傅里叶变换显微红外光谱技术研究大气SO_(2)/NO_(2)与MgCl_(2)单液滴的非均相氧化反应

Heterogeneous Reaction of Atmospheric SO_(2)/NO_(2) Using Micro-FTIR Spectroscopy

硫酸盐是我国大气PM_(2.5)的重要成分之一,当前大气化学模型普遍严重低估雾霾期间大气硫酸盐的浓度,说明我们对SO_(2)大气转化机制的认识仍然不足。SO_(2)与NO_(2)在气溶胶微液滴内的协同氧化,被认定是一种硫酸盐颗粒物的关键额外来源。然而,在变化氛围(反应气体摩尔比、相对湿度)条件下,SO_(2)/NO_(2)与微液滴反应的关键动力学参数,目前仍然得不到准确的测定。本研究利用傅里叶变换显微红外光谱技术,在变化SO_(2)/NO_(2)摩尔比的条件下,原位测定了海盐气溶胶MgCl_(2)液滴中SO_(4)^(2-)与NO_(3)^(-)浓度的时间演化。我们发现:MgCl_(2)单液滴与SO_(2)/NO_(2)反应生成了SO_(4)^(2-)和NO_(3)^(-),并且在SO_(2)/NO_(2)摩尔比为1∶5时SO_(4)^(2-)的生成速率最快。本研究将为大气模型提供可靠参数,为制定有效的PM_(2.5)防控政策提供支撑。

Sulfate is a major component of the urban PM_(2.5) in China.The current air-quality models consistently underestimate the particulate sulfate formation during haze episodes,indicating that our understanding on the mechanism of atmospheric SO_(2) conversion remains incomplete.Recently,the synergistic oxidation of SO_(2) and NO_(2) within aerosol microdroplets has been recognized as a key additional pathway for SO_(2) atmospheric conversion.However,the influence of ambient conditions(such as molar ratio of reactant gases and relative humidity)on the reaction kinetics remains understudied.Here we adopt micro-Fourier transform infrared(micro-FTIR)spectroscopy to measure the time-evolution of SO_(4)^(2-)and NO_(3)^(-)concentration within a single MgCl_(2) microdroplet,under various SO_(2)/NO_(2) molar ratio.We observed that:The single droplet of MgCl_(2) reacts with SO_(2)/NO_(2) to form SO_(4)^(2-)and NO_(3)^(-),and that the formation rate of SO_(4)^(2-)is the fastest when the molar ratio of SO_(2)/NO_(2) is 1:5.Our research will provide reliable kinetic parameters for air-quality model,which will in turn aid the policy makers to device informed PM_(2.5) containment strategies.