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Harmonizing Molecular Marker Analyses of Organic Aerosols

Analysis of molecular markers in aerosol samples using GC-MS has become widely used in air pollution studies. There is considerable variability in the analytical details of molecular marker analyses across different research and regulatory groups. These discrepancies result in the use of different methods for the interpretation of source and ambient measurements used in source apportionment and atmospheric particulate studies. As a demonstration of the utility of harmonizing laboratorial methods, inter-laboratory comparison experiments were conducted in which two laboratories used similar methods, including extraction, derivatization, instrumental analyses, and quantification algorithms. Duplicate samples, including ambient and source aerosol samples, were analyzed. Results showed that when using the same analytical methods, good agreement was achieved between laboratories. The results of the molecular marker analyses at both laboratories were suitable for use in source apportionment. Non-and moderately polar compounds, including hopanes and steranes showed the best agreements of the compounds analyzed by both labs with a relative deviation of 7.7%. Although consistent results for all key molecular markers were obtained, the sensitivity of different compounds and compound groups to analytical parameters were examined to assess analytical accuracies. Quantification was most sensitive to internal standard reference due to varying recoveries for different internal standards.