ИСТИНА

The weekly cycle of the surface concentrations of five trace atmospheric gases in Moscow has been analyzed based on continuous automatic once-a-minute measurements. The data of joint ecological station of the Institute of Atmospheric Physics and Moscow State University for nine years (2002–2010) were used. Results of spectral analysis demonstrate statistically significant maximum of spectral density close to 7 days. The fact that the influence of human activity on urban air composition changes with a weekly periodicity is confirmed by statistically significant difference between concentrations of trace gases on working days and on Sunday (when emissions from both the traffic and the industrial sources are minimal). On average, both primary pollutants (nitrogen oxide and carbon oxide) and the secondary ones (NO2) show the lowest concentrations of the week on Sunday whereas ozone, by contrast, peaks on this day. Besides, usual diurnal cycle of air pollutants is transformed on Sunday – e.g., secondary nocturnal maximum of ozone in the city is absent on Sunday like at rural area. On Saturday concentrations of trace gases are in between working days and Sunday; this ‘Saturday effect’ is a result of a gradual clearing of the urban air. An additional effect is that in the first half of Monday (before noon)surface concentrations of NO and NO2 are generally less, whereas the concentration of O3 is, on the contrary, a bit higher than at the same time on the rest of working days. The ‘Monday effect’ is a result of the gradual contamination of the urban air after week-end. Unlike other trace gases, sulphur dioxide doesn’t demonstrate clear weekly cycle because the urban heating, the main source of it, has the same intensity on any day of the week.