Temporal and Spatial Evolution Study of Air Pollution in Portugal

Resumen

This study provides an analysis of the spatial distribution and temporal evolution of NO, NO2 and O3 seasonal and annual concentrations in Portugal during the period 1995-2010. The contribution of nitrogen oxides and several meteorological variables to the variation of O3 concentration was evaluated with multiple regression analysis in Entrecampos and Douro Norte stations. The variation in NO concentration shows a marked seasonality and presents a significant decreasing annual trend in most of the urban type stations considered, especially those under the influence of road traffic. Despite the downward trend in the concentration of NO, a statistically significant trend in NO2 concentration is not observed in most of the monitoring stations, except those less influenced by traffic, in which the emission of primary NO2 is much lower and the reduction in NO emissions leads to less photochemical production of NO2. The pattern of O3 concentration is completely opposed to that observed in NO. Several stations showed a significant upward trend in O3 concentration as a result of the decrease in NO/NO2 ratio. The correlation between the pollutants and ozone was stronger in Entrecampos than in Douro Norte. In this rural background station, the ozone concentration showed a strong correlation with meteorological variables. In Entrecampos urban station, 68% of the variance in ozone concentration was explained by the variables introduced in the regression model, being the NO2/NOX ratio the variable that explained most of the variance. In Douro Norte rural background station, only 43.4% of the variance in ozone concentration was explained by such variables. Therefore, long-range transport, high biogenic volatile organic compounds (BVOCs) concentration and the local geography may play a key role at this station.