The Health Effects Institute

Synopsis
Research Report Number 79

Improvement of a Respiratory Ozone Analyzer

James S. Ultman, Abdellaziz Ben-Jebria, Craig S. MacDougall,and Marc L. Rigas
Department of Chemical Engineering, Pennsylvania State University,University Park, PA

BACKGROUND

In many people, exposure to ozone, an irritant gas and ubiquitous air pollutant, causes reversible decreases in some measures of lung function, increases in airway reactivity, and the appearance of indicators of airway inflammation in lung fluids. Individuals having the greatest risk of developing such effects appear to be those who exercise or engage in moderate-to-strenuous physical activity. To estimate the health risk that ozone exposure may pose to humans, regulators need to know how much ozone reaches the target tissues in the respiratory tract.

Measuring respiratory dose requires an instrument that (1) can monitor ozone concentrations at the airway opening (mouth or nose) rather than in the ambient air; (2) responds dynamically at a rapid rate relative to an individual's breathing rate; and (3) is sensitive enough to measure ozone levels at or below ambient levels (0.07 to 0.20 ppm in urban areas) for both resting and exercising subjects. With previous HEI support, Dr. James Ultman and his colleagues developed a rapidly responding analyzer to measure the dose of inhaled ozone. To use it, a subject at rest inhaled air containing a predetermined bolus dose of ozone and then exhaled into the instrument, which quantified the amount of ozone exhaled. By comparing the amounts of ozone inhaled and exhaled, the investigators calculated how much ozone had been absorbed by the respiratory tract. However, this first-generation instrument proved to not be suitable for measuring ozone at levels less than 0.5 ppm or in individuals engaged in moderate-to-strenuous physical activity. HEI funded this follow-on study to improve the first-generation ozone analyzer by increasing its ozone sensitivity and its response time, thereby allowing ozone uptake to be measured at ambient levels in exercising subjects.

APPROACH

Dr. Ultman and his colleagues redesigned their first-generation analyzer to reduce electronic noise (interference) and improve the signal's stability. To do so, they adjusted each parameter that influenced the analyzer's performance: the flow of the air sample into the instrument, the pressure in the chamber where the air sample and the reactant gas mixed, the relative amounts of the reactant gas and air sample, and electronic variables (frequency and voltage). Through trial and error, they determined the combination of parameters that would produce the fastest response time, the strongest and most stable signal, and the least interference from noise. To evaluate the success of their modifications, they conducted a pilot test to measure ozone uptake in the respiratory tracts of two human subjects.

RESULTS AND IMPLICATIONS

The investigators made significant advances in improving their first-generation ozone analyzer. By redesigning that instrument, they were able to accurately measure ozone levels below 0.2 ppm. The investigators also improved the instrument's response time, even though they were unable to markedly reduce the interference from electronic noise. Further improvements in design are needed to reduce the inherent electronic noise of the instrument.

Nevertheless, because of the improved response characteristics, the second-generation ozone analyzer was able to measure ozone respiratory uptake in a pilot test using two subjects with breathing rates corresponding to moderate exercise while being exposed to 0.11 ppm ozone. In its current configuration, the instrument can be used when the subject's maximal breathing rate is 30 breaths per minute and the exposure concentration of ozone is approximately 0.1 ppm or greater. Thus, using the second-generation analyzer, more detailed clinical studies to quantify respiratory ozone uptake in exercising human subjects should be possible.

TABLE OF CONTENTS

Investigator's Report
James S. Ultman, Abdellaziz Ben-Jebria, Craig S. MacDougall,and Marc L. Rigas

Commentary
Health Review Committee

CODE:ULTMAN79

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