the specific chlorine atom precursors has proven difficult. One potential approach is the measurement of definitive products of chlorine atom reactions, for example with biogenic hydrocarbons. We report here product studies of the chlorine atom reaction with isoprene using ppm concentrations at one atmosphere air and 298 K in a NOx-free system using atmospheric pressure ionization-mass spectrometry (API-MS) as well as GC-MS. 1-chloro-3-methyl-3-butene-2-one (CMBO) is identified as a unique product of this reaction, and there is evidence of the formation of three additional isomers of CMBO as well. Methyl vinyl ketone (MVK) is formed in small yields (9 + 5 %), consistent with earlier studies of this reaction in which an upper yield of 13% was reported. The stable product expected from allylic hydrogen atom abstraction (measured in earlier kinetic studies to be 15% of the total reaction), 2-methylene-3-butenal, is also tentatively identified using API-MS. Assuming that similar chemistry occurs at the ppb-ppt levels found in the atmosphere, identification of CMBO and/or its isomers in field studies could provide strong evidence of chlorine atom chemistry in low NO x environments where there are also sources of isoprene.

Secondary organic aerosol from chlorine-initiated oxidation of isoprene

“…S12). The formation of C 5 H 8 O from chlorine-isoprene oxidation has been proposed in the literature (Nordmeyer et al, 1997). Previous studies that observed C 5 H 8 O during OH-initiated oxidation of isoprene identified it as 2-methylbut-3-enal, but its formation mechanism remains unclear (Brégonzio-Rozier et al, 2015;Healy et al, 2008) and is beyond the scope of this work.…”

“…Previous studies that observed C 5 H 8 O during OH-initiated oxidation of isoprene identified it as 2-methylbut-3-enal, but its formation mechanism remains unclear (Brégonzio-Rozier et al, 2015;Healy et al, 2008) and is beyond the scope of this work. It should be noted that CMBO has long been identified as a unique gas-phase marker for isoprene-chlorine oxidation (Chang and Allen, 2006;Nordmeyer et al, 1997;Riemer et al, 2008;Tanaka et al, 2003). Degradation of CMBO by OH is implemented in some air quality models, though only with inferred reaction rates ).…”

“…Chlorine-initiated oxidation of isoprene could either proceed via the dominant (85 %) chlorine-addition pathway or a minor (15 %) hydrogen-abstraction pathway (Fantechi et al, 1998;Lei and Zhang, 2000;Nordmeyer et al, 1997;Orlando et al, 2003). Major gas-phase products include methyl vinyl ketone (MVK), methacrolein (MACR), chloroacetone, chloroacetaldehyde, hydrochloric acid, and isomers of 1-chloro-3-methyl-3-butene-2-one (CMBO), a unique tracer for atmospheric chlorine chemistry (Nordmeyer et al, 1997;Riemer et al, 2008;Tanaka et al, 2003).…”

“…Major gas-phase products include methyl vinyl ketone (MVK), methacrolein (MACR), chloroacetone, chloroacetaldehyde, hydrochloric acid, and isomers of 1-chloro-3-methyl-3-butene-2-one (CMBO), a unique tracer for atmospheric chlorine chemistry (Nordmeyer et al, 1997;Riemer et al, 2008;Tanaka et al, 2003). The rate constant of the isoprene-chlorine reaction at 25 • C (2.64-5.50 × 10 −10 molecules −1 cm 3 ; Fantechi et al, 1998;Orlando et al, 2003;Ragains and Finlayson-Pitts, 1997) is much larger than the rate constant of the isoprene-OH reaction (1.00 × 10 −10 molecules −1 cm 3 ; Atkinson and Arey, 2003), suggesting that isoprene-chlorine chemistry could compete with isoprene-OH chemistry under certain conditions.…”

Past and present-day biogenic volatile organic compound emissions in East Asia

“…Isoprene and the monoterpenes are also quite reactive and have atmospheric lifetimes of considerably less than a day. Like most VOC, the daytime oxidation of biogenic VOC is initiated primarily by reaction with OH, however reaction with O 3 , NO 3 , and Cl can also be important under some circumstances for some compounds (Atkinson, 1994(Atkinson, , 1997Atkinson and Arey, 1998;Nordmeyer et al, 1997;Paulson et al, 1992a, b).…”