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https://doi.org/10.5194/egusphere-2023-1381
https://doi.org/10.5194/egusphere-2023-1381
14 Aug 2023
 | 14 Aug 2023

Temperature-dependent aqueous OH kinetics of C2-C10 linear and terpenoid alcohols and diols: new rate coefficients, structure-activity relationship and atmospheric lifetimes

Bartłomiej Witkowski, Priyanka Jain, Beata Wileńska, and Tomasz Gierczak

Abstract. Aliphatic alcohols (AAs), including terpenoic alcohols (TAs), are ubiquitous in the atmosphere due to their widespread emissions from natural and man-made sources. Hydroxyl radical (OH) is the most important atmospheric oxidant in both aqueous and gas phases. Consequently, the aqueous oxidation of the TAs by the OH inside clouds and fogs is a potential source of aqueous secondary organic aerosols (aqSOAs). However, the kinetic data, necessary to estimate the time scales of such reactions is limited. Here, bimolecular rate coefficients (kOHaq) for the aqueous oxidation of twenty-nine, C2-C10 AAs by hydroxyl radicals (OH) were measured with the relative rate method in the temperature range 278–328 K. kOHaq values for the fifteen AAs were measured for the first time after validating the experimental approach. The kOHaq values measured for the C2-C10 AAs at 298 K were between 1.80×109 and 6.5×109 M-1s-1. The values of activation parameters (activation energy (7–17 kJ/mol) and average Gibbs free energy of activation=20 kJ/mol) strongly indicated the predominance of the H-atom abstraction mechanism. The estimated rates of the complete diffusion-limited reactions revealed up to 44 % diffusion contribution to the measured kOHaq values for the C8-C10 AAs.

The kinetic data acquired here, and the literature data, for AAs, carboxylic acids, and carboxylate ions were used to develop a modified structure-activity relationship (SAR). The new SAR developed in this work predicted the temperature-dependent kOHaq for all compounds under investigation with higher accuracy as compared with the previous models. In the modified model, an additional neighboring parameter was introduced (F≥(CH2)6, using the measured kOHaq values for the homolog (C2-C10) linear alcohols and diols. Good accuracy of the new SAR at 298 K (slope=1.05, R2=0.75) was achieved for the AAs and carboxylic acids under investigation. The kinetic database kOHaq values in this work and compiled literature data) was also used to further enhance the ability of SAR to predict temperature-dependent values of kOHaq in the temperature range 278–328 K.

The calculated atmospheric lifetimes indicate that terpenoic alcohols and diols will react with the OH in aerosol, cloud, and fog water with (LWC≥0.1 g/m3) and (LWC≥10-4 g/m3), respectively. The preference of terpenoic diols to undergo aqueous oxidation by the OH under realistic atmospheric conditions is comparable with terpenoic acids, which makes them potentially effective precursors of aqSOAs. In clouds, a decrease in the temperature will strongly favor the aqueous reaction with the OH, primarily due to the increased partitioning into the aqueous phase following Henry’s law equilibrium.

Bartłomiej Witkowski et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of ACP submission egusphere-2023-1381', Anonymous Referee #2, 02 Sep 2023
    • AC2: 'Reply on RC1', Bartlomiej Witkowski, 06 Nov 2023
  • RC2: 'Comment on egusphere-2023-1381', Anonymous Referee #1, 04 Sep 2023
    • AC1: 'Reply on RC2', Bartlomiej Witkowski, 06 Nov 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of ACP submission egusphere-2023-1381', Anonymous Referee #2, 02 Sep 2023
    • AC2: 'Reply on RC1', Bartlomiej Witkowski, 06 Nov 2023
  • RC2: 'Comment on egusphere-2023-1381', Anonymous Referee #1, 04 Sep 2023
    • AC1: 'Reply on RC2', Bartlomiej Witkowski, 06 Nov 2023

Bartłomiej Witkowski et al.

Bartłomiej Witkowski et al.

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Short summary
This article reports the results of the kinetic measurements for the aqueous oxidation of the 28 aliphatic alcohols by hydroxyl radical (OH) at different temperatures. The data acquired and the literature data were used to optimize a model for predicting the aqueous OH reactivity of alcohols and carboxylic acids and to estimate the atmospheric lifetimes of five terpenoic alcohols. The kinetic data provided new insights into the mechanism of aqueous oxidation of aliphatic molecules by the OH.