Radiative impact of an extreme Arctic biomass-burning event

The aim of the presented study was to investigate the impact on the radiation budget of a biomass-burning plume, transported from Alaska to the High Arctic region of Ny-Ålesund, Svalbard, in early July 2015. Since the mean aerosol optical depth increased by the factor of 10 above the average summer background values, this large aerosol load event is considered particularly exceptional in the last 25 years. In situ data with hygroscopic growth equations, as well as remote sensing measurements as inputs to radiative transfer models, were used, in order to estimate biases associated with (i) hygroscopicity, (ii) variability of single-scattering albedo profiles, and (iii) plane-parallel closure of the modelled atmosphere. A chemical weather model with satellite-derived biomass-burning emissions was applied to interpret the transport and transformation pathways. The provided MODTRAN radiative transfer model (RTM) simulations for the smoke event (14:00 9 July–11:30 11 July) resulted in a mean aerosol direct radiative forcing at the levels of −78.9 and −47.0 W m ^-2 at the surface and at the top of the atmosphere, respectively, for the mean value of aerosol optical depth equal to 0.64 at 550 nm. This corresponded to the average clear-sky direct radiative forcing of −43.3 W/m ^2, estimated by radiometer and model simulations at the surface. Ultimately, uncertainty associated with the plane-parallel atmosphere approximation altered results by about 2 W m^−2. Furthermore, model-derived aerosol direct radiative forcing efficiency reached on average −126 W m^−2/τ550 and −71 W^m−2/τ550 at the surface and at the top of the atmosphere, respectively. The heating rate, estimated at up to 1.8 K day^−1 inside the biomass-burning plume, implied vertical mixing with turbulent kinetic energy of 0.3 m^2s^−

Własności optyczne i radiacyjne aerozolu absorbującego w europejskiej części Arktyki

Aerosols play a major role in the Earth's climate system by influencing light propagation in the atmosphere. Unlike well-mixed greenhouse gases, that induce warming of the Earth's climate system, aerosols indicate its cooling in the first approximation. In turn, particle mixture containing absorbing aerosols may induce radiative warming when they exist over bright surfaces. Complicated mechanisms underlying aerosol interactions with components of the Earth's climate system lead to the propagation of high uncertainties in estimating radiative forcing. Studying underlying systematic error levels in radiative forcing is crucial in environments sensitive to climate change (e.g. in the polar regions). Therefore aerosols are a subject to many studies in the field of atmospheric research. This doctoral dissertation aims to characterise aerosol optical, micro-physical and radiative properties governing the European Arctic region in spring focusing mainly on their long-term variability (in a temporal and vertical sense) and statistical relationships. Research conducted here was based on data from 4 field experiments carried out in the European Arctic, namely Ny-Alesund (78.9°N, 11.9°E), Svalbard in spring 2014 - 2017. Field campaigns provided a unique set of ground-based data as well as profiles of aerosol optical and microphysical properties. Analyses were complemented by similar in-situ surface measurements obtained from monitoring stations in the High Arctic as well as data-sets provided from the reanalysis of global transport models. Further to this, a theoretical study concerning the impact of aerosol optical and microphysical properties on local radiative balance is being investigated using radiative transfer simulations. Analyses performed in this dissertation revealed weak vertical variability in aerosol optical and microphysical properties (absorption coefficient and total particle number concentration) within the Arctic boundary layer and above it. This likely indicates a lack of strong local aerosol sources and relates to the fact that most aerosol in the Arctic is long-range transported, preferentially in the free troposphere, from mid-latitudes. In the last decade, main trajectories of air advection into the Arctic as well as the efficiency of far aerosol sources seem to undergo noticeable changes, likely as a result of modifications in atmospheric circulation patterns, economical transformations as well as climate change. Presented conclusions are in line with performed analysis on temporal variability in aerosol extensive properties, that have shown a statistically-significant negative trend in aerosol optical depth in spring, i.e. -0.02 ± 0.01 10/yr and a positive one in summer of 0.02 ± 0.01 10/yr. Research concerning theoretical studies on the impact of aerosol on radiative transfer in the Arctic atmospheric column has indicated that aerosol mixture present during iAREA campaigns on average had a cooling effect on the local radiative balance of the atmosphere. Radiative forcing calculated at the top of the atmosphere was negative, reaching -1.5 ± 1.3 W/m2 over surfaces covered with snow, whereas its value over the ocean surface was as high as -8.9 ± 4.8 W/m2. Aerosol having primarily cooling radiative effect even over bright surfaces relates to the high efficiency of ageing processes, active during particle long-range transport, which causes a significant decline in aerosol light-absorption ability.Aerozole pełnią ważną funkcję w systemie klimatycznym wpływając na modyfikacje strumieni promieniowania elektromagnetycznego w atmosferze. W przeciwieństwie do gazów cieplarnianych, odpowiedzialnych za ogrzewanie układu klimatycznego Ziemi, aerozole w pierwszym przybliżeniu przyczyniają się do jego ochładzania. Mieszanina aerozolu wzbogacona o cząstki absorbujące fotony, może jednak przyczynić się do ogrzewania systemu klimatycznego Ziemi w szczególności, gdy znajduje się ponad powierzchnią o wysokim albedo. Skomplikowane mechanizmy oddziaływań bezpośrednich i pośrednich aerozolu z komponentami systemu klimatycznego Ziemi wpływa na wysoki stopień niepewności w oszacowaniu wymuszenia radiacyjnego. Błędy te mają szczególne znaczenie w środowiskach wrażliwych na zmiany klimatu, n.p. w obszarach polarnych. Badanie własności aerozolu w Arktyce stanowi ważną i często poruszaną problematykę w dziedzinie nauk o środowisku. Niniejsza praca doktorska wpisuje się w główny nurt badań nad zmianami klimatu obszarów polarnych. Celem dysertacji były rozważania nad własnościami optycznymi, mikro-fizycznymi oraz radiacyjnymi aerozolu obserwowanego wiosną w Europejskiej części Arktyki. W szczególności, zwrócono uwagę na długookresowe zmiany (czasowe i pionowe) powyższych zmiennych oraz związki statystyczne pomiędzy własnościami aerozolu. Wyniki badań zawarte w dysertacji uzyskano na podstawie 4 wiosennych eksperymentów naukowych zorganizowanych w latach 2014 - 2017 w europejskiej części Arktyki, tj. Ny-Alesundzie (78.9°N, 11.9°E) na Svalbardzie. Kampanie pomiarowe dostarczyły unikalnego zestawu danych o zmienności pionowej oraz czasowej własności optycznych i mikro-fizycznych aerozolu atmosferycznego. Analizę danych wzbogacono o podobne dane pozyskane ze stacji monitoringu jakości powietrza oraz informacje pochodzącę z reanaliz globalnych modeli transportu zanieczyszczeń. Na podstawie modelu transferu radiacyjnego przeprowadzono teoretyczne badania nad wpływem własności fizycznych mieszaniny aerozolu na lokalny bilans radiacyjny. Wyniki analiz wykazały słabą zmienność pionową parametrów optycznych (współczynnika absorpcji oraz całkowitej koncentracji aerozolu) w warstwie granicznej atmosfery oraz powyżej niej. Wskazuje to na brak lokalnych źródeł emisji cząstek co związane jest z faktem, że główna kontrybucja aerozolu w Arktyce pochodzi z transportu dalekozasięgowego z niższych szerokości geograficznych. Transport ten odbywa się głównie w wolnej troposferze. Wydajność źródeł aerozolu oraz główne korytarze transportu wydają się podlegać w ostatnich 10 latach zmianom, które związane są prawdopodobnie z modyfikacjami cyrkulacji atmosferycznej, przeobrażeniami ekonomicznymi oraz zmianami klimatu. Wnioski te wynikają z przeprowadzonej analizy czasowej zmienności optycznych parametrów ekstensywnych aerozolu (istotny statystycznie ujemny trend aerozolowej grubości optycznej wiosną t.j., -0.02 ± 0.01 na dekadę i dodatni latem t.j. 0.02 ± 0.01 na dekadę). Przeprowadzone rozważania teoretyczne nad wpływem aerozolu na transfer promieniowania w Arktyce wykazały, że obserwowana podczas kampanii iAREA mieszanina cząstek ma negatywny efekt na lokalną równowagę bilansu radiacyjnego atmosfery. Wymuszanie radiacyjne na górnej granicy atmosfery nad obszarami pokrytymi śniegiem jest równe -1.5 ± 1.3 W/m2 natomiast nad powierzchnią oceanu wolną od lodu wynosi aż -8.9 ± 4.8 W/m2. Ujemne wartości wymuszeń radiacyjnych wynikają z faktu, że transportowany aerozol nad obszary polarne podlega procesom starzenia, w efekcie powodując znaczące zmniejszenie zdolności mieszaniny do absorpcji promieniowania słonecznego

Vertical variability of aerosol single-scattering albedo and equivalent black carbon concentration based on in-situ and remote sensing techniques during the iAREA campaigns in Ny-Ålesund.

This work presents a methodology for obtaining vertical profiles of aerosol single scattering properties based on a combination of different measurement techniques. The presented data were obtained under the iAREA (Impact of absorbing aerosols on radiative forcing in the European Arctic) campaigns conducted in Ny-Ålesund (Spitsbergen) during the spring seasons of 2015-2017. The retrieval uses in-situ observations of black carbon concentration and absorption coefficient measured by a micro-aethalometer AE-51 mounted onboard a tethered balloon, as well as remote sensing data obtained from sun photometer and lidar measurements. From a combination of the balloon-borne in-situ and the lidar data, we derived profiles of single scattering albedo (SSA) as well as absorption, extinction, and aerosol number concentration. Results have been obtained in an altitude range from about 400 m up to 1600 m a.s.l. and for cases with increased aerosol load during the Arctic haze seasons of 2015 and 2016. The main results consist of the observation of increasing values of equivalent black carbon (EBC) and absorption coefficient with altitude, and the opposite trend for aerosol concentration for particles larger than 0.3μm. SSA was retrieved with the use of lidar Raman and Klett algorithms for both 532 and 880 nm wavelengths. In most profiles, SSA shows relatively high temporal and altitude variability. Vertical variability of SSA computed from both methods is consistent; however, some discrepancy is related to Raman retrieval uncertainty and absorption coefficient estimation from AE-51. Typically, very low EBC concentration in Ny-Ålesund leads to large error in the absorbing coefficient. However, SSA uncertainty for both Raman and Klett algorithms see ms to be reasonable, e.g. SSA of 0.98 and 0.95 relate to an error of ±0.01 and ±0.025, respectively

Impact of biomass burning plume on radiation budget and atmospheric dynamics over the arctic

The aim of the research was to determine the impact of July 2015 biomass burning event on radiative budget, atmospheric stratification and turbulence over the Arctic using information about the vertical structure of the aerosol load from the ground–based data. MODTRAN simulations indicated very high surface radiative cooling (forcing of –150 Wm–2) and a heating rate of up to 1.8 Kday–1 at 3 km. Regarding LES results, a turbulent layer at around 3 km was clearly seen after 48 h of simulation

Impact of biomass burning plume on radiation budget and atmospheric dynamics over the arctic

The aim of the research was to determine the impact of July 2015 biomass burning event on radiative budget, atmospheric stratification and turbulence over the Arctic using information about the vertical structure of the aerosol load from the ground–based data. MODTRAN simulations indicated very high surface radiative cooling (forcing of –150 Wm–2) and a heating rate of up to 1.8 Kday–1 at 3 km. Regarding LES results, a turbulent layer at around 3 km was clearly seen after 48 h of simulation

2014 iAREA campaign on aerosol in Spitsbergen Part 1: Study of physical and chemical properties

This paper presents the results of measurements of aerosol physical and chemical properties during iAREA2014 campaign that took place on Svalbard between 15th of Mar and 4th of May 2014. With respect to field area, the experiment consisted of two sites: NyeÅlesund (78�550N, 11�560E) and Longyearbyen (78�130N, 15�330E) with further integration of Aerosol Robotic Network (AERONET) station in Hornsund (77�000N, 15�330E). The subject of this study is to investigate the inesitu, passive and active remote sensing observations as well as numerical simulations to describe the temporal variability of aerosol singleescattering properties during spring season on Spitsbergen. The retrieval of the data indicates several event days with enhanced singleescattering properties due to the existence of sulphate and additional seaesalt load in the atmosphere which is possibly caused by relatively high wind speed. Optical results were confirmed by numerical simulations made by the GEMeAQ model and by chemical observations that indicated up to 45% contribution of the seaesalt to a PM10 total aerosol mass concentration. An agreement between the in-situ optical and microphysical properties was found, namely: the positive correlation between aerosol scattering coefficient measured by the nephelometer and effective radius obtained from laser aerosol spectrometer as well as negative correlation between aerosol scattering coefficient and the Ångstrom exponent indicated that slightly larger particles dominated during special events. The inesitu surface observations do not show any significant enhancement of the absorption coefficient as well as the black carbon concentration which might occur during spring. All of extensive singleescattering properties indicate a diurnal cycle in Longyearbyen, where 21:00e5:00 data stays at the background level, however increasing during the day by the factor of 3e4. It is considered to be highly connected with local emissions originating in combustion, traffic and harbour activities. On the other hand, no daily fluctuations in NyeÅlesund are observed. Mean values in NyeÅlesund are equal to 8.2, 0.8 Mm�1 and 103 ng/m3 for scattering, absorption coefficients and black carbon concentration; however in Longyearbyen (only data from 21:00e05:00 UTC) they reach 7.9, 0.6 Mm�1 as well as 83 ng/ m3 respectively. Overall, the spring 2014 was considerably clean and seaesalt was the major aerosol componen