Articles | Volume 16, issue 19
Research article
12 Oct 2016
Research article |  | 12 Oct 2016

Source characterization of highly oxidized multifunctional compounds in a boreal forest environment using positive matrix factorization

Chao Yan, Wei Nie, Mikko Äijälä, Matti P. Rissanen, Manjula R. Canagaratna, Paola Massoli, Heikki Junninen, Tuija Jokinen, Nina Sarnela, Silja A. K. Häme, Siegfried Schobesberger, Francesco Canonaco, Lei Yao, André S. H. Prévôt, Tuukka Petäjä, Markku Kulmala, Mikko Sipilä, Douglas R. Worsnop, and Mikael Ehn

Abstract. Highly oxidized multifunctional compounds (HOMs) have been demonstrated to be important for atmospheric secondary organic aerosols (SOA) and new-particle formation (NPF), yet it remains unclear which the main atmospheric HOM formation pathways are. In this study, a nitrate-ion-based chemical ionization atmospheric-pressure-interface time-of-flight mass spectrometer (CI-APi-TOF) was deployed to measure HOMs in the boreal forest in Hyytiälä, southern Finland. Positive matrix factorization (PMF) was applied to separate the detected HOM species into several factors, relating these “factors” to plausible formation pathways. PMF was performed with a revised error estimation derived from laboratory data, which agrees well with an estimate based on ambient data. Three factors explained the majority (> 95 %) of the data variation, but the optimal solution found six factors, including two nighttime factors, three daytime factors, and a transport factor. One nighttime factor is almost identical to laboratory spectra generated from monoterpene ozonolysis, while the second likely represents monoterpene oxidation initiated by NO3. The exact chemical processes forming the different daytime factors remain unclear, but they all have clearly distinct diurnal profiles, very likely related to monoterpene oxidation with a strong influence from NO, presumably through its effect on peroxy radical (RO2) chemistry. Apart from these five “local” factors, the sixth factor is interpreted as a transport related factor. These findings improve our understanding of HOM production by confirming current knowledge and inspiring future research directions and provide new perspectives on using factorization methods to understand short-lived atmospheric species.

Short summary
Highly oxidized multifunctional compounds (HOMs) are known to have a significant contribution to secondary aerosol formation, yet their dominating formation pathways remain unclear in the atmosphere. We apply positive matrix factorization (PMF) on HOM data, and successfully retrieve factors representing different formation pathways. The results improve our understanding of HOM formation, and provide new perspectives on using PMF to study the variation of short-lived specie.
Final-revised paper