『Abstract
　Recently, specific air quality problems have been detected in the northern region of Portugal. The nitrogen oxide (NO2) annual limit value has been surpassed at several air quality monitoring stations in the northern region, and according to European legislation, air quality plans must be designed and implemented to reduce those levels. The analysis of the air quality data from the stations concerning NO2 exceedances indicates that traffic is responsible for an increase of more than 40％ compared with the urban background value. Specific measures to reduce NOx emissions have been selected and are related nor only mainly to the traffic sector but also to the industrial and residential combustion sectors. The main objective of this study is to investigate the impact of the selected measures on the ambient levels of NO2 in northern Portugal using a numerical modelling tool - The Air Pollution Model (TAPM). TAPM was applied over the study region using a 120×120-km² simulation domain and a spatial resolution of 4.8×4.8 km². The entire year of 2010 was simulated and was set as the base year to analyse the impact of the selected measures. Two scenarios have been defined and simulated: the base situation, which considers current NOx emissions, and the reduction scenario for which NOx emissions were re-estimated considering the implementation of the measures. The modelling results demonstrate a decrease of 4-5μgm^-3 in the annual NO2 levels in the study region. Moreover, the implementation of the selected measures will allow compliance with the NO2 annual limit values in three of the five air quality stations that measured levels surpassing those established by legislation. This situation demands additional measures that should be implemented at the local level and that particularly focus on the traffic sector.

Keywords: NO2 pollution; Air quality directive; Air quality plan; Traffic contribution; Emission control measures; Numerical modelling』

1. Introduction
2. NO2 monitoring data over northern Portugal
3. Estimation of traffic contribution
4. NO2 emission abatement measures
　4.1. NOx emission reduction - Estimation methodology
5. Air quality modelling
　5.1. The air quality model the air pollution model and its application
　5.2. Air quality modelling validation
　5.3. Evaluation of the impact of the measures
6. Summary and conclusions
Acknowledgments
References