AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Morphology of Aerosol Particles at Freeway On-Ramps
SWARUP CHINA, Neila Salvadori, Claudio Mazzoleni, Michigan Technological University
Abstract Number: 603 Working Group: Combustion
Abstract Atmospheric aerosols impact the environment and climate by affecting Earth’s radiation balance, cloud formation and atmospheric chemistry. Vehicles are the dominant source of pollution in urban environments. Diesel and gasoline particulate matter emissions are primarily composed of agglomerated soot particles and volatile organic and sulfur compounds. The morphology of atmospheric particles influences their optical properties and therefore their radiative forcing; the morphology also affects the particles’ transport and lifecycle. In this study we investigated morphological and structural properties of road-side aerosol particles at six different cloverleaf freeway on‐ramps in the Detroit–Ann Arbor geographical area in Southern Michigan. The aerosol samples were collected on nuclepore polycarbonate filters and characterized by scanning electron microscope. Qualitative elemental compositions were determined using energy dispersive X–ray spectroscopy.
Particles were found in various shapes such as spherical, fractal-like aggregates or soot, irregularly shaped, and particles with multiple inclusions. Particles were divided into few groups based on their morphology. The fraction of fractal-like particles with respect to the total number of particles counted was then associated with the traffic density (number of passing vehicles per minute) and the vehicle type (e.g.; passenger vehicle vs. truck) to study the contribution of traffic to the ambient soot concentration near freeways. Three dimensional fractal properties of soot aggregates were studied using 2d projected images for different driving conditions. Morphological parameters (i.e. aspect ratio, circularity and roundness) showed a good correlation with particle size. We will present the variability in soot particle morphology at different times of the day and the morphology dependence with several influencing factors such as the vehicle specific power (that represents the driving conditions), the vehicle model year and fuel type, and the local meteorological conditions.