How economic crisis influence air quality over Portugal (Lisbon and Porto)?

The aim of this specific study is to discuss the impact of the economic crisis on air quality in Portugal, with focus on particulate matter and nitrogen dioxide. For this purpose, a long-term period of economic and air quality monitoring data was analysed, including both periods before and after the crisis (2004-2015). The analysis was focused on the main urban areas of Portugal - Lisbon and Porto municipalities. All the economic indicators highlight a decreasing trend since 2007, which is also evident for energy consumption, while for Gross Domestic Product (GDP) and disposal income there are signs of recovery after 2010. In terms of pollutants concentration, there is a negative trend since 2007 with reductions in the annual values higher in Porto (about 40% for NO2 and PM10) than in Lisbon (25-30% of NO2 and PM10). Correlations were found between pollutant concentrations and energy consumption, with a correlation factor superior to 0.7, for both Lisbon and Porto municipalities. No evidence of a linear relationship was found for the disposable income per capita. The results presented in the study support the notion that a significant alteration is undergoing to the air quality in Portugal, directly related to the reduction of energy consumption, consequence of the economic crisis, that starts to be registered after 2007 and after 2012 stops decreasing. While the economic indicators like GDP and disposable income reveal an increase after 2010-2102, no positive trend was found on the annual average of pollutants concentration.