Department of Atmospheric Sciences, National Taiwan University, No. 1 , Sec. 4, Roosevelt Road, Taipei, 10617 Taiwan.
J Phys Chem A. 2013 Jan 10;117(1):108-16. doi: 10.1021/jp309470z. Epub 2012 Dec 27.
The reactive aging of films of secondary organic material (SOM) to ozone, irradiation, and water was studied by attenuated total reflectance infrared spectroscopy (ATR-IR). The films were prepared by deposition onto the ATR elements of particles produced by reaction of isoprene with hydroxyl radicals and of α-pinene with ozone in the Harvard Environmental Chamber (HEC). The infrared spectra showed that the isoprene-derived film had strong hydroxyl absorptions whereas the α-pinene-derived film had strong carbonyl absorptions. The organic films were exposed to dry and humid flows of ozone, as well as to ultraviolet irradiation, to mimic reactive aging processes that can occur in the troposphere. Both the isoprene- and α-pinene-derived films were nonreactive with respect to ozone exposure, for both dry and humid conditions, indicating that the secondary organic material consisted mostly of saturated organic species. Both films, however, were susceptible to aging by ultraviolet radiation possibly due to the presence of organic hydroperoxides, and all functional groups other than carbonyls decreased upon irradiation. In regard to hygroscopicity, as a benchmark the ratio x(W_CO) for oxalic acid of the intensity of the water-bending peak to that of carbonyl absorption (arising from carboxylic acids) was recorded from 20% to 80% relative humidity (RH). This quantity was then also measured for the isoprene- and α-pinene-derived organic films. The result of (x(W_CO))(isoprene) > (x(W_CO))(benchmark) across the range of studied RH values shows that species other than carboxylic acids contributed significantly to the hygroscopicity of the isoprene-derived film. The spectra were consistent with alcohols and hydroperoxides as the hygroscopic components. By comparison, the result of (x(W_CO))(pinene) ≈ (x(W_CO))(benchmark) indicates a dominance of carboxylic acids with respect to the hygroscopicity of this film.
采用衰减全反射红外光谱（ATR-IR）研究了二次有机物质（SOM）膜对臭氧、辐照和水的反应性老化。这些膜是通过将异戊二烯与羟基自由基反应和α-蒎烯与臭氧反应生成的颗粒沉积在哈佛环境室（HEC）的 ATR 元件上制备的。红外光谱表明，异戊二烯衍生的膜具有强的羟基吸收，而α-蒎烯衍生的膜具有强的羰基吸收。将有机膜暴露于干燥和潮湿的臭氧流以及紫外线辐射下，以模拟可能在对流层中发生的反应性老化过程。对于干燥和潮湿条件，异戊二烯和α-蒎烯衍生的膜都与臭氧暴露不反应，表明二次有机物质主要由饱和有机物质组成。然而，由于存在有机过氧化物，两种膜都容易受到紫外线辐射的老化，并且所有除羰基以外的官能团在辐照后都会减少。关于吸湿性，作为基准，草酸的水弯曲峰强度与羰基吸收（来自羧酸）强度的比值 x（W_CO）在 20%至 80%相对湿度（RH）范围内记录。然后还测量了异戊二烯和α-蒎烯衍生的有机膜的 x（W_CO）。在所研究的 RH 值范围内，(x(W_CO))(isoprene) > (x(W_CO))(benchmark) 的结果表明，除羧酸以外的物质对异戊二烯衍生膜的吸湿性有重要贡献。该结果与醇和过氧化物作为吸湿性成分一致。相比之下，(x(W_CO))(pinene) ≈ (x(W_CO))(benchmark) 的结果表明，对于该膜的吸湿性，羧酸占主导地位。
