The concentration of carbon dioxide exiting a car's tailpipe is approximately 12% on a volume basis. assuming the exhaust-gas temperature is 500°C, determine the concentration of CO2 in the fas stream in the units and temperature specified:

a) ppmv at 500°C and 25°C respectively

b) μg/m³ at 500°C and 25°C respectively

I think I need to know what the emissions are; e.g. 12% of what?