Products and mechanisms of the reactions of chlorine atoms with 1,3-butadiene and 2-methyl-1,3-butadiene (Isoprene) in air at room temperature

Chlorine atoms may be generated in coastal areas by reactions of sea salt particles transported inland with air masses. Chlorine atom precursors, such as Cl2 and HOCl, which can be photolyzed to give chlorine atoms, have been measured at coastal sites, and in the Arctic at polar sunrise. Once chlorine atoms are generated, they will react with ozone or organics in air. A potential approach to investigate chlorine atom production in the troposphere is to identify and measure unique chlorine-containing products of the reactions of Cl with organics, such as 1,3-butadiene, in air. 1,3-Butadiene was classified as a hazardous air pollutant under 1990 Clean Air Act. It is widely used as a major component of synthetic rubber and it can also be emitted from motor vehicles. Both chlorine atoms and 1,3-butadiene can be present in the urban coastal areas. If any unique chlorine-containing products can be determined from the reaction of Cl with 1,3-butadiene, they could serve as "markers" for chlorine atom chemistry in coastal areas. Product studies of the reactions of chlorine atoms with 1,3-butadiene, or isoprene, were carried out using atmospheric pressure ionization-mass spectrometry (API-MS), GC-MS and FTIR. 4-Chlorocrotonaldehyde (CCA) has been identified as a unique chlorine-containing product from the Cl-butadiene reaction in the presence or absence of NO in 1 atm air at room temperature. The yield of CCA is (29 +/- 7)% (2sigma) in the absence of NO and (65 +/- 20)% (2sigma) in the presence of NO. The yield of chloromethyl vinyl ketone (CMVK), another chlorine-containing compound from this reaction, is (19 +/- 4)% (2sigma) in the absence of NO. In the presence of NO, CMVK was not observed. CCA could serve as a marker for Cl chemistry in coastal urban areas.;Preliminary product studies of the reaction of chlorine atoms with 2-methyl-1,3-butadiene (isoprene) in the absence of NO were also performed. 1-Chloro-3-methyl-3-butene-2-one (CMBO) has been identified from the Cl-isoprene reaction in the absence of NO in 1 atm air at room temperature. It could serve as a marker for chlorine atom chemistry in low NOx environments in coastal areas where there are both sources of chorine atoms and isoprene.