I may be wrong but I believe the nitrogen-oxygen compound in the lower atmosphere is NO_2 (nitric oxide for old-timers, nitrogen dioxide for those born in the last fifty years) and not N_2O (nitrous oxide / dinitrogen oxide to the IUPAC fans).
Be that as it may, satellite monitoring has shown a truly dramatic decrease in the concentration of nitrogen oxides in mainland China recently. https://earthobservatory.nasa.gov/images/146362/airborne-nitrogen-dioxide-plummets-over-china has more detail. (Incidentally it supports my claim that NO_2 is the compound in question.)