二氧化氮
Nitrogen dioxide (NO2): The NOM defines that the maximum allowable limit is 0.210 ppm as an hourly average. To comply with the standard, the established limit must not be exceeded more than once a year. In all monitoring stations in Mexico City where this NOM was evaluated, concentrations below the limit were recorded during 2015 to 2017. However, this NOM has not been updated since 1993 and the World Health Organization recommends as a guide that the limit of the hourly average for NO2: be set to 0.106 ppm. Regarding the distribution of air quality by NO2, monitoring stations dominated the days with good air quality in Mexico City between 2015 and 2017. In each of the years more than 90% of the days presented good air quality.