Relationship between black carbon (BC) and heavy traffic in Sao Paulo, Brazil

Black carbon (BC) concentration measurements were performed using a multi-angle absorption photometer (MAAP) in the eastern region of Sao Paulo city (EACH site) showing the dominance of heavy-duty diesel vehicle (HDV) emissions. The measurements were combined with traffic counts from a main road (the Ayrton Senna highway) that connects the city to the airport (Guarulhos) and to other important cities and estimated dilution rates from current NOx measurements to compute vehicle BC emission factors (EFBC). The BC emissions represented real operating traffic conditions and were distinguished between HDVs and light-duty gasoline-driven vehicles (LDVs). The EFBC were estimated according to the time of day to distinguish between different fleet compositions and source emission contributions as well as driving and meteorological conditions. Estimates of both the HDVs (170 +/- 259 mg km(-1)) and the LDVs (41 +/- 63 mg km(-1)) show that emissions from HDVs (EFBC(HDVs)) are around 4 times those from LDVs (EFBC(LDVs)). EF estimates for HDVs are consistent with measurements given in the literature not, however, with emission factors for LDVs whose values are slightly higher than those given in the studies reviewed. The correct determination of the EFBC, both for diesel and gasoline vehicles, is necessary so as to give complete knowledge of the BC impacts on external costs, such as air quality, climate and environment, to establish ad-hoc transportation policies and mitigation strategies. (AU)