Air pollution is one of the major environmental problems affecting both developed and developing countries. According to reports from the World Health Organization, 9 out of 10 people breathe air that exceeds the limit concentrations of pollutants established in its regulations (WHO, 2018). The pandemic of COVID-19 infection has caused an unprecedented global health and economic crisis. To prevent the spread of the virus, mobility restrictions and strict lockdowns were imposed in most countries. Due to reductions in urban traffic, the main source of NOⅹ and PM₁₀ emissions, by as much as 90%, air pollution experienced a drastic decrease. This event has given rise to a large number of studies throughout the world. The objective of this master's thesis has been to analyse the impacts caused by COVID- 19 restrictions on air quality in Cantabria. For this purpose, the pollutant levels in 2020 are compared with the average of the previous seven years (2013-2019), day by day, dividing the calendar year into different periods (lockdown, de-escalation, etc.) corresponding to that established by the state and regional government. First, percent changes have been obtained from the observed concentrations. These values have been then corrected by removing the influences of meteorology and emission trends, using deweather package, to recalculate the percentages so that they are exclusively attributable to changes resulting from COVID-19 restrictions. The results obtained from the comparison of the values observed in 2020 versus the reference years have shown significant NOⅹ reductions, with averages of -65% in levels during confinement. Change in PM₁₀ and ozone were less noticeable (-10%). In addition, deweathered/detrended results have shown a very similar trend to those observed for all the pollutants.
