Only eastern part is comparatively low and open for penetration of dry air masses. Distribution of precipitation on the bottom, foothills and mountains is different as well. Mean annual precipitation in the city centre is 510 mm, only 450 mm in Digomi Valley, and 525 mm in Ortachala. Consequently, in summer period there are frequent cases of photochemical smog. These cause visibility reduction, eye irritation for humans and serious plant damage.
Transport is one of the major mean of environmental problems in Tbilisi.
In recent years traffic intencity has reached dramatic value that is main cause of increased air pollution. The quality of fuel is not regulated. Orography of the city contributes to spread of noise from the centre to the hillsides. During the last years a new problem emerged mini-bus taxis. The influx of these, majority of them being out of order, cause serious problems of pollution and noise.