AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
A Long Path Absorbance Photometer for the Determination of Peroxide Content and Brown Carbon in Organic Aerosol
JOSEF DOMMEN, Peter Mertes, Stephen Platt, Imad El Haddad, Lisa Pfaffenberger, Andre Prévôt, Markus Kalberer, Urs Baltensperger, Paul Scherrer Instiute
Abstract Number: 311 Working Group: Instrumentation and Methods
Abstract Organic aerosols are composed of thousands of different organic molecules. These compounds have low vapour pressures and must therefore contain many functional groups, e.g. alcohols, carbonyls, carboxylic acids and peroxides. Of these groups, organic peroxides are the least understood. They are difficult to measure and they have been quantified in only few studies. Furthermore it is assumed that they contribute to adverse health effects because of their high reactivity and high oxidation potential.
Not only black carbon but also many organic compounds are light absorbing. The occurrence of such compounds in organic aerosols has been referred to as brown carbon. Incomplete combustion, especially associated with biomass burning has been shown to produce particulate brown carbon. However, brown carbon formation and its removal by photochemical oxidation is not well understood.
Here we present an instrument for the quantification of peroxides in aerosol particles based on iodometry and long path absorption photometry (Peroxide-LOPAP). Extraction, chemical conversion and subsequent measurement of the aerosol samples are performed in a closed, oxygen-free environment. The limit of detection is 0.1 micromolar peroxide, which is orders of magnitude lower than previously obtained.
The method measures quantitatively all peroxides except for very stable compounds like tert-butyl hydroperoxide. Thus, with this instrument the total concentration of peroxides in the aerosol is effectively measured. Since the measurement technique relies on absorption we also measured the light absorbance of other species extracted from the aerosols.
Primary and secondary organic aerosols (POA, SOA) from the following sources were investigated for peroxides and absorbance: SOA from ozonolysis and photooxidation of alpha-pinene, POA and SOA of emissions from wood burning, a diesel car, a two-stroke scooter and cooking.
The highest amount of peroxides with 34% (assuming a molecular weight MW of 300 g/mol) was found in freshly generated SOA from alpha-pinene ozonolysis.