Urban greenery contributes to improve air quality through carbon dioxide sequestration and to increase air humidity by transpiration. These processes are dependent on diurnal physiological activity of vegetation as well as its spatial distribution. In our study we aimed to find out (1) how urban greenery can change the atmospheric conditions during a day and (2) if there is a difference between a housing estate interior with abundant greenery and a wide street of heavy traffic. The examination was carried out a suburban district of Warsaw, in two sites of contrasting characteristics: in a street with heavy traffic during rush hours and in a housing estate nearby. Gas measurements were carried out using an infrared gas analyser included in a portable photosynthesis system on two sunny days in July 2021. On each day measurements of air water vapour pressure and atmospheric carbon dioxide were taken in both locations from early morning to the evening. The results showed that water vapour pressure in the air increased from ca. 12 to nearly 18 hPa from 6:45 a.m. to 9:00-9:30 a.m., respectively, and then gradually decreased until 7:00 p.m. on both measurement days. Carbon dioxide concentration in the atmosphere in the early morning hours exceeded 430-450 ppm and then decreased to 400 ppm or even less than 360 ppm depending on the day. We concluded that the site characteristics had not an important effect on relative humidity and carbon dioxide concentration, but vapour pressure deficit was higher in the street.