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Extreme weather conditions and widespread drying induced by climate change will increase the risk and severity of wildfires increasing the importance of the wildfire emissions in the climate system. Aerosol emissions from the wildfires may affect the cloud formation by increasing the concentration of cloud condensation nuclei (CCN) and by affecting the composition and hygroscopicity (k) of the aerosol population. In this study, we investigate the effect of long range transported (originated from South-Eastern Europe) wildfire plume on cloud microphysics at two sites: Puijo SMEAR IV in Eastern Finland, and Zeppelin Observatory in Svalbard, high Arctic. We use both in-situ and satellite observations to investigate the changes in aerosol population, cloud activation and cloud properties.During the wildfire plume period, the aerosol hygroscopicity slightly increased compared to clean periods at Puijo station, but decreased at Zeppelin. A substantial increase in aerosol number concentration in the accumulation mode size range was observed at both stations. Despite the increase in k, the increase in critical diameter for activation was observed as the water supersaturation was decreased due to increased aerosol concentration at Puijo station. A substantial increase in CCN concentration and cloud droplet number concentration (CDNC) was observed based on in-situ observations at both stations during the wildfire plume period. Also satellite observations revealed a comparable change in CDNC and cloud optical thickness over Puijo station. Our results demonstrate that the long range transported (3-5 days) wildfire plume can significantly affect cloud formation in environments where the background concentrations are relatively low., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Black carbon (BC) from anthropogenic or natural sources can be transported to the Arctic, where it affects the surface radiation budget by scattering and absorbing solar radiation or by acting as cloud condensation nuclei. The extent to which BC is involved in Arctic cloud formation remains uncertain due to the lack of direct and long-term observations. Here, we present a 4-year study on observations of BC concentrations of aerosols and cloud residuals (i.e. dried cloud particles) using a counterflow virtual impactor inlet at Zeppelin Observatory, Svalbard. We will show that the scavenging of BC follows a clear seasonal cycle with almost complete scavenged fractions of BC in summer and smaller scavenged fractions in late winter and early fall during the Arctic haze period. The scavenged BC fractions were positively correlated with cloud water content and showed a dependence on air temperature most likely due to cloud-microphysical processes. A source analysis showed that clouds at the site are mainly of marine origin, in opposite to non-cloudy air, where anthropogenic BC sources over land are more dominant., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

To constrain uncertainties in radiative forcings associated with aerosol–cloud interactions, improved understanding of Arctic cloud formation is required, yet long-term measurements of the relevant cloud and aerosol properties remain sparse. We present the first long-term study of cloud residuals, i.e. particles that were involved in cloud formation and cloud processes, in Arctic low-level clouds measured at Zeppelin Observatory, Svalbard. To continuously sample cloud droplets and ice crystals and separate them from non-activated aerosol, a ground-based counter-flow virtual impactor inlet system (GCVI) was used. A detailed evaluation of the GCVI measurements, using concurrent cloud particle size distributions, meteorological parameters, and aerosol measurements, is presented for both warm and cold clouds, and the potential contribution of sampling artefacts is discussed in detail. We find an excellent agreement of the GCVI sampling efficiency of liquid clouds using two independent approaches. The 2-year data set of cloud residual size distributions and number concentrations reveals that the cloud residuals follow the typical seasonal cycle of Arctic aerosol, with a maximum concentration in spring and summer and a minimum concentration in the late autumn and winter months. We observed average activation diameters in the range of 58–78 nm for updraught velocities below 1 m s−1. A cluster analysis also revealed cloud residual size distributions that were dominated by Aitken mode particles down to around 20–30 nm. During the winter months, some of these small particles may be the result of ice, snow, or ice crystal shattering artefacts in the GCVI inlet; however, cloud residuals down to 20 nm in size were also observed during conditions when artefacts are less likely.