The oxidation of self assembled organic monolayers by nitrate radicals using time of flight secondary ion mass spectrometry
EMSL Project ID
27590
Abstract
Field measurements have shown that organic material is abundant in the atmosphere, comprising 10-70% of the total fine particulate mass. This organic material can be in the form of pure organic particles, or alternatively the organic material can be mixed with inorganic material. In the latter case the organic material can form organic coatings on the surface of aqueous particles, or organic coatings adsorbed on the surface of solid particles, such as mineral dust. While in the atmosphere, these organic particles and organic surfaces can be modified by reactions with atmospheric oxidants such as O3, NO3, and OH. These heterogeneous reactions are expected to change the hygroscopicity and toxicity of these organic particles and organic surfaces. Due to the potential atmospheric importance of these heterogeneous reactions, they need to be understood and quantified.We propose to study in detail the NO3-initiated oxidation of organic surfaces using time of flight secondary ion mass spectrometry. For these studies we will use organic self assembled monolayers such as octadecanethiol (ODT, C18 alkane) and undecenethiol (UDT, C11 terminal alkene) on gold, which serve as proxies for organic aerosol surfaces or organic amphiphilic coatings on aqueous aerosols. One of the objectives of the proposed research is to determine the condensed phase products of the reaction of two hydrocarbon monolayers (alkane and terminal alkene) with NO3 radicals. X-ray photoelectron spectroscopy (XPS), infrared (IR) spectroscopy and contact angle measurements have already shown that NO3 reacts with both monolayers in atmospherically relevant times. XPS and IR gave first indications of functional groups formed in these reactions. The proposed ToF-SIMS measurements at PNNL will complement these product studies and give more detailed information on functional groups formed during NO3 radical reaction on alkane and terminal alkene surfaces.
This proposal will build on our previous work carried out at EMSL (proposal 17098). In the previous proposal we carried out preliminary studies, but the experiments were inconclusive due to low NO3 concentrations used in the experiments. The proposed experiments will utilize higher concentrations.
Project Details
Project type
Exploratory Research
Start Date
2007-09-04
End Date
2008-09-07
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
S. Gross and A. K. Bertram, Products and Kinetics of the Reactions of an Alkane Monolayer and a Terminal Alkene Monolayer with NO3 Radicals, Journal of Geophysical Research, D02307, DOI: 10.1029/2008JD010987, 2009.