Consistent histories of anthropogenic western European air pollution preserved in different Alpine ice cores
Authors: Eichler Anja , Legrand Michel , Jenk Theo M. , Preunkert Susanne , Andersson Camilla , Eckhardt Sabine , Engardt Magnuz , Plach Andreas , Schwikowski Margit 
Published: May 2023

Abstract. Individual high-Alpine ice cores have been proven to contain a well-preserved history of past anthropogenic air pollution in western Europe. The
question of how representative one ice core is with respect to the reconstruction of atmospheric composition in the source region has not been
addressed so far. Here, we present the first study systematically comparing longer-term ice-core records (1750–2015 CE) of various anthropogenic
compounds, such as major inorganic aerosol constituents (NH4+, NO3-, SO42-), black carbon (BC), and trace
species (Cd, F−, Pb). Depending on the data availability for the different air pollutants, up to five ice cores from four
high-Alpine sites located in the European Alps analysed by different laboratories were considered. Whereas absolute concentration levels can partly
differ depending on the prevailing seasonal distribution of accumulated precipitation, all seven investigated anthropogenic compounds are in
excellent agreement between the various sites for their respective, species-dependent longer-term concentration trends. This is related to common
source regions of air pollution impacting the four sites less than 100 km away including western European countries surrounding the
Alps. For individual compounds, the Alpine ice-core composites developed in this study allowed us to precisely time the onset of pollution caused by
industrialization in western Europe. Extensive emissions from coal combustion and agriculture lead to an exceeding of pre-industrial
(1750–1850) concentration levels already at the end of the 19th century for BC, Pb, exSO42- (non-dust, non-sea salt
SO42-), and NH4+, respectively. However, Cd, F−, and NO3- concentrations started surpassing
pre-industrial values only in the 20th century, predominantly due to pollution from zinc and aluminium smelters and traffic. The observed maxima of
BC, Cd, F−, Pb, and exSO42- concentrations in the 20th century and a significant decline afterwards clearly
reveal the efficiency of air pollution control measures such as the desulfurization of coal, the introduction of filters and scrubbers in power plants
and metal smelters, and the ban of leaded gasoline improving the air quality in western Europe. In contrast, NO3- and NH4+
concentration records show levels in the beginning of the 21th century which are unprecedented in the context of the past 250 years, indicating
that the introduced abatement measures to reduce these pollutants were insufficient to have a major effect at high altitudes in western Europe. Only
four ice-core composite records (BC, F−, Pb, exSO42-) of the seven investigated pollutants correspond well with
modelled trends, suggesting inaccuracies of the emission estimates or an incomplete representation of chemical reaction mechanisms in the models for
the other pollutants. Our results demonstrate that individual ice-core records from different sites in the European Alps generally provide a spatially
representative signal of anthropogenic air pollution trends in western European countries.