Pollution decrease following COVID-19 measured

Researchers from Valencia’s Polytechnic University have studied the fall in nitrogen dioxide concentrations in recent weeks in different Spanish cities. Of those analysed, Barcelona is where it has decreased the most – 83%.Nitrogen Oxide levels in Spain

The levels of concentration of nitrogen dioxide, one of the main culprits of air pollution, have decreased on average by 64% in the main Spanish cities after the measures implemented to fight against COVID-19. They have decreased the most in Barcelona (83%). In Madrid they have fallen by 73%, and in Valencia, by 64%.

These are some of the results of a study conducted by researchers of Valencia’s Polytechnic University (UPV), belonging to the Centre of Physics Technologies. To do so, the team of the UPV has analysed satellite images from the Sentinel-5P mission of the Copernicus programme of the European Space Agency (ESA), comparing data from two timeframes: from 10 to 14 March on one hand, and from 15 to 20 March on the other. From this data, they generated a series of maps that show the concentrations of nitrogen dioxide in some of the main Spanish cities.

As highlighted by Elena Sánchez-García, researcher from the Land and Atmosphere Remote Sensing group (LARS-UPV) belonging to the Centre for Physics Technologies of the UPV, nitrogen dioxide is a significant indicator of air quality. “High concentrations of this gas can affect the respiratory system and worsen certain pathologies. Furthermore, this gas is linked to the formation of acid rain,” she adds.

Nitrogen oxides such as NO2 in the urban air come from the combustion reactions at high temperatures that mainly take place within motorised vehicles. Oxygen and nitrogen combine to create nitric oxide (NO) which then partially oxidises, creating nitrogen oxide.

As has been verified in the case of Wuhan (China) or northern Italy, our study confirms that the measures of confinement and economic activity decrease have translated into a clear fall in atmospheric pollution nationwide,” adds Elena Sánchez-García.

More data

As well as Valencia, Madrid and Barcelona, the study also gathered data from seven other cities. In the Valencia Community, the province where the levels of nitrogen dioxide have decreased the most has been Castellón (76%) – the second largest fall in pollution of all cities analysed, only behind Barcelona -, and in Alicante, it has decreased by 68%. Although atmospheric variability (winds and rains) can affect the numbers gathered for each city, the effect of the current situation of confinement is predominant.

Of the other cities studied, in Bilbao pollution has fallen by 66%, in Gijón by 65%, in Málaga by 55%, in Zaragoza by 52% and in Seville by 36%.

This work is framed within the research conducted by the LARS-UPV group of the UPV, in which researchers Elena Sánchez García, Itziar Irakulis Loitxate and Luis Guanter have taken part. Their work is focused on developing remote sensing techniques for the global monitoring of the emission of gases into the atmosphere.


City NO2 µmol/m2 10-14 March 2020 NO2 µmol/m2

15-20 March 2020

Difference %
Valencia 114 42 64
Alicante 79 25 68
Castellón 94 22 76
Madrid 208 56 73
Barcelona 256 42 83
Gijón 68 24 65
Bilbao 85 29 66
Málaga 69 31 55
Seville 53 33 36
Zaragoza 89 43 52
Average difference 64%