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[AAS11-P13] Liquid-phase decomposition of α-alkoxyalkyl-hydroperoxides derived from the reactions of Criegee intermediates with butanediols
Keywords:Aerosol, Criegee intermediate, Secondary organic aerosol
Introduction
In the study of climate change and global warming, atmospheric aerosol is one of the important factors. Secondary organic aerosols (SOA) account for a large fraction of atmospheric aerosols, and it has been suggested that its physical and chemical properties change with oxidations. SOA contain organic hydroperoxides (ROOHs) as a large fraction of component, that would participate in the oxidation process. The reaction of Criegee intermediates (CIs) formed by ozonolysis of biogenic volatile organic compounds (BVOCs) is a major source of ROOHs in the atmosphere. It has been reported that α-hydroxyalkyl hydroperoxides (α-HHs) derived from the hydration of CIs decompose very quickly in aqueous phases. On the other hand, the aqueous-phase fates of α-alkoxyalkyl hydroperoxides (α-AHs), derived from the reaction of CIs with alcohols, are not known well. Especially, the decomposition mechanism of α-AHs remains to be elucidated.
Method
In this study, we measured the decomposition of α-AHs, which are produced from the reaction of butanediol with CIs generated by ozone oxidation of α-terpineol (α-Tp), one of BVOCs emitted from plants and household products. α-AHs were formed by the ozonolysis of α-Tp in a solution of water and 1,2-butanediol (1:1 = vol : vol) and their decomposition time was measured by electrospray mass spectrometry. To detect them, sodium chloride was added to the solution because α-AHs can be detected as chloride ion adducts. The pH dependence was investigated by adding hydrochloric acid to the solution. The activation energy was obtained by varying the temperature of solutions. Further experiments were carried out using 1,3-butanediol and 1,4-butanediol, which have hydroxyl groups at different positions from 1,2-butanediol, and the obtained results were compared.
Result and Discussion
It was found that the rate coefficient k for the decomposition of α-AHs formed in the system of 1,2-butanediol increased exponentially with decreasing pH. By extrapolating the experimental results, we estimated that k = 0.4 - 3.9 s-1 for ambient atmospheric aerosols (pH 1-2). This suggests that the lifetime of α-AHs derived from α-Tp CIs + 1,2-butanediol in aerosols is only a few seconds. The activation energies for the decomposition of α-AH in these three systems were derived to be 12.5 ± 0.9 kcal/mol for 1,2-butanediol, 9.3 ± 2.3 kcal/mol for 1,3-butanediol and 10.0 ± 1.0 kcal/mol for 1,4-butanediol. The present study suggest that the lifetimes of α-AHs in aerosols are affected by pH and local temperatures under different environmental conditions such as altitude, day/night, season, and weather. The derived activation energies for the decomposition of the α-AHs could be incorporated in atmospheric modeling as a representative value of ROOH.
References:
Hu et al., Environ. Sci.: Atmos., 2022, DOI: 10.1039/d1ea00076d.
Hu et al., Phys. Chem. Chem. Phys., 2021, 23, 4605-4614.
Enami, J. Phys. Chem. A., 2021, 125, 4513-4523.
In the study of climate change and global warming, atmospheric aerosol is one of the important factors. Secondary organic aerosols (SOA) account for a large fraction of atmospheric aerosols, and it has been suggested that its physical and chemical properties change with oxidations. SOA contain organic hydroperoxides (ROOHs) as a large fraction of component, that would participate in the oxidation process. The reaction of Criegee intermediates (CIs) formed by ozonolysis of biogenic volatile organic compounds (BVOCs) is a major source of ROOHs in the atmosphere. It has been reported that α-hydroxyalkyl hydroperoxides (α-HHs) derived from the hydration of CIs decompose very quickly in aqueous phases. On the other hand, the aqueous-phase fates of α-alkoxyalkyl hydroperoxides (α-AHs), derived from the reaction of CIs with alcohols, are not known well. Especially, the decomposition mechanism of α-AHs remains to be elucidated.
Method
In this study, we measured the decomposition of α-AHs, which are produced from the reaction of butanediol with CIs generated by ozone oxidation of α-terpineol (α-Tp), one of BVOCs emitted from plants and household products. α-AHs were formed by the ozonolysis of α-Tp in a solution of water and 1,2-butanediol (1:1 = vol : vol) and their decomposition time was measured by electrospray mass spectrometry. To detect them, sodium chloride was added to the solution because α-AHs can be detected as chloride ion adducts. The pH dependence was investigated by adding hydrochloric acid to the solution. The activation energy was obtained by varying the temperature of solutions. Further experiments were carried out using 1,3-butanediol and 1,4-butanediol, which have hydroxyl groups at different positions from 1,2-butanediol, and the obtained results were compared.
Result and Discussion
It was found that the rate coefficient k for the decomposition of α-AHs formed in the system of 1,2-butanediol increased exponentially with decreasing pH. By extrapolating the experimental results, we estimated that k = 0.4 - 3.9 s-1 for ambient atmospheric aerosols (pH 1-2). This suggests that the lifetime of α-AHs derived from α-Tp CIs + 1,2-butanediol in aerosols is only a few seconds. The activation energies for the decomposition of α-AH in these three systems were derived to be 12.5 ± 0.9 kcal/mol for 1,2-butanediol, 9.3 ± 2.3 kcal/mol for 1,3-butanediol and 10.0 ± 1.0 kcal/mol for 1,4-butanediol. The present study suggest that the lifetimes of α-AHs in aerosols are affected by pH and local temperatures under different environmental conditions such as altitude, day/night, season, and weather. The derived activation energies for the decomposition of the α-AHs could be incorporated in atmospheric modeling as a representative value of ROOH.
References:
Hu et al., Environ. Sci.: Atmos., 2022, DOI: 10.1039/d1ea00076d.
Hu et al., Phys. Chem. Chem. Phys., 2021, 23, 4605-4614.
Enami, J. Phys. Chem. A., 2021, 125, 4513-4523.