Fabrication of Reference Filter for Measurements of EC (Elemental Carbon) and OC (Organic Carbon) in Aerosol Particles

Reference filters with uniformly deposited, known masses of elemental carbon (EC) and organic carbon (OC) were produced by a spray-drying method and a carbon aerosol sampling system. Submicrometer carbon particles were produced by nebulizing a carbon black hydrosol and a potassium hydrogen phthalate (KHP; C 6 H 4 (COOK)(COOH)) solution. Total carbon (TC) concentrations measured at three different locations on the filter showed that the carbon particles were uniformly distributed on the filter. Reference filters were analyzed using thermal optical analysis methods (TOA) IMPROVE and NIOSH 5040-NIIH, and the measured concentrations of TC, EC, and OC were compared to the gravimetrically measured concentrations. TC measurements by both TOA methods used were in excellent agreement with gravimetrically measured TC. It was found that the IMPROVE method produced approximately 3.5 times as much pyrolytically generated elemental carbon (PEC) as did the NIOSH 5040-NIIH method. However, no PEC was detectable on reference filters when both EC and OC were present. This led to discrepancies in EC and OC measurement between the TOA and gravimetric methods. Better agreement was found when PEC generation of pure OC reference filters was taken into account and measurements on filters with both EC and OC deposited were corrected for PEC generation. These data imply that, when both EC and OC are present on the filter, TOA methods are often inaccurate in correctly measuring the amount of PEC generated, with the magnitude of measurement error dependent upon the type of EC and OC present in the sample. In addition, reference filters with OC deposited on top of EC and EC deposited on top of OC were generated and analyzed. From these reference filters, it was found that PEC measurements are also affected by the way in which the EC and OC deposit on the filter. Overall, the method devised here to create reference EC/OC filters is a simple technique in which EC, OC, and mixed EC-OC particles of a controlled size and chemical composition can be deposited uniformly onto filters and such reference filters will be invaluable in evaluation of TOA methods of EC/OC measurement.