As a pristine region, the Antarctic peninsula can be a model for the preindustrial atmospheric environment and, accordingly, give insights in processes related to climate change. Most studies performed in this region focus on either aerosol sources, for example the ocean, or the chemical composition of aerosol particles. Wind and wave driven physical mechanisms for particle mobilization (e.g. bubble bursting) lead to the formation of sea-spray aerosol particles (SSA) consisting of sea salt together with primary organic aerosol (POA), which is rich in organic matter (OM). The molecular nature of this OM is not fully understood to this day. The second-largest fraction of OM are likely proteins, which consist of amino acids (AA). AA contribute massively to the global nitrogen cycle and have impact on cloud chemistry, for example by acting as cloud condensation nuclei (CCN) or ice nucleating particles (INP).

             To date, chemical analysis of AAs is often provided as sum parameter, as robust methods for their analysis in original form are lacking. Therefore, individual differences between sample sets cannot be determined and information on biotic or abiotic transfers are lacking. For that reason, we developed a hydrophilic interaction liquid chromatography electrospray ionization time-of-flight mass spectrometry (HILIC-ESI-TOF-MS) method, utilizing the potential of HILIC to separate more polar analytes, compared to standard LC methods. Advantages of the developed method are not only its broad window of analytes, but also its robustness as it can be applied to complex marine samples with a short sample preparation, as derivatization steps are not needed.

This new method was applied to Antarctic low volume size segregated aerosol samples. Due to the nature of HILIC, the polar analytes show a good retention and separation from matrix components. Through these measurements, further insights can be gained on the enrichment and chemo-selective transfer of AA from the ocean to the atmosphere and their respective degradation processes. A higher variation and concentration of FAA than in previous literature was observed, with dominating marine derived FAAs. First results, also regarding the influence of air masses to the composition of different AA and comparison with other constituents, will be shown.

Sources

Jaber et al. (2021) Biogeosciences, 18, 1067–1080.

Zeppenfeld et al. (2021), ACS Earth Space Chem. 5, 1032−1047

How to cite: Breitenstein, C., van Pinxteren, M., Zeppenfeld, S., and Herrmann, H.: Insight in Antarctic aerosol particle composition regarding free amino acids, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10160, https://doi.org/10.5194/egusphere-egu24-10160, 2024.

Aerosols play a crucial role in the radiative balance of the Arctic, a place that is warming at faster rates than anywhere else on Earth. As a function of their physicochemical state (size, abundance, chemical composition, degree of aging and mixing state), aerosols can directly interact with the incoming solar radiation by absorbing or scattering light, and/or serve as seeds for cloud formation, thus indirectly modulating the amount of shortwave and longwave radiation respectively reaching and escaping the Earth’s surface. In the central Arctic Ocean, observations of the aerosols’ physicochemical characteristics have mostly been limited to summertime. As a result, large knowledge gaps remain on the role of aerosols in the central Arctic radiative budget throughout the year, in particular during the dark autumn and winter months, with great implications for model performances. Here, we present the first annual central Arctic Ocean observations of the chemical composition of submicron aerosols, as measured by a high-resolution time-of-flight aerosol mass spectrometer (AMS) during the “Multidisciplinary drifting Observatory for the Study of Arctic Climate” (MOSAiC) expedition. Measurements from the Arctic Ocean 2018 expedition close the summer data gap when no chemical composition measurements were available during MOSAiC. Based on the size-resolving and high-time resolution capabilities of the AMS, we further investigate the sources, emission processes, and potential radiative impacts of aerosols during the aerosol-sensitive autumn season. We find that episodic events of blowing snow and long-range transport of pollutants from lower latitudes are key contributors to the submicron aerosol and cloud condensation nuclei number concentrations, where blowing snow represents the only source of Aitken mode aerosols.

Focusing on the spring and summer, we also present the results of a source apportionment study focused on the chemical and geographical sources of organic aerosols (OAs). Using a statistical method called positive matrix factorization, we find that anthropogenic OAs, of Eurasian origin, dominate the central Arctic Ocean OAs budget until at least the month of May. Warm air mass intrusions in mid-April are found to bring large amount of pollution to the central Arctic, with a chemical composition distinct from that of the background haze. Episodic bursts in naturally-sourced marine OAs, originating from the marginal ice-zone and open ocean regions, become increasingly important during summer.

Together, the results from these studies will serve to greatly improve our understanding of aerosol sources and related physicochemical properties in the central Arctic Ocean, as well as their role in the central Arctic radiative budget.

How to cite: Heutte, B., Dada, L., El Haddad, I., Pernov, J. B., Chen, G., Daellenbach, K. R., Moschos, V., Angot, H., Boyer, M., Bergner, N., Creamean, J. M., Pratt, K. A., Mirrieless, J. A., Kirpes, R., Ault, A. P., Shupe, M. D., Henning, S., Zieger, P., Jokinen, T., and Schmale, J. and the the EERL and INAR teams (continued): Sources and processes governing the annual cycle of aerosol chemical composition in the central Arctic Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8132, https://doi.org/10.5194/egusphere-egu24-8132, 2024.

The Alaskan Layered Pollution and Chemical Analysis (ALPACA) field campaign was conducted during the winter months of January and February 2022 to examine urban pollution sources and transformations in Fairbanks, Alaska. Several data collection sites were set up throughout the city to investigate the less-explored dynamic, physical, and chemical mechanisms governing air pollution events during the cold and dark winter.

The vertical dispersion of pollutants was investigated from an observation site in the suburban area just outside downtown Fairbanks. It featured ground-based measurements, a ten-meter mast for eddy covariance measurements, and a tethered balloon for vertical profiling of the atmosphere. Sampling included measurements of aerosol microphysical characteristics and trace gases (CO, CO₂, O₃, NO_x).  Meteorological parameters were also continuously measured at 2m and 10m from the mast, and also during the balloon flights. The tethered balloon was deployed to assess the vertical mixing of pollutants under stable atmospheric conditions from sources located at the surface but also at higher elevations, such as emissions from high power plant stacks.

A total of 148 individual profiles (up to a maximum altitude of 350 m above ground level) from 24 flights were collected between January 26 and February 25, 2022. The atmospheric conditions featured surface-based temperature inversions (SBI) in 86% of the cases due to the upwelling longwave radiation dominating the surface energy budget. Interestingly, eight flights captured elevated pollution plumes from power plants located downtown.   

The analysis of profiles reveals that the atmospheric stability and mixing of the surface layer was affected by two mechanisms. On one hand, radiative cooling promoted strong SBI locally, suppressing turbulence. On the other hand, a drainage flow at the surface from a nearby valley increased the shear stress at the surface, promoting mechanical turbulence near the surface. The measurements show how these two competing mechanisms affect the mixing of the surface layer.

The second part of the study focuses on the vertical dispersion of elevated plumes. The vertical mixing of pollutant plumes and their potential to contribute to surface pollution are investigated using the chemical and physical signature of the plumes and their vertical extents.

Together, the results of this study contribute to improving our understanding of pollution mixing under the very stable conditions typical of the Arctic winter and can help to design pollution mitigation strategies by identifying the conditions and mechanisms leading to high pollution events. 

How to cite: Pohorsky, R., Baccarini, A., Barret, B., Brett, N., Bekki, S., Dieudonné, E., Pappaccogli, G., Scoto, F., Donateo, A., Busetto, M., Decesari, S., Arnold, S., Fochesatto, J., Simpson, W., Law, K., and Schmale, J.: Analysis of the vertical dispersion of pollution layers in the urban Arctic during the ALPACA 2022 field campaign, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10025, https://doi.org/10.5194/egusphere-egu24-10025, 2024.

Cold-climate urban areas often face severe air pollution events in wintertime because of residential heating and vehicle emissions into shallow surface inversion layers. Many state-of-the-art regional chemistry-transport models cannot capture the small spatio-temporal scale of the transport and chemical processes occurring in these environments.

Here we introduce a new version of our one-dimensional atmospheric chemistry and transport model, PACT-1D that includes continuous exchange of atmospheric air with the interstitial air of a snow layer and a kinetic treatment of multi-phase chemical processes in air and snow. PACT-1D allows modeling and assessment of the interaction of transport, chemistry, and emissions on the time and length scales relevant to polluted wintertime environments.

We use the model to analyze observations made during the ALPACA campaign (Jan. and Feb. 2022 in Fairbanks, AK, USA). Many atmospheric and snow parameters were recorded, including measurements of the vertical distribution of trace species in the atmosphere and snow. The near surface transport is constrained by a passive tracer method, using reported sulfur dioxide emissions and respective profile measurements. We present preliminary model results and analyze sources of oxidants in the snow and the influence of the snow layer on the near-surface atmospheric compositions.

How to cite: Kuhn, J., Stutz, J., Cesler-Maloney, M., Simpson, W. R., Bartels-Rausch, T., Roberts, T. J., Thomas, J. L., Dibb, J., Heinlein, L., Sunday, M. O., Anastasio, C., Fahey, K., Flynn, J. H., and Guo, F.: A study of the near-surface vertical distribution and chemistry of pollutants in cold-climate urban areas with the novel PACT-1D model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13109, https://doi.org/10.5194/egusphere-egu24-13109, 2024.

As a high-latitude city, Fairbanks, Alaska, undergoes prolonged, cold winters with limited sunlight, and strong surface temperature inversions. These conditions coupled with its position at the bottom of the Tanana Valley lead to cold, dark, stagnant weather conditions, which when combined with demands for heating and transportation contribute to substantial degradations in air quality. These factors have led to Fairbanks exceeding the Environment Protection Agency PM2.5 standard and being classified as a serious nonattainment area for air quality. 

The ability to mitigate harmful pollution concentrations in Fairbanks is hampered by a lack of knowledge of the physicochemical processes which drive localised extreme pollution episodes during wintertime. For example, low levels of sunlight and ozone concentrations inhibit the well-established formation mechanisms of HO_x via photolysis or radical reactions. However, nitrous acid (HONO) can be a major source of OH radicals even in cold, dark, polluted environments. Despite being a major source of OH radicals, the formation of HONO is poorly represented in models. HONO is directly emitted from vehicles or formed via gas-phase reactions or via heterogeneous reactions such as those occurring from the surface of aerosols.

Using observations made during the Alaska Layered Pollution and Chemical Analysis Campaign (ALPACA), which took place in Fairbanks during January – February 2022, we conducted constrained chemical box model experiments to investigate HONO and oxidant sources during the ALPACA campaign. Our results show that gas-phase only reactions cannot account for observed HONO concentrations nor correctly reproduce diurnal trends. This suggests additional sources of HONO present in Fairbanks, potentially including formation from the surface of aerosols, which is not currently well constrained, especially at temperatures and relative humidities pertinent to wintertime Fairbanks.

Here, we present laboratory results aimed at addressing the lack of studies into HONO formation on the surface of aerosols in cold, dark environments and provide a wider atmospheric context via chemical box modelling constrained to observations from the ALPACA campaign. We purpose-built a chamber designed to reach temperatures similar to wintertime conditions in Fairbanks to study the formation of HONO from aerosol samples collected on filters during the ALPACA campaign, as well as filters collected from idealised single-source emission experiments in the laboratory. The generated HONO was detected in the gas-phase following its photolysis at 355 nm to OH and NO, with the OH detected via OH laser-induced fluorescence spectroscopy. We comprehensively studied HONO formation from aerosol filter samples as a function of aerosol surface area, NO₂ concentration, relative humidity, and temperature under actinic light levels applicable to wintertime conditions in Fairbanks. Inclusion of our experimental results into the chemical box model suggests enhancement of HONO concentrations over gas-phase only reactions alongside improved diurnal trends.

How to cite: James, R. L., Arnold, S. R., Heard, D. E., Stone, D., and Whalley, L. K. and the ALPACA Team: A laboratory and 0D box modelling study of the wintertime formation of HONO from aerosol surfaces in Fairbanks, Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17270, https://doi.org/10.5194/egusphere-egu24-17270, 2024.

Dry depositions contribute to regulate the lifetime of the aerosol in the atmosphere and at the same time they are responsible for the surface flux of nutrients, reactive compounds and pollutants. In polar areas, in particular, atmospheric depositions represent an important source of uncertainty in assessing the lifetime of particulate matter and short-living climate forcers (including black carbon, cloud condensation nuclei and ice nuclei). Dry depositions are deemed to affect snow composition (in terms of reactive compounds, light-absorbing species and persistent pollutants), although its relative importance with respect to wet depositions remains undetermined. There is a paucity of observational data of size-segregated particle fluxes in polar areas, which remains a challenge for the development of reliable parameterizations, given the peculiarities of the turbulence in the polar boundary layer as it is affected by the low solar angles, the presence of a snowpack, the strong surface radiative cooling.

The Alaskan Layered Pollution and Chemical Analysis (ALPACA) experiment is the first, comprehensive air quality study at a urban Arctic location. In the frame of ALPACA, atmospheric transport and vertical distribution of anthropogenic aerosols were investigated by a suite of experimental and modelling approaches. At the same time, the characteristic of the atmospheric boundary layer and surface fluxes of energy and particles have been investigated, while the composition of surface snow was determined on a daily basis. ALPACA was conducted in Fairbanks (AK, US) in Jan – Feb 2022 and comprehensive boundary layer observations were carried out at the sub-urban “Farm” location, over a large, flat terrain with little local pollution sources. In the dark Arctic winter, minimum temperatures dropped as low as -35 °C during the first part of the campaign. As a result of the surface cooling, the temperature gradient reached 10 °C in the first 10 meters above the ground. However, surface-based inversions were systematically perturbed by changes in the surface radiative budget caused by the intermittent presence of clouds and by surface winds promoted the thermal gradients between the Fairbanks plain and the surrounding elevated terrains. Whenever the surface inversions shrank and sufficient amount of aerosol was present in the lower levels, a clear surface particle surface flux was observed by means of an eddy-covariance technique. Such fluxes were intensified during the first part of the campaign when anthropogenic pollution developed in the lower atmospheric layers. In the same period, inorganic and organic compounds in surface snow progressively accumulated in absence of precipitations. The assessment of size-segregated particle fluxes and the analysis of particulate matter composition enabled to quantitatively assess atmospheric dry depositions. Their contribution to the evolution of snow chemistry was species-dependent, but in general dry depositions were found to be a significant sources of pollutants in snow during ALPACA. The effect of meteorology, vertical aerosol distribution and aerosol mixing state on the fluxes on the snowpack are discussed.

How to cite: Decesari, S., Pappaccogli, G., Scoto, F., Busetto, M., Zangrando, R., Gambaro, A., Spolaor, A., Pohorsky, R., Schmale, J., Fochesatto, J., and Donateo, A.: Assessment of aerosol dry depositions and their impact on snow composition at an Arctic urban site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18934, https://doi.org/10.5194/egusphere-egu24-18934, 2024.

The atmosphere is an important reservoir for the essential elements selenium (Se) and sulfur (S) as well as for the toxic element arsenic (As). Atmospheric deposition is a source of these elements to terrestrial and marine environments, which can affect ecosystems and human health. The mobility and bioavailability of Se, S, and As in surface environments depend on their chemical forms (speciation). The factors that determine elemental speciation in atmospheric deposition are likely controlled by the speciation of these elements at the source (atmospheric emissions) and by their (bio)chemical transformations during transport. In addition, atmospheric transport of trace elements and their deposition patterns might be strongly linked to the atmospheric water cycle in particular cloud and precipitation formation, because wet deposition during precipitation is an important removal mechanism of trace elements from the atmosphere. To investigate the dynamical processes that govern the cycles of atmospheric water and trace elements in polar regions, including their sources, transport pathways, and sinks, we performed various chemical measurements (total element concentrations and speciation of Se, S and As) on atmospheric samples collected during the Arctic Century Expedition in the Kara and Laptev Seas (August-September 2021). Notably, trace element analyses were combined with a 4-week continuous time series of ship-based measurements of the isotopic composition of water vapour (i.e., δ²H and δ¹⁸O). Air parcel backward trajectories were used to identify atmospheric transport patterns of elemental and water isotope signatures, based on three-dimensional wind fields from the ERA5 atmospheric reanalysis dataset. Based on our chemical and meteorological observations and transport diagnostics, we present new insights into the variability of Se, S, and As concentration and speciation in atmospheric deposition and how they are linked to the atmospheric polar water cycle.

How to cite: Breuninger, E. S., Thurnherr, I., Tolu, J., Aemisegger, F., Wernli, H., and Winkel, L. H. E.: Exploring links between the atmospheric water and trace element cycles in the Kara and Laptev Seas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10928, https://doi.org/10.5194/egusphere-egu24-10928, 2024.

Mixed-phase stratocumulus clouds in the polar region affect high-latitude climate in many ways, not least by regulating the boundary layer moisture and energy budgets. Sea ice coverage and thickness are decreasing sharply under global warming, changing the characteristics of the surface underlying much of the polar boundary layer, and the circulation patterns that govern lower tropospheric temperature and humidity inversions may change as well. Given the strength of ocean-ice-atmosphere interactions in the polar boundary layer, it is imperative to understand how different surface and atmospheric inversion conditions affect cloud formation and characteristics from both microphysical and macrophysical perspectives. Stable water isotopes have excellent potential as a tool to study the water cycle in the polar boundary layer, but their applications to understanding mixed-phase clouds in the polar region are limited by the lack of both direct observations and isotope-enabled models at appropriate spatial and temporal scales. Recent observational campaigns such as MOSAiC have observed isotopic composition at and near the Arctic surface under a range of different conditions, creating opportunities to expand the use of isotopes in Arctic water cycle research. Previous research has also established the ability of large-eddy simulations (LESs) to explicitly resolve boundary layer processes in the Arctic region and simulate the sensitivity of Arctic clouds to different atmospheric and surface conditions. To better exploit the potential of recent isotopic observations, we have developed an isotope-enabled large eddy model based on the PyCLES (Python Cloud Large Eddy Simulation) model framework to close some of the gaps between observations and modeling in the study of polar boundary layer clouds. iPyCLES is equipped with a two-moment microphysics scheme and includes representations of all essential isotopic fractionation processes at the surface and within clouds. In this presentation, we briefly introduce a series of sensitivity experiments targeting different surface and tropospheric inversion conditions to evaluate the isotopic signatures of surface-ice-atmosphere interactions within the polar boundary layer. The simulations are based on two well-studied field campaigns conducted near Barrow, Alaska, one in spring and one in autumn. Together with standard metrics of cloud evolution and turbulence mixing, isotope ratios in water vapor, cloud liquid and ice, and snow are tracked during the simulation. Isotopic signatures of each experiment are evaluated for their potential to provide observable constraints on polar clouds and boundary layer processes.

How to cite: Hu, Z. and Wright, J.: Large-Eddy Simulations of the Isotopic Signatures of Arctic Mixed-Phase Stratocumulus Clouds Under Different Surface and Atmospheric Conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7284, https://doi.org/10.5194/egusphere-egu24-7284, 2024.

Direct measurements using eddy covariance methodology of turbulent heat and momentum fluxes were observed from the Met City tower during MOSAiC. In models, these fluxes are parameterized using bulk aerodynamic algorithms for which the transfer coefficients must be found. In practice, the coefficients are constrained iteratively to resolve the co-dependence between Obukhov Length (necessary for calculating the coefficients) and the friction velocity, u* (an expression of the Reynold’s stress solved for by the algorithm). The aerodynamic roughness length, z0, is also needed to calculate the coefficients. For calculations over the global ocean, z0 is coupled to the atmosphere through u*. However, over sea ice the meteorological correlation is weak and the physical surface roughness is heterogeneous and decoupled from the atmosphere. This introduces a vulnerability into the calculation and necessitates assumptions about z0. At MOSAiC, the tower measurements of z0 show an evolution from early- to late-winter of nearly 2 orders of magnitude where 1 order nominally corresponds to a 30-40% differences in the derived fluxes. In this presentation we evaluate the error in bulk calculations due to the z0 assumption to assess what could be gained from a surface aware scheme.

How to cite: Cox, C., Gallagher, M., Persson, O., Fairall, C., Shupe, M., Bariteau, L., Thompson, E., and Blomquist, B.: Evaluation of errors in bulk aerodynamic parameterizations over snow-covered sea ice due to approximations of roughness length, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6685, https://doi.org/10.5194/egusphere-egu24-6685, 2024.