颗粒态硝酸盐在黑碳表面的光解机制研究

As an important constitute of fine particulates in the troposphere, nitrate (NO3-) has traditionally been considered as a permanent sink of NOx. Recent studies have shown that surface-adsorbed NO3- on particulates would undergo rapid photochemical transformation to generate NOx and HONO, and afterwards releasing them back to the troposphere. Such process is named as“renoxification”, which plays a central role on the formation of hydroxyl radical and ozone. However, up to date, the photolysis mechanism of nitrate on the fine particulate surfaces still remain unclear. To solve this problem, in this project black carbon (BC), another important constitute of particulates, which shows strong solar absorbing ability, is chosen as a model of particulates to investigate the photochemical behavior of nitrate on its surface. A new analytical method to detect nitrate on the particulate surface will be built, on the basis of this method the degradation kinetics of nitrate on BC will be explored; the degradation pathways and interaction mechanisms of nitrate with BC will be revealed; and impacts of different environmental factors as well as the constitutes of fine particulates on photolysis kinetics and pathways will also be studied systematically. The results of the study will provide scientific evidence for a thorough understanding of photochemical fate of nitrate on particulate surface, and for the fully assessment of NOx and HONO sources in the troposphere.

硝酸盐作为大气细颗粒物中的重要组分，通常被认为是大气氮氧化物（NOx）在对流层中固定的汇。然而最新的研究表明颗粒物表面吸附的硝酸盐可以通过快速光解的方式产生NOx及亚硝酸（HONO）并重新释放回大气。这一过程被称作“再NOx”化，其对大气中羟基自由基(∙OH)和臭氧(O3)的生成均有重要影响,但目前硝酸盐在细颗粒物表面的光解机制尚不明确。本项目拟针对这一问题，选取大气细颗粒物中具有强吸光性的黑碳作为模拟物，研究硝酸盐在其表面的光化学行为。本项目将构建颗粒物表面硝酸盐新的分析方法，在此基础上掌握黑碳表面硝酸盐光解的表观反应动力学规律;探讨其光化学转化过程中的微观反应机理以及与黑碳的相互作用机制；系统考察不同环境因素和颗粒物组分对光解动力学和路径的影响。为全面理解颗粒物表面硝酸盐的光化学归趋，综合评估大气NOx及HONO来源提供科学依据。

硝酸盐是大气细颗粒物的重要组分，颗粒态硝酸盐可以通过光化学转化方式产生氮氧化物(NOx)并重新释放回大气；同时，作为大气颗粒物重要组成部分的黑碳，由于具有很强的吸光性，不可避免会影响硝酸盐的光化学行为，然而硝酸盐的光解过程及其与黑碳潜在的相互作用机制尚未引起学术界足够的关注。本项目针对这一问题，系统开展了黑碳表面硝酸盐的光解动力学及机制研究。研究发现，多种来源的生物质黑碳均能显著促进其表面颗粒态硝酸盐的光化学还原过程；在此基础上，本项目系统探讨了相对湿度、硝酸盐结晶速率、共存阳离子、颗粒物有机质等环境因素及颗粒物组分对光解动力学及路径的影响；基于含时密度泛函理论，构建了黑碳表面硝酸盐激发态计算模型；结合理化性质表征与量子化学计算，本项目阐明了模拟阳光辐射下硝酸盐与黑碳的相互作用机制，揭示了硝酸盐异构化过程是黑碳影响硝酸盐光解路径的关键步骤。在本项目的资助下，共发表SCI论文14篇，培养博士研究生2名，硕士研究生2名。本项目取得的研究结果可为全面理解颗粒物表面硝酸盐的环境化学归趋，综合评估大气NOx来源提供新的科学依据。