Associating Traffic Related Aerosol in the Near-Road Environment to Urban Characteristics
RICARDO MORALES BETANCOURT, Daniela Mendez, Diego Roberto Rojas-Neisa, Luis Angel Guzman, Universidad de los Andes
Abstract Number: 694
Working Group: Urban Aerosols
Abstract
Traffic related air pollution (TRAP) is a dominant source of exposure to particulate matter in urban areas. Due to the rapid introduction of low- and zero-exhaust emission vehicles around the world, the aerosol particles in the near-road environment are evolving rapidly. Understanding how different factors such as road geometry, traffic volume and vehicle technology, urban-background concentrations, and urban tree cover affect exposure to traffic related air pollutants in the near road environment is key to implement effective interventions to reduce such exposure. The city of Bogotá, in Colombia, which still faces serious air pollution levels, has recently adopted cleaner public policies aiming at improving air quality. Among these, the city is planning to transform one of the main roads in the city by increasing public space for pedestrians and cyclists, allowing only fully electric public transport buses along the road, and decreasing the number of mixed-traffic lanes. In this work, we report on the characterization of the near-road aerosol particles in a 22 km stretch of this main road with the purpose of understanding, through measurements, the most relevant factors determining exposure to TRAP. Our measurements determined the aerosol size distribution and particle number concentration (from 10 nm to 10 µm), as well as black carbon, PM2.5 and CO2. The measurements were carried out in 9 bus-stops, as well as personal exposure measurements for pedestrians and cyclists collected over hundreds of km traveled along the main road. During the sampling period, we recorded traffic counts every 5 minutes. Categories for motorcycles, light-duty vehicles, SUVs, and different types of public transport buses (either CNG, fully electric, or diesel-powered) were also recorded. The geometry of the road was carefully determined to establish an “urban canyon” index. The results of this observational study demonstrated high concentrations of black carbon (19.1 µg/m3) and ultra fine particles (55,000 #/cm3) throughout the campaign. For the analysis, the concentration time-series were decomposed in a slow- and a rapid-varying component. We found a strong association between the fast-varying aerosol field and traffic volume, while the slow-varying part was closely associated with background concentrations and street geometry. Furthermore, our data suggests that the frequency of high BC concentration events can be explained by the frequency of heavy-duty diesel vehicles. These events, however, only explain a minor fraction of the observed BC concentration, suggesting that motorcycles and light-duty vehicles are significant sources of BC and UFP in this road.