Sur une nouvelle methode de dosage du dioxyde d'azote present dans les atmospheres polluees, derivee de la methode de Griess-Saltzmann

Abstract

This paper discusses a procedure involving absorption of NO₂ on triethanolamine impregnated-papers according to a recent study of Levaggi, Siu and Feldstein.

The used solid surfaces are Millipore filters, first impregnated by stirring them in a solution containing triethanolamine, glycerol and acetone before drying in an oven. Storage is made in a closed glass container.

For sampling, check air flow rate to be about 30 l h⁻¹ through filters. The sampling time depends on the actual concentration. Samples are then analyzed in a laboratory under Saltzman's colorimetric reaction. The composition of the reagents is slightly modificated (acetic acid is replaced by phosphoric acid to obtain pH 1). Color development needs 30 min and then absorbance is compared with a standardization curve built from dilute solutions of Na NO₂.

Absorption efficiencies of over 95% are attained with two impregnated filters in a filter holder and at about 301 h⁻¹ flow rate. Stability of filters after sampling is evaluated at 2 or 3 weeks, so it is possible to store several filters before sending them (for example by mail) to the laboratory for analysis.

The stoichiometric factor depends on the weight (expressed in μg) of NO₂ collected on the filters and varies between 1.0 and 0.84.

To measure NO, oxidation into NO₂ is first required, for example with an O₃ lamp.