Ion–Molecule Rate Constants for Reactions of Sulfuric Acid with Acetate and Nitrate Ions

Abstract

Atmospheric nucleation from precursor gases is a significant source of cloud condensation nuclei in the troposphere and thus can affect the Earth’s radiative balance. Sulfuric acid, ammonia, and amines have been identified as key nucleation precursors in the atmosphere. Studies have also shown that atmospheric ions can react with sulfuric acid to form stable clusters in a process referred to as ion-induced nucleation (IIN). IIN follows similar reaction pathways as chemical ionization, which is used to detect and measure nucleation precursors via atmospheric pressure chemical ionization mass spectrometers. The rate at which ions form clusters depends on the ion–molecule rate constant. However, the rate constant varies based on the ion composition, which is often not known in the atmosphere. Previous studies have examined ion–molecule rate constants for sulfuric acid and nitrate ions but not for other atmospherically relevant ions like acetate. We report the relative rate constants of ion–molecule reactions between nitrate and acetate ions reacting with sulfuric acid. The ion–molecule rate constant for acetate and sulfuric acid is estimated to be a factor of 1.9–2.4 times higher than that of the known rate constant for nitrate and sulfuric acid. Using quantum chemistry, we find that acetate has a higher dipole moment and polarizability than nitrate. This may contribute to an increase in the collision cross-sectional area between acetate and sulfuric acid and lead to a greater reaction rate constant than nitrate. The ion–molecule rate constant for acetate with sulfuric acid will help quantify the contribution of acetate ions to atmospheric ion-induced new particle formation.

Role of Methanesulfonic Acid in Sulfuric Acid–Amine and Ammonia New Particle Formation

“…Acetate ionization was used to measure SA and MSA concentrations during the particle observations for MA and TMA when varying [MSA]. The reaction rate constant was 2 × 10 –9 cm 3 s −1 for nitrate and 4.6 × 10 –9 cm 3 s −1 for acetate. − Additionally, it is assumed that MSA is ionized by nitrate and acetate at the same rate as SA, as no previous measurements have been conducted on its ionization rate constant. Hydronium ions (and its larger clusters) were used to ionize the basic gases.…”

“…Hydronium ions (and its larger clusters) were used to ionize the basic gases. Ion signals are converted to concentrations using the method described in Fomete et al, with a chemical ionization time of 0.02 s. Mass-dependent transmission efficiency values for the MCC were used to account for differences in the detection due to ion mass . The systematic uncertainty of the MCC has been estimated to be a factor of two .…”

Sulfuric Acid Nucleation Potential Model Applied to Complex Reacting Systems in the Atmosphere

“…Once in the atmosphere, SA reacts with numerous precursor compounds at rates spanning several orders of magnitude to form stable particles. These compounds include ammonia (Coffman & Hegg, 1995; Hanson & Eisele, 2002), amines (Glasoe et al., 2015; Jen et al., 2014; Kurtén et al., 2008; Kürten et al., 2018), oxidized organics (Riccobono et al., 2012), alkanolamines (Fomete et al., 2022a), and ions (Eisele et al., 2006; Fomete et al., 2022b; Kirkby et al., 2011, 2016). In addition, methanesulfonic acid (MSA), which can exist in tandem with SA, has been shown to nucleate with and without SA in terrestrial and marine environments (Chen & Finlayson‐Pitts, 2017; Dawson et al., 2012; Elm, 2022; Johnson & Jen, 2023a; Saltzman et al., 1983).…”

Advances in Atmospheric Chemical and Physical Processes

“…New particle formation, of particular importance in pristine areas of the atmosphere, is a topic of study, with work presented including improved parametrizations of the temperature dependence of formation of sulfuric acid/water clusters 24 and determinations of the kinetics of reaction of acetate and nitrate ions with sulfuric acid, of potential importance in ion-induced new particle formation. 25 Reactions on surfaces are examined, including a kinetic and mechanistic study of gas−solid and gas-phase ozonolysis of nitrogen-containing alkenes, 26 and the formation of organic nitrates in the heterogeneous reaction of α-pinene with mineral surfaces. 27 Laboratory studies of the air−water interface demonstrate surface adsorption of H 2 O 2 , 28 as well as determining the structure of hydroxy organic acids of varying size at the interface.…”

“…Studies of heterogeneous chemistry , chemistry involving multiple phases, occurring at the interface between phases, or involving transfer of chemical species between phases, are prevalent in this virtual special issue. New particle formation, of particular importance in pristine areas of the atmosphere, is a topic of study, with work presented including improved parametrizations of the temperature dependence of formation of sulfuric acid/water clusters and determinations of the kinetics of reaction of acetate and nitrate ions with sulfuric acid, of potential importance in ion-induced new particle formation . Reactions on surfaces are examined, including a kinetic and mechanistic study of gas–solid and gas-phase ozonolysis of nitrogen-containing alkenes, and the formation of organic nitrates in the heterogeneous reaction of α-pinene with mineral surfaces .…”