Abstract
Abstract. The identification of different sources of the carbonaceous aerosol (organics and black carbon) was investigated at a mountain forest site located in central Germany from September to October 2010 to characterize incoming air masses during the Hill Cap Cloud Thuringia 2010 (HCCT-2010) experiment. The near-PM1 chemical composition, as measured by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), was dominated by organic aerosol (OA; 41 %) followed by sulfate (19 %) and nitrate (18 %). Source apportionment of the OA fraction was performed using the multilinear engine (ME-2) approach, resulting in the identification of the following five factors: hydrocarbon-like OA (HOA; 3 % of OA mass), biomass burning OA (BBOA; 13 %), semi-volatile-like OA (SV-OOA; 19 %), and two oxygenated OA (OOA) factors. The more oxidized OOA (MO-OOA, 28 %) was interpreted as being influenced by aged, polluted continental air masses, whereas the less oxidized OOA (LO-OOA, 37 %) was found to be more linked to aged biogenic sources. Equivalent black carbon (eBC), measured by a multi-angle absorption photometer (MAAP) represented 10 % of the total particulate matter (PM). The eBC was clearly associated with HOA, BBOA, and MO-OOA factors (all together R2=0.83). Therefore, eBC's contribution to each factor was achieved using a multi-linear regression model. More than half of the eBC (52 %) was associated with long-range transport (i.e., MO-OOA), whereas liquid fuel eBC (35 %) and biomass burning eBC (13 %) were associated with local emissions, leading to a complete apportionment of the carbonaceous aerosol. The separation between local and transported eBC was well supported by the mass size distribution of elemental carbon (EC) from Berner impactor samples. Air masses with the strongest marine influence, based on back trajectory analysis, corresponded with a low particle mass concentration (6.4–7.5 µg m−3) and organic fraction (≈30 %). However, they also had the largest contribution of primary OA (HOA ≈ 4 % and BBOA 15 %–20 %), which was associated with local emissions. Continental air masses had the highest mass concentration (11.4–12.6 µg m−3), and a larger fraction of oxygenated OA (≈45 %) indicated highly processed OA. The present results emphasize the key role played by long-range transport processes not only in the OA fraction but also in the eBC mass concentration and the importance of improving our knowledge on the identification of eBC sources.
Highlights
Atmospheric aerosol particles affect global climate, through direct and indirect radiative forcing (IPCC, 2013), human health (Lelieveld et al, 2015; Burnett et al, 2014; Pope et al, 2011) and the ecosystems (Bohlmann et al, 2005; Jickells et al, 2005)
A total of five factors were identified from the source apportionment of the OA, including two primary organic aerosols related to fossil fuel combustion, namely hydrocarbon-like OA (HOA) (3 % of total OA), biomass burning combustion biomass burning OA (BBOA) (13 %), and three oxygenated organic aerosols, including a semivolatile SV-oxygenated OA (OOA) (19 %), a more oxidized OOA (MO-OOA) (28 %) associated with long-range transport of polluted continental air masses, and a low oxidized OOA (LO-OOA) (37 %) related to aged biogenic aerosol
Using the correlation between HOA, BBOA, and MO-OOA with Equivalent black carbon (eBC), a multilinear regression approach was applied to perform the source apportionment of eBC. This analysis highlights eBC contributions related to the sources of HOA (35 %), BBOA (13 %), and MO-OOA (52 %)
Summary
Atmospheric aerosol particles affect global climate, through direct and indirect radiative forcing (IPCC, 2013), human health (Lelieveld et al, 2015; Burnett et al, 2014; Pope et al, 2011) and the ecosystems (Bohlmann et al, 2005; Jickells et al, 2005). One of the most significant aerosol particle components influenced by atmospheric aging processes is the OA fraction, which can represent up to 90 % of the fine aerosol particle mass (e.g., Zhang et al, 2007). Local sources drive the aerosol particle chemical composition; long-range transport, influenced by air mass origin, plays an important role in local number size distribution and aerosol particle chemical composition (e.g., van Pinxteren et al, 2016, 2019; Waked et al, 2018). The present work investigates the aerosol particle chemical composition and the different sources of carbonaceous particles reaching a site close to the village of Goldlauter in the Thuringian forest in central Germany. The presented results speak for themselves but can be used to further interpret HCCT2010 results and guide associated modeling and future experimental studies in the Schmücke area
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