Air quality data obtained by the Athens air pollution monitoring syste
m from the nine-year period started in 1986 were analysed to determine
time variations and the effect of various meteorological parameters o
n air quality by CO. From the ten monitoring stations measuring CO, th
e station located in a street with high traffic was selected since thi
s site had the longest time record and presented the highest values of
CO during the period examined. The time variations show that higher c
oncentrations of CO were measured during the winter months, on working
days and between 09.00 and 23.00 hours. The long-term trend shows a d
efinite decline of CO concentrations after 1990 resulting from the sub
stitution of gasoline-powered vehicles with vehicles equipped with thr
ee-way catalysts. Finally, it was found that during days with calm or
S-SW blowing light winds the CO concentrations presented their higher
values.