Major ions in PM2.5 and PM10 released from buses: The use of diesel/biodiesel fuels under real conditions

Currently, in Brazil, it is mandatory to use the fuel blend of 95% petro diesel and 5% biodiesel (B5) for heavy-duty vehicles. However, there is a lack of information about the emissions profile of major ions from the combustion of this blend under real conditions. In this study, aerosol samples were collected at an underground bus terminal in Salvador, Brazil between April and May 2010. PM2.5 and PM10 high volume samplers were used to collect particulate matter (PM) in parallel during daytime and nighttime. Ion chromatography technique was used to determine low-molecular weight carboxylate and water-soluble inorganic ions. The results showed that the mean mass concentrations for the PM2.5 were 201 ± 56 μg m−3 during the daytime and 47 ± 24 μg m−3 at nighttime. The PM10 mass concentrations were 309 ± 99 μg m−3 and 78 ± 47 μg m−3, respectively. The mean concentrations for the total carboxylate anions in PM2.5 were 139 ± 33 ng m−3 during the day and 60 ± 18 ng m−3 at night. The corresponding values for PM10 were 180 ± 44 ng m−3 during the day and 93 ± 15 ng m−3 at night. Monocarboxylate anions (propionate, acetate and formate) were the most abundant, followed by ketocarboxylate anions (pyruvate), while the dicarboxylate anions (oxalate and malonate) were the least abundant. Mg2+ was the most important cation and NO3- the main anionic species in PM2.5, while Na+ and SO42- were the most abundant cation and anion in PM10 during the day and at night. The main sources were found to be fuel combustion and gas-to-particle conversion for PM2.5 whereas they were fuel combustion and soil resuspension for PM10. We explain some of our results considering chemical reactions occurred during fuel combustion until formation of carboxylate anions at the bus terminal. Certainly, such an approach used in this study would provide information on the atmospheric transformations of engine exhausts, vehicular emissions, and their contribution to general air pollution in Brazilian cities what would, in turn, contribute to other cities around the world.