The dataset is real-life and long-term indoor air quality (IAQ) data captured over a period of a year in 2019, including all four seasons in the Nordic climate, and comprises of about 22.6 million samples acquired from total of 62 sensor nodes in 13 rooms at VTT premises in Northern Finland. IAQ parameters in the dataset include o Temperature (T, in Celcius), o Relative humidity (H, in RH-%), o Air pressure (P, in hPa), o Carbon dioxide concentration (CO2, in ppm), and o Activity level (based on PIR senor, an integer in range 0..12 limits inclusive). For further information on the dataset, please see the attached file README.txt.