Ozone concentrations were measured

Ozone concentrations were measured using the 2B Technologies Model 202 Ozone Monitor.
Concentrations were logged every 10 seconds to the instrument’s internal memory for at least
5 minutes each upstream and downstream of both the experimental filter banks and the
reference filter banks. The technician walked into the appropriate rooms of the air handlers to
access locations upstream and downstream of filter banks and held the instrument at least
three feet above the floor at a central location (several feet upstream or downstream of the
filter bank) while data were logged. Because accurate measurements of low ozone
concentration with portable instruments are very difficult, the measurements occurred mid-tolate
afternoon when outdoor air concentrations were expected to be highest. Our prior
experience showed that relative humidity above approximately 65% could lead to significant
measurement errors and that passing the instrument’s inlet air sample through moisturepermeable
Nafion tubing located in a lower humidity environment greatly reduced such
errors. Consequently, in our study the ozone-containing air sample was passed through
Nafion tubing coiled inside a container containing silica gel desiccant. The air sample
passed through two sections of 0.5 m long tubing (internal and external diameter were 1.06
and 1.35 mm, respectively) installed in parallel.