Measurement of long-term average carbon dioxide concentrations using passive diffusion sampling

A diffusive sampling device is proposed for long-term determination of average airborne concentration of CO2 in urban and industrial areas, as well as in indoor sites. A hydro-alcoholic barium hydroxide solution is employed as a CO2 reagent sink. The analytical method is based on the determination of the solute barium hydroxide remained after the acid–base reaction, in which its insoluble carbonate salt precipitates. Indoor laboratory experiments show that this technique exhibits a good precision and reproducibility. A 6-week internal consistency test demonstrates that this device has a constant uptake rate, allowing us to propose it as a suitable and inexpensive tool in performing the monitoring of urban and industrial sites over long periods and in indoor–outdoor studies, like those involved in the sick-building syndrome problem.