Atmospheric Chemistry of α‐Diketones: Kinetics of C₅and C₆Compounds with Cl Atoms and OH Radicals

Abstract

Carbonyls play an important role in atmospheric chemistry due to their formation in the photooxidation of biogenic and anthropogenic volatile organic compounds and their high atmospheric reactivity. The Cl-initiated kinetics of two α-diketones (2,3-pentanedione (PTD) and 2,3-hexanedione (HEX)) have been determined as well as the OH + HEX rate constant using atmospheric simulation chamber experiments and the relative rate method. Up to three different reference compounds were used to assess robust results. The following rate constants (in cm 3 molecule −1 s −1 ) have been obtained at 298 K: k(Cl + PTD) = (1.6 ± 0.2) × 10 −11 , k(Cl + HEX) = (8.8 ± 0.4) × 10 −11 , and k(OH + HEX) = (3.6 ± 0.7) × 10 −12 with a global uncertainty of 30%. The present determinations of Cl-and OH-reaction rate constants for HEX constitute first measurements. Using the present measurements, a recently improved structure-activity relationship for Cl + ketone reactions has been updated by introducing an F(-COCO-) factor of 8.33 × 10 −4 . Atmospheric lifetime calculations indicate that chlorine-initiated oxidation may be a significant α-diketone sink in the marine-boundary layer or in places where high Cl concentrations may be found. C

Gas-Phase Ozone Reaction Kinetics of C5–C8Unsaturated Alcohols of Biogenic Interest

“…Alcohol calibration curves (Figures S1−S6) were carefully determined through FTIR spectroscopy using a White cell with a 10 m optical length. 30 The formation of the OH radical through the ozonolysis of hexenols was reported by Atkinson et al 21 alcohol but would not affect the ozone decay in a significant manner at the high initial alcohol/ozone concentration ratios employed. The two experiments noted above were carried out to confirm the absence of an effect on the O 3 decay.…”

“…The ozone decay was monitored by a UV-absorption O 3 analyzer (Environment SA 42M) with a resolution time of 10 s. Preliminary tests showed that the investigated alcohols did not absorb at the wavelength of the ozone instrument (253.7 nm). Alcohol calibration curves (Figures S1–S6) were carefully determined through FTIR spectroscopy using a White cell with a 10 m optical length …”