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Carbon monoxide concentrations were measured over an 8-day period (March 1997) in freshly fallen snow samples collected at Mount Sonnblick (Austria). Diurnal changes were systematically observed in the snow, with higher CO during daytime, indicating that light-dependent CO production processes are active in surface snow layers. Mean daytime CO concentrations in snow varied significantly from one day to another and were found to be well correlated with the daily mean atmospheric CO concentrations. Thus, the more polluted the air mass during the snow fall, the more CO was produced through photolytical processes. Furthermore closed chamber experiments were made, giving similar observations: rapid increases of CO concentration occurred within the chamber when the snow was exposed to sunlight. In the dark, however, CO concentrations decreased. CO fluxes between the surface of the snowpack and the atmosphere were estimated at 0.6 ppb/day which may be significant in the local CO budget but not on a global scale. Laboratory experiments showed that CO was rapidly formed when melted snow samples were exposed to the light from a solar simulator and that the initial CO formation rate was strongly correlated with the concentrations of Total Organic Carbon in the melted snow samples. This correlation indicates that organic compounds present in snow precipitation are the major substrate for the photochemical CO production observed in freshly fallen snow. Recent studies have reported high formaldehyde concentrations in the snowpack and we suggest HCHO photolysis to be partly responsible of CO production in snow. 相似文献
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B. Ervens P. Herckes G. Feingold T. Lee J. L. Collett Jr. S. M. Kreidenweis 《Journal of Atmospheric Chemistry》2003,46(3):239-269
Concentration differences between small (r < 8.5 m) and large droplets(r > 8.5 m) were observed for formic acid, acetic acid and formaldehyde in fog droplets collected in California's Central Valley. The concentration ratios (large/small droplets) of these compounds were investigated by a stepwise model approach. Assuming thermodynamic equilibrium (KH
eff) results in an overestimate of the concentration ratios. Considering the time dependence of gas phase diffusion and interfacial mass transport, it appears that the lifetime of fog droplets might be sufficiently long to enable phase equilibrium for formaldehyde and acetic acid, but not for formic acid (at pH 7). Oxidation by the OH radical has no effect on formaldehyde concentrations but reduces formic acid concentrations uniformly in all drop size classes. The corresponding reaction for acetic acid is less efficient so that only in large droplets, where replenishment is slowed because the uptake rate of acid from the gas phase is slower, is the acid concentration reduced leading to a smaller concentration ratio. Formaldehyde concentrations in fog can be higher than predicted by Henry's Law due to the formation of hydroxymethanesulfonate. Its formation is dependent on the sulfur(IV) concentration. At high pH values the uptake rate for sulfur(IV) is drop-size dependent. However, the observed concentration ratios for formaldehyde cannot be fully explained by the adduct formation. Finally, it is estimated that mixing effects, i.e., the combination of individual droplets into a bulk sample, have a minor influence (<15%) on the measured heterogeneities. 相似文献
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建立一种室内甲醛的测定方法,以稀硫酸为吸收液研究室内装修后甲醛的释放规律,采用毛细管气相色谱法(CGC)来测定其变化值,再通过制作环境舱与实际现场测得的新装修室内甲醛的释放规律相对比,测出此种方法的回收率,从而得出甲醛的释放规律。实验表明,该方法最低能够检测甲醛气体量为0.164 mg/L,回收率为94.19%。 相似文献