| Autor: |
Bondy AL; Department of Chemistry, University of Michigan , Ann Arbor, Michigan 48109 United States., Craig RL; Department of Chemistry, University of Michigan , Ann Arbor, Michigan 48109 United States., Zhang Z; Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States., Gold A; Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States., Surratt JD; Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States., Ault AP; Department of Chemistry, University of Michigan , Ann Arbor, Michigan 48109 United States.; Department of Environmental Health Sciences, University of Michigan , Ann Arbor, Michigan 48109, United States. |
| Abstrakt: |
Isoprene, the most abundant biogenic volatile organic compound (BVOC) in the atmosphere, and its low-volatility oxidation products lead to secondary organic aerosol (SOA) formation. Isoprene-derived organosulfates formed from reactions of isoprene oxidation products with sulfate in the particle phase are a significant component of SOA and can hydrolyze forming polyols. Despite characterization by mass spectrometry, their basic structural and spectroscopic properties remain poorly understood. Herein, Raman microspectroscopy and density functional theory (DFT) calculations (CAM-B3LYP level of theory) were combined to analyze the vibrational modes of key organosulfates, 3-methyltetrol sulfate esters (racemic mixture of two isomers), and racemic 2-methylglyceric acid sulfate ester, and hydrolysis products, 2-methyltetrols, and 2-methylglyceric acid. Two intense vibrational modes were identified, ν(RO-SO 3 ) (846 ± 4 cm -1 ) and ν s (SO 3 ) (1065 ± 2 cm -1 ), along with a lower intensity δ(SO 3 ) mode (586 ± 2 cm -1 ). For 2-methylglyceric acid and its sulfate esters, deprotonation of the carboxylic acid at pH values above the pK a decreased the carbonyl stretch frequency (1724 cm -1 ), while carboxylate modes grew in for ν s (COO - ) and ν a (COO - ) at 1413 and 1594 cm -1 , respectively. The ν(RO-SO 3 ) and ν s (SO 3 ) modes were observed in individual atmospheric particles and can be used in future studies of complex SOA mixtures to distinguish organosulfates from inorganic sulfate or hydrolysis products. |
