The influence of a time shift on the pollution maxima over an urban site

Several European countries have chosen to go on “summer time” from April to October, corresponding to a shift of 2-h from universal time (UT + 2), instead of 1-h for winter time (UT + 1). Because of this shift, pollutant emissions are released into the atmosphere under different conditions of stability, especially in the morning and evening.Using a box model applied to the experimental results obtained in an urban center, the effect of the time shift on the Aitken nuclei concentration in the air is calculated. The use of UT + 2 can give rise to an increase of about 30 % in the morning, and a decrease of nearly 50 % in the evening.