二次有机物对气溶胶中氨-胺非均相置换反应的影响

Amines are important alkaline gaseous compounds besides ammonia in the atmosphere. Although the gas-phase amine concentration is 2–3 orders of magnitude lower than ammonia, the enrichment of amines is much more enhanced in atmospheric particulate matter (PM) compared to that of ammonia. Hence, it is vital to understand the role of amines in the fate of ambient PM. The heterogeneous exchange reaction between ammonia and amines has been thought to significantly alter the relative abundance of these two species in PM, while the effect of secondary organic material (SOM), one of the main components in PM, on the ammonia-amine exchange reaction is highly uncertain. This project will investigate the influence of different types of SOM on the ammonia-amine exchange reactions. Single-particle experiments poses the advantage to comprehensively understand the physicochemical properties of PM such as phase state, mixing of different components and optical properties. In this project, single-particle experiments using home-made electrodynamic balance and aerosol flow cells will be conducted to in situ characterize the transient particle mass and chemical compositional changes in real time. Offline experiments will be carried out to investigate the light extinction properties of the sample particles. The thermodynamic (e.g. ammonia-amine exchange percentage) and kinetic parameters (e.g. uptake coefficient) as well as their dependence on SOM will be quantified. The obtained information will serve as good constraints for heterogeneous aerosol chemistry models. in order to completely reveal the role of amines in aerosol aging mechanisms.

胺类物质是大气中含量仅次于氨的碱性气体，尽管其在气相中的含量比氨低2–3个数量级，但在大气颗粒物中却比氨明显富集，因此研究胺类物质在大气颗粒物生成和老化机制中的作用具有重要意义。氨-胺的非均相置换反应已被认为能显著改变二者在大气颗粒物中的相对含量，而作为大气颗粒物的主要组分的二次有机物对该非均相过程的影响尚不明确。本项目拟利用电动天平和气溶胶流动池开展氨-胺非均相置换反应的研究，并重点关注不同种类二次有机物对该过程的影响。通过单颗粒层面的实验室模拟，对氨-胺置换反应过程中颗粒物质量和化学组成的变化进行实时原位检测、对吸光特性进行离线测试，并依据经典理论计算该非均相过程的热力学、动力学关键参数，定量表征其与二次有机物含量的相关性。本项目的成果能够为准确地约束气溶胶化学模型提供实验依据，以更完整地揭示胺类物质在大气颗粒物老化机制中的作用。

本项目开展了气态有机胺与硫酸铵-二次有机物混合颗粒物之间的非均相反应研究，并结合外场观测数据分析了实际大气环境中氨与有机胺置换反应对PM2.5化学组成的影响。在反应热力学方面，二次有机物含量不影响氨-胺置换反应的最终状态，在反应达到平衡后，硫酸铵可被有机胺全部置换。在动力学方面，通过实验发现老化后的二次有机气溶胶与新鲜二次有机气溶胶相比，可减缓氨-胺非均相置换反应，非均相摄取系数下降30%~40%左右，可能由于老化后的有机物黏度增加。通过分析海洋环境综合观测数据发现，氨-二甲胺-三甲胺会对中和气溶胶中的酸性成分存在竞争；但当大气中酸性成分过量时，氨不足以中和全部酸度，铵根离子浓度和有机胺阳离子浓度可同步出现峰值。本研究结果可为空气质量模型、气溶胶数值模式提供参数优化方案，在今后为大气污染防治特别是氨/胺污染治理提供科学依据。