A week after the first phase of the lack of definition began, the environmental association Zero again analyzed the air quality in the two main cities in the country. And the conclusions go in the opposite direction.
In Lisbon, the average concentration of nitrogen dioxide on the weekdays of the last week, already in a state of calamity (4 to 8 May), was lower in all seasons compared to the average concentration on weekdays since the state of alert until the end of the state of emergency (March 16 to April 30). These values were already well below the average observed since the beginning of the year until the state of alert.
In Porto, and having as points of analysis the two quality monitoring stations that have data since April, the average concentration on working days between the last week of state of emergency and the last week increased, although the values are lower than the nitrogen dioxide concentrations seen in the weeks between 13 and 24 April. Zero also safeguards that the station near Campanhã is close to a traffic light, which can interfere with the data.
Zero marks the record of two months with excellent air quality that coincide with the greatest restrictions on circulation due to the pandemic. The concentrations of nitrogen dioxide at the Avenida da Liberdade monitoring station continue to set successive records in several analyzes.
“In this case, and considering a longer period beginning on March 16, 2020 with the state of alert and until this last Friday, May 8, it was possible to identify that the average concentration of this pollutant had never been so low since 1994 (the year the station started operating) for so long (almost two months) ”.
Nitrogen dioxide is a good indicator of pollution associated with human activity and has been used by several entities and universities worldwide to assess the impact of falling economic activity and mobility on air quality.