Abstract
Abstract. We present the vibrational sum frequency generation spectra of organic particles collected in a boreal forest in Finland and a tropical forest in Brazil. These spectra are compared to those of secondary organic material produced in the Harvard Environmental Chamber. By comparing coherent vibrational spectra of a variety of terpene and olefin reference compounds, along with the secondary organic material synthesized in the environmental chamber, we show that submicron aerosol particles sampled in Southern Finland during HUMPPA-COPEC-2010 are composed to a large degree of material similar in chemical composition to synthetic α-pinene-derived material. For material collected in Brazil as part of AMAZE-08, the organic component is found to be chemically complex in the coarse mode but highly uniform in the fine mode. When combined with histogram analyses of the isoprene and monoterpene abundance recorded during the HUMPPA-COPEC-2010 and AMAZE-08 campaigns, the findings presented here indicate that if air is rich in monoterpenes, submicron-sized secondary aerosol particles that form under normal OH and O3 concentration levels can be described in terms of their hydrocarbon content as being similar to α-pinene-derived model secondary organic aerosol particles. If the isoprene concentration dominates the chemical composition of organic compounds in forest air, then the hydrocarbon component of secondary organic material in the submicron size range is not simply well-represented by that of isoprene-derived model secondary organic aerosol particles but is more complex. Throughout the climate-relevant size range of the fine mode, however, we find that the chemical composition of the secondary organic particle material from such air is invariant with size, suggesting that the particle growth does not change the chemical composition of the hydrocarbon component of the particles in a significant way.
Highlights
Plants in boreal and tropical forests emit pinene, isoprene, and related terpenes, and these volatile compounds undergo atmospheric oxidation reactions
These two types of forest were the focus of two recent field campaigns, namely HUMPPA-COPEC2010, which was conducted in Southern Finland
We use the coherent second-order nonlinear vibrational spectroscopy sum frequency generation (SFG) (Zhu et al, 1986; Guyot-Sionnest et al, 1987a) to study organic aerosol particles from a boreal and a tropical forest and compare the results to SFG responses obtained from synthetic organic aerosol particles prepared in an environmental chamber
Summary
Plants in boreal and tropical forests emit pinene, isoprene, and related terpenes, and these volatile compounds undergo atmospheric oxidation reactions. Isoprene is the main gas phase emission found in tropical forests, whereas α-pinene is often the most abundant biogenic volatile organic compound in boreal forests. These two types of forest were the focus of two recent field campaigns, namely HUMPPA-COPEC2010, which was conducted in Southern Finland The extensive datasets available for the particle and the gas phases of atmospheric aerosol sampled at the two locations provide key fundamental information for introducing coherent vibrational laser spectroscopic methods to atmospheric chemistry and physics with the goal of deepening our understanding of the formation, microphysics, and fate of aerosol particles in tropical vs boreal forests
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