Atmospheric Carbonaceous Species Measurement Methods Comparison Study: General Motors Results

Abstract

The General Motors Research Laboratories participated in both the field sampling and round-robin portions of the Carbonaceous Species Intercomparison study that was held in Glendora, CA, during the summer of 1986. Five samplers were operated during the field study. The average particulate elemental carbon (EC) concentrations determined from the five samplers agreed to within 12%. Large differences were observed in the concentrations of particulate organic carbon (OC) determined from the five samplers. Some of the differences are attributed to losses of OC from the filters due to volatilization during the collection period. The amount of volatilization varies with the length of the sampling time and the filter face velocity. In addition, the adsorption of gas-phase organic compounds caused a significant positive interference in the determination of OC. Our OC and EC results for the round-robin samples were compared to the values obtained by the other participating laboratories. The average ratio of our results to the mean of the other laboratories was 0.97 for all the OC data and 1.23 for EC from all but the ambient wood-burning and organic aerosol samples. The ratios for the latter samples were 1.9 or greater. It is concluded that EC can be collected and analyzed with high precision; however, the accuracy of the measurements is unknown since standards for EC in atmospheric particulate do not exist.