An In Situ, Time-Resolved Analyzer for Aerosol Organic and Elemental Carbon

An in situ carbon analyzer has been developed to investigate the aerosol chemistry of organic carbon. Uncertainties because of sample handling and loss of organic carbon during storage were eliminated by combining the sampling and analysis functions into a single instrument which could operate on a time cycle as short as 90 minutes. Carbon analysis was accomplished with a thermal-optical method with corrections made for the vapor adsorption artifact and for pyrolytic conversion of organic to elemental carbon during the carbon analysis. Total aerosol carbon uncertainties are 3.1% with detection limits of 0.2 μg of carbon. The in situ carbon analyzer was operated during the Carbonaceous Species Methods Comparison Study in Glendora, California, in the summer of 1986. Concentrations of total, organic, and elemental carbon showed strong diurnal variations with peaks occurring during the daylight hours. Comparison of the diurnal profile of organic carbon with those of elemental carbon, a tracer for primary combustion aerosol, and ozone, and indicator of photochemical activity, provided evidence for the secondary formation of organic aerosol in the atmosphere.