Concentração de partículas atmosféricas finas em ônibus do transporte público urbano no Brasil

Abstract

The main source of air pollutants in urban environments is the emission by the motor vehicle fleet. Although the proportion of time spent by the population in traffic microenviornments is small compared to other activities, high concentrations of particulate matter (PM) contribute to a significant fraction of daily personal exposure. For the first time in Brazil, monitoring of fine PM was carried out on public urban transit buses comparing a mid-sized city (Londrina, PR), a large city (Curitiba, PR) and a megacity (São Paulo, SP). Measurements of black carbon (BC), particles with a diameter of less than 2.5 m (PM2.5) and particle number concentrations (PNC) were made on routes with traffic dominated by light- and heavy-duty vehicles and motorcycles, and similar urban characteristics (junctions managed by traffic signals, canyon structures, etc.) The results show a large spatial variability of the median concentrations of BC and CNP, and relatively lower for PM2.5. Curitiba's buses were the most polluted in terms of BC and PM2.5 and the Cabral Terminal was the most polluted. The older bus fleet in Curitiba, combined with relatively higher urban background concentrations, may have contributed to larger PM values. The buses in Londrina were the cleanest, whilst São Paulo stood out with high concentrations of CNP. The mean concentrations of BC, PM2.5 and PNC in the buses were, respectively, 5.4 μg m-3, 16.1 μg m-3 and 34038 # cm-3 in Londrina, 16.9 μg m -3, 31.0 μg m-3 and 45075 # cm-3 in Curitiba, and 8.9 μg m-3, 29.5 μg m-3 and 53479 # cm-3 in São Paulo. In most cases the bus speed and heavy-duty vehicle fraction had a negative and positive relation, respectively, with PM concentrations. A detailed analysis of a specific profile showed that the occurrence of traffic signals and bus stops caused instantaneous peaks of PM concentrations. An objective methodology applied to detect hotspots (areas with concentrations greater than the 95th percentile of BC, PM2.5 or PNC) showed that their most likely locations were roads where canyon structure, high fraction of heavy-duty vehicles, bus stops and traffic signals occurred. In the city of São Paulo, a hotspot was detected at the exit of Anhangabaú Tunnel (caused by the piston effect) and near to the Terminal Bandeira, located in the vicinity of two highly-trafficked avenues (9 of July and 23 of May avenues). The results highlight the occurrence of extremely high MP concentrations on public transport, with possible deleterious effects on the health of users and workers within the sector.