无机离子对左旋葡聚糖光降解的影响

Effect of inorganic ions on photodegradation of Levoglucosan

左旋葡聚糖(LG)被广泛作为生物质燃烧的示踪剂.然而,近年来研究表明左旋葡聚糖在大气中不稳定而会发生光降解.此外,对于大气中含量较高的SO_(4)^(2-)、NO_(3)-、NO_(2)-无机离子对LG光解的影响罕有报到.为此,本文模拟了液相中SO_(4)^(2-)、NO_(3)-、NO_(2)-对LG光氧化行为的影响.结果表明,Na2SO_(4)、NaNO_(3)、NaNO_(2)条件下LG光解速率常数分别为0.208、0.182、0.165 min^(-1),均低于对照组(0.266 min-1),这表明无机离子的存在会减缓LG光降解速率.此外,这3种无机离子对LG光解产物中的低分子脂肪酸分布,甲酸/乙酸(C1/C2)比率均有重要的影响.其中,SO_(4)^(2-)存在下产物中戊二酸较多、NO_(3)-存在下产物中甲酸较多、NO_(2)-存在下产物中乙酸较多;NO_(2)-存在下产物中的C1/C2比率小于1与一般二次源中的C1/C2比率不一致,这表明由单一反应引起的C1/C2并不总是大于1.这些结果对于我们深刻理解大气液相中的有机物转化具有重要的参考价值.

Levoglucosan(LG)is widely used as a tracer for biomass combustion.However,recent studies have shown that LG is unstable in the atmosphere and undergoes photodegradation.In addition,the effects of relatively high levels of SO_(4)^(2-),NO_(3)-,and NO_(2)-on LG photolysis have not been reported.To this end,the effects of SO_(4)^(2-),NO_(3)-,and NO_(2)-in the liquid phase on the photooxidative degradation of LG were simulated.The results showed that the photodegradation rate constants of LG under the conditions of Na2SO_(4),NaNO_(3),and NaNO_(2)were 0.208,0.182,and 0.165 min^(-1),which were all lower than those of the control group(0.266 min-1).This indicated that the presence of inorganic ions would slow the LG photodegradation rate.In addition,these three inorganic ions had important effects on the distribution of low-molecular-weight fatty acids and the formic acid/acetic acid(C1/C2)ratio in LG photolysis products.Among them,there was more glutaric acid in the product in the presence of SO_(4)^(2-),more formic acid in the product in the presence of NO_(3)-,more acetic acid in the product in the presence of NO_(2)-;The C1/C2 ratios in the secondary sources were not consistent,which indicated that the C1/C2 caused by a single reaction was not always>1.These results had important reference value for our deep understanding of the conversion of organics in the atmospheric liquid phase.