This study is aimed at assessing ambient air quality in city centres, in Minna metropolis, Niger State, North-Central part of Nigeria. Thirty points of commercial transportation locations within the city centre were considered, three thousand observations of CO, CO2, LEL, H2S and O2 were collected at different West African time (6 am, 8 am, 10 am, 12 noon and 6 pm) during the wet season in 2018 and analysed. Instruments including RKI GX-2009 and BW Technologies GasAlert® Multi-Gas, AMPROBE CO2-100, gas detection instrument with self-calibration capability of ±30 ppm, ±5%rdg (0–5000) accuracy and Garmin CX60 handheld global positioning system were used to obtain the Universal Transverse Mercator coordinates. The results showed higher mean CO2 emission values of > 499 ppm and < 551 ppm. It was also observed that these values were contrary to and exceeded the American Society of Heating, Refrigerating and Air-Conditioning Engineers and Occupational Safety and Health Administration normal outdoor level standards of 350 to 450 ppm. These higher CO2 values were found to have displaced O2 and increased its value to 22.5% above the standard (20.9%). The results also showed emission of H2S in the commercial city centres; if these pollutants are not monitored and controlled they will have adverse effects on human health and impact on the environment. This scenario would be in contrast to the Sustainable Development Goals (SDGs), especially SDG 11. Effective city planning and development control with emphasis on transportation planning, improving the soft landscaping component of the city through planting of trees to sequestrate the CO2 and environmental awareness campaigns by relevant state authorities and non-governmental organisations.
Key words: Air quality levels, carbon emissions, transportation, green-cities, pollution.