On the post-1970 changes in Greenland ice core sulfate and other chemical impurities

The Arctic climate is sensitive to aerosol abundance, making accurate historical records of atmospheric aerosols essential for understanding the recent rapid Arctic warming. We present 235-year ice core records of sulfate (SO42-), nitrate (NO3-), chloride (Cl-) and other impurities from central Greenland, and compare them with emission inventories in the surrounding continents. The comparisons reveal a high correlation between the ice core records and North American emissions, consistent with that North America as the dominant pollution source region to Greenland. Since around 1970, SO42-, NO3- and Cl- exhibit divergent patterns relative to their pre-1970 increasing trends paralleling with anthropogenic emissions. In particular, SO42- declined in step with North American SO2 emissions but decreased more rapidly after ~1990, probably due to combined effects from the enhanced sulfate loss in the source regions due to intensified in-cloud sulfur oxidation and the reduced transport efficiency. Nitrate tracked NOX emissions since ~ 1900 until 1990, but remained high after 1990 when anthropogenic emissions in all source regions decreased. This post-1990 pattern may arise from the increasing natural NOX emissions in the Arctic, while feedbacks of atmospheric chemistry to a changing atmospheric acidity during this period may also contribute through affecting the phase partitioning and then long-range transport of nitrate. Chloride also paralleled with anthropogenic emissions since the 1960s but was further modulated by acid displacement processes, as indicated by the covariation of Cl- excess with reconstructed snow acidity. Our results demonstrate that Arctic aerosols reflect both emission controls and their modulation by atmospheric chemistry and transport.