We quantify the main sources that have contributed to fine particulate matter (PM_2.5) between 1998 and 2012 in Santiago's downtown. We calculate the long-term trend as well as abrupt changes in the time series and show how these relate to particular government policies implemented to improve air quality in specific years. We thus identify which measures successfully reduced individual sources and which sources need measures to avoid episodes when PM_2.5 concentrations surpass Chilean standards.