PM_(2.5)中二次硫酸盐和硝酸盐生成机制

Formation Mechanisms of Secondary Sulfate and Nitrate in PM_(2.5)

二次无机硫酸盐和硝酸盐是PM_(2.5)的关键化学组分,对区域霾污染的形成有十分重要的作用。厘清两者的生成机制对于消除PM_(2.5)污染至关重要。二次硫酸盐和硝酸盐的生成机理十分复杂,包括气相、液相和非均相等多种反应。最近的实验和观测研究揭示了SO_(2)和NO_(2)生成硫酸盐和硝酸盐的新机理和详细的反应动力学,其被用于空气质量模型后可有效提升数值模式对硫酸盐和硝酸盐的时空分布特征及生成过程的模拟。本文系统总结了PM_(2.5)中二次硫酸盐和硝酸盐生成机制的最新进展,重点阐述了SO_(2)和NO_(2)氧化生成硫酸盐和硝酸盐的重要反应途径的机理和反应动力学结果,讨论了影响SO_(2)和NO_(2)氧化速率的因素以及在表征反应动力学时出现的重大实验挑战,同时探讨了硝酸盐对氮氧化物(NO_(x))、挥发性有机物(VOCs)、氨(NH_(3))减排的敏感性。最后,对未来研究发展方向提出了建议。

Secondary inorganic sulfate and nitrate,as the key chemical components of PM_(2.5),play important roles in the formation of severe regional haze events.The deteriorating sulfate and nitrate pollution has brought more serious challenges to the continuous improvement of air quality.Thus,elucidating the formation pathways and key factors of controlling the formation of inorganic sulfate and nitrate is crucial to eliminate PM_(2.5)pollution in the atmosphere.The formation of sulfate and nitrate involves complex chemical reactions,including gas-and aqueous-phase reactions and multi-phase reactions.Recent experimental and filed studies have revealed new reaction mechanisms and detailed reaction kinetics for the oxidation of SO_(2) and NO_(2) to form sulfate and nitrate.Merging new formation pathways of sulfate and nitrate with updating reaction kinetics based on laboratory measurements and field observations,air quality model performance is effectively improved to capture the spatial-temporal variations of sulfate and nitrate and identify their chemical formation pathways.This review provides a synthetic synopsis of recent advances in the fundamental mechanisms of sulfate and nitrate formation.In particular,the mechanisms and reaction kinetic results for a series of individual reaction pathways of current interest for the SO_(2) and NO_(2) oxidation are emphasized.The key factors affecting the SO_(2) and NO_(2) oxidation rates and significant challenges in laboratory studies of characterizing the reaction kinetics are also discussed.In addition,the sensitivity of nitrate to emission reductions of nitrogen oxides(NO_(x)),volatile organic compounds(VOCs)and ammonia(NH_(3))is investigated.Finally,suggestions are put forward for the future research directions to improve the understanding of sulfate and nitrate formation.