CHRISTOPHER MIELE
Applying optical remote sensing techniques to monitor community particulate pollution
Industrial Hygiene and Safety, MS
Preceptor: Michael Yost, PhD
Community air pollution is one of the most highly visible and debated environmental health topics for the public and working populations. A criteria air pollutant that is of extreme importance is particulate matter. The size of the particles is directly related to their potential for causing health problems. Of particular importance, are fine particles that are 2.5 micrometers in diameter and smaller. These fine particles when inhaled generally pass through the nose and throat and penetrate deep into lung tissue. Diesel particulate matter (DPM), a fine particle, currently is among the highest priority concerns for air toxics monitoring by the Puget Sound Clean Air Agency (PSCAA). DPM is not only a priority for community air pollution, there is also growing concern for DPM exposure in occupational settings.
In order to control DPM effectively, we need a method to measure emissions quickly and effectively. A novel way for monitoring DPM continuously and in real-time is by utilizing optical remote sensing techniques such as ultraviolet differential optical absorption spectroscopy (UV DOAS). The Cerex Environmental, Inc. UV Sentry utilizes UV DOAS technology to measure multiple air pollutants within an open path up to 1000 meters in length. The PSCAA presently uses this UV-DOAS system for ambient gas monitoring but the system also may be capable of measuring particles by optical extinction. All particles scatter and absorb light to some extent, and this phenomenon is a complex function of optical wavelength, particle size, shape, refractive index, and concentration. By quantifying this loss of light along the beam path (known as optical extinction) over a range of wavelengths, it may be possible to estimate the particle concentration.
DOAS measurements were carried out at a PSCAA air monitoring site at Olive Street in Seattle, Washington. The monitoring site is located in downtown Seattle adjacent to Interstate 5 and is subject to heavy air quality impacts from mobile traffic sources. The open beam path was set-up across Interstate 5 with a pathlength of 100 meters. The Olive Street DOAS measurements will be validated through laboratory calibration using a fixed gas cell, intercomparison with point monitors collected simultaneously at the site, and proportional pathlength measurements collected with a known diesel concentration at the Northlake Diesel Exposure Chamber.
It is hoped that these findings will demonstrate the feasibility of UV DOAS for DPM measurement and represent another step in the monitoring and control of diesel exhaust in our community and workplaces.
