Consistent histories of anthropogenic Western European air pollution preserved in different Alpine ice cores

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, 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 long-term ice-core records (AD 1750–2015) of various anthropogenic compounds, such as major inorganic aerosol constituents (NH₄⁺, NO₃^-, SO₄^2-), black carbon (BC), and trace species (Cd, F^-, Pb). Several ice cores from four high-Alpine sites located in the European Alps analysed by different laboratories for this set of air pollutants were used. All seven investigated anthropogenic compounds feature an excellent agreement in the species-dependent long-term concentration trends at the different sites. This is related to common source regions of air pollution impacting the less than 100 km distant four sites including Western European countries surrounding the Alps, i.e. Switzerland, France, Italy, Germany, Austria, Slovenia, and Spain. 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 (AD 1750–1850) concentration levels already at the end of the 19^th century for BC, Pb, exSO₄^2- (non-dust, non-sea salt SO₄^2-) and NH₄⁺, respectively. However, Cd, F^-, and NO₃^- concentrations started surpassing pre-industrial values only in the 20^th century, predominantly due to pollution from zinc and aluminium smelters and traffic. The observed maxima of BC, Cd, F^-, Pb, and exSO₄^2- concentrations in the 20^th century and a significant decline afterwards, clearly reveal the efficiency of air pollution control measures such as desulphurisation 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, the composite records of NO₃^- and NH₄⁺ show levels in the beginning of the 21^th 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, exSO₄^2-) of the seven investigated pollutants correspond well with modelled trends. Our results demonstrate that individual ice-core records from different sites in the European Alps provide a spatial representative signal of anthropogenic pollution from Western European countries and are essential to constrain emission or deposition data of air pollutants in this region.