Medellin, the second largest city in Colombia, is located in the Aburrá Valley and exhibits the lowest level of air quality of the country due to PM2.5 (IDEAM, 2016).The topographic characteristics, meteorological conditions and anthropogenic emissions facilitate pollutant accumulation in the air of the Aburrá Valley. According to the emissions inventory carried out in 2013, mobile sources of pollution contribute with about 60% of emissions of primary and secondary PM 2.5. Due to the critical situation of air quality in the Aburrá Valley, the local authorities recently approved on November 2016 the Operational Plan to face Critic Periods of Air Quality (POECA), which consists of a set of short-run policy measures to improve air quality, when the air quality monitoring system shows very high levels of pollution. The goal of this project is to assess the cost-effectiveness of the Plan (POECA) which was implemented in March 2017 to address bad air quality events in Medellin. We will use data on pollutant concentrations recorded by the air quality network of the Aburrá Valley in order to evaluate whether the policy actions implemented were effective to improve air quality during the recent critical episodes of air pollution in the Aburra Valley, and to estimate the cost associated with the implementation of the policy actions in order to identify the least expensive one.