The pulse laser photolysis/laser induced fluorescence (PLP-LIF) technique has been used to measure the rate constants of the reactions of OH radicals with dimethyl ether and methyl-tert-butyl ether. OH radicals were produced by photolysis of H 2 O 2 at λ ) 266 nm. The photolysis cell was heated by a small electric furnaces in order to obtain information on the temperature dependency of the rate constants in the domain of 295-660 K. A preliminary study of the reaction of OH with methane was carried out to control the experimental setup. The Arrhenius expression obtained in the temperature range of 295-668 K, k OH+CH 4 ) (5.65 ( 0.49) × 10 -21 T 3.01 exp[-(959 ( 36)/T], is in very good agreement with previous determinations (bimolecular rate constant units: cm 3 molecule -1 s -1 ; error limits ( 2σ). For the reactions of OH with ethers, the Arrhenius expressions derived from our own results are k OH+DME (295-618 K) ) (3.02 ( 0.10) × 10 -20 T 2.85 exp[(618 ( 13)/T] and k OH+MTBE (297-616 K) ) (6.59 ( 0.43) × 10 -19 T 2.40 exp ([(499 ( 22)/T]. Combining these data with those from previous experimental studies allows us to derive Arrhenius expressions in larger temperature domains: k OH+DME (230-650 K) ) (4.59 ( 0.21) × 10 -19 T 2.46 exp[(476 ( 14)/T] and k OH+MTBE (230-750 K) ) (1.58 ( 0.09) × 10 -20 T 2.93 exp([(716 ( 18)/T].

No abstract

Rate coefficients for the gas-phase reactions of OH radicals with four unsaturated alcohols, 3-methyl-3-buten-1-ol (k1), 2-buten-1-ol (k2), 2-methyl-2-propen-1-ol (k3) and 3-buten-1-ol (k4), were measured using two different techniques, a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. The Arrhenius rate coefficients (in units of cm(3) molecule(-1) s(-1)) over the temperature range 263-371 K were determined from the kinetic data obtained as k1 = (5.5 +/- 1.0) x 10(-12) exp [(836 +/- 54)/T]; k2 = (6.9 +/- 0.9) x 10(-12) exp [(744 +/- 40)/T]; k3 = (10 +/- 1) x 10(-12) exp [(652 +/- 27)/T]; and k4 = (4.0 +/- 0.4) x 10(-12) exp [(783 +/- 32)/T]. At 298 K, the rate coefficients obtained by the two methods for each of the alcohols studied were in good agreement. The results are presented and compared with those obtained previously for the same and related reactions of OH radicals. Reactivity factors for substituent groups containing the hydroxyl group are determined. The atmospheric implications for the studied alcohols are considered briefly.

The nitrogen oxides (NO(x)) decomposition on illuminated TiO(2) surfaces has been widely studied, but little is known about the subsequent formation of non-nitrogen containing products. In this study, TiO(2) coated glass surfaces and TiO(2) films with nitrate anions (either premixed with TiO(2) as KNO(3) or deposited from gaseous NO(x)) are irradiated with broad-band light. Upon irradiation, detected gas phase products include NO(2), HNO(2), and O(3). To the best of our knowledge, this is the first study that reveals the production of O(3) from TiO(2) surfaces. By surface charge transfer reactions, nitrate anions are oxidized into nitrate radicals and their photochemistry (almost in the visible) leads to O(3) formation, enhancing the oxidizing power of these surfaces.

No abstract

During the European Life+ project PhotoPAQ (Demonstration of Photocatalytic remediation Processes on Air Quality), photocatalytic remediation of nitrogen oxides (NOx), ozone (O3), volatile organic compounds (VOCs), and airborne particles on photocatalytic cementitious coating materials was studied in an artificial street canyon setup by comparing with a colocated nonactive reference canyon of the same dimension (5 × 5 × 53 m). Although the photocatalytic material showed reasonably high activity in laboratory studies, no significant reduction of NOx, O3, and VOCs and no impact on particle mass, size distribution, and chemical composition were observed in the field campaign. When comparing nighttime and daytime correlation plots of the two canyons, an average upper limit NOx remediation of ≤2% was derived. This result is consistent only with three recent field studies on photocatalytic NOx remediation in the urban atmosphere, whereas much higher reductions were obtained in most other field investigations. Reasons for the controversial results are discussed, and a more consistent picture of the quantitative remediation is obtained after extrapolation of the results from the various field campaigns to realistic main urban street canyon conditions.

The atmospheric oxidation of benzyl alcohol has been investigated using smog chambers at ICARE, FORD, and EUPHORE. The rate coefficient for reaction with OH radicals was measured and an upper limit for the reaction with ozone was established; kOH = (2.8 ± 0.4) × 10(-11) at 297 ± 3 K (averaged value including results from Harrison and Wells) and kO(3) < 2 × 10(-19) cm(3) molecule(-1) s(-1) at 299 K. The products of the OH radical initiated oxidation of benzyl alcohol in the presence of NOX were studied. Benzaldehyde, originating from H-abstraction from the -CH(2)OH group, was identified using in situ FTIR spectroscopy, HPLC-UV/FID, and GC-PID and quantified in a yield of (24 ± 5) %. Ring retaining products originating from OH-addition to the aromatic ring such as o-hydroxybenzylalcohol and o-dihydroxybenzene as well as ring-cleavage products such as glyoxal were also identified and quantified with molar yields of (22 ± 2)%, (10 ± 3)%, and (2.7 ± 0.7)%, respectively. Formaldehyde was observed with a molar yield of (27 ± 10)%. The results are discussed with respect to previous studies and the atmospheric oxidation mechanism of benzyl alcohol.

No abstract