Pulse radiolysis and FT-IR smog chamber experiments were used to investigate the atmospheric fate of C6H5O(•) radicals. Pulse radiolysis experiments gave σ(C6H5O(•))235  nm = (3.82 ± 0.48) × 10-17 cm2 molecule-1, k(C6H5O(•) + NO) = (1.88 ± 0.16) × 10-12, and k(C6H5O(•) + NO2) = (2.08 ± 0.15) × 10-12 cm3 molecule-1 s-1 at 296 K in 1000 mbar of SF6 diluent. No discernible reaction of C6H5O(•) radicals with O2 was observed in smog chamber experiments, and we derive an upper limit of k(C6H5O(•) + O2) < 5 × 10-21 cm3 molecule-1 s-1 at 296 K. These results imply that the atmospheric fate of phenoxy radicals in urban air masses is reaction with NO x . Density functional calculations and gas chromatography−mass spectrometry are used to identify 4-phenoxyphenol as the major product of the self-reaction of C6H5O(•) radicals. As part of this study, relative rate techniques were used to measure rate constants for reaction of Cl atoms with phenol [k(Cl + C6H5OH) = (1.93 ± 0.36) × 10-10], several chlorophenols [k(Cl + 2-chlorophenol) = (7.32 ± 1.30) × 10-12, k(Cl + 3-chlorophenol) = (1.56 ± 0.21) × 10-10, and k(Cl + 4-chlorophenol) = (2.37 ± 0.30) × 10-10], and benzoquinone [k(Cl + benzoquinone) = (1.94 ± 0.35) × 10-10], all in units of cm3 molecule-1 s-1. A reaction between molecular chlorine and C6H5OH to produce 2- and 4-chlorophenol in yields of (28 ± 3)% and (75 ± 4)% was observed. This reaction is probably heterogeneous in nature, and an upper limit of k(Cl2 + C6H5OH) ≤ 1.9 × 10-20 cm3 molecule-1 s-1 was established for the homogeneous component. These results are discussed with respect to the previous literature data and to the atmospheric chemistry of aromatic compounds.

It is important to characterize the chemical properties of particulate matter in order to understand how low doses, inhaled by a susceptible population, might cause human health effects. The formation of reactive oxygen species catalyzed by neutral, aqueous extracts of two ambient particulate samples, National Institute of Standards & Technology (NIST) Standard Reference Materials (SRM) 1648 and 1649, and two diesel particulate samples, NIST SRM 1650 and SRM 2975, were measured. The formation of reactive oxygen species was estimated by measuring the formation of malondialdehyde from 2-deoxyribose in the presence of ascorbic acid; H2O2 was not added to this assay. SRM 1649, ambient particulate matter collected from Washington, DC, generated the most malondialdehyde, while SRM 2975, diesel particulate matter collected from a forklift, yielded the least amount. Desferrioxamine inhibited the formation of malondialdehyde from the particulate samples providing additional data to support the observation that transition metals were involved in the generation of reactive oxygen species. Six transition metal sulfates (iron sulfate, copper sulfate, vanadyl sulfate, cobalt sulfate, nickel sulfate, and zinc sulfate) were assayed for their ability to generate reactive oxygen species under the same conditions used for the particulate samples in order to facilitate comparisons between particles and these transition metals. The concentration of transition metals was measured in aqueous extracts of these particulate samples using ion-coupled plasma mass spectrometry (ICP-MS) analysis. There was qualitative agreement between the concentrations of Fe, Cu, and V and the amount of malondialdehyde produced from extracts of these particulate samples. These data suggest that transition metals can be dissolved from particles in neutral, aqueous solutions and that these metals are capable of catalyzing the formation of reactive oxygen species.

The rate constant for the reaction of dimethoxymethane (DMM) with OH radicals was determined to be (4.6 ( 1.6) × 10 -12 at 346 ( 3 K using a pulse radiolysis/transient UV absorption absolute rate technique and (5.3 ( 1.0) × 10 -12 cm 3 molecule -1 s -1 at 295 ( 2 K using an FTIR-smog chamber relative rate technique. The reaction of OH radicals with DMM occurs via an H-atom abstraction mechanism with 76% of the attack occurring on the -CH 3 end groups and 24% on the central -CH 2 -unit. The atmospheric fate of the alkoxy radicals CH 3 OCH 2 OCH 2 O(•) and CH 3 OCHO(•)OCH 3 at 296 K in 700 Torr of air was investigated using an FTIR-smog chamber technique. The sole atmospheric fate of CH 3 OCHO(•)OCH 3 radicals is reaction with O 2 to give dimethyl carbonate (CH 3 OC(O)OCH 3 ) and HO 2 radicals. At least three loss processes were identified for CH 3 OCH 2 OCH 2 O(•) radicals. In 1 atm of air at 295 K, 84 ( 4% of the CH 3 OCH 2 OCH 2 O(•) radicals react with O 2 while 7 ( 3% undergo H-atom elimination; the fate of the remaining 9% is unclear. OH radical-initiated oxidation of DMM in 1 atm of air at 296 K results in a yield of 24% dimethyl carbonate and 69% methoxymethyl formate; the oxidation mechanism of the remaining 7% of DMM is unclear. Relative rate techniques were used to measure rate constants for the reaction of Cl atoms with CH 3 OCH 2 OCH 3 and CH 3 OCH 2 OCHO of (1.4 ( 0.2) × 10 -10 and (3.6 ( 0.6) × 10 -11 cm 3 molecule -1 s -1 , respectively. Results are discussed in the context of the atmospheric chemistry of DMM. X Abstract published in AdVance ACS Abstracts, June 15, 1997.

We describe a quantitative method for using the quartz crystal microbalance (QCM) to characterize the high frequency viscoelastic response of glassy polymer coatings with thicknesses in the 5-10 μm regime. By measuring the frequency and dissipation at the fundamental resonant frequency (5 MHz) and at the third harmonic (15 MHz), we obtain three independent quantities. For coatings with a predominantly elastic response, characterized by relatively low phase angles, these quantities are the mass per unit area of the coating, the density-shear modulus product, and the phase angle itself. The approach was demonstrated with a model polyurethane coating, where the evolution of these properties as a function of cure time was investigated. For fully cured films, data obtained from the QCM are in good agreement with results obtained from traditional dynamic mechanical analysis.