The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of hexamethyldisiloxane (MM, (CH 3 molecule Ϫ1 s Ϫ1 , respectively. Investigation of the OH ϩ siloxane reaction products yielded trimethylsilanol, pentamethyldisiloxanol, heptamethyltetrasiloxanol, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and other compounds. Several of these products have not been reported before because these siloxanes and the proposed reaction mechanisms yielding these products are complicated. Some unusual cyclic siloxane products were observed and their formation pathways are discussed in light of current understanding of siloxane atmospheric chemistry.

The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of 2-propoxyethanol (2PEOH, CH 3 CH 2 CH 2 OCH 2 CH 2 (OH)). 2PEOH reacts with OH with a bimolecular rate constant of (21.4 Ϯ 6.0) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 at 297 Ϯ 3 K and 1 atm total pressure, which is a little larger than previously reported [1]. Assuming an average OH concentration of 1 ϫ 10 6 molecules cm Ϫ3 , an atmospheric lifetime of 13 h is calculated for 2PEOH. In order to more clearly define this hydroxy ether's atmospheric reaction mechanism, an investigation into the OH ϩ 2PEOH reaction products was also conducted. The OH ϩ 2PEOH reaction products and yields observed were: propyl formate (PF, 47 Ϯ 2%, CH 3 CH 2 CH 2 OC(" O)H), 2 propoxyethanal (CH 3 CH 2 CH 2 OCH 2 C("O)H 15 Ϯ 1%), and 2-ethyl-1,3-dioxolane (5.4 Ϯ 0.4%). The 2PEOH reaction mechanism is discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. The findings reported here can be related to other structurally similar alcohols and may impact regulatory tools such as ground-level ozone-forming potential calculations (incremental reactivity) [2].

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