I believe the car-free day is more of a symbol rather than an efficient way to reduce air pollution. There will be air pollution all year long no matter how much emissions of polluted air we reduce in that single day, but it’s still helpful to draw some social attention to cleaner air circumstances. Emissions are not truly countable. We would never say ‘1 emission’ so it’s better to use much instead of many. Also, ‘cleaner air circumstances’ doesn’t sound right. Maybe ‘the cause’ would be better, or ‘to how dirty our air is’...’cleaner air circumstances’ is a bit vague and I think that’s why it sounds odd.

I believe the car-free day is more a symbol rather than an efficient way to reduce air pollution. There will be air pollution all year long no matter how many emissions of polluted air we reduce in that single day, but it 's still helpful to arouse some social attention for cleaner air circumstances.