if i where to make a city some thing i would do to make it green. first i would make it so everyone could use public transport to have less cars. second i would ban gas lawn mowers and only have push mowers, so cutting gras would no longer produce co2. lastly i would put a green space in any empty spot. wether it was an unused ally way or a empty patch of land.

I agree but I would also focus on converting to a mainly solar powered city with wind power backups as they are both very efficient for power use. Though for the grass I would transition out of  grass lawns as they perpetuate a monoculture of plants. Instead I would try to encourage native plants to grow in its place and specifically plant matter that could cater to native pollinators. I completely agree with you for greenspaces but instead of putting them in empty spots as a second thought they could take main stage of the city, combining the city's architecture with plants would provide a better air quality.