Department of Civil and Environmental Engineering, the Hong Kong Polytechnic University, Hong Kong, 999077, China.
Department of Ambient Air Quality Monitoring, China National Environmental Monitoring Center, Beijing, 100012, China.
Nat Commun. 2022 Feb 17;13(1):939. doi: 10.1038/s41467-022-28383-9.
Chlorine atoms (Cl) are highly reactive and can strongly influence the abundances of climate and air quality-relevant trace gases. Despite extensive research on molecular chlorine (Cl), a Cl precursor, in the polar atmosphere, its sources in other regions are still poorly understood. Here we report the daytime Cl concentrations of up to 1 ppbv observed in a coastal area of Hong Kong, revealing a large daytime source of Cl (2.7 pptv s at noon). Field and laboratory experiments indicate that photodissociation of particulate nitrate by sunlight under acidic conditions (pH < 3.0) can activate chloride and account for the observed daytime Cl production. The high Cl concentrations significantly increased atmospheric oxidation. Given the ubiquitous existence of chloride, nitrate, and acidic aerosols, we propose that nitrate photolysis is a significant daytime chlorine source globally. This so far unaccounted for source of chlorine can have substantial impacts on atmospheric chemistry.
氯原子（Cl）具有很高的反应活性，能够强烈影响气候和空气质量相关痕量气体的丰度。尽管人们对极地大气中的分子氯（Cl）和氯的前体进行了广泛的研究，但其他地区的氯来源仍知之甚少。本研究报告了在香港沿海地区观测到的高达 1 ppbv 的白天氯浓度，揭示了氯的一个重要白天来源（中午 2.7 pptv s）。现场和实验室实验表明，在酸性条件（pH < 3.0）下，阳光对颗粒态硝酸盐的光解可以激活氯离子，从而解释了观测到的白天氯的产生。高浓度的氯显著增加了大气的氧化作用。鉴于氯化物、硝酸盐和酸性气溶胶的普遍存在，我们提出硝酸盐光解是全球范围内一个重要的白天氯源。这个迄今未被考虑的氯源可能对大气化学产生重大影响。
