The response of PM10 concentrations to reductions in emission sources was analyzed by evaluating the impacts obtained by applying a sensitivity analysis method that predicts various levels of emissions reduction (brute force) using two chemical transport models (CAMx and FARM) and the contributions obtained with the method based on reactive tracers (CAMx with PSAT module). The study focused on the main sources of secondary inorganic aerosol precursors in the Po Valley (Northern Italy): agriculture, road transport, industry and residential combustion. In this study, interaction terms between sources obtained from a factor decomposition analysis are used as a measure of nonlinearity of the model response. These interaction terms were also analyzed in light of the free ammonia/total nitrate gas ratio to determine the relationships between the chemical regime and nonlinearity at selected sites. The impacts of the different sources are not proportional to the emissions reductions and this non-linearity is more relevant when comparing 100% emission reduction levels with smaller reduction levels (50% and 20%). These differences are related to how emission reductions change the chemical regime compared to the base case. The nonlinearity is mainly associated with agriculture and the interaction of this source with road transport and, to a lesser extent, with industry. Notably, the PM10 mass concentration assigned to agriculture by the TS and BF approaches is significantly different when a 100% emissions reduction is applied. However, in many situations the non-linearity of annual PM10 averages is negligible and the TS and BF approaches provide comparable results. PM mass concentrations assigned to different sources by TS and BF were highly comparable in terms of spatial patterns and quantification of source influence (contribution or impact) for industry, transportation, and residential combustion. The conclusions obtained in this study, relating to PM10, are also applicable to PM2.5.