In order to better understand the role of Hg in the atmosphere, in this work, we investigated how much Hg is found in the Urban Dust reference material SRM1649b, in outdoor PM2.5 and PM10 samples, in samples freshly and directly emitted by heavy-duty vehicles, and in blended and unblended biodiesel and fossil diesel fuels (B0, B4, B7, B12, and B100). In the SRM1649b analysis, we found Hg at 1.75 +/- 0.01 mg kg(-1), which is equivalent to more than 97.2% recovery when compared to the certified value. Particulate Hg in ambient samples was 1.82 +/- 0.87 mu g g(-1) (site 3, Itaparica, ITA) to 9.11 +/- 4.17 mu g g(-1) (site 1, Navy Base of Aratu, BNA) for PM2.5 and 1.31 +/- 0.89 mu g (ITA) to 3.57 +/- 1.25 mu g (BNA), for PM10. In order to evaluate particulate Hg emissions under near real-life conditions, we collected PM2.5 and PM10 samples from an underground floor bus station. Total Hg levels for the bus station were 2.90 +/- 1.15 mu g g(-1) for PM2.5 and 2.19 +/- 1.00 mu g g(-1) for PM10. Either in the bus station or ambient samples, we found that the PM2.5 mass is about 60% of the PM10 mass, which explains why particulate-bound Hg is mainly found in fine particles. With regard to fuels, the Hg levels were found to be B0 (0.83 mu g kg(-1)), B4 (0.38 mu g kg(-1)), B7 (0.50-1.10 mu g kg(-1)), B12 (0.03-1.29 mu g kg(-1)), and B100 (0.19 mu g kg(-1)). Therefore, these results show that adding more biodiesel to diesel gradually decreases the Hg amount in the final blend. Risk assessment through inhalation was done for adults, adolescents, children, and infants. Although the highest daily inhalation exposure (DIE) values were observed for the bus station and the lowest DIE values were found to be from ITA, the risk levels are considered low.