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Abstract
<p class="first" id="d1041977e53">During the months of March and April 2020 we witnessed
the largest-scale experiment
in history in terms of air quality in cities. Any prediction of this experiment's
results may be obvious to science, as it was totally expected, the air quality has
improved substantially. Simply stated, it comes as no surprise. The lockdown has made
it possible to quantify the limit of decrease in pollution in light of this drastic
reduction in traffic, in Madrid and Barcelona showed a significant decrease of the
order of 75%. In the case of Spain's two largest cities, the reductions of NO2 concentrations
were 62% and 50%, respectively. Hourly measurements were obtained from 24 and 9 air
quality stations from the monitoring networks during the month of March 2020. These
results allow us to see the limits that can be achieved by implementing low emission
zones (LEZ), as well as the amount of contamination that must be eliminated, which
in the cases of Madrid and Barcelona, represent 55%. This value defines the levels
of effort and scope of actions to be taken in order to ensure that both cities achieve
a clean and healthy atmosphere in terms of NO2.
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