Wintertime enhancements of sea salt aerosol in polar regions consistent with a sea ice source from blowing snow

Abstract

Abstract. Sea salt aerosols (SSA) are generated via air bubbles bursting at the ocean surface as well as by wind mobilization of saline snow and frost flowers over sea-ice-covered areas. The relative magnitude of these sources remains poorly constrained over polar regions, affecting our ability to predict their impact on halogen chemistry, cloud formation, and climate. We implement a blowing snow and a frost flower emission scheme in the GEOS-Chem global chemical transport model, which we validate against multiyear (2001–2008) in situ observations of SSA mass concentrations at three sites in the Arctic, two sites in coastal Antarctica, and from the 2008 ICEALOT cruise in the Arctic. A simulation including only open ocean emissions underestimates SSA mass concentrations by factors of 2–10 during winter–spring for all ground-based and ship-based observations. When blowing snow emissions are added, the model is able to reproduce observed wintertime SSA concentrations, with the model bias decreasing from a range of −80 to −34 % for the open ocean simulation to −2 to +9 % for the simulation with blowing snow emissions. We find that the frost flower parameterization cannot fully explain the high wintertime concentrations and displays a seasonal cycle decreasing too rapidly in early spring. Furthermore, the high day-to-day variability of observed SSA is better reproduced by the blowing snow parameterization. Over the Arctic (> 60° N) (Antarctic, > 60° S), we calculate that submicron SSA emissions from blowing snow account for 1.0 Tg yr−1 (2.5 Tg yr−1), while frost flower emissions lead to 0.21 Tg yr−1 (0.25 Tg yr−1) compared to 0.78 Tg yr−1 (1.0 Tg yr−1) from the open ocean. Blowing snow emissions are largest in regions where persistent strong winds occur over sea ice (east of Greenland, over the central Arctic, Beaufort Sea, and the Ross and Weddell seas). In contrast, frost flower emissions are largest where cold air temperatures and open leads are co-located (over the Canadian Arctic Archipelago, coastal regions of Siberia, and off the Ross and Ronne ice shelves). Overall, in situ observations of mass concentrations of SSA suggest that blowing snow is likely to be the dominant SSA source during winter, with frost flowers playing a much smaller role.

Evaporating brine from frost flowers with electron microscopy and implications for atmospheric chemistry and sea-salt aerosol formation

“…The 3-D X-ray micro computer tomography experiments suggest that salt impurities are present mostly on the ice surface (Hutterli et al, 2008). Such a finding is consistent with our observation and can be well understood, tak- Figure 6.…”

“…Blowing snow on sea ice, as hypothesized by Yang et al (2008), can produce SSA through a sublimation process. Recent modelling studies have shown that this process could reproduce well the polar winter SSA peaks in most polar sites (Levine et al, 2014;Huang and Jaeglé, 2017;Rhodes et al, 2017). As indicated in the present study, FFs are ruled out as a direct source of SSA, thus making blown salty snow particles more likely to be an efficient SSA source, as suggested previously.…”

“…The relative importance of these two sea-ice-sourced SSA to the polar winter sea-salt budget is still under debate (e.g. Huang and Jaeglé, 2017;Xu et al, 2016;Rhodes et al, 2017). In any case (FFs or salty snow), the formation of SSA from salty ice particles requires its size to be reduced via the loss of water through either the evaporation or the sublimation processes, depending on the temperature.…”

Long-term study on coarse mode aerosols in the Amazon rain forest with the frequent intrusion of Saharan dust plumes

“…In this overall picture, the coarse mode seasonality shows different trends. This can be seen in the plot of the surface size distribution 4 (i.e., from 1 to 10 µm, burning smoke (mostly in the accumulation mode), and sea spray (in the coarse and accumulation modes) (Quinn et al, 1996;O'Dowd et al, 2008;Wang et al, 2016;Aller et al, 2017;Huang and Jaeglé, 2017). Accordingly, the image plot of the aerosol size distribution shows (pronounced) LRT pulses in both, the superand submicron size ranges.…”

“…The arrival of African LRT plumes clearly corresponds with increased equivalent black carbon mass concentrations (M BCe ) and light scattering coefficients (σ sp ), underlining that the LRT aerosols typically rep-30 resent mixtures of Saharan dust, biomass burning smoke, and sea spray (Talbot et al, 1990;Quinn et al, 1996;O'Dowd et al, 2008;Wang et al, 2016;Aller et al, 2017;Huang and Jaeglé, 2017). The degree of 'smokiness' of the arriving LRT plumes decreases towards the end of the wet season (Apr) which is consistent with the decreasing biomass burning activity in Africa, and simultaneously marks the cleanest periods at the ATTO site.…”