The completion and opening of the tunnel in Glòries has allowed traffic to be shifted below ground, reducing levels of NO2 and PM10 air pollutants in this part of the city. Nitrogen dioxide is poisonous and can be fatal if inhaled in large quantities. PM10 or so-called particulate matter (PM) is a generic terms for small hazardous particles created by various sources, like diesel engines. The number '10' refers to the size of the particles. The smaller the number, the smaller the particles and the more hazardous they are, as they penetrate into humans' lungs more easily.

Noise levels have also been reduced by 9 decibels at all hours.

Here is the English translation of Ajuntament de Barcelona information;

The opening of the Glòries tunnel has made it possible to reduce the presence of NO2 and PM10 in this area of the city by 39% and 7%

The completion of the tunnels, the opening of the infrastructure and the undergrounding of private traffic has made it possible to reduce the level of pollutants that were recorded in this area during the construction period

Today, NO2 and PM10 levels are also -40% and -13% lower than those recorded by the Eixample air pollution station, which is the reference station for heavy traffic routes like the Gran Via

With the complete opening of the tunnel, a reduction of 9 decibels has also been recorded in the central area of the Gran Via. This reduction acoustically equates to being in a pedestrianized area of the city

The Barcelona City Council, through the Barcelona Public Health Agency, has made an analysis of the evolution of the levels of atmospheric pollutants around the Glòries tunnel comparing them with the fixed station of the Eixample of the Atmospheric Pollution Monitoring and Forecasting Network, which is the reference station for heavy traffic routes such as the Gran Via. The pollutants that have been analyzed are NO2, a pollutant closely related to traffic emissions, and PM10 particles, related to the impact of fugitive emissions from works.

Based on this, the levels of these pollutants have been studied in the Glòries area during the construction phase (period between January 6, 2018 and November 5, 2021), during the opening of the tunnel in one direction (period between 6 November 2021 and 23 December 2021) and finally with the full opening of both directions of the tunnel (period between 25 May 2022 and 7 of June 2022). The data recorded during the declaration of the State of Alarm due to the COVID-19 have not been taken into account, given that there are days in which the Mobile Unit was stopped.

The analysis concludes that since the opening of the tunnel, NO2 levels have decreased around the Glòries measurement point, as can be seen in the table below which includes a comparison with the fixed station of the Eixample. The data show a -39% reduction in the presence of NO2 between the construction period and the full opening of the tunnel. If the current emissions that are being registered at this point are compared with those of the Eixample station, it can be seen that in the Glòries area they are -40.8% lower.

Regarding PM10 particles, the levels have also decreased since the opening of the tunnel and the completion of the construction works. In this case the reduction was -7.6%. If you compare the data with the current figures for the Eixample station, the Glòries area is -13.2% below.

https://ajuntament.barcelona.cat/premsa/2022/08/19/lobertura-del-tunel-de-glories-ha-permes-reduir-en-un-39-i-un-7-la-presencia-de-no2-i-pm10-en-aquest-ambit-de-la-ciutat/