AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Variation of Particle Number Concentration in a Street Canyon and an Urban Background Site
KAARLE HAMERI, Vanessa Dos Santos-Juusela, Tuukka Petäjä, Anu Kousa, University of Helsinki, Department of Physics
Abstract Number: 248 Working Group: Urban Aerosols
Abstract We measured spatial and temporal variation of ultrafine particles in a street canyon and an urban background site in Helsinki for six months. The particles were counted using condensation particle counters. In addition, we evaluated the effects of temperature, wind speed and wind direction on ultrafine particles, as well as the correlation with PM2.5, PM10 and black carbon inside the street canyon. The results show that the ultrafine particles in the street canyon were highly correlated with black carbon (R2 = 0.78) and weakly correlated with PM2.5 (R2 = 0.34) and PM10 (R2 = 0.05). Number concentrations in the street canyon were inversely proportional to temperature and wind speed, and highly dependent on wind direction. The highest concentrations occurred during northeastern winds while the lowest occurred during southeastern winds. As both of these directions are perpendicular to the street axes, the results are most likely influenced by the formation of wind vortices inside the canyon, as suggested by previous studies. Although the temporal correlation of particle number concentration between the sites was moderate (R2 = 0.50), the concentrations in the street canyon were 3 - 5 times higher than the urban background levels, depending on the time scale. This study estimates the levels of ultrafine particles observed in a typical busy air pollution hotspot, and suggests that urban microenvironments should be evaluated in epidemiological studies. Additionally, it reinforces that regulations based on PM2.5 and PM10 mass concentrations may be insufficient for preventing the adverse health effects of airborne particles, as these fractions are only weakly correlated with UFP concentrations.