Measurements of Organic Acids and Hydroperoxides in Ambient Urban Air by Chemical Ionization Mass Spectrometry (CIMS)EPA Grant Number: FP916334
Title: Measurements of Organic Acids and Hydroperoxides in Ambient Urban Air by Chemical Ionization Mass Spectrometry (CIMS)
Investigators: Crounse, John D.
Institution: California Institute of Technology
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2004 through December 31, 2006
Project Amount: $111,688
RFA: STAR Graduate Fellowships (2004) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Air Quality and Air Toxics , Fellowship - Atmospheric Sciences
The objective of this project is to further our understanding of gas/aerosol phase chemistry within the polluted urban environment, through direct in situ measurements of photochemical products including inorganic acids, organic acids, and hydroperoxides.
I will use negative ion chemical ionization mass spectrometry (NICIMS) to measure many trace species directly in air. My chosen reagent ion, CF3O-, reacts either by: (1) fluoride transfer to more acidic species, including nitric acid, formic acid, acetic acid, and peroxynitric acid, or (2) ion clustering with less acidic species, including hydrogen peroxide, methyl hydrogen peroxide, hydroxy methyl hydrogen peroxide, and water. The specific product ions are monitored by tuning the quadrupole mass filter to the corresponding ion mass. The quadrupole allows only ions of the “tuned” mass-to-charge ratio to pass through to the detector. For high sensitivity, I use a channel electron multiplier that is run in pulse counting mode. In principle, these measurements are straightforward in the sense that the ion intensity for a specific product ion is proportional to the concentration of neutral parent. The primary difficulty to overcome in this project is to account for interferences that exist at the product ion mass (other ions with same mass, i.e., background signals). I propose to use MS/MS to measure the background signals. Calibration will be conducted by addition of an isotopically labeled analog for each target molecule to the analyte air stream. This allows calibration to be done simultaneously with measurements without interfering with the measurements. The instrument electronics and data collection are controlled through a personal computer, allowing the instrument to run effectively without direct operator control.