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气溶胶老化是目前大气颗粒物物理化学领域的研究热点之一。通过真空型傅里叶红外光谱仪原位观测并对比了油酸(OA)薄膜和油酸包覆粉煤灰两种样品分别与臭氧发生的化学反应动力学,并评估了其中粉煤灰在非均相化学反应中所起到的作用。除了指纹区特征峰的不同,在反应前纯油酸薄膜和纯油酸包覆粉煤灰样品的主要红外特征吸收峰是相似的。当两种样品分别处于20ppm臭氧浓度、室温和干燥的反应环境中,=CH的特征吸收峰(3 050cm-1)强度降低而—OH伸缩振动特征峰(3 430cm~(-1))强度增加。此外,随着臭氧氧化反应的进行,处于1 710cm-1的羧酸C=O伸缩振动特征峰强度下降,反之,产物酯类物质的伸缩振动特征峰在1 740cm~(-1)出现并增强。通过红外光谱的变化趋势能够得到两组样品的OA成分在反应中逐步消耗并转化为含有羟基和酯类官能团的产物。通过位于1 740cm-1处的C=O特征峰的变化能够得到准一级反应速率常数Kapp和摄取系数γ。粉煤灰样品的准一级反应速率常数大体是油酸薄膜反应体系的两倍。对于比表面积,粉煤灰样品要大于油酸薄膜,而两种反应体系的臭氧浓度一致,油酸薄膜和油酸包覆粉煤灰的γ值分别为(2.70±0.11)×10~(-4)和(3.70±0.13)×10~(-4)。较大的催化表面积和较快的催化效率是导致粉煤灰样品较油酸薄膜反应快的原因。由此证明了当粉煤灰与不饱和有机酸结合并处在臭氧氧化环境中时会常易促进二次有机气溶胶的形成。
Aerosol aging is one of the hot topics in the field of physical and chemical properties of atmospheric particles. The reaction kinetics of oleic acid (OA) film and oleic acid-coated fly ash with ozone respectively were observed and compared in situ by vacuum Fourier transform infrared spectroscopy Homogeneous chemical reaction played a role. In addition to the different characteristic peaks in the fingerprint region, the main infrared characteristic absorption peaks of pure oleic acid film and pure oleic acid-coated fly ash samples before the reaction are similar. The intensity of the characteristic absorption peak (3 050cm -1) of CH and the intensity of -OH stretching vibration (3 430cm -1) increased when the two samples were at 20ppm ozone concentration, room temperature and dry reaction environment respectively . In addition, the intensity of the C = O stretching vibration of the carboxylic acid at 1 710 cm-1 decreased with the progress of ozone oxidation reaction. On the contrary, the characteristic peak of the stretching vibration of the product ester appeared and enhanced at 1 740 cm -1 . Through the infrared spectroscopy, the OA composition of the two groups of samples can be gradually consumed in the reaction and transformed into the product containing hydroxyl and ester functional groups. The quasi-first-order reaction rate constant Kapp and the uptake coefficient γ can be obtained from the change of the C = O characteristic peak at 1 740 cm-1. The quasi-first-order reaction rate constant of fly ash samples is roughly twice that of the oleic acid film reaction system. For the specific surface area, the fly ash samples were larger than the oleic acid films, and the ozone concentrations of the two reaction systems were the same. The γ values of oleic acid film and oleic acid coated fly ash were (2.70 ± 0.11) × 10 ~ (- 4) and (3.70 ± 0.13) × 10 ~ (-4). The larger catalytic surface area and faster catalytic efficiency are responsible for the faster reaction of the fly ash sample than the oleic acid film. It proves that the formation of secondary organic aerosol tends to be facilitated when fly ash is combined with unsaturated organic acids and is in an ozonation environment.