城区表面尘垢与二氧化氮非均相光化学反应生成亚硝酸研究

Nitrous acid (HONO) is an important precursor of the hydroxyl radical (OH). Attributing sources of HONO during daytime is of great importance for the study of atmospheric oxidative capacity. However, recent field measurements in the urban areas using very sensitive HONO instruments have shown that daytime HONO concentrations are much higher than previously assumed and that the contribution of HONO to the OH radical formation was underestimated in the past. The scientific knowledge about these processes is still in its infancy and there is still a huge discrepancy between the field measurements and the photochemical models. .This project will focus on light induced (photosensitized) heterogeneous processing of adsorbed organic material on urban surfaces by gas-phase NO2 as a potential source of daytime HONO in urban areas. The urban grime will be firstly collected on glass plates and glass beads over various collection time in direct sunlight and in the shade. The glass plates will be then inserted in a horizontal flow tube photo-reactor to investigate kinetics, reaction products and mechanistic pathways of HONO formation from the NO2 light induced heterogeneous processes under laboratory conditions. Meanwhile the collected glass beads will be tested under more realistic conditions in a smog chamber facility to differentiate between the two HONO sources: photolysis of adsorbed HNO3 versus light-induced heterogeneous reactions of NO2 with the organic content of the grime. The obtained results from the flow tube experiments and chamber simulations will be compared and implemented in the 0D model especially developed for this purpose to simulate the impact of renoxification processes on the urban air quality in Guangzhou. The studies will shed new insights into the “missing source” of HONO during daytime and benefit understanding the nitrogen chemistry and oxidation processes in the atmosphere.

亚硝酸（HONO）光解是大气OH自由基的重要来源，精准解析白天HONO的来源对于研究大气氧化能力至关重要。然而野外高精度观测表明，城区白天HONO浓度测量值常大于模型估算值，其对OH的贡献可能被相对低估，因而HONO来源的科学认识尚有待深入。本项目拟重点探讨城区表面附着尘垢中有机质与NO2光化学反应对HONO的潜在贡献。在典型时段采集日照和背阴处尘垢附载于玻璃平板或玻璃珠上，利用流动管反应器研究NO2与尘垢非均相反应生成HONO的主要产物、机制与动力学过程，并通过烟雾箱模拟探讨尘垢中硝酸盐光解、NO2与尘垢中有机质非均相光化学反应这两个生成途径对HONO的相对贡献。流动管反应器和烟雾箱结果将进行比对并应用于零维模式来探讨这些过程的潜在空气质量影响。项目研究有利于深入认识城区HONO日间未知源以及大气氮化学和大气氧化过程。

气相亚硝酸（HONO）的光解是大气OH自由基的重要初级来源，然而当前对HONO的来源过程仍缺乏深入认识，精准解析白天HONO的来源对于研究大气氧化能力至关重要。城市表面作为特殊的不透水薄膜，与气溶胶相比具有更大的比表面积（S/V），暴露在太阳光照射下时可以诱发薄膜的物理化学性质发生改变并使其活化，促进大气中典型氧化剂的非均相光化学反应过程。本项目重点探讨了城区表面附着尘垢中有机质与NO2非均相光化学过程，作为当前一种HONO来源的实验基础研究。利用真实的以及模拟的城市灰垢表面作为发生光化学反应的有机活性表面，针对NO2与不同表面反应的摄取动力学，反应机理以及产物生成情况进行了相应的研究。不透水的城市表面可被视为NO2以及其他大气氧化剂潜在的反应性媒介，导致HONO的生成并通过光解产生OH自由基，对于评估大气的氧化能力具有重要意义。