What is more environmentally friendly? An A320 or a car?
I'm going to simplify and assume that jets and cars burn the same fuel, and output the same exhaust, CO2, NOx and all. I'm going to compare only short-haul flights against cars.

According to Wikipedia, an A-320-NEO does 1.95L/100km per seat. Assuming flying at 80% capacity, that gives us 2.4L/100km per seat. According to 
The Car Guide, a 2019 Honda Civic does 6.5L/100km. Assuming an average car carries 2 people, that gets 3.2L/100km. It would seem like flying is slightly better, using this simplistic measure.

Keep in mind that the longer you fly, the better the mileage, since the takeoff and climb are the fuel guzzling segments.