Research Projects

Project at a Glance

Project Status: complete

Title: Comparison of sampling methods for carbonaceous aerosols in ambient air

Principal Investigator / Author(s): Hering, S. V.

Contractor: University of California, Los Angeles

Contract Number: A5-154-32


Research Program Area: Atmospheric Processes


Abstract:

Measurement methods for fine particle carbon ( < 2.5 Ķm ) were compared under field sampling conditions. For nine consecutive days in August 1986, samplers were operated side-by-side in the Los Angeles Basin. Sampling methods included filtration, impaction and adsorption corrected filtration. Analytical methods were compared separately. For ambient sampling of organic carbon, the mean results over the study period from the individual laboratories varied by more than a factor of two. However, in the analytical comparison for organic carbon, the individual laboratory means were within 13% of the grand mean. For elemental carbon, differences among laboratories for both the analytical comparison and the ambient sampling were much as a factor of three.

Most of the observed differences in ambient measurements of organic carbon are attributed to differences in sampling methodology. The highest reported concentrations were obtained by quartz filter sampling, with method mean values three percent to 21% higher than the grand mean. The lowest values were from the impactors, excluding the quartz after-filters, which gave method mean values 45% to 54% lower than the grand mean. Comparison of results from the different sampling systems and analysis of back-up filter data indicate organic carbon adsorption artifacts on quartz fiber filters can be significant. For the two-impactor systems, the after-filters contained a large proportion of organic carbon (38 % and 47%), but very little elemental carbon (5 % and 12%). For systems employing tandem filters, the carbon found on the back-up filters was 14% to 53% of the aerosol carbon.


 

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