An airport air quality study was carried out at the Athens International Airport (AIA) by BUW, FZK and NKUA on September 13-16, 2007. One objective of this campaign was to determine aircraft emissions downwind from the runway. A mobile air quality monitoring station was installed and used to measure nitrogen oxide (NO), nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO), carbon dioxide (CO2), formaldehyde (HCHO), total hydrocarbons (THC), particle number size distribution and total particle number (PM1) of the exhaust plume. From the measurement data emission indices (EIs; mass per kg burnt fuel) for nitrogen oxides (NOx), CO, THC, HCHO and particle number (PM1) for a variety of commercial aircraft were calculated in real world conditions during the take-off phase. In addition, the direct NO2/NOx emission ratio was also measured. Minimum and maximum EIs for NOx, CO, THC, HCHO and particle number (PM1) were found to be in the range of 10.6-36.1 g kg-1, 0.8-1.8 g kg-1, 1.7-2.0 g kg-1, 0.1-0.3 g kg-1, and 1.5·1015-2.9·1016 kg-1, respectively. The calculated EIs were compared with the database of the International Civil Aviation Organization (ICAO). The measured EIs for NOx were in agreement with the ICAO EIs (correlation factor: 1.09±0.08), whereas the measured EIs for CO and THC exhibited somewhat larger differences compared to the ICAO EIs. The number size distribution of emitted particles for the naturally diluted aircraft plume was dominated by a nucleation mode in the range of 15-40 nm. This result and the measured EIs for particles were in good agreement with other studies as was the elevated direct NO2/NOx emission ratio of 0.17±0.11.