Middle and lower troposphere aerosol characteristics and ozone concentrations over northwestern Greece during STAAARTE 1997

Accumulation aerosol particle distributions were measured on 14 June 1997 d uring two research flights over northwestern Greece, including the greater Thessaloniki area (GTA), At flight altitudes of about 5000m (<550mb), accum ulation mode number particle size distributions appeared to be unimodal wit h a maximum in the first bin of the measured number size distribution with a mid-point of 0.11 <mu>m. At lower altitudes and over the GTA, accumulatio n mode particle size distributions were bimodal with a first mode peak at 0 .125 mum and a second mode peak at 0.275 mum. The second mode was more pron ounced in areas of higher relative humidity, thus indicating the presence o f deliquescent aerosols, but also in areas where high O-3 concentrations we re measured. Ozone concentrations ranged between 25 and 60 ppb at high alti tudes east of GTA and between 50 and 110ppb over the city of Thessaloniki w ith the maximum measured at an altitude of about 500 m, This is consistent with the local topographical and meteorological conditions, mainly due to t he nocturnal inversion and the development of local circulation flows (land and sea breeze) over the city. (C) 2001 Elsevier Science Ltd. All rights r eserved.