Laboratory evaluation of a prototype photochemical chamber designed to investigate the health effects of fresh and aged vehicular exhaust emissions

Abstract

Laboratory experiments simulating atmospheric aging of motor vehicle exhaust emissions were conducted using a single vehicle and a photochemical chamber. A compact automobile was used as a source of emissions. The vehicle exhaust was diluted with ambient air to achieve carbon monoxide (CO) concentrations similar to those observed in an urban highway tunnel. With the car engine idling, it is expected that the CO concentration is a reasonable surrogate for volatile organic compounds (VOCs) emissions. Varying the amount of dilution of the exhaust gas to produce different CO concentrations, allowed adjustment of the concentrations of VOCs in the chamber to optimize production of secondary organic aerosol (SOA) needed for animal toxicological exposures. Photochemical reactions in the chamber resulted in nitric oxide (NO) depletion, nitrogen dioxide (NO₂) formation, ozone (O₃) accumulation, and SOA formation. A stable SOA concentration of approximately 40 μg m⁻³ at a chamber mean residence time of 30 min was achieved. This relatively short mean residence time provided adequate chamber flow output for both particle characterization and animal exposures. The chamber was operated as a continuous flow reactor for animal toxicological tests. SOA mass generated from the car exhaust diluted with ambient air was almost entirely in the ultrafine mode. Chamber performance was improved by using different types of seed aerosol to provide a surface for condensation of semivolatile reaction products, thus increasing the yield of SOA. Toxicological studies using Sprague-Dawley rats found significant increases of in vivo chemiluminescence in lungs following exposure to SOA.

Keywords::

• Photochemical chamber
• secondary organic aerosol
• vehicular emissions

Acknowledgements

This publication was made possible by USEPA grants R-832416 and RD 83479801. Its contents are solely the responsibility of the grantee and do not necessarily represent the official views of the USEPA. Further, USEPA does not endorse the purchase of any commercial products or services mentioned in the publication. This work was also supported by the Harvard NIEHS Center for Environmental Health (grant P30ES000002). We thank Dr. Stephen Rudnick for reading the manuscript and providing helpful suggestions. We also thank Dr. Choong-Min Kang and Samuel Pueringer for the analytical support. Technical assistance was provided by John Tosti, Vivian Hatakeyama, Brenno Gomes, and Yasser Calil.

Declaration of interest

The authors report no declarations of interest.