基于NO_(2)光解光通量计量法测定流动管反应室内硝酸盐光解频率  

Determination of nitrate photolysis frequency inside flow tube reactor using NO_(2) actinometry

作　　者：刘新然 施晓雯 陈晨 宁禾山 庞贻友 黄子旋 郑军[1] LIU Xinran;SHI Xiaowen;CHEN Chen;NING Heshan;PANG Yiyou;HUANG Zixuan;ZHENG Jun(School of Environmental Science and Engineering,Nanjing University of Information Science&Technology,Nanjing 210044,China;Reading Academy,Nanjing University of Information Science&Technology,Nanjing 210044,China)

机构地区：[1]南京信息工程大学环境科学与工程学院,江苏南京210044 [2]南京信息工程大学雷丁学院,江苏南京210044

出　　处：《大气与环境光学学报》2024年第6期636-645,共10页Journal of Atmospheric and Environmental Optics

基　　金：国家自然科学基金(41730106,41975172);江苏省研究生实践创新计划项目(SJCX22_0371)。

摘　　要：近年来的研究表明硝酸盐的光解可能是日间大气亚硝酸(HONO)的重要来源之一。然而,现有文献报道的硝酸盐光解频率范围较大,跨度可达1~2个量级,严重影响日间HONO来源解析的准确性。硝酸盐光解频率的测定方法主要通过实验室流动管实验获得,利用人工光源模拟太阳辐射,其中对光源辐射强度的测定具有极大的不确定性。本文基于二氧化氮(NO_(2))光解通量计量法对流动管内光源辐射强度进行了直接、精确测定并据此推导出硝酸盐光解频率。其原理为NO_(2)在光解后与氧气(O_(2))产生臭氧(O_(3))和一氧化氮(NO),臭氧光解的同时又与NO迅速反应生成NO_(2),达到准静态,因此NO_(2)在流动管内的光解频率J(NO_(2))可以根据实测的氮氧化物(NO_(x))和O_(3)浓度计算得到。在获得J(NO_(2))基础上再运用已有研究的经验公式即可获得硝酸盐的光解频率J(HNO_(3))。该方法与传统的硝酸盐水溶液光度计法相比,避免了由于水溶液对光强的影响而导致的测量误差,同时该方法不受流动管内几何构型的影响,直接获得流动管内各处光解通量的集合,使测定结果更加准确。在温度为25℃、气压为101.325 kPa的条件下,使用500 W氙灯光源,将光源置于天顶角为θ=0°的正上方,气体通过时间为61.7 s,使用NO_(2)光解法测得的J(NO_(2))为6.78×10^(-3)s^(-1),进而获得的J(HNO_(3))为3.40×10^(-7)s^(-1)。Recent studies have shown that the photolysis of particulate nitrate may be one of the important sources of daytime atmospheric nitrous acid(HONO).However,the existing laboratory studies have reported a wide range of measured photolysis frequency of nitrate,spanning 1 to 2 orders of magnitude,which significantly affects the accurate assessment of the contribution of nitrate photolysis to daytime HONO formation.A common practice to determine the photolysis rates of nitrates is to use a flow tube reactor,where artificial light-source are commonly used to simulate solar radiation,so how to accurately obtain the radiation intensity of light sources is a critical step for this kind of experiments and may induce a significant uncertainty in measuring photolysis rates of nitrates.In this study,nitrogen dioxide(NO_(2))actinometry was used to determine the radiation intensity inside a flow tube.The principle is that NO_(2) will be photolyzed into NO and swiftly form ozone(O_(3))at the present of oxygen(O_(2)).At the same time,O_(3) reacts with NO rapidly to form NO_(2).Eventually,a dynamic equilibrium will be reached.Therefore,the actinic flux and photolysis rates of NO_(2) J(NO_(2))can be deduced from the measured concentrations of NO_(x) and O_(3),and then the photolysis frequency of nitrate J(HNO_(3))can be obtained by using the empirical formula.Different from the traditional nitrate solution actinometry,which uses nitrate actinometry to measure the absorbed radiation,the method proposed in this work avoids the bias of light absorption caused by water since no aqueous solution is present.Meanwhile,the NO_(2) actinometry does not depend on the physical configuration of the flow tube in this method and thus can provide more accurate measurement results.When a xenon light source(500 W)was set directly above the flow tube(i.e.,zenith angleθ=0°)and the gas passage time was 61.7 s under 1 standard atmospheric pressure and at 25℃,the J(NO_(2))measured by the NO_(2) photolysis method was 6.78×10^(-3) s^(-1),and J(HNO_(3)

关 键 词：紫外辐射 光解频率 亚硝酸 硝酸盐 大气氧化能力 

分 类 号：X851[环境科学与工程—环境工程] P401[天文地球—大气物理学与大气环境]