Research Projects

Project at a Glance

Project Status: complete

Title: Intercomparison of methods for the measurement of carbonaceous aerosol species

Principal Investigator / Author(s): Appel, Bruce R

Contractor: Air and Industrial Hygiene Laboratory, California Department of Health Services

Contract Number: A4-158-32


Research Program Area: Atmospheric Processes


Abstract:

A field study was performed evaluating methods for the measurement of carbonaceous atmospheric aerosols. The sampling techniques assessed included a proposed fine particulate carbon sampler operating for 12-hour sampling periods and two tandem filter samplers operating at face velocities of 47 and 10 cm/set, respectively, for four- or eight-hour periods. Samples were analyzed for elemental or black carbon with a light absorption technique, and for total carbon and carbonate carbon with a coulometric detector. Organic carbon was estimated by difference. Samplers were operated at Citrus College, Glendora, California during the period August 12 - August 20, 1986 in parallel with samplers operated by other investigators.

The proposed fine particulate carbon sampler consisted of a cyclone, parallel plate diffusion denuder packed with coarse, activated alumina, and a quartz fiber filter followed by a fluidized bed of activated alumina. The denuder was intended to prevent sorption of vapor-phase carbonaceous material on the quartz filter, particulate matter thereon, or the fluidized bed. The fluidized bed was intended to trap carbonaceous material lost from the filter by volatilization following collection in the particulate state.

Based on QA studies as well as atmospheric particulate sample results, the alumina denuder was judged ineffective in eliminating the positive error in organic aerosol sampling with quartz filters. The results indicate that compounds not retained efficiently on alumina are being sorbed by quartz filters to produce a positive artifact in carbonaceous aerosol sampling. The contrast in denuder effectiveness between the present trials and our earlier studies is discussed. The failure of the denuder in the present work also prevents interpretation of carbon recoveries on the fluidized bed of Al2O3 regarding the significance of volatilization of particulate carbon from a quartz filter sampler.

Comparing particulate organic carbon results as a function of prefilter face velocity, measured airborne concentrations were about 50% higher at 10 compared to 47 cm/set. With tandem filter samplers, after-filter C was about 20% of the total recovered carbon at both 10 and 47 cm/set. Expressed in Ķg/m3, after-filter results at 10 cm/set were about twice the level at 47 cm/set, consistent with greater efficiency for sorption of vapor-phase organic compounds at lower face velocity. Subtracting the after-filter carbon results from the organic carbon (i.e. particle plus sorbed vapor phase carbon) measured on the prefilter did not greatly improve the agreement in organic carbon concentrations measured with the prefilters of the samplers at the two face velocities. Thus, neither measurement of particulate organic carbon can be considered accurate.

AIHL carbon analyses of atmospheric particulate samples were compared to those by S. Cadle, General Motors Research Laboratory. The total carbon and organic carbon data sets for the two laboratories were highly correlated (r > 0.94). AIHL total carbon results averaged 4% lower; organic carbon averaged 15% higher, and elemental carbon averaged 17% lower than those by GM.


 

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