Air quality modelling as a supplementary assessment method in the framework of the European Air Quality Directive

Abstract

According to the European Air Quality (AQ) Directive, Member States must report annually their AQ to the European Commission (EC). This report can be based on modelling data if the concentration levels do not exceed the established lower assessment thresholds (LAT), or on combining data from modelling and monitoring systems (supplementary assessment methods), if concentrations levels are below the upper assessment threshold (UAT). For the remaining cases, modelling techniques could be applied to provide additional information. In Portugal, the report has been based on monitored data. However, the AQ assessment for the 5-years period 2006-2010 indicates that modelled data can be used alone or combined with monitored data for almost the entire country. This work presents a methodology that combines air pollutant concentration values from monitored data and from a numerical modelling system to deliver information to the AQ assessment report. The AQ combined data were evaluated using the DELTA tool, developed under the FAIRMODE’s activity, verifying the fulfilment of all the defined quality criteria. Additionally, crossing improved concentration fields with geo-databases of land cover, road-maps and demography, using GIS tools, it is possible to quantify exceeding areas, population exposed to exceeding levels or vegetation areas exposed to pollutant levels higher than the vegetation protection thresholds. This methodology produces improved information, especially for areas where the amount of fixed monitoring stations is sparse or non-existent, allowing to obtain a better and broader overview of the AQ in Portugal using this modelling approach to support AQ reporting to the European Commission.