Homogeneous and heterogeneous photolysis of nitrate in the atmosphere: state of the science, current research needs, and future prospects
Yiqun Cao, Qingxin Ma, Biwu Chu, Hong He
Abstract
Abstract Nitrate is an important component of atmospheric particulate matter and affects air quality, climate, human health, and the ecosystem. Nitrate was previously considered a permanent sink for nitrogen oxides (NO x ). However, this viewpoint has been challenged in recent years because growing research evidence has shown the transformation of nitrate into NO x (i.e., renoxification). The photolysis of nitrate/HNO 3 , especially in the particulate phase or adsorbed on particles, can be a significant renoxification process in the atmosphere. The formation and photolysis of nitrate in aerosol not only change the diurnal variation of NO x , but also provide long-distance transport of NO x in the form of nitrate, which affects local and regional atmospheric chemistry and air quality. This review summarizes recent advances in the fundamental understanding of the photolysis of nitrate/HNO 3 under various atmospheric conditions, with a focus on mechanisms and key factors affecting the process. The atmospheric implications are discussed and future research is recommended.