The dataset makes available measurements of the mobility distributions of charged molecular clusters and fine aerosol particles in unpolluted atmospheric air at a rural area. The charged molecules and clusters up to 1.6 nm in diameter are called small air ions, the charged aerosol particles of size 1.6–7.4 nm are called intermediate air ions, and the charged aerosol particles of size 7.4–70 nm are called large air ions. The dataset includes results of simultaneous measurements of positive and negative air ions in Tahkuse Air Monitoring Station from 11.09.1993 to 23.10.1994. The station is located in the Sepa farmhouse in Tahkuse village about 27 km northeast of the city of Pärnu, Estonia. Geographical coordinates are 58º31'28"N, 24º55'32"E, 24 m a.s.l. The farmhouse is surrounded with flat open landscape with some tree groups, grassland and agricultural land. The air ion mobility spectrometers are installed in a thermostat container in the attic of the building. The air intake is at a height of 5 m above ground. The air ion measurements are accompanied with basic meteorological data: wind speed, wind direction, air temperature, relative humidity, and concentration of air pollution gas NO2. The detailed description of the landscape, station, and instruments is presented in the thesis by Hõrrak, U. (2001) Air ion mobility spectrum at a rural area. Dissertationes Geophysicales Universitatis Tartuensis, vol. 15, 157 pp., Tartu Univ. Press, Tartu, Estonia. https://dspace.ut.ee/handle/10062/50218. Full set of measurements is saved into a single file Tahkuse_1993_1994_data.xls as a tab-separated ANSI text. It should be downloaded from the present website and operated in the personal computer of the scientist. The data can be immediately opened and analyzed using MS Excel as well as by means of different computer programs, which are able to process the ANSI text. The file consists of a table with 59 columns and 9793 rows. The columns correspond to variables and rows to measurement hours. The first row is the header and it is composed of short names of the variables. Other 9792 rows contain numbers, which present the one-hour average values of the variables. The rows are written without omissions for 24 hours per day even when the measurements were stopped or failed and the values of variables are unknown. The missing values are marked with the code –99. The data file is accompanied with the description file Tahkuse_data_1993_1994.pdf.