Absolute OH quantum yields in the laser photolysis of nitrate, nitrite and dissolved H2O2 at 308 and 351 nm in the temperature range 278?353 K

Abstract

Absolute quantum yields for the formation of OH radicals in the laser photolysis of aqueous solutions of NO], NO2 and H202 at 308 and 351 nm and as a function ofpH and temperature have been measured. A scavenging technique involving the reaction between OH and SCN-ions and the time resolved detection by visible absorption of the (SCN)~ radical ion was used to determine the absolute OH yields. The following results were obtained:(1) NO] -photolysis: 308 nm: ~OH(298 K)=0.017 +_0.003 for 4~<pH~<9, Selected experiments at 351 nm indicate that these results are essentially unchanged.(2) NO~ -photolysis: 308 nm: ~OH(298 K) = (0.07 ± 0.01) for 4 ~<pH ~< 9, 351 nm: q~OH (298 K) = (0.046 + 0.009) for pH = 8, (3) H202 -photolysis: 308 nm: ~OH(298 K) = (0.98 _+0.03) • oH(T) = ~OH(298 K) exp 351 nm: ~OH(298 K)= (0.96 ±0.04) OoH(T) = ~OH(298 K) exp for pH = 7, [(660--_ 190)(29--~8 -1)], forpH = 7, [(580--160) (29--~8 -~T)]" Together with the absorption coefficients and an assumed actinic flux within atmospheric droplets of twice the clear air value, the partial photolytic lifetimes (rOH) of these molecules at 298 K are estimated as 10.5 d, 5.4h and 30.3 h for NO 3, NO2 and H202, respectively. These lifetimes 412 R. ZELLNER, M. EXNER, AND H. HERRMANNwill increase by a factor of two (NO~, NO 2) and by 15% (H202) at T=278 K. Using average ambient concentrations in tropospheric aqueous droplets, the photolytic OH source strengths from these species are calculated to be 2.8 × 10 -ll, 1.3 × 10 -jl and 1.4× 10 -jl mol 1-1 s -l for NO~, NO2 and H202 respectively.

Snow optical properties at Dome C (Concordia), Antarctica; implications for snow emissions and snow chemistry of reactive nitrogen

“…The quantum yield reported in Chu and Anastasio (2003) broadly agrees with the work of Dubowski et al (2002) and is considered a good phenomological representation of the photolysis of nitrate in snow and ice. Other available quantum yield data for 308 nm photolysis of nitric acid on ice films of 0.92 ± 0.26 (Zhu et al, 2010) seem extremely high compared with previous data (Warneck and Wurzinger, 1988;Zellner et al, 1990;Dubowski et al, 2002;Chu and Anastasio, 2003), but if correct would potentially increase the NO 2 production by a factor of ∼400.…”

The effect of cations on NO2 production from the photolysis of aqueous thin water films of nitrate salts

“…The corresponding average value of F(OH) is (1.1 AE 0.4) Â 10 À2 (see Chu and Anastasio 97 for details of the calculation), which agrees well with past studies reporting a value of B0.01 at room temperature. 82,[90][91][92][93]97 These OH experiments thus suggest that the nature of the cations is not influencing the production of nitrate photo-products in the bulk. However, the bulk-phase measurements were conducted at concentrations that were a factor of 600 (for RbNO 3 ) to 2040 (for NaNO 3 ) times lower than the thin film experiments due to the low solubility of benzene in aqueous solution (23 mM).…”

“…At room temperature the bulk-phase quantum yields are B0.01 for OH production and an order of magnitude lower (B0.001) for O( 3 P) formation (1b) at 305 nm. 82,[90][91][92][93] In smaller water clusters (32-300 water molecules), 86 NO 3 À ions are predicted to be present at the air-water interface. In the interface region, nitrate ions are less solvated than those in the bulk, 86 resulting in increased NO 2 production yields.…”

Photochemical processes involving the UV absorber benzophenone-4 (2-hydroxy-4-methoxybenzophenone-5-sulphonic acid) in aqueous solution: Reaction pathways and implications for surface waters

“…Figure 3 reports the initial transformation rates of 20 µM BP-4 at pH 4 (HA − ) and 10 (A 2− ), upon irradiation of 1.0 mM H 2 O 2 under the TL 01 lamp (see Figure 1), in the presence of variable concentration values of the • OH scavenger 2-propanol. Competition kinetics between BP-4 and 2-propanol for • OH would involve the following reactions (Buxton et al, 1988;Zellner et al, 1990;Martell et al, 1997): …”