Relationships between spectroscopic properties of high-altitude organic aerosols and Sun photometry from ground-based remote sensing

Abstract

Organic aerosols are important light-absorbing compounds in the atmosphere that influence climate by filtering solar radiation and interact with the biosphere via deposition to aquatic and terrestrial ecosystems. There is a limited understanding of their chemical properties and even less is known about the relationships between fluorescent properties and widely used optical properties of aerosols in the vertical air column, such as aerosol optical depth (δAλ), aerosol size distribution, and single scattering albedo (ω0Aλ). In this study, we examined relationships between spectroscopic (fluorescence and absorbance) properties of the water-soluble organic compounds (WSOC) in aerosol deposition and ground-based remote sensing measurements of aerosols in the atmospheric column. With both techniques, we found important differences between Saharan- and marine-dominated organic aerosols. Saharan-dominated WSOC had more intense fluorescence and higher content of reduced quinone-like fluorescent components than marine-dominated WSOC, and amino acid-like fluorescence was substantial in both types of deposition. Both particulate matter loading and molar absorption in the UV range were significantly related to iron content and may reflect a contribution from iron to light absorption. Saharan-dominated aerosols generally had higher δAλ and volume concentration of coarse mode particles (>0.5 μm; Vc2) than marine-dominated aerosols. Using fluorescence spectroscopy and PARAFAC modeling, we found that reduced quinone-like compounds were significantly and positively related to δAλ and Vc2. The relationships that emerged from this study provide a basis for relating WSOC and columnar measurements in the future.