The diffusive sampler is based on the diffusion of ozone along a tube to an absorbing medium. The chemisorption of ozone takes place by reaction with 1,2-di(4-pyridyl)-ethylene (DPE); the ozonide formed undergoes cleavage and yields an aldehyde. The amount of aldehyde is finally determined spectrophotometrically by the MBTH method at 442 nm.The diffusive sampler for ozone consists of a polypropylene tube. At the closed end there is a glass fiber filter dipped in a solution of DPE in acetic acid.To protect the samplers against weather conditions and to eliminate the light effect on DPE, a special shelter was developed.
The figure shows the result of an intercomparison of integrated ozone methods in the Euopean Alps. The results are averaged over 6 monitoring sites at various heights from 100 to 1780 m above sea level .
Samplingrate: PS [mabs] = 0.0255 [mg/m3 . h] r = 0.83
Working range: 5 – 240 µg/m3
Sampling time: 1 to 2 weeks
Detection limit: 5.1 µg/m3 weekly exposures
wind speed: influence of wind speed < 10% up to 2.0 m/sec using protection shelters
temperature: no influence between 10 to 30oC
humidity: no influence between 20 to 80%
sunlight: special shelter needed
before use: 6 months
after exposure: 4 months
Cross sensitivity: oxidants
Expanded uncertainty*: 28.4 % at concentration levels 100 µg/m3