UNIQUE PRODUCTS OF THE REACTION OF ISOPRENE WITH ATOMIC CHLORINE - POTENTIAL MARKERS OF CHLORINE ATOM CHEMISTRY

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 chlo rine atom precursors has proven difficult. One potential approach is t he 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 o ne atmosphere air and 298 K in a NOx-free system using atmospheric pre ssure 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 t his reaction, and there is evidence of the formation of three addition al isomers of CMBO as well. Methyl vinyl ketone (MVK) is formed in sma ll yields (9 +/- 5 %), consistent with earlier studies of this reactio n in which an upper yield of 13% was reported. The stable product expe cted from allylic hydrogen atom abstraction (measured in earlier kinet ic studies to be 15% of the total reaction), 2-methylene-3-butenal, is also tentatively identified using API-MS. Assuming that similar chemi stry occurs at the ppb-ppt levels found in the atmosphere, identificat ion of CMBO and/or its isomers in field studies could provide strong e vidence of chlorine atom chemistry in low NOx environments where there are also sources of isoprene.