Instrument: Three Condensation Particle Counters (CPCs, TSI Model 7610) with different lower threshold diameters (4, 12, and 18 nm) measure the number concentration of submicrometer aerosol particles in three different size ranges. The three CPCs were modified for low-pressure and aircraft application. The counting efficiency of the instruments was determined in the pressure range 160-1000 hPa. Data format: Dataset consists of 11 columns representing: Date, Time (UT), Lon., Lat., Alt.(feet), Static Press.(hPa), Static Temp.(K), Particle Number Concentrations in the size ranges N4-12: 4 nm to 12 nm, N12: 12 nm to 1300 nm, N18: 18 nm to 135 nm or 1300 nm, and a column containing a binary information about airmass origin: measurement in UT airmasses = 0, measurement in LS airmasses = 100. This classification was made using either in situ measured ozone data or, if these were not available, model derived PV values. The upper threshold diameter of the particle measurements (1300 nm) is determined by the 50 % sampling efficiency point of the inlet system. For some flights (99.03.13 - 00.08.17), a pre-impactor was used upstream of the third CPC. For these flights the smaller upper threshold diameter of 135 nm is valid. As the concentration of ultrafine particles (N4-12) is determined by subtracting the readings of the first two CPCs, for statistical reasons, N4-12 can show negative values (difference is normally smaller 10 % and within the experimental error). Using the data, you can assume N4-12 equal to zero in such cases. Given number concentrations are corrected for pressure dependent counting efficiency, coincidence, particle losses in the sampling line, and inlet sampling efficiency. Concentrations are given as "particles/cm^3" at standard conditions (1013.25 hPa, 273.15 K). Only data obtained during level flight are included, data from aircraft ascent and descent were omitted. Data points for which no reliable values are available are indicated by "-9999".