Physicochemical properties and origin of organic groups detected in boreal forest using an aerosol mass spectrometer

Abstract

An Aerodyne quadrupole aerosol mass spectrometer (Q-AMS) was deployed in Hyytiälä, a forested rural measurement site in southern Finland, during a 2-week measurement campaign in spring 2005. Q-AMS measures mass concentrations of non-refractory species including sulphate, nitrate, ammonium and organics from submicron particles. A positive matrix factorization method was used in identifying two oxygenated organic aerosol (OOA) groups from the measured total organic mass. The properties of these groups were estimated from their diurnal concentration cycles and correlations with additional data such as air mass history, particle number size distributions, hygroscopic and ethanol growth factors and particle volatility. It was found that the aged and highly oxidized background organic aerosol (OOA1 or LV-OOA) species have a wide range of hygroscopic growth factors and volatilization temperatures, but on the average OOA1 is the less volatile and more hygroscopic organic group. Hygroscopic properties and volatilities of the OOA1 species are correlated so that the less volatile species have higher hygroscopic growth factors. The other, less oxidized organic aerosol group (OOA2 or SV-OOA) is more volatile and non-hygroscopic. Trajectory analysis showed that OOA1 and the inorganic species are mainly long-range transported anthropogenic pollutions. OOA2 species and its precursor gases have short atmospheric life times, so they are from local sources. These results span the range of previous observations of oxygen content, volatility and hygroscopic growth factor, simultaneously coupling all three measurements for the first time.