The aim of the paper is to investigate the co-influence of noise and carbon dioxide on people in different situations (inside/outside houses/classrooms) depending on the traffic intensity, the fuel used for heating in residential buildings etc.). All the measurements and the questionnaire have been carried out during the autumn of 2019 (at the mean temperature of 5-10° C). Riga has a more intensive traffic compared to Tallinn and has greater problems of exceeding the permissible noise levels. The levels of carbon dioxide inside classrooms are also very high in Latvia (1500-2000 ppm). The concentration of carbon dioxide outside buildings is low in the forest areas (measured in the south of Estonia), being 340-350 ppm. In regional towns, it is 500 ppm (measured in autumn-winter near a busy street). The co-influence of noise and carbon dioxide on the residents has been investigated by using the Weinstein questionnaire. High carbon dioxide levels cause fatigue. Although it was not particularly pointed out by the residents questioned in a panel house with small apartments, the air was considered to be stuffy. The house is situated near a busy street, so the problems with noise are higher. ANOVA statistics has been used for the questionnaire (p<0.001, α=0.93). The decrease of noise and carbon dioxide levels help people stay healthy and the environmental impact from the investigation is emphasising the necessity and providing possibilities to decrease the concentration of CO2 in the ambient air