A simple, cost-effective passive sampler is described that is suitable for measuring parts per billion (ppb) levels of photochemical oxidants (ozone + nitrogen dioxide + peroxyacetyl nitrate + peroxypropionyl nitrate) in ambient air. The passive sampler makes use of oxidant-fugitive colorants, and color changes are proportional to the oxidant dose, i.e. the product of oxidant concentration and sampling duration. Field tests have been carried out at a southern California mountain forest location with co-located passive samplers and continuous measurements of O3, NO2, PAN and PPN. Consistency with laboratory tests of the color change with oxidants studied singly (O3, NO2, PAN) or as a mixture is discussed. Interferences from formaldehyde and sulfur dioxide are negligible. Four colorants have been tested and yield detection limits ranging from 8 to 54 ppb. day (1-8 ppb. week, and so on).
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