Passive samplers are an effective tool in the air environment to determine time-weighted averages of concentration levels of dissolved air pollutants. Passive samplers prove to be optimal devices for the measurement of long term and cumulative concentrations in remote and inaccessible areas eliminating errors caused by short-term variations in concentrations.

An example is the reference study conducted by the Swiss Federal Institute for Forest, Snow and Landscape research WSL with the aim to examine long term ozone concentration in relation to the onset and development of visible foliar injury on numerous forests, shrub and herb species in southern Switzerland. Amongst others, the main goals of the study were

• firstly assess the sensitivity of ozone of different plant species and determination of dose-response relationships, and
• secondly to assess and validate visible and non visible ozone symptoms.

LEFT: typical damage on plant leaves. – RIGHT: forestial monitoring site in action