1Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA
2Scripps Institution of Oceanography and the University of California, San Diego, La Jolla, CA 92093, USA
3Earth System Laboratory, National Center for Atmospheric Research, Boulder, CO 80307, USA
4Department of Physics, 00014, University of Helsinki, Finland
5Max Planck Institute for Chemistry, 55128 Mainz, Germany
6School of Engineering and Applied Sciences & Department of Earth and Planetary Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, USA
7Institute of Physics, University of São Paulo, Rua do Matão, Travessa R, 187, 05508-090, São Paulo, Brazil
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.