Air quality improvements following implementation of Lisbon's Low Emission Zone

- PM10 and NO2 levels in Lisbon have been exceeding the legal limit values since 2001.
- An action plan was developed with a set of measures including a LEZ in Lisbon.
- We assessed air quality and traffic data before and after LEZ full implementation.
- Results show positive evolution between 2011 (before LEZ) and 2013 (after LEZ).
- Stricter restrictions and enforcement are fundamental in future stages of the LEZ.

Air pollution levels within Lisbon city limits have been exceeding the limit values established in European Union and national legislation since 2001, with the most problematic cases related to the levels of fine particles (PM10) and nitrogen dioxide (NO2), mainly originated by road traffic. With the objective of answering this public health issue, an Air Quality Action Plan was developed in 2006 and the respective Enforcement Plan was published in 2009. From the overall strategy, one of the major measures presented in this strategy was the creation of a Low Emission Zone (LEZ) in Lisbon, which has been operating since July 2011. Implemented at different stages it has progressively expanded its area, including more vehicle types and adopting more stringent requirements in terms of minimum emission standards (currently LEZ phase 2 with EURO 2 in the city center - zone 1 and EURO 1 in the rest of the LEZ area - zone 2). At the same time the road axis comprised of Marquês de Pombal square and Avenida da Liberdade was subjected to profound changes in its traffic circulation model, reducing road traffic volumes.The analysis of the air quality data before and after the LEZ phase 2 has shown positive evolution when comparing the period between 2011 (before measures) and 2013 (after measures). In 2013, there was a reduction in PM10 annual average concentration of 23% and NO2 annual average concentrations of 12%, compared with the year 2011. Although PM10 reductions were more significant inside the LEZ area, the same was not valid for NO2, suggesting that the implementation of these measures was not as effective in reducing NO2 levels as shown by results in other cities like Berlin and London. The results from road traffic characterization indicate a relevant effect on fleet renewal with an overall decrease in the relative weight of pre-EURO 2 vehicles in 2012/2013, compared with data from 2011. An important increase in the share of EURO 4 and EURO 5 vehicles was also observed. Our conclusions show that the level of ambition is relevant for the observed effects. Therefore, stricter restriction standards should be enforced in the future stages of the Lisbon LEZ in conjunction with a higher effort and investment on LEZ enforcement.