Field tests of a passive sampler for atmospheric ozone at California mountain forest locations

Field tests of a colorant-based ozone passive sampler have been carried out during the 1990 smog season at five mountain forest locations in California. Co-located measurements of ambient ozone were made at all field sites using the passive sampler and a reference method, ultraviolet (u.v.) photometry. The sampling duration ranged from 3 to 30 days. Nitrogen dioxide, aldehydes and the phytotoxic oxidants peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) were measured at one location to assess possible interferences. The average precision of the measurements, calculated from data for 42 sets of colocated passive samplers, was 12%. Data for all field locations could be reduced to a single equation relating color change (ΔE units) to ozone dose (units: ppb-days). This polynomial equation could be reduced to a linear equation for color changes not exceeding 8 ΔE units (equivalent to sampling durations of up to 15 days), with good agreement between field data and earlier calibration results obtained in the laboratory. Both polynomial and linear equations can be used to obtain quantitative, time-integrated measurements of ambient ozone. The performance of the passive sampler showed no dependence on changes in ambient temperature and humidity. Interferences from air pollutants other than ozone contributed a total positive bias of less than 5% to the measured ozone concentrations: 3% for NO₂, 1.3% for PAN, 0.2% for PPN, and 0.% or less for formaldehyde and acetaldehyde.