Diesel and biodiesel emissions are important sources of ambient air pollution. Therefore, the influence of using different blending percentages of biodiesel to diesel as fuel on redox activity, particulate matter (PM) and polycyclic aromatic hydrocarbons (PAH) emission profiles, and the corresponding carcinogenicity index (BaPE) size distributions are not well known. In this way, the present work aims to investigate the effect of diesel/ biodiesel blends on the physical, chemical, and toxicological properties of diesel engine exhaust at low condition, through the study of the changes in size-distribution and emission factors of PAH associated to PM, corresponding carcinogenicity index (BaPE) size distributions and PM redox activity. For that, particle emissions from commercial petroleum-based diesel with 4% of soy biodiesel (B4), a biodiesel blend of 25% and 50% (B25 and B50) and also pure biodiesel (B100) were measured on a steady-state dynamometer in a test using a diesel engine at low load. Size-fractionated PM samples were collected by using the NanoMOUDI impactor and analyzed for the 16 priority PAH by HPLC-fluorescence detector. In addition, PM2.5 samples were collected and analyzed for redox activity by DTT assay. PM was distributed in all sizes, while PAH size distribution was found in higher levels in the accumulation mode (30 nm < Dp < 2.5 lm). Total PAH emission factors (ng kg(-1) fuel) for B4, B25, B50 and B100 were: 237,111,182 and 319 ng kg(-1) fuel, respectively. Individual PAH emission factors showed that PAH containing four or more rings (MW > 202) such as BBF, BAA, PYR and BGP were the main PAH emitted by the four studied fuels. The percentage reductions of individual PAH emission factors for the blend fuels in comparison with B4 were 37% and 22% for B25 and B50, respectively, and an increase around 31% for B100. On the other hand it was observed increase in redox activity for B25, B50 and B100 when compared to B4. In general, the results from our study suggest that emissions from pure waste cooking biodiesel may not be the better fuel choice in terms of PM, PAH and BaPE particle size distribution and emission factors as well as redox activity. However, B25 and B50 blends presented some improvements in terms of PM, HPA, BaPE size distribution and redox activity of engine exhaust in comparison to B4. This suggests that addition of low percentages biodiesel to diesel promotes benefices in both environmental and human health concerns. (C) 2013 Elsevier Ltd. All rights reserved.