I need to write a research paper on any topic but I am thinking of doing the relationship between car emissions on air quality on cities and I was thinking of doing 4 cities- toronto, vancouver, la,...

I need to write a research paper on any topic but I am thinking of doing the relationship between car emissions on air quality on cities and I was thinking of doing 4 cities- toronto, vancouver, la, and new york. So car emissions as in the number of cars/ miles driven and im not sure any other variables relatedAlso, please send me some data sources