On 19/12/2013, European Commission (EC) adopted the "The Clean Air Policy Package", where it proposes new air pollution reduction objectives for the period up to 2030, as well as instruments to deliver those objectives. Before the European Commission can propose a new initiative, it mandatorily has to conduct an Impact Assessment, evaluating the potential economic, social and environmental consequences. This paper explains in detail the modelling done with a Computable General Equilibrium model, GEM-E3, for the Impact Assessments accompanying this recent EU policy proposal. The GEM-E3 model is a recursive dynamic computable general equilibrium model which covers the interactions between the economy, the energy system and the environment. In general the paper illustrates how quantitative modelling can directly contribute to real world policy decisions by providing an assessment of socio-economic impacts of air quality policies.