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Title: Molecular Characterization of Brown Carbon (BrC) Chromophores in Secondary Organic Aerosol Generated From Photo-Oxidation of Toluene

Abstract

Atmospheric Brown carbon (BrC) is a significant contributor to light absorption and climate forcing. However, little is known about a fundamental relationship between the chemical composition of BrC and its optical properties. In this work, light-absorbing secondary organic aerosol (SOA) was generated in the PNNL chamber from toluene photo-oxidation in the presence of NOx (Tol-SOA). Molecular structures of BrC components were examined using nanospray desorption electrospray ionization (nano-DESI) and liquid chromatography (LC) combined with UV/Vis spectroscopy and electrospray ionization (ESI) high-resolution mass spectrometry (HRMS). The chemical composition of BrC chromophores and the light absorption properties of toluene SOA (Tol-SOA) depend strongly on the initial NOx concentration. Specifically, Tol-SOA generated under high-NOx conditions (defined here as initial NOx/toluene of 5/1) appears yellow and mass absorption coefficient of the bulk sample (MACbulk@365nm = 0.78 m2 g-1) is nearly 80 fold higher than that measured for the Tol-SOA sample generated under low-NOx conditions (NOx/toluene < 1/300). Fifteen compounds, most of which are nitrophenols, are identified as major BrC chromophores responsible for the enhanced light absorption of Tol-SOA material produced in the presence of NOx. The integrated absorbance of these fifteen chromophores accounts for 40-60% of the total light absorbance by Tol-SOA at wavelengthsmore » between 300 nm and 500 nm. The combination of tandem LC-UV/Vis-ESI/HRMS measurements provides an analytical platform for predictive understanding of light absorption properties by BrC and their relationship to the structure of individual chromophores. General trends in the UV/vis absorption by plausible isomers of the BrC chromophores were evaluated using theoretical chemistry calculations. The molecular-level understanding of BrC chemistry is helpful for better understanding the evolution and behavior of light absorbing aerosols in the atmosphere.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1222078
Report Number(s):
PNNL-SA-110255
39717; 44638
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Physical Chemistry Chemical Physics. PCCP, 17(36):23312-23325
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP, 17(36):23312-23325
Country of Publication:
United States
Language:
English
Subject:
Environmental Molecular Sciences Laboratory

Citation Formats

Lin, Peng, Liu, Jiumeng, Shilling, John E., Kathmann, Shawn M., Laskin, Julia, and Laskin, Alexander. Molecular Characterization of Brown Carbon (BrC) Chromophores in Secondary Organic Aerosol Generated From Photo-Oxidation of Toluene. United States: N. p., 2015. Web. doi:10.1039/c5cp02563j.
Lin, Peng, Liu, Jiumeng, Shilling, John E., Kathmann, Shawn M., Laskin, Julia, & Laskin, Alexander. Molecular Characterization of Brown Carbon (BrC) Chromophores in Secondary Organic Aerosol Generated From Photo-Oxidation of Toluene. United States. doi:10.1039/c5cp02563j.
Lin, Peng, Liu, Jiumeng, Shilling, John E., Kathmann, Shawn M., Laskin, Julia, and Laskin, Alexander. Mon . "Molecular Characterization of Brown Carbon (BrC) Chromophores in Secondary Organic Aerosol Generated From Photo-Oxidation of Toluene". United States. doi:10.1039/c5cp02563j.
@article{osti_1222078,
title = {Molecular Characterization of Brown Carbon (BrC) Chromophores in Secondary Organic Aerosol Generated From Photo-Oxidation of Toluene},
author = {Lin, Peng and Liu, Jiumeng and Shilling, John E. and Kathmann, Shawn M. and Laskin, Julia and Laskin, Alexander},
abstractNote = {Atmospheric Brown carbon (BrC) is a significant contributor to light absorption and climate forcing. However, little is known about a fundamental relationship between the chemical composition of BrC and its optical properties. In this work, light-absorbing secondary organic aerosol (SOA) was generated in the PNNL chamber from toluene photo-oxidation in the presence of NOx (Tol-SOA). Molecular structures of BrC components were examined using nanospray desorption electrospray ionization (nano-DESI) and liquid chromatography (LC) combined with UV/Vis spectroscopy and electrospray ionization (ESI) high-resolution mass spectrometry (HRMS). The chemical composition of BrC chromophores and the light absorption properties of toluene SOA (Tol-SOA) depend strongly on the initial NOx concentration. Specifically, Tol-SOA generated under high-NOx conditions (defined here as initial NOx/toluene of 5/1) appears yellow and mass absorption coefficient of the bulk sample (MACbulk@365nm = 0.78 m2 g-1) is nearly 80 fold higher than that measured for the Tol-SOA sample generated under low-NOx conditions (NOx/toluene < 1/300). Fifteen compounds, most of which are nitrophenols, are identified as major BrC chromophores responsible for the enhanced light absorption of Tol-SOA material produced in the presence of NOx. The integrated absorbance of these fifteen chromophores accounts for 40-60% of the total light absorbance by Tol-SOA at wavelengths between 300 nm and 500 nm. The combination of tandem LC-UV/Vis-ESI/HRMS measurements provides an analytical platform for predictive understanding of light absorption properties by BrC and their relationship to the structure of individual chromophores. General trends in the UV/vis absorption by plausible isomers of the BrC chromophores were evaluated using theoretical chemistry calculations. The molecular-level understanding of BrC chemistry is helpful for better understanding the evolution and behavior of light absorbing aerosols in the atmosphere.},
doi = {10.1039/c5cp02563j},
journal = {Physical Chemistry Chemical Physics. PCCP, 17(36):23312-23325},
number = ,
volume = ,
place = {United States},
year = {2015},
month = {9}
}