Concentrations of higher dicarboxylic acids C5 – C13 in fresh snow samples collected at the High Alpine Research Station Jungfraujoch during CLACE 5 and 6

Samples of freshly fallen snow were collected at the high alpine research station Jungfraujoch (Switzerland) in February and March 2006 and 2007, during the Cloud and Aerosol Characterization Experiments (CLACE) 5 and 6. In this study a new technique has been developed and demonstrated for the measurement of organic acids in fresh snow. The melted snow samples were subjected to solid phase extraction and resulting solutions analysed for organic acids by HPLC-MS-TOF using negative electrospray ionization. A series of linear dicarboxylic acids from C5 to C13 and phthalic acid, were identified and quantified. In several samples the biogenic acid pinonic acid was also observed. In fresh snow the median concentration of the most abundant acid, adipic acid, was 0.69 micro g L -1 in 2006 and 0.70 micro g L -1 in 2007. Glutaric acid was the second most abundant dicarboxylic acid found with median values of 0.46 micro g L -1 in 2006 and 0.61 micro g L -1 in 2007, while the aromatic acid phthalic acid showed a median concentration of 0.34 micro g L -1 in 2006 and 0.45 micro g L -1 in 2007. The concentrations in the samples from various snowfall events varied significantly, and were found to be dependent on the back trajectory of the air mass arriving at Jungfraujoch. Air masses of marine origin showed the lowest concentrations of acids whereas the highest concentrations were measured when the air mass was strongly influenced by boundary layer air

Temperature dependence of UV absorption cross sections and atmospheric implications of several alkyl iodides

The ultraviolet absorption spectra of a number of alkyl iodides which have been found in the troposphere, CH_3I, C_2H_5I, CH_3CH_2CH_2I, CH_3CHICH_3, CH_2I_2, and CH2_ClI, have been measured over the wavelength range 200–380 nm and at temperatures between 298 and 210 K. The absorption spectra of the monoiodides C_H3I, C_2H_5I, CH_3CH_2CH_2I, and CH_3CHICH_3 are nearly identical in shape and magnitude and consist of single broad bands centered near 260 nm. The addition of a chlorine atom in CH_2ClI shifts its spectrum to longer wavelengths (σ_(max) at 270 nm). The spectrum of CH_2I_2 is further red‐shifted, reaching a maximum of 3.85×10^(−18) cm^2 molecule^(−1) at 288 nm and exhibiting strong absorption in the solar actinic region, λ>290 nm. Atmospheric photolysis rate constants, J values, have been calculated assuming quantum efficiencies of unity for different solar zenith angles as a function of altitude using the newly measured cross sections. Surface photolysis rate constants, calculated from the absorption cross sections measured at 298 K, range from 3×10^(−6) s^(−1) for CH)3I to 5×10^(−3) s^(−1) for CH)2I)2 at a solar zenith angle of 40°

Temperature dependence of UV absorption cross sections and atmospheric implications of several alkyl iodides

The ultraviolet absorption spectra of a number of alkyl iodides which have been found in the troposphere, CH_3I, C_2H_5I, CH_3CH_2CH_2I, CH_3CHICH_3, CH_2I_2, and CH2_ClI, have been measured over the wavelength range 200–380 nm and at temperatures between 298 and 210 K. The absorption spectra of the monoiodides C_H3I, C_2H_5I, CH_3CH_2CH_2I, and CH_3CHICH_3 are nearly identical in shape and magnitude and consist of single broad bands centered near 260 nm. The addition of a chlorine atom in CH_2ClI shifts its spectrum to longer wavelengths (σ_(max) at 270 nm). The spectrum of CH_2I_2 is further red‐shifted, reaching a maximum of 3.85×10^(−18) cm^2 molecule^(−1) at 288 nm and exhibiting strong absorption in the solar actinic region, λ>290 nm. Atmospheric photolysis rate constants, J values, have been calculated assuming quantum efficiencies of unity for different solar zenith angles as a function of altitude using the newly measured cross sections. Surface photolysis rate constants, calculated from the absorption cross sections measured at 298 K, range from 3×10^(−6) s^(−1) for CH)3I to 5×10^(−3) s^(−1) for CH)2I)2 at a solar zenith angle of 40°

Pressure Dependence Of The Photooxidation Of Selected Carbonyl Compounds In Air: N-Butanal And N-Pentanal

Dilute mixtures of n-butanal and n-pentanal in synthetic air (up to 100 ppm) were photolyzed with fluorescent UV lamps (275--380 nm) in air at 298 K. The main photooxidation products, identified and quantitatively analyzed by FT-IR spectroscopy, were ethene (n-butanal) or propene (n-pentanal), CO, vinylalcohol and ethanal. The photolysis rates and the absolute quantum yields # of both compounds were found to be slightly dependent on the total pressure. At 100 Torr, in the photolysis of n-butanal and n-pentanal # 100 0.02 and 0.40 0.04, whereas at 700 Torr, the total quantum yields were # 700 0.38 0.02 and 0.32 0.01, respectively. These results could be explained by the collisional deactivation of photoexcited molecules. Two decomposition channels were identified in both cases: the radical channel RCHO R HCO, and the molecular channel C x H y CHO C x-1 H y-3 CH 2 =CHOH, having the relative yields of 68 3% (n-butanal), and 20 4% (n-pentanal) at 700 Torr. The product, CH 2 =CHOH, tautomerizes to ethanal. UV absorption cross-sections were measured prior to photolysis. For the comparison, the products were also analyzed after photolysis of both compounds in teflon bags using direct sunlight. 2001 Elsevier Science B.V. All rights reserved