Issue 36, 2015

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@365 nm = 0.78 m2 gāˆ’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 40ā€“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.

Graphical abstract: Molecular characterization of brown carbon (BrC) chromophores in secondary organic aerosol generated from photo-oxidation of toluene

Supplementary files

Article information

Article type
Paper
Submitted
05 May 2015
Accepted
22 Jun 2015
First published
23 Jun 2015

Phys. Chem. Chem. Phys., 2015,17, 23312-23325

Author version available

Molecular characterization of brown carbon (BrC) chromophores in secondary organic aerosol generated from photo-oxidation of toluene

P. Lin, J. Liu, J. E. Shilling, S. M. Kathmann, J. Laskin and A. Laskin, Phys. Chem. Chem. Phys., 2015, 17, 23312 DOI: 10.1039/C5CP02563J

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements