The invention relates to a portable, handheld spirometer (1) comprising a MEMS-based thermal fluid flow sensor (13, 13.1, 13.2) for generating a signal in response to a fluid flow generated during inhalation or exhalation； and a microcontroller (14) for calculating the fluid flow from the signal generated by the flow sensor (13, 13.1, 13.2). The spirometer (1) may be connected to other devices, such as a smartphone or a personal computer or any other computing unit which is adapted to collect, store, analyse, exchange and/or display data. The invention further describes the use of the spirometer (1) in measuring a user's lung performance and/or monitoring it over time. Furthermore, the spirometer (1) may be provided in a system together with an air quality measurement device for determining the air quality at a location of interest； and a computing unit for collecting, analysing and correlating the user's lung performance data obtained from the spirometer (1) with the air quality data, and optionally geolocalisation data of said location.
