Investigation of HO uptake onto Cu()- and Fe()-doped aqueous inorganic aerosols and seawater aerosols using laser spectroscopic techniques

• Published in: Environmental science: atmospheres 2023-10, Vol.3 (1), p.1384-1395
• Main Authors: Li, Jiaru, Sakamoto, Yosuke, Sato, Kei, Morino, Yu, Kajii, Yoshizumi
• Format: Article
• ISSN: 2634-3606
• DOI: 10.1039/d3ea00093a

Heterogeneous HO 2 uptake onto aerosols, which affects tropospheric chemistry, is known as a potential sink of HO x (&z.tbd;OH + HO 2 +RO 2 ); however, the associated reaction kinetics are still unclear. Also, the measurement of the HO 2 uptake coefficient ( γ ) remains challenging and the γ values reported so far based on laboratory studies vary by orders of magnitude depending on the aerosol properties, initial HO 2 concentration, and the experimental conditions. Here, we established a novel approach for detecting the loss rate of HO 2 uptake by inorganic aerosols derived from NaCl, (NH 4 ) 2 SO 4 , Na 2 SO 4 , or diluted seawater using laser-pump and laser-induced fluorescence techniques and clarified the effects of transition metal ions (TMIs), Cu( ii ) and Fe( ii ) on the process. Our results confirmed the enhancement effects of Cu( ii ) and Fe( ii ) on the uptake process. Furthermore, soluble Cu( ii ) enhanced the uptake with a kinetic reaction rate coefficient two orders of magnitude higher than that of Fe( ii ) ions. The second order rate constants of bulk phase reactions for Cu( ii )- and Fe( ii )-doped (NH 4 ) 2 SO 4 are 1.5 × 10 7 M −1 s −1 and 1.3 × 10 5 M −1 s −1 , respectively. However, uncertainties regarding the pH of the aerosols and TMI participation in the aerosol phase still exist. Notwithstanding, the uptake coefficients here reported will complement current IUPAC recommendations. Additionally, future studies can benefit from investigations of the effects of aerosol pH on the HO 2 uptake process, the determination of uptake onto other TMI-doped aerosol types, and testing with ambient aerosols. Our findings can also be incorporated into multiphase kinetic models for a better understanding of the bulk and surface processes and for the evaluation of spatiotemporal oxidation products under ambient atmospheric conditions. This work establishes the determination of the uptake coefficient of HO 2 onto a series of inorganic aerosols by LP-LIF.