Infrared properties of atmospheric aerosol constituents: Polyaromatic hydrocarbons and terpenes

Abstract

The infrared spectra (2–20 μm) of six terpene samples and six polyaromatic hydrocarbon (PAH) samples are presented and compared with similar spectra obtained from standard grade petroleum (fog oil) samples. The selected samples are representative of the various different molecular structures that may be present in atmospheric aerosol sources, particularly fire smokes. Results are presented in terms of the wavelength-dependent complex refractive indices as obtained from bulk phase (thin layer) transmittance measurements and the Kramers-Kronig relationships. All samples exhibit a characteristic complex absorption spectra with numerous line absorption features in the 8–14-μm atmospheric window regions with peak imaginary indices nominally around 0.10–0.12 for the terpene samples and on the order of 1.0–1.2 for the PAH samples, although there are far fewer lines in the PAH samples than in the terpene samples. The terpenes also exhibit absorption features in the 3–5-μm window which are much like those found in the standard samples but are not observed in the PAH samples. © 1994 Elsevier Science Inc.