Design and Evaluation of a Photochemical Chamber to Investigate the Health Effects of Fresh and Aged Vehicular Emissions

VASILEIOS PAPAPOSTOLOU (1), Joy E. Lawrence (1), Stephen T. Ferguson (1), Jack M. Wolfson (1), Petros Koutrakis (1)

(1) Harvard School of Public Health, Boston

     Abstract Number: 131
     Last modified: April 22, 2010

Abstract
The TERESA (Toxicological Evaluation of Realistic Emission Source Aerosol) methodology was adapted to investigate the health effects of fresh and aged vehicular emissions. The ventilation stack for a large urban highway tunnel in the northeastern US was used as the source of primary vehicular emissions for sampling, characterization, and exposure. We present the design and optimization of a new, large photochemical chamber that can be used to form secondary organic aerosol from primary vehicular emissions. The chamber is approximately a cube of 8m$^3 volume and consists of Teflon film on a Teflon-coated aluminum framework. The chamber is a well-mixed-flow reactor that is operated in a dynamic flow mode. To produce secondary organic aerosol, direct tunnel primary vehicular emissions were diluted with clean air inside the chamber. Ozone was added to titrate the baseline nitric oxide concentrations in the chamber in order to initiate the photochemical reactions. To maximize the secondary organic aerosol yield, and also to have adequate chamber flow output for animal exposures and particle characterization, the chamber performance was optimized by varying the chamber residence time and the baseline concentrations of primary particle mass and nitric oxide in the chamber. Higher baseline primary particle mass concentrations resulted in lower amounts of SOA formation. Over a course of 72 hours with the lights on, the chamber produced on average a total of 70 micrograms/m$^3 of secondary organic aerosol as measured by an SMPS and an APS. Particle losses ranged from 5 to 20% across the particle size range of 15-500 nm (mobility diameter). The chamber was coupled directly with an exposure system to determine the animal toxicity of both primary and secondary vehicular emissions.