Use of an Iridium Tracer To Determine the Size Distribution of Aerosol Emitted from a Fleet of Diesel Sanitation Trucks

• Published in: Environmental science & technology 1998-05, Vol.32 (10), p.1522-1529
• Main Authors: Suarez, A. E, Caffrey, P. F, Borgoul, P. V, Ondov, J. M, Divita, F
• Format: Article
• Language: English
• Subjects: Aerosols; Air pollution; Applied sciences; Atmospheric pollution; Diesel fuels; Exact sciences and technology; Industrial trucks; Pollution; Pollution sources. Measurement results; Sanitation; Sanitation services; Transports
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es970774o

To determine the size distributions of soot from a fleet of heavy-duty diesels, size-segregated ambient outdoor aerosol was collected with 9-stage micro-orifice impactors (MOI) during two 30 day periods when 800 diesel sanitation vehicles (SV) operated by the City of Baltimore burned fuel tagged with iridium(III) 2,4-pentanedionate. Ambient background samples were collected between and after release periods. Additionally, several tagged emission samples were collected with an eight-stage MOI mounted down stream of a radial diluter installed on-board a diesel SV in normal operation. Ambient, background, and emis sions samples were analyzed gravimetrically for particulate mass, for iridium by instrumental neutron activation analysis, and for organic and elemental carbon (OC and EC) by a thermal/optical reflectance method. Size distributions of freshly emitted Ir-containing particles contained a major accumulation aerosol peak at a modal aerodynamic diameter of 0.12 μm; however, 43 ± 1% of the Ir mass was contained in particles with diameters between 0.22 and 1.8 μm. Fractions of particulate mass, OC and EC contained in this interval were similar. Tagged soot aerosol collected in Baltimore contained modes at 0.4 and, sometimes, 2.4 μm, in addition to the primary particle mode at 0.12 μm. Submicrometer modes are attributed to fresh SV emissions, whereas the 2.5 μm mode is attributed to resuspension. The results suggest that inferences on the evolution of urban soot aerosol made from size distribution data may be invalid unless a unique tracer is employed.