Development and Deployment of a Novel Peroxy Radical Detector

Drexel University, Philadelphia PA

Investigators

Abstract

This project is focused on the development and testing of a new instrument for measuring atmospheric concentrations of peroxy radicals in the atmosphere. The new method will use a novel acetaldehyde/nitric oxide chemical amplification approach to greatly improve upon the traditional chemical amplification technique that uses carbon monoxide (CO) for measuring peroxy radicals. A prototype version of the instrument has been developed and successfully tested it in the laboratory at the University of Massachusetts, Amherst. Peroxy radicals are important because they react with nitric oxide in the atmosphere to form ozone, a potent greenhouse gas and an air pollutant with adverse health and ecological impacts on humans and plants. The acetaldehyde-based amplification factor is predicted to be relatively stable and is not expected to vary significantly with relative humidity, as does the CO factor. The method also will enable the peroxy radicals to be speciated due to differences in wall loss rates resulting from the addition of a sampling scrubber made of a material that is much more reactive to the hydroperoxy radical (HO2) than to RO2 (peroxy radical where R is an organic substituent). Several candidate materials have been identified and will be thoroughly investigated in the project. Prior to field-testing, the instrument will be tested for interferences by peroxyacetyl nitrate, nitrate radical, and other possible interferents and calibrated using multiple calibration sources to provide confidence that the measurements are not compromised by systematic errors associated with any particular calibration method. A preliminary field test will be conducted in outdoor air in Amherst over a period of a week or more, with periodic automated standard additions of nitrogen dioxide and HO2. Deployments of the new instrument will take place during the summers of 2015 to 2017 at forest sites that with different environmental conditions, such as differences in nitrogen oxide concentrations and/or types of emissions of biogenic volatile organic hydrocarbons. During these deployments, several other scientific teams will bring their instruments to participate in an intercomparison of peroxy radical measurement methods. This project addresses key knowledge gaps relevant to climate change and air pollution science.