Arctic haze in a climate changing world: the 2010-2020 trend (HAZECLIC)

This is chapter 4 of the State of Environmental Science in Svalbard (SESS) report 2020 (https://sios-svalbard.org/SESS_Issue3). The phenomenon of Arctic haze was studied in Ny-Ålesund at two observatories close to each other but at different altitudes (Gruvebadet and Mt Zeppelin, 50 m and 700 m a.s.l.). The sites are influenced by a different mix of sources and transport processes: mainly long-range sources and free troposphere at Mt Zeppelin and short-range inputs at Gruvebadet. These two complementary sites offer a way to better understand advection of polluted air masses to Svalbard at continental and local-to-regional scale. The data series from Mt Zeppelin covers the last 27 years while the Gruvebadet data series begins in 2010. Here we present the first comparison of the available data on chemical tracers for this potentially harmful phenomenon (sulphate and ammonium), to be developed further by taking into account other tracers. Sulphate concentrations in the atmosphere have been decreasing in the Arctic since the 1990s (in line with falling SO2 emissions). Our data show continued decreases at roughly the same rate also in the first decade of the 21st century. Moreover, we find that this decrease is particularly intense during Arctic haze months (winter and early spring), whereas in autumn the concentrations are constant or slightly rising. Decreases in sulphate may have opposing fallouts on climate, environment and human health in Svalbard, since the atmosphere is becoming poorer in sulphuric acid, favouring an additional warming of the atmosphere (lower scattering effect on incoming solar radiation) and modifying the chemistry of the atmosphere (towards a more alkaline character, richer in ammonia)