The use of passive diffusion tubes for measuring concentrations of nitrogen dioxide in air

Passive diffusion tubes have been widely used in Europe for spatial and temporal measurement of NO2 concentrations. The method is cheap, simple, and provides concentration data in most circumstances that are sufficiently accurate for assessing exposure and compliance with Air Quality criteria. Tube-type diffusion samplers are prone to several sources of uncertainty, arising from the materials of construction, the absorbent used, the methods of preparation, the details of their deployment (including the exposure time) and the analytical methods used to establish the concentration of nitrite ion absorbed. This review considers the major sources of uncertainty, and reports on the many experiments aimed at identifying and minimising uncertainties, including modifications to the simple open tube devices that were originally developed in the 1970s.