Atmospheric submicron aerosol composition and particulate organic nitrate formation in a boreal forestland–urban mixed region

摘要

The Puijo aerosol–cloud observation station is a unique measurement site forits location in the mixed region between the boreal forestland and themunicipality of Kuopio, Finland. A measurement campaign was carried out atthe station during fall 2010. An Aerodyne high-resolution time-of-flightaerosol mass spectrometer (HR-Tof-AMS) was deployed to characterize theatmospheric submicron aerosols. Positive matrix factorization (PMF) wasapplied to the unified high-resolution mass spectra organic species withNO and NO ions to discover the intrinsic relationshipsbetween the organic and inorganic species and their daily cycles. Onaverage, the submicron aerosols in this study were dominated by organic andsulfate species, composing 48.2 and 28.7% of total observed aerosolmass, respectively, with smaller contributions from ammonium (9.3%),nitrate (4.9%), chloride (0.8%) and BC (8.1%). The sources of thesespecies included the primary emissions originating from the city area,secondary formation from both natural and anthropogenic emissions andregional transport. The PMF analysis succeeded in separating the mixedorganic and inorganic spectra into three distinct organic and one inorganicfactors. For organic factors, the semi-volatile oxygenated organic aerosol(SVOOA) and low-volatility oxygenated OA (LVOOA) accounted for 54.8 and36.3% of total organic masses, respectively, while the hydrocarbon-likeorganic aerosol (HOA) accounted for 8.9% of total organics, with its mainsource from urban emissions. The inorganic factor is identified asNHNO, comprising 6.9% of the fitted aerosol mass by PMF.Based on the PMF results, the nitrate species were separated into organicand inorganic components, with the organic nitrates contributing one-third of thetotal nitrate mass. The results highlight both anthropogenic and biogenicemissions as important atmospheric aerosol sources in a forest–urban mixedregion.