A Passive Diffusion Tube Sampler for the Measurement of Atmospheric NO₂. A New Approach

Abstract

Methods currently used for the determination of NO₂ in the atmosphere require power supplies and some protection from the environment and, in the case of the generally accepted chemiluminescence analyser, a large initial capital outlay for the purchase of the instrument, data logger and retrieval systems as well as regular skilled maintenance in use. These disadvantages have hindered the accumulation of a data base of NO₂ concentrations similar to that available for SO₂ in some countries.

Recently a passive diffusion tube sampler has been validated for ambient NO₂ sampling. This simple and inexpensive device collects by molecular diffusion of the gas along a tube of accurately known dimensions to an efficient absorbent of triethanolamine coated onto stainless steel mesh discs. Nitrogen dioxide is determined by the well established Griess-Saltzman spectrophotometric method.

The sampler described is an integrating device and its reliance on diffusion for NO₂ collection renders it unsuitable for short term measurements. Its collection rate of “72 cm³ hr^-1” gives, however a limit of detection of about 200 ppb hours allowing concentrations down to 1–2 ppb to be measured with sampling periods of one week.

In this paper the preparation, analysis and performance of the sampler are discussed and data are presented for its validation in the field against the chemiluminiscence method. Finally examples are included of its use in environmental investigations, some of which could hardly have been contemplated with hitherto available methods.