Drivers of atmospheric deposition of polycyclic aromatic hydrocarbons at European high-altitude sites
Authors: Arellano Lourdes , Fernández Pilar , van Drooge Barend L. , Rose Neil L. , Nickus Ulrike , Thies Hansjoerg , Stuchlík Evzen , Camarero Lluís , Catalan Jordi , Grimalt Joan O. 
Published: November 2018

Abstract. Polycyclic aromatic hydrocarbons (PAHs) were analysed in bulk
atmospheric deposition samples collected at four European high-mountain
areas, Gossenköllesee (Tyrolean Alps), Redon (Central Pyrenees), Skalnate
Pleso (High Tatra Mountains),
and Lochnagar (Grampian Mountains) between 2004
and 2006. Sample collection was performed monthly in the first three sites
and biweekly in Lochnagar. The number of sites, period of study and sampling
frequency provide the most comprehensive description of PAH fallout in high
mountain areas addressed so far. The average PAH deposition fluxes in Gossenköllesee, Redon and Lochnagar
ranged between 0.8 and 2.1 µg m−2 month−1, and in Skalnate
Pleso it was 9.7 µg m−2 month−1, showing the influence
of substantial inputs from regional emission sources. The deposited
distributions of PAHs were dominated by parent phenanthrene, fluoranthene and
pyrene, representing 32 %–60 % of the total. The proportion of
phenanthrene, the most abundant compound, was higher at the sites of lower
temperature, Gossenköllesee and Skalnate Pleso, showing higher transfer
from gas phase to particles of the more volatile PAHs. The sites with lower
insolation, e.g. those located at lower altitude, were those with a higher
proportion of photooxidable compounds such as benz[a]anthracene. According to the data analysed, precipitation is the main driver of PAH
fallout. However, when rain and snow deposition were low, particle settling
also constituted an efficient driver for PAH deposition. Redon and Lochnagar
were the two sites receiving the highest amounts of rain and snow and the fallout of PAH
fluxes was related to this precipitation. No significant association was
observed between long-range backward air trajectories and PAH deposition in
Lochnagar, but in Redon PAH fallout at higher precipitation was essentially
related to air masses originating from the North Atlantic, which were
dominant between November and May (cold season). In these cases, particle-normalised PAH fallout was also associated with higher precipitation as these
air masses were concurrent with lower temperatures, which enhanced gas to
particle partitioning transfer. In the warm season (June–October), most of
the air masses arriving at Redon originated from the south and particle
deposition was enhanced as consequence of Saharan inputs. In these cases,
particle settling was also a driver of PAH deposition despite the low overall
PAH content of the Saharan particles. In Gossenköllesee, the site receiving lowest precipitation, PAH fallout
was also related to particle deposition. The particle-normalised PAH fluxes
were significantly negatively correlated to temperature, e.g. for air masses
originating from central and eastern Europe, showing a dominant transfer from
gas phase to particles at lower temperatures, which enhanced PAH fallout,
mainly of the most volatile hydrocarbons. Comparison of PAH atmospheric deposition and lacustrine sedimentary fluxes
showed much higher values in the latter case of
24–100 µg m−2 yr−1 vs.
120–3000 µg m−2 yr−1. A strong
significant correlation was observed between these two fluxes, which is
consistent with a dominant origin related to atmospheric deposition at each
site.