Search Results (14)

This study presents a comprehensive assessment of longwave radiation variability in the Arctic based on unique measurements collected at the North Pole drifting station SP-28 in 1987. The primary objective is to compare these historical observations with modern datasets from the Surface Heat Budget of the Arctic Ocean (SHEBA, 1997–1998) and the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC, 2019–2020) to evaluate long-term changes in the Arctic radiation regime. Continuous longwave radiation measurements were obtained using high-precision spectral pyrgeometers to identify Arctic haze. The results show that in 1987, Arctic haze layers enhanced the downward longwave flux by 15–20 W·m⁻² and increased atmospheric emissivity. In contrast, MOSAiC observations reveal emissivity values that closely match aerosol-free model calculations, indicating a substantial decline in Arctic haze and the diminishment of radiatively significant aerosol layers. This shift is in alignment with the long-term reduction of global anthropogenic sulfur dioxide emissions across the Northern Hemisphere. Full article

In this work, we revise the retrieval of extinction coefficient profiles from Raman Lidar. This is an ill-posed problem, and we show that methods like Levenberg–Marquardt or Tikhonov–Phillips can be applied. We test these methods for a synthetic Lidar profile (known solution) with different noise realizations. Further, we apply these methods to three different cases of data from the Arctic: under daylight (Arctic Haze), under daylight with a high and vertically extended aerosol layer, and at nighttime with high extinction. We show that our methods work and allow a trustful derivation of extinction up to clearly higher altitudes (at about half a signal-to-noise ratio) compared with the traditional, non-regularized Ansmann solution. However, these new methods are not trivial and require a choice of parameters, which depend on the noise of the data. As the Lidar signal quality quickly decreases with range, a separation of the profile into several sub-intervals seems beneficial. Full article

The climate impact of Arctic aerosols, like the Arctic Haze, and their origin are not fully understood. Therefore, long-term aerosol observations in the Arctic are performed. In this study, we present a homogenised data set from a sun and star photometer operated in the European Arctic, in Ny-Ålesund, Svalbard, of the 20 years from 2004–2023. Due to polar day and polar night, it is crucial to use observations of both instruments. Their data is evaluated in the same way and follows the cloud-screening procedure of AERONET. Additionally, an improved method for the calibration of the star photometer is presented. We found out, that autumn and winter are generally more polluted and have larger particles than summer. While the monthly median Aerosol Optical Depth (AOD) decreases in spring, the AOD increases significantly in autumn. A clear signal of large particles during the Arctic Haze can not be distinguished from large aerosols in winter. With autocorrelation analysis, we found that AOD events usually occur with a duration of several hours. We also compared AOD events with large-scale processes, like large-scale oscillation patterns, sea ice, weather conditions, or wildfires in the Northern Hemisphere but did not find one single cause that clearly determines the Arctic AOD. Therefore the observed optical depth is a superposition of different aerosol sources. Full article

This study presents the hygroscopic properties of aerosols from the Arctic free troposphere by means of contemporary lidar and radiosonde observations only. It investigates the period from the Arctic Haze in spring towards the summer season in 2021. Therefore, a one-parameter growth curve model is applied to lidar data from the Koldewey Aerosol Raman Lidar (AWIPEV in Ny-Ålesund, Svalbard) and simultaneous radiosonde measurements. Hygroscopic growth depends on different factors like aerosol diameter and chemical composition. To detangle this dependency, three trends in hygroscopicity are additionally investigated by classifying the aerosol first by its dry color ratio, and then by its season and altitude. Generally, we found a complex altitude dependence with the least hygroscopic particles in the middle of the troposphere. The most hygroscopic aerosol is located in the upper free troposphere. A hypothesis based on prior lifting of the particles is given. The expected trend with aerosol diameter is not observed, which draws attention to the complex dependence of hygroscopic growth on geographical region and altitude, and to the development of backscatter with the aerosol size itself. In a seasonal overview, two different modes of stronger or weaker hygroscopic particles are additionally observed. Furthermore, two special days are discussed using the Mie theory. They show, on the one hand, the complexity of analyzing hygroscopic growth by means of lidar data, but on the other hand, they demonstrate that it is in fact measurable with this approach. For these two case studies, we calculated that the aerosol effective radius increased from $0.16\mathsf{\mu }\mathrm{m}$ (dry) to $0.18\mathsf{\mu }\mathrm{m}$ (wet) and from $0.28\mathsf{\mu }\mathrm{m}$ to $0.32\mathsf{\mu }\mathrm{m}$ for the second case. Full article

An Nd:YAG-based Raman lidar provides a mature technology to derive profiles of the optical properties of aerosols over a wide altitude range. However, the derivation of micro-physical parameters is an ill-posed problem. Hence, increasing the information content of lidar data is desirable. Recently, ceilometers and wind lidar systems, both operating in the near-infrared region, have been successfully employed in aerosol research. In this study, we demonstrate that the inclusion of additional backscatter coefficients from these two latter instruments clearly improves the inversion of micro-physical parameters such as volume distribution function, effective radius, or single-scattering albedo. We focus on the Arctic aerosol and start with the typical volume distribution functions of Arctic haze and boreal biomass burning. We forward calculate the optical coefficients that the lidar systems should have seen and include or exclude the backscatter coefficients of the ceilometer (910 nm) and wind lidar data (1500 nm) to analyze the value of these wavelengths in their ability to reproduce the volume distribution function, which may be mono- or bimodal. We found that not only the coarse mode but also the properties of the accumulation mode improved when the additional wavelengths were considered. Generally, the 1500 nm wavelength has greater value in correctly reproducing the aerosol properties. Full article

Polar-orbiting satellite observations are of fundamental importance to explore the main scientific challenges in the Arctic Ocean, as they provide information on bio-geo-physical variables with a denser spatial and temporal coverage than in-situ instruments in such a harsh and inaccessible environment. However, they are limited by the lack of coverage near the North Pole (Polar gap), the polar night, and frequent cloud cover or haze over the ocean and sea ice, which prevent the use of optical satellite instruments, as well as by the limited availability of external validation data. The satellite sensors’ coverage and repeat cycles may also have limitations in properly identifying and resolving the dominant spatial and temporal scales of atmospheric, ocean, cryosphere and land variability and their interactive processes and feedback mechanisms. In this paper, we provide a state of the art of contribution of satellite observations to the understanding of the polar environment and climate scientific challenges tackled within the Arktalas Hoavva project funded by the European Space Agency. We identify the current limitations to the wider use of polar orbiting remote sensing data, as well as the observational gaps of the existing satellite missions. A comprehensive overview of all satellite missions and applications is given provided with a primary focus on the European satellites. Finally, we assess the expected capability of the approved future satellite missions to answer today’s scientific challenges in the Arctic Ocean. Full article

Aerosol vertical distributions impact both the direct and indirect radiative effects of aerosols. High Spectra Resolution Lidar (HSRL) separates between atmospheric molecular signals and aerosol particle signals and therefore can provide reliable measurements of aerosol properties. Six years of HSRL measurements between 2014 and 2019 from the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA) atmospheric observatory at Utqiaġvik are used to statistically analyze Arctic aerosol vertical distributions. The annual cycle of aerosol vertical distributions in terms of aerosol particulate backscatter coefficient (${\beta }_p$), lidar scattering ratio (SR), and aerosol particulate depolarization ratio (${\delta }_p$) profiles at the wavelength of 532 nm shows that Arctic Haze events are prevalent in later winter and spring at the NSA site. Mineral dust is frequently presented in strong aerosol layers in the spring, fall, and winter seasons. Over the summer season, the NSA site has large aerosol loadings that are dominated by small spherical aerosol particles. Full article

In this work, we present Raman lidar data (from a Nd:YAG operating at $355$ nm, $532$ nm and $1064$ nm) from the international research village Ny-Ålesund for the time period of January to April 2020 during the Arctic haze season of the MOSAiC winter. We present values of the aerosol backscatter, the lidar ratio and the backscatter Ångström exponent, though the latter depends on wavelength. The aerosol polarization was generally below 2%, indicating mostly spherical particles. We observed that events with high backscatter and high lidar ratio did not coincide. In fact, the highest lidar ratios (LR > 75 sr at $532$ nm) were already found by January and may have been caused by hygroscopic growth, rather than by advection of more continental aerosol. Further, we performed an inversion of the lidar data to retrieve a refractive index and a size distribution of the aerosol. Our results suggest that in the free troposphere (above ≈2500 m) the aerosol size distribution is quite constant in time, with dominance of small particles with a modal radius well below $100$ nm. On the contrary, below ≈2000 m in altitude, we frequently found gradients in aerosol backscatter and even size distribution, sometimes in accordance with gradients of wind speed, humidity or elevated temperature inversions, as if the aerosol was strongly modified by vertical displacement in what we call the “mechanical boundary layer”. Finally, we present an indication that additional meteorological soundings during MOSAiC campaign did not necessarily improve the fidelity of air backtrajectories. Full article

Haze pollution in central North China has become a hot topic in recent decades due to its serious environmental and health effects. In this work, the interannual relationship between haze days in December–January (DJ_HD) and leaf area index in August–September (AS_LAI) over central North China, along with the possible physical mechanisms involved, are investigated. The relationship varies in different periods, being significant during 1982–2000 (P1) but insignificant during 2001–2014 (P2). During P1, there is an in-phase relationship between AS_LAI and surface evaporation, and an out-of-phase relationship between AS_LAI and surface albedo in August–September. The surface evaporation and albedo anomalies persist to October–November and are associated with lower top-layer volumetric soil water, upward sensible heat flux and downward latent heat flux anomalies in October–November, which act as the bridge in the relationship between AS_LAI and DJ_HD. Both the volumetric soil water and heat fluxes anomalies persist to December–January and correspond to atmospheric circulations similar to the weakened East Asian winter monsoon pattern, which is the dominant system for winter haze events. Thus, the ventilation conditions in December–January are favorable for the accumulation of haze particles. However, during P2, the relationships are not significant between AS_LAI and volumetric soil water or surface soil temperature during October–January. Meanwhile, the East Asian winter monsoon is likely strengthened and tends to be more significantly affected by factors including Arctic sea ice, Arctic Oscillation, etc. Therefore, the effects of AS_LAI on the monsoon may become insignificant and, in turn, the relationship between AS_LAI and DJ_HD becomes insignificant during P2. Full article

In this study, the information potential of a two-step sequential extraction procedure was evaluated. For this purpose, first of all the elemental composition of Arctic PM₁₀ samples collected in Ny-Ålesund (Svalbard Islands) from 28 February 2015 to 21 October 2015 was investigated. Enrichment Factors, Principal Component Analysis and Hierarchical Cluster Analysis were performed to identify PM₁₀ sources and to understand the effects of short- and long-range transport processes. The investigation of the potential source areas was also aided by taking into account back-trajectories. Then, the sequential extraction procedure was applied to some of the samples in order to obtain more information on these sources. This approach allowed us to establish that most of the elements prevalently having an anthropogenic origin not only were present in higher concentrations, but they were also more easily extractable in late winter and early spring. This confirms the common statement that the anthropogenic portion of the elements present in a sample is generally loosely bound to the particulate matter structure, and so it is more easily extractable and releasable on the Arctic snowpack. Moreover, in the samples collected in late winter and early spring, even the elements prevalently having a crustal origin were more easily extractable, probably due to the particle size selection occurred during the long-range transport. Full article

While more and more studies are being conducted on carbonaceous fractions—organic carbon (OC) and elemental carbon (EC)—in urban areas, there are still too few studies about these species and their effects in polar areas due to their very low concentrations; further, studies in the literature report only data from intensive campaigns, limited in time. We present here for the first time EC–OC concentration long-time data records from the sea-level sampling site of Ny-Ålesund, in the High Arctic (5 years), and from Dome C, in the East Antarctic Plateau (1 year). Regarding the Arctic, the median (and the interquartile range (IQR)) mass concentrations for the years 2011–2015 are 352 (IQR: 283–475) ng/m³ for OC and 4.8 (IQR: 4.6–17.4) ng/m³ for EC, which is responsible for only 3% of total carbon (TC). From both the concentration data sets and the variation of the average monthly concentrations, the influence of the Arctic haze on EC and OC concentrations is evident. Summer may be interested by high concentration episodes mainly due to long-range transport (e.g., from wide wildfires in the Northern Hemisphere, as happened in 2015). The average ratio of EC/OC for the summer period is 0.05, ranging from 0.02 to 0.10, and indicates a clean environment with prevailing biogenic (or biomass burning) sources, as well as aged, highly oxidized aerosol from long-range transport. Contribution from ship emission is not evident, but this result may be due to the sampling time resolution. In Antarctica, a 1 year-around data set from December 2016 to February 2018 is shown, which does not present a clear seasonal trend. The OC median (and IQR) value is 78 (64–106) ng/m³; for EC, it is 0.9 (0.6–2.4) ng/m³, weighing for 3% on TC values. The EC/OC ratio mean value is 0.20, with a range of 0.06–0.35. Due to the low EC and OC concentrations in polar areas, correction for the blank is far more important than in campaigns carried out in other regions, largely affecting uncertainties in measured concentrations. Through the years, we have thus developed a new sampling strategy that is presented here for the first time: samplers were modified in order to collect a larger amount of particulates on a small surface, enhancing the capability of the analytical method since the thermo-optical analyzer is sensitive to carbonaceous aerosol areal density. Further, we have recently coupled such modified samplers with a sampling strategy that makes a more reliable blank correction of every single sample possible. Full article

In this work, we analysed aerosol measurements from lidar and PM${}_{10}$ samples around the European Arctic site of Ny-Ålesund during late winter–early spring 2019. Lidar observations above 700 m revealed time-independent values for the aerosol backscatter coefficient (β$\mathsf{\beta }$), colour ratio (CR), linear particle depolarisation ratio (δ$\mathsf{\delta }$) and lidar ratio (LR) from January to April. In contrast to previous years, in 2019 the early springtime backscatter increase in the troposphere, linked to Arctic haze, was not observed. In situ nss-sulphate (nss-SO${}_4^{2-}$) concentration was measured both at a coastal (Gruvebadet) and a mountain (Zeppelin) station, a few kilometres apart. As we employed different measurement techniques at sites embedded in complex orography, we investigated their agreement. From the lidar perspective, the aerosol load (indicated by β$\mathsf{\beta }$) above 700 m changed by less than a factor of 3.5. On the contrary, the daily nss-SO${}_4^{2-}$ concentration erratically changed by a factor of 25 (from 0.1 to 2.5 ng m${}^{-3}$) both at Gruvebadet and Zeppelin station, with the latter mostly lying above the boundary layer. Moreover, daily nss-SO${}_4^{2-}$ concentration was remarkably variable (correlation about 0.7 between the sites), despite its long-range origin. However, on a seasonal average basis the in situ sites agreed very well. Therefore, it can be argued that nss-SO${}_4^{2-}$ advection mainly takes place in the lowest free troposphere, while under complex orography it is mixed downwards by local boundary layer processes. Our study suggests that at Arctic sites with complex orography ground-based aerosol properties show higher temporal variability compared to the free troposphere. This implies that the comparison between remote sensing and in situ observations might be more reasonable on longer time scales, i.e., monthly and seasonal basis even for nearby sites. Full article

On the basis of sun photometer measurements located at the German-French polar research base AWIPEV in Ny-Ålesund ( ${78.923}^{°}$ N, ${11.928}^{°}$ E), Svalbard, long-term changes (2001–2017) of aerosol properties in the European Arctic are analyzed with the main focus on physical aerosol properties like Aerosol Optical Depth (AOD) and the Ångström exponent during the Arctic haze season in spring compared with summer and autumn months. In order to gain more information from the photometer data and to reduce the error of fitting the data to the Ångström law, a new approach with an Ångström exponent, which depends linearly on wavelength, is presented in this paper. With the Mie program of libRadtran, a calculator for long- and short-wave radiation through the Earth’s atmosphere, artificial aerosol size distributions were created to extend the physical understanding of this modified Ångström law. Monthly means of the measured AOD of the years 1994–2017 are presented to analyze long-term changes of aerosol properties and its load. Because photometer data in general have no height information, a comparison with a Lidar located at the same site is presented. The so-obtained data are then compared with the previous Mie calculus. More homogeneous aerosol properties were found during spring and more heterogeneous in summer. To study possible aerosol sources and sinks, five-day back-trajectories were calculated with the FLEXPART model at three different arriving heights at 11 UTC in the village Ny-Ålesund. Besides the pollution pathway of the aerosol into the European Arctic based on the calculated back-trajectories, the influence of the boundary layer parameterized by the lowermost 100 hPa atmospheric layer is analyzed and compared to the measured aerosol load by the photometer in Ny-Ålesund additionally. During spring, the open ocean acts as a sink for aerosols, whereas sea ice clearly reduces their sinks. Hence, trajectories over sea ice are correlated to higher aerosol loads. Thus, both sources and sinks must be considered to understand aerosol occurrences in the Arctic. Full article

Aerosol properties over the Arctic snow-covered regions are sparsely provided by temporal and spatially limited in situ measurements or active Lidar observations. This introduces large uncertainties for the understanding of aerosol effects on Arctic climate change. In this paper, aerosol optical depth (AOD) is derived using the advanced along-track scanning radiometer (AATSR) instrument. The basic idea is to utilize the dual-viewing observation capability of AATSR to reduce the impacts of AOD uncertainties introduced by the absolute wavelength-dependent error on surface reflectance estimation. AOD is derived assuming that the satellite observed surface reflectance ratio can be well characterized by a snow bidirectional reflectance distribution function (BRDF) model with a certain correction direct from satellite top of the atmosphere (TOA) observation. The aerosol types include an Arctic haze aerosol obtained from campaign measurement and Arctic background aerosol (maritime aerosol) types. The proper aerosol type is selected during the iteration step based on the minimization residual. The algorithm has been used over Spitsbergen for the spring period (April–May) and the AOD spatial distribution indicates that the retrieval AOD can capture the Arctic haze event. The comparison with AERONET observations shows promising results, with a correlation coefficient R = 0.70. The time series analysis shows no systematical biases between AATSR retrieved AOD and AERONET observed ones. Full article