Air quality can be assessed through continuous monitoring using instruments that provide real-time data. However, automatic air quality monitors are expensive and require frequent maintenance. Consequently, their deployment is often limited, restricting the possibility of simultaneous measurements at multiple locations. Passive samplers, such as diffusion tubes, overcome some of the limitations associated with automatic monitoring systems and are particularly useful for simultaneous deployment at multiple sampling sites, including locations with limited accessibility or frequent power outages. Initially developed for occupational hygiene applications, diffusion tubes have also been successfully applied in outdoor environments. These devices are small, lightweight, often reusable, relatively inexpensive, silent, and do not require an external power source. Their operation is based on the principle of molecular diffusion, whereby pollutants naturally diffuse from an area of higher concentration (the surrounding atmosphere) toward the absorbing medium inside the tube. The samplers are exposed at the selected site for extended periods, typically ranging from one to four weeks, after which they are analyzed in the laboratory to determine the average pollutant concentration over the exposure period. Although passive samplers provide only time-averaged concentrations over relatively long exposure periods, they are highly suitable for spatial assessments, enabling the characterization of concentration variability between locations and facilitating air quality evaluation across multiple sites simultaneously. However, passive samplers do not provide exact real-time concentration values and are unable to capture short-term pollution peaks or episodic events. Therefore, to improve the reliability of the data obtained, passive sampling results should be compared with and validated against measurements from continuous automatic analyzers or reference methods for the target pollutant.
Publication Date: 2026-06-19