Simulation Of Liquid-phase Photochemical Reactions Of Carbohydrates In The Atmosphere

Carbohydrate compounds are widely present in the atmospheric environment,and their concentration is relatively high,which has an important impact on local and even global climate change.In addition,some carbohydrate compounds are used as tracers for biomass burning,secondary organic aerosols,etc.Due to their good stability,low-molecular fatty acids are important components of fine particulate matter(PM_2.5)in the atmosphere.They can participate in the formation of cloud condensation nodules,affect the energy balance of the global atmospheric system,and can increase the acidity of atmospheric precipitation and affect the visibility of cities.However,recent studies have shown that individual carbohydrate compounds are not stable in the atmosphere,and the carbohydrate compounds may generate low molecular fatty acids during the degradation process.However,there are few studies on low molecular fatty acids,degradation products of carbohydrate compounds.Therefore,this paper simulates the photochemical reaction of carbohydrates in the atmosphere in a liquid phase system,and explores the photochemical reaction behavior of carbohydrates in the atmosphere.In addition,the relationship between carbohydrates and low molecular fatty acids in PM2.5 in the summer,autumn and winter of 2017～2018 was analyzed.The following conclusions were obtained:（1）Carbohydrate compounds will undergo degradation reaction under ultraviolet light irradiation,and different carbohydrate compounds have different degradation rates and half-lives.In the degradation rate of carbohydrate compounds,sugar alcohol>sugar>dehydrated sugar,sugar alcohol in the half-life<sugar<dehydrated sugar.（2）Inorganic ions(SO₄^2-,NO₃^-,and NO₂^-)have a certain influence on the photochemical reaction of carbohydrate compounds.For levglucosan,the presence of inorganic ions will slow down its photodegradation rate.（3）The photochemical reaction of carbohydrate compounds in the atmosphere will produce low molecular fatty acids,and the concentration distribution and average yield of these low molecular fatty acids have certain differences.The concentration of formic acid and oxalic acid in dehydrated sugar is relatively high,and the concentration of acetic acid and oxalic acid in sugar and sugar alcohol is relatively high.The average yield of low molecular fatty acids in dehydrated sugar can reach 50%to 170%under some ultraviolet bands.Under the 254 nm band reaction,the average yield of low-molecular fatty acids of sugar and sugar alcohol is 10%～30%.The average concentration range is 2～4.5 mg·m^-3.（4）Among the degradation products of carbohydrate compounds,formic acid/acetic acid（C1/C2）are all less than 1,which is inconsistent with the result of C1/C2>1 when the secondary source is dominant,which indicates that C1/C2 is caused by a single reaction Value is not always greater than 1.（5）There is a certain correlation between carbohydrate compounds and low-molecular fatty acids in atmospheric environment PM_2.5.Overall,the correlation between carbohydrate compounds and low-molecular fatty acids is-0.2～0.75.These results need to consider the case of underestimation of any method based on the concentration of stable carbohydrate compounds in the atmosphere as a tracer.And it has an important reference value for our profound understanding of the transformation of organic matter in the atmospheric liquid phase.