Real-Time Analysis of PAH Bound to Size-Resolved Atmospheric Particles by Tandem Time of Flight Mass SpectrometersEPA Grant Number: R825391
Title: Real-Time Analysis of PAH Bound to Size-Resolved Atmospheric Particles by Tandem Time of Flight Mass Spectrometers
Investigators: Smith, Kenneth A.
Current Investigators: Smith, Kenneth A. , Worsnop, Douglas R.
Institution: Massachusetts Institute of Technology
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1996 through September 30, 1999 (Extended to November 30, 2000)
Project Amount: $375,000
RFA: Exploratory Research - Air Engineering (1996) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Land and Waste Management , Air , Engineering and Environmental Chemistry
Fine particles and the associated organic compounds are of current concern because of their putative health effects. Of particular concern are polycyclic aromatic hydrocarbons (PAH) which are mutagenic air pollutants formed as by-products of combustion. They are a subset of Polycyclic Organic Matter listed as hazardous air pollutants in the Clean Air Act. In the atmosphere, PAH partition among the gas phase and atmospheric particles. Measurements of the amount of PAH associated with different aerosol size fractions are critical for a complete understanding of the environmental fate of and human exposure to fine particles and the associated PAH. Current methods to quantify PAH bound to size-segregated atmospheric particles require long sampling times (? 100 h) and laborious chemical analysis (? 1000 man-hours).
The goal of the proposed research is to develop and demonstrate an instrument able to quantify PAH associated with individual size-segregated atmospheric particles in real time. We propose a new approach that will combine a particle mass spectrometer that is under development at Aerodyne Research, Inc., with sensitive PAH detection. Particles will be vaporized on a heated filament and a pulsed ultraviolet excimer laser will be focused into the vapor plume to selectively and sensitively ionize PAH species via resonant enhanced multiphoton ionization (REMPI). A second TOF MS, triggered after the ionization laser pulse, will mass analyze the molecular ions, providing PAH molecular distribution data for each vaporized particle. Detailed modeling of the dynamics of particle vaporization will be used to optimize filament/laser coupling for maximum sensitivity and selectivity of the PAH detection process.
The instrument will be calibrated using well characterized emissions from three combustors, a flat flame burner, jet stirred reactor/plug flow reactor, and diesel engine. The instrument will be demonstrated for ambient particle sampling and analysis using parallel particle collection with a cascade impactor followed by GC/MS analysis. The prototype field portable instrument will then be available for future novel measurements of particulate PAH in the atmosphere. Successful demonstration of ambient aerosol PAH sampling and analysis will provide the basis for commercial instrumentation for monitoring of atmospheric particulate PAH distributions, deployable on fixed site or mobile platforms, with the fine temporal and spatial resolution needed to better understand the risks to human health resulting from PAH emissions.