Hygroscopic properties of oxalic acid and atmospherically relevant oxalates
Hygroscopic properties of oxalic acid and atmospherically relevant oxalates
复制标题
DOI：
10.1016/j.atmosenv.2012.12.011
复制
发表时间：
2013-04
期刊：
影响因子：
--
通讯作者：
Qingxin Ma;Hongquan He;Chang Liu
中科院分区：
文献类型：
--
作者：
Qingxin Ma;Hongquan He;Chang Liu
草酸和草酸盐是大气有机气溶胶的重要组成部分，然而，对这些颗粒的吸湿行为知之甚少。本研究利用拉曼光谱仪和气相吸附分析仪研究了草酸及其大气相关的草酸盐（H2 C2 O 4、（NH 4）2C 2 O 4、CaC 2 O 4和FeC 2 O 4）的吸湿行为。在相对湿度为10- 90%的环境中，草酸和草酸盐几乎不潮解，吸湿性较低，但在潮解和除湿过程中会发生无水颗粒和水合颗粒之间的转化。在水吸附过程中，无水H_2C_2O_4、（NH_4）_2C_2O_4、CaC_2O_4和FeC_2O_4转化为它们的水合颗粒（即，H2 C2 O 4·2 H2O、（NH 4）2C 2 O 4·H2O、CaC 2 O 4·H2O和FeC 2 O 4·2 H2O）分别在约20%RH、55%RH、10%RH和75%RH下发生。水在水合草酸钙和草酸铁颗粒上的吸收可以用多层吸附等温线来描述。在除湿过程中，H2 C2 O 4·2 H2O和（NH 4）2C 2 O 4·H2O在5%RH下发生脱水，而CaC 2 O 4·H2O和FeC 2 O 4·2 H2O不发生脱水。这些结果表明，水合粒子代表了大气中草酸和草酸盐的最稳定状态。此外，根据吸湿行为的测量结果，对1610-1650 cm-1范围内的拉曼频移带进行了归属。
Oxalic acid and oxalates represent an important fraction of atmospheric organic aerosols, however, little knowledge about the hygroscopic behavior of these particles is known. In this study, the hygroscopic behavior of oxalic acid and atmospherically relevant oxalates (H2C2O4, (NH4)2C2O4, CaC2O4, and FeC2O4) were studied by Raman spectrometry and vapor sorption analyzer. Under ambient relative humidity (RH) of 10–90%, oxalic acid and these oxalates hardly deliquesce and exhibit low hygroscopicity, however, transformation between anhydrous and hydrated particles was observed during the humidifying and dehumidifying processes. During the water adsorption process, conversion of anhydrous H2C2O4, (NH4)2C2O4, CaC2O4, and FeC2O4to their hydrated particles (i.e., H2C2O4·2H2O, (NH4)2C2O4·H2O, CaC2O4·H2O, and FeC2O4·2H2O) occurred at about 20% RH, 55% RH, 10% RH, and 75% RH, respectively. Uptake of water on hydrated Ca-oxalate and Fe-oxalate particles can be described by a multilayer adsorption isotherm. During the dehumidifying process, dehydration of H2C2O4·2H2O and (NH4)2C2O4·H2O occurred at 5% RH while CaC2O4·H2O and FeC2O4·2H2O did not undergo dehydration. These results implied that hydrated particles represent the most stable state of oxalic acid and oxalates in the atmosphere. In addition, the assignments of Raman shift bands in the range of 1610–1650 cm−1were discussed according to the hygroscopic behavior measurement results.