  Air-quality in urban areas and its relation with public health is one of the
most critical concerns for governments. For this reason, they implement actions
aimed at reducing the concentration of the most critical atmospheric
pollutants, among others the implementation of Low-Emission Zones. Madrid
Central is a major initiative of Madrid city council for reducing motor traffic
and the associated air pollution at the city center. It is created by enlarging
a previous and smaller area of restricted motor traffic. This initiative starts
at the end of 2018, but the first fully-operational period corresponds to
2019Q2 (second quarter of 2019). The activation of Low-Emission Zones has
social and economic impacts, besides environmental ones. For this reason, their
impact must be assessed to ensure the achievement of the commitments in the
reduction of atmospheric pollutants levels. In this work, two metrics for
evaluating the impact of Madrid Central in the reduction of nitrogen dioxide
concentration are proposed. Mean daily concentrations of NO2 from 2010 to 2019
corresponding to the Plaza del Carmen monitoring station are employed for the
evaluation of the impact of Madrid Central. Two other monitoring stations
around Madrid Central are analysed for ascertaining the rise of detrimental
effects due to an increment of the motor traffic around the traffic restricted
area. In consequence, two methodologies pollutant-independent for evaluating
the impact and the evolution of LEZs, as well as a statement about the impact
of the first year of Madrid Central are presented.
