Elemental, ionic and organic composition of atmospheric aerosols in Chicago during summer time

Atmospheric aerosols have been collected at the Loyola University Chicago Air Station (LUCAS) for subsequent analysis of elemental, ionic and organic species during the summers of 2002-2005. The station is located in close proximity to Lake Michigan and thus exposed to different air currents ranging from clean air coming from Lake Michigan to polluted air originating from the highly industrialized southern part of Chicago. Basic weather parameter and reactive trace gas mixing ratios of nitrogen oxides and ozone have been monitored in parallel to the aerosol collections to determine boundary layer conditions. Chemical analysis comprised of total reflection X-ray fluorescence spectrometry (TXRF) for elemental species, ion chromatography (IC) for inorganic anions and cations as well as small organic acids and liquid chromatography coupled with mass spectrometry (LC/MS) for organic species. The predominant species were calcium, iron, zinc, and sulfur as elements, nitrate, sulfate and oxalate as ions as well as phthalic and phenylbutyric acid as organic species. Based on meteorological parameter, reactive trace gas mixing ratios and aerosol chemical composition three different cases could be distinguished, clean air, moderately polluted and polluted air. Cluster analysis has been applied in order to verify the findings and highlight the correlations of the data obtained. Possible reaction pathways for the formation of selected species will be discussed as well as the influence of the lake breeze on aerosol chemical composition.