In-situ observations of aerosol-cloud interactions in Ny-Ålesund, Svalbard, during fall 2019 and spring 2020

Paraskevi Georgakaki, Ghislain Gilles Jean-Michel Motos, Athanasios Nenes, Jörg Wieder
2021
Discussion par affiche

Résumé

The Arctic region suffers an extreme vulnerability to climate change, with an increase in surface air temperatures that have reached twice the global rate during several decades (McBean et al., 2005). The role of clouds, and in particular low-levels clouds and fog, in this arctic amplification by regulating the energy transport from and to space has recently gained interest among the scientific community. The NASCENT 2019-2020 campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) based in Ny-Ålesund, Svalbard (79º North) aimed at studying the microphysical and chemical properties of low-level clouds using measurements both at the sea level and at the Zeppelin station (475 m a.s.l.). Specifically, the susceptibility of droplet formation, which has recently been shown to be highly dependent on aerosol levels in European alpine valleys (Georgakaki et al., under review), could strongly vary between the fall to winter months, with pristine-like conditions, and the higher particle concentrations generally found in spring, known as the arctic haze. First results using a scanning mobility particle sizer (SMPS) and a cloud condensation nuclei counter (CCNC) confirmed that aerosol concentrations in the range 10 < Dpart [nm] < 500 were approximatively 4-5 times higher during the months of spring 2021 compared to those of fall 2020. In addition, we found relatively low values of the aerosol hygroscopic parameter κ, generally below 0.3, consistently with previous studies in the arctic region (Moore et al., 2011). Georgakaki, P., Bougiatioti, A., Wieder, J., Mignani, C., Kanji, Z. A., Henneberger, J., Hervo, M., Berne, A. and Nenes, A.: On the drivers of droplet variability in Alpine mixed-phase clouds, , 34, under review. McBean, G., Alekseev, G., Chen, D., Førland, E., Fyfe, Groisman, J., P. Y., King, R., Melling, H., Voseand, R., Whitfield, P. H.: Arctic climate: past and present. Arctic Climate Impacts Assessment (ACIA), C. Symon, L. Arris and B. Heal, Eds., Cambridge University Press, Cambridge, 21-60, 2005. Moore, R. H., Bahreini, R., Brock, C. A., Froyd, K. D., Cozic, J., Holloway, J. S., Middlebrook, A. M., Murphy, D. M. and Nenes, A.: Hygroscopicity and composition of Alaskan Arctic CCN during April 2008, Atmospheric Chemistry and Physics, 11(22), 11807–11825, https://doi.org/10.5194/acp-11-11807-2011, 2011.

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Paraskevi Georgakaki, Ghislain Gilles Jean-Michel Motos, Athanasios Nenes, Jörg Wieder
2021
Discussion par affiche

Résumé

Official source

https://infoscience.epfl.ch/record/291480?ln=fr

À propos de ce résultat

Concepts associés (21)

Concepts associés

Chargement

Publications associées (32)

Publications associées

Chargement

In-Situ Observations Of Aerosol Hygroscopicity And Cloud Droplet Formation In Ny-Ålesund, Svalbard, During Fall 2019 And Spring 2020

Paraskevi Georgakaki, Ghislain Gilles Jean-Michel Motos, Athanasios Nenes, Jörg Wieder

The Arctic region suffers an extreme vulnerability to climate change, with an increase in surface air temperatures that have reached twice the global rate during several decades (McBean et al., 2005). The role of clouds, and in particular low-levels clouds and fog, in this arctic amplification by regulating the energy transport from and to space has recently gained interest among the scientific community. The NASCENT 2019-2020 campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) based in Ny-Ålesund, Svalbard (79º North) aimed at studying the microphysical and chemical properties of low-level clouds using measurements both at the sea level and at the Zeppelin station (475 m a.s.l.). First results using a scanning mobility particle sizer (SMPS) and a cloud condensation nuclei counter (CCNC) confirmed that aerosol concentrations in the range 10 < Dpart [nm] < 500 were approximatively 4-5 times higher during the months of Spring 2021 compared to those of Fall 2020. In addition, we found filterpack-derived values of the aerosol hygroscopic parameter κ around 0.7. Combined with temperature and pressure data, these results were used as input parameters for the Morales Betancourt and Nenes (2014) parameterization in order to investigate the susceptibility of droplet formation, which has recently been shown to be highly dependent on aerosol levels in European alpine valleys (Georgakaki et al., 2021). We found strong variations between the Fall to Winter months, known for pristine-like conditions, and the higher particle concentrations generally found in Spring, known as the arctic haze. Specifically, droplet formation was always limited by the low aerosol concentrations in Fall/Winter, whereas updraft-limited cloud formation occurred in Spring. Reviewing relevant literature tells that the relationship between the limiting droplet number concentration and the updraft velocity during NASCENT agrees with that of various locations worldwide, which tends to confirm the universality of this relationship. Georgakaki, P., Bougiatioti, A., Wieder, J., Mignani, C., Ramelli, F., Kanji, Z. A., Henneberger, J., Hervo, M., Berne, A., Lohmann, U., and Nenes, A.: On the drivers of droplet variability in alpine mixed-phase clouds, 21, 10993–11012, https://doi.org/10.5194/acp-21-10993-2021, 2021. McBean, G., Alekseev, G., Chen, D., Førland, E., Fyfe, Groisman, J., P. Y., King, R., Melling, H., Voseand, R., Whitfield, P. H.: Arctic climate: past and present. Arctic Climate Impacts Assessment (ACIA), C. Symon, L. Arris and B. Heal, Eds., Cambridge University Press, Cambridge, 21-60, 2005. Morales Betancourt, R. and Nenes, A.: Droplet activation parameterization: the population-splitting concept revisited, 7, 2345–2357, https://doi.org/10.5194/gmd-7-2345-2014, 2014.

2021

Chargement

Iodine Drives New Particle Formation in the Central Arctic Ocean

Andrea Baccarini, Julia Schmale

The Arctic is warming faster than Earth on average (Arctic amplification) and the extent of the sea ice coverage has decreased dramatically over the past decades, especially in summer. However, the underlying processes behind this amplification are not well understood because of many feedback mechanisms between the ocean, the atmosphere and the cryosphere. Clouds are an important player in the Arctic radiative budget, as they almost always have a net surface warming effect. However, models struggle to reproduce Arctic clouds partly because aerosol processes and aerosol sources in this area are poorly understood. This is particularly true in the central Arctic Ocean where aerosols can reach extremely low concentrations and clouds may even become limited by cloud condensation nuclei (CCN) availability. New particle formation (NPF) has been identified as a potential source of CCN in this region, and a modelling study showed that NPF is needed to explain the observed Aitken mode particle concentration. However, no conclusive results were reported concerning the nature of these NPF events and the chemical composition of the nucleating vapours. In this contribution we present the first comprehensive physicochemical characterization of several NPF events in the central Arctic Ocean during the Arctic Ocean 2018 expedition. We identified a marked increase of the iodic acid concentration towards the end of the summer, potentially associated with the onset of the freeze-up season and a concurrent increase of the ozone concentration. Moreover, our results indicate that iodic acid is a main driver for the formation of new particles and their early growth. The frequency of new particle formation events follows the same seasonal trend as the ultrafine particle concentration, which is one order of magnitude higher in fall compared to summer. In addition, we developed a simple parametrization that describes iodic acid variability, providing an estimate of the iodine precursor emission rates. Finally, we also provide direct evidences that Aitken mode particles activate as cloud condensation nuclei suggesting that iodine NPF can influence the formation of clouds and their properties in the central Arctic.

2020

Chargement

The fourth report of the Intergovernmental Panel of Climate Change (IPCC) unambiguously indicates that the climate is changing. Climate change is induced by changes in atmospheric abundances of greenhouse gases and aerosols, solar radiation and land surface properties, which all alter the radiative balance of the Earth. Among them, greenhouse gases and aerosols are likely the compounds affecting the climate the most. While greenhouse gases warm the Earth, aerosols influence its radiative balance by scattering and absorbing solar radiation (the direct effect), and by modifying cloud amount and properties (the indirect effect). The radiative forcing of aerosols on the climate is however the less understood among the various forcings currently considered in the IPCC assessment. This is likely related to the lack of comprehensive and accurate observations of aerosols (and in particular of their vertical distribution) which thus makes global aerosol models difficult to constrain. Recent model intercomparisons have indicated that different assumptions regarding aerosol emissions, formation and growing properties, and removal processes generate large diversities within models. These large diversities are found in particular in the Arctic and the upper troposphere region where extreme surrounding conditions take place, limiting instrument sensitivity and accuracy. The objectives of this thesis are to better quantify the processes driving the aerosol distribution in regions where the uncertainties are the largest, including the Arctic region and the upper troposphere, and to assess the quality of CALIOP observations. For this purpose, we used the fully coupled global climate-aerosol-chemistry ECHAM5-HAMMOZ model conjointly with a suite of remote sensing observations including the CALIOP satellite instrument, which provides the vertical distribution of aerosols. The model predicts the size distribution and composition of aerosols as well as the number concentration of cloud droplets and ice crystals. We first investigated the processes that drive the transport of soluble and insoluble compounds toward the Arctic in the ECHAM5-HAMMOZ model. Recognizing that scavenging processes may be an issue in global models, we "re-visited" their properties in ECHAM5-HAMMOZ. We find that the model better reproduces the aerosol vertical distribution in the northern mid- and high-latitudes, especially in the free troposphere, by decreasing aerosol scavenging coefficients in the model. Using smaller aerosol scavenging coefficients results in an increase of aerosol burden and lifetime, especially in the Arctic. In addition, the Arctic haze phenomenon is better represented in the simulation using decreased aerosol scavenging coefficients. The relative contributions of different processes governing the transport of aerosols from the midlatitudes toward the Arctic together with the relative contributions of different geopolitical source regions were then quantified. We find that Europe and Siberia contribute the most to the Arctic pollution even though Asian anthropogenic emissions are much larger. The model suggests that BC emitted in Siberia and Europe is ten times more efficiently deposited onto the Arctic than BC emitted in Asia. We next investigated an aerosol layer that forms in the vicinity of the tropical tropopause layer (TTL) over the southern Asian and Indian Ocean region. Aerosols in this layer are observed with the CALIOP instrument even though ice clouds partly mask their signal. The aerosol layer follows the Inter Tropical Convergence Zone (ITCZ), which indicates that these aerosols are likely transported during convective processes. The ECHAM5.5-HAM2 model reproduces such an aerosol layer in the TTL over the same region but clearly overestimates CALIOP data. Model results suggest that aerosols in this layer are mostly sulfate particles transported during convective processes and originating from natural sources. The shortwave forcing of this aerosol layer is estimated. Finally, we assessed the accuracy of aerosol extinction retrievals from the CALIOP satellite instrument by comparing them with remote sensing observations such as AERONET, MODIS and MISR over the last four years. Overall, standard CALIOP products underestimate by 50% observed aerosol extinctions. However, this comparison is substantially improved by screening CALIOP data. The comparison of the CALIOP screened product with the ECHAM5.5-HAM2 model shows large disparities in model results. The model reproduces quite well the observed interannual variability and vertical distribution of aerosols in Europe and North Africa while it underestimates them in America and Asia. This is likely due to an underestimate of dust and anthropogenic emissions in North America and Asia.

EPFL2012

Chargement

In-Situ Observations Of Aerosol Hygroscopicity And Cloud Droplet Formation In Ny-Ålesund, Svalbard, During Fall 2019 And Spring 2020

Paraskevi Georgakaki, Ghislain Gilles Jean-Michel Motos, Athanasios Nenes, Jörg Wieder

The Arctic region suffers an extreme vulnerability to climate change, with an increase in surface air temperatures that have reached twice the global rate during several decades (McBean et al., 2005). The role of clouds, and in particular low-levels clouds and fog, in this arctic amplification by regulating the energy transport from and to space has recently gained interest among the scientific community. The NASCENT 2019-2020 campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) based in Ny-Ålesund, Svalbard (79º North) aimed at studying the microphysical and chemical properties of low-level clouds using measurements both at the sea level and at the Zeppelin station (475 m a.s.l.). First results using a scanning mobility particle sizer (SMPS) and a cloud condensation nuclei counter (CCNC) confirmed that aerosol concentrations in the range 10 < Dpart [nm] < 500 were approximatively 4-5 times higher during the months of Spring 2021 compared to those of Fall 2020. In addition, we found filterpack-derived values of the aerosol hygroscopic parameter κ around 0.7. Combined with temperature and pressure data, these results were used as input parameters for the Morales Betancourt and Nenes (2014) parameterization in order to investigate the susceptibility of droplet formation, which has recently been shown to be highly dependent on aerosol levels in European alpine valleys (Georgakaki et al., 2021). We found strong variations between the Fall to Winter months, known for pristine-like conditions, and the higher particle concentrations generally found in Spring, known as the arctic haze. Specifically, droplet formation was always limited by the low aerosol concentrations in Fall/Winter, whereas updraft-limited cloud formation occurred in Spring. Reviewing relevant literature tells that the relationship between the limiting droplet number concentration and the updraft velocity during NASCENT agrees with that of various locations worldwide, which tends to confirm the universality of this relationship. Georgakaki, P., Bougiatioti, A., Wieder, J., Mignani, C., Ramelli, F., Kanji, Z. A., Henneberger, J., Hervo, M., Berne, A., Lohmann, U., and Nenes, A.: On the drivers of droplet variability in alpine mixed-phase clouds, 21, 10993–11012, https://doi.org/10.5194/acp-21-10993-2021, 2021. McBean, G., Alekseev, G., Chen, D., Førland, E., Fyfe, Groisman, J., P. Y., King, R., Melling, H., Voseand, R., Whitfield, P. H.: Arctic climate: past and present. Arctic Climate Impacts Assessment (ACIA), C. Symon, L. Arris and B. Heal, Eds., Cambridge University Press, Cambridge, 21-60, 2005. Morales Betancourt, R. and Nenes, A.: Droplet activation parameterization: the population-splitting concept revisited, 7, 2345–2357, https://doi.org/10.5194/gmd-7-2345-2014, 2014.

2021

Iodine Drives New Particle Formation in the Central Arctic Ocean

Andrea Baccarini, Julia Schmale

2020

EPFL2012