Semicontinuous aerosol carbon measurements: Comparison of Atlanta supersite measurements

An intensive field campaign of the Atlanta Supersite Experiment was carried out at a ground-based measurement site on Jefferson 0Street in midtown Atlanta, Georgia, from 3 August to 1 September 1999. This paper examines the semicontinuous particulate organic and elemental measurements that were made as a part of the experiment. Measurements were made using a Rutgers University/Oregon Graduate Institute in situ thermal-optical carbon analyzer, Rupprecht and Patashnick 5400 ambient carbon particulate monitor, Radiance Research particle soot absorption photometer, Aerosol Dynamics flash vaporization carbon analyzer, and Magee Scientific AE-16 Aethalometer. The "intersampler precision" with which semicontinuous particulate total carbon (TC), organic carbon (OC), and elemental carbon (EC) were measured is 7, 13, and 26%, expressed as pooled coefficients of variation of 2, 3, and 4 instruments, respectively. Correlations between pairs of OC measurements are moderate (R² = 54-73%), and correlations between pairs of EC measurements are high (R² = 74-97%). Differences in reported OC concentrations are small compared to differences in EC concentrations; intersampler EC concentration differences result from differences (1) in the operational definitions of OC and EC, (2) in the calibration of optical instruments, and (3) because EC values are closer to limits of detection. This agreement between semicontinuous samplers is quite good, especially in light of previous particulate carbon comparisons. Reasons for measurement differences and benefits of automated time-resolved measurements are discussed.