The global increase in the number of motor vehicles in the urban environment has greatly contributed to the increase in the amount of carbon dioxide released to the atmosphere which contributes to global warming. The study analyzed the relationship between the total CO2 emission from motorized road transport and the atmospheric CO2 concentration using the digital CO2 meter to sample atmospheric air to determine the atmospheric CO2 concentration in parts per million by volume at various time intervals in the Kisumu Bus Park and within the city and its neighborhoods’. The theoretical framework of this study was the Kinetic Theory of Gases. The study recommended that the government should invest heavily in the public transport sector by enacting laws and policies aimed at discouraging the importation and use of low seating capacity vehicles and invest in the high seating capacity vehicles (BRT) and non-motorized road transport.