Tropospheric delay is a dominant error source in high-precision Global Navigation Satellite System (GNSS) positioning. However, when estimated through precise processing, it serves as a physically meaningful atmospheric observable directly linked to the thermodynamic state of the lower atmosphere. The Zenith Total Delay (ZTD), routinely estimated in Precise Point Positioning (PPP), integrates the refractivity of dry gases and atmospheric water vapour and can be exploited for meteorological monitoring and atmospheric research. This thesis evaluates the physical consistency, temporal stability, and spatial representativeness of GNSS-derived tropospheric delays, with a focus on the performance of low-cost GNSS receivers. The research is structured around three complementary objectives.