HR: 0830h
AN: A51F-0759    [PDF]
TI: Patterns in Hygroscopicity of Ambient Particulate Matter at Urban, Rural and Forested Sites
AU: * Aklilu, Y
EM: yaklilu@yorku.ca
AF: York University, Petrie Science Building, 4700 Keele street, Toronto, ON M3J 1P3 Canada
AU: Mozurkewich, M
EM: mozurkew@yorku.ca
AF: York University, Petrie Science Building, 4700 Keele street, Toronto, ON M3J 1P3 Canada
AU: Leaitch, R
EM: Richard.Leaitch@ec.gc.ca
AF: Meteorological Service of Canada, 4905 Dufferin Street, Toronto, ON M3H 5T4 Canada
AB: Hygroscopicity of ambient particles was measured at four sampling sites, using a Hygroscopic Tandem Differential Mobility Analyzer (HTDMA). Particles were first dried to about 10% relative humidity, monodisperse particles were then selected; these particles were humidified to relative humidities ranging from 50 to 85% and the size distribution measured to determine growth due to water sorption. Data was collected at an urban site, a forested site, and two sites with a mixture of urban and rural influences. A common feature observed at all the sites was the existence of particles that sorbed only small amounts of water even at high relative humidity. These particles showed a small and gradual increase in size with increase in relative humidity; at 80% relative humidity, these less hygroscopic particles typically had growth factor of 1.1. At the urban and mixed sites, these less hygroscopic particles were observed on good air quality days; at the forested site, they constituted almost all the particles. Particles with higher hygroscopicity were observed on more polluted days. These particles had growth factors as high as 1.4 at 80% relative humidity. The more hygroscopic particles took up a significant amount of water at higher relative humidity while still behaving like the less hygroscopic particles at lower relative humidities. The point at which this transition occurred ranged from 70% to 75%, and varied more from site to site than over time. On a number of the polluted days, these more hygroscopic particles were externally mixed with less hygroscopic particles, resulting in both less and more hygroscopic mode in the humidified particle distributions. Compositional data will be used to investigate the role of the organic fraction in the hygroscopic growth of these particles.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0345 Pollution--urban and regional (0305)
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting