Source apportionment and impact of long-range transport on carbonaceous aerosol particles in central Germany during HCCT-2010

• Main Authors: L. Poulain, B. Fahlbusch, G. Spindler, K. Müller, D. van Pinxteren, Z. Wu, Y. Iinuma, W. Birmili, A. Wiedensohler, H. Herrmann
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-03-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://acp.copernicus.org/articles/21/3667/2021/acp-21-3667-2021.pdf

<p>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-PM<span class="inline-formula">₁</span> 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 <span class="inline-formula"><i>R</i>²=0.83</span>). 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.</p> <p>Air masses with the strongest marine influence, based on back trajectory analysis, corresponded with a low particle mass concentration (6.4–7.5 <span class="inline-formula">µ</span>g m<span class="inline-formula">⁻³)</span> and organic fraction (<span class="inline-formula">≈30</span> %). However, they also had the largest contribution of primary OA (HOA <span class="inline-formula">≈</span> 4 % and BBOA 15 %–20 %), which was associated with local emissions. Continental air masses had the highest mass concentration (11.4–12.6 <span class="inline-formula">µ</span>g m<span class="inline-formula">⁻³</span>), and a larger fraction of oxygenated OA (<span class="inline-formula">≈45</span> %) 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.</p>