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Record-breaking wildfires raged in southeastern Australia in late December 2019 and early January 2020. Rather strong pyrocumulonimbus (pyroCb) convection developed over the fire areas and lifted enormous amounts of biomass-burning smoke into the tropopause region and caused the strongest wildfire-related stratospheric aerosol perturbation ever observed around the globe. We discuss the geometrical, optical, and microphyscial properties of the stratospheric smoke layers and the decay of this major stratospheric perturbation. A multiwavelength polarization Raman lidar at Punta Arenas (53.2°S, 70.9°W), southern Chile, and an elastic-backscatter Raman lidar at Río Grande (53.8°S, 67.7°W) in southern Argentina were operated to monitor the major record-breaking event until the end of 2021. These lidar measurements can be regarded as representative for mid to high latitudes in the Southern Hemisphere. A unique dynamical feature, an anticyclonic, smoke-filled vortex with 1000 km horizontal width and 5 km vertical extent, which ascended by about 500 m per day, was observed over the full last week of January 2020. The key results of the long-term study are as follows: The smoke layers extended, on average, from 9 to 24 km in height. The smoke partly ascended to more than 30 km height as a result of self-lifting processes. Clear signs of a smoke impact on the record-breaking ozone hole over Antarctica in September-November 2020 were found. A slow decay of the stratospheric perturbation detected by means of the 532 nm aerosol optical thickness (AOT) yielded an e-folding decay time of 19-20 months. The maximum smoke AOT was around 1.0 over Punta Arenas in January 2020 and thus two to three orders of magnitude above the stratospheric aerosol background of 0.005. After two months with strongly varying smoke conditions, the 532 nm AOT decreased to 0.03-0.06 from March-December 2020 and to 0.015-0.03 throughout 2021. The particle extinction coefficients were in the range of 10-75 Mm-1 in January 2020, and later on mostly between 1 and 5 Mm-1. Combined lidarphotometer retrievals revealed typical smoke extinction-to-backscatter ratios of 69±19 sr (at 355 nm), 91±17 sr (at 532 nm), and 120±22 sr (at 1064 nm). An ozone reduction of 20-25% in the 15-22 km height range was observed over Antarctic and New Zealand ozonesonde stations in the smoke-polluted air with particle surface area concentrations of 1-5 µm² cm-3. [ABSTRACT FROM AUTHOR]

A remote sensing method, based on fluorescence lidar measurements, that allows to detect and to quantify the smoke content in upper troposphere and lower stratosphere (UTLS) is presented. The unique point of this approach is that, smoke and cirrus properties are observed in the same air volume simultaneously. In the article, we provide results of fluorescence and multiwavelength Mie-Raman lidar measurements performed at ATOLL observatory from Laboratoire d'Optique Atmosphérique, University of Lille, during strong smoke episodes in the summer and autumn seasons of 2020. The aerosol fluorescence was induced by 355 nm laser radiation and the fluorescence backscattering was measured in a single spectral channel, centered at 466 nm of 44 nm width. To estimate smoke properties, such as number, surface area and volume concentration, the conversion factors, which link the fluorescence backscattering and the smoke microphysical properties, are derived from the synergy of multiwavelength Mie-Raman and fluorescence lidar observations. Based on two case studies, we demonstrate that the fluorescence lidar technique provides possibility to estimate the smoke surface area concentration within freshly formed cirrus layers. This value was used in smoke INP parameterization scheme to predict ice crystal number concentrations in cirrus generation cells. [ABSTRACT FROM AUTHOR]

This article presents a study of long-range transported biomass burning aerosols (BBA) originated from the North American wildfires in September 2020. The BBA plumes presented in this study were in the troposphere and underwent 1-2 weeks aging before arriving at the observations site. A novel dataset 2α+3β+3δ+φ (α: extinction coefficient, β: backscatter coefficient, δ: particle linear depolarization ratio, PLDR, φ: fluorescence capacity) derived from lidar observations is provided for the characterization of long-range transported BBA. The fluorescence capacity describes the ability of aerosols in producing fluorescence when exposed to UV excitation. In the observations of BBA episode, plumes from different wildfire activities have been characterized. In the BBA plumes, we detected low PLDRs, i.e. lower than 0.03 at all wavelengths, as well as enhanced PLDRs (PLDR355,532,1064 ≈ 0.15-0.18, 0.12-0.14, 0.01-0.02) with a similar spectral dependence that had been observed in the aged BBA plumes in the upper troposphere and lower stratosphere (Canadian smoke in 2017 and Australian smoke in 2019-2020). Obvious variations in Angström exponent (−0.3-1.5), lidar ratios (20-50 sr at 355 nm, 42-90 sr at 532 nm) and fluorescence capacity (1.0 × 10−4- 4.0 × 10−4) are also observed during the BBA episode. These variations are coupled with the variation of altitudes, water vapor content and wildfire events. It reflects that the properties of aged BBA particles are highly varied and depend on complex mechanisms, such as burning process and the aging process. The results also pointed out the inhomogeneity of the aging process in the BBA plumes, which means that particles in the core of the plume aged differently with those at the plume edge due to the impact of water vapor, temperatures, particle concentration and so on. These chemical and physical processes involved in BBA aging and how they could impact the particle properties are not yet well understood. In addition, our observations identified the ice crystals mixing with BBA particles, which indicates that BBA could act as ice nucleating particles (INP) at tropospheric conditions. The lidar fluorescence proves to be an efficient tool in studying the interaction of clouds and BBAs due to its high sensitivity. Recent studies claimed that aged BBA particles are more effective INPs than they were thought. As BBAs are becoming an important atmospheric aerosols with growing global wildfires, our observations could improve our characterization about aged BBA particles and the understanding of their importance in ice cloud formation. [ABSTRACT FROM AUTHOR]

This work focuses on the characterization of vertically-resolved aerosol hygroscopicity properties and their direct radiative effects through a unique combination of ground-based and airborne remote sensing measurements during the DISCOVER-AQ 2011 field campaign in the Washington D.C. - Baltimore metropolitan area. To that end, we combined measurements from a multiwavelength Raman lidar located at NASA Goddard Space Flight Center and the airborne NASA Langley HSRL-1 lidar system. In-situ measurements on board the P-3B airplane and ground-based AERONET-DRAGON served to validate and complement quantifications of aerosol hygroscopicity from lidar measurements and also to extend the study both temporally and spatially. The focus here is on the 22nd and 29th of July, 2011 which were very humid days and characterized by a stable atmosphere and increasing relative humidity with height in the planetary boundary layer (PBL). Combined lidar and radiosonde measurements allowed the retrieval of the Hänel hygroscopic growth factor which agreed with that obtained from airborne in-situ measurements, and also explained the significant increase of extinction and backscattering with height. Airborne measurements also confirmed aerosol hygroscopicity throughout the entire day in the PBL and identified sulfates and water soluble organic carbon as the main species of aerosol particles. The combined Raman and HSRL-1 measurements permitted the inversion for aerosol microphysical properties revealing an increase of particle radius with altitude consistent with hygroscopic growth. Aerosol hygroscopicity was identified as the main reason to explain aerosol optical depth increases during the day, particularly for fine mode particles. Lidar measurements were used as input to the libRadtram radiative transfer code to obtain vertically-resolved aerosol radiative effects and heating rates under dry and humid conditions, and the results reveal that aerosol hygroscopicity is responsible for larger cooling effects in the shortwave range (7-10 W/m2 depending on aerosol load) near the ground, while heating rates produced a warming of 0.12 K/day near the top of PBL where aerosol hygroscopic growth was highest. [ABSTRACT FROM AUTHOR]

During the one-year MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition the German icebreaker Polarstern drifted through the Arctic Ocean ice from October 2019 to May 2020, mainly at latitudes between 85° N and 88.5° N. A multiwavelength polarization Raman lidar was operated aboard the research vessel and continuously monitored aerosol and cloud layers up to 30 km height. The highlight of the lidar measurements was the detection of a persistent, 10 km deep wildfire smoke layer in the upper troposphere and lower stratosphere (UTLS) from about 7-8 km to 17-18 km height. The smoke layer was present throughout the winter half year until the polar vortex, the strongest of the last 40 years, collapsed in late April 2020. The smoke originated from major fire events, especially from extraordinarily intense and long-lasting Siberian fires in July and August 2019. In this article, we summarize the main findings of our seven-month smoke observations and characterize the aerosol properties and decay of the stratospheric perturbation in terms of geometrical, optical, and microphysical properties. The UTLS aerosol optical thickness (AOT) at 532 nm ranged from 0.05-0.12 in October-November 2019 and was of the order of 0.03-0.06 during the central winter months (December-February). As an unambiguous sign of the dominance of smoke, the particle extinction-to-backscatter ratio (lidar ratio) at 355 nm was found to be much lower than the respective 532 nm lidar ratio. Mean values were 55 sr (355 nm) and 85 sr (532 nm). We further present a review of previous height resolved Arctic aerosol observations (remote sensing) in our study. For the first time, a coherent and representative view on the aerosol layering features in the Central Arctic from the surface up to 27 km height during the winter half year is presented. Finally, a potential impact of the wildfire smoke aerosol on the record-breaking ozone depletion over the Arctic in the spring of 2020 is discussed based on smoke, ozone, and polar stratospheric cloud observations. [ABSTRACT FROM AUTHOR]

An advanced multiwavelength polarization Raman lidar was operated aboard the icebreaker Polarstern during the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition, lasting from September 2019 to October 2020, to contiuously monitor aerosol and cloud layers in the Central Arctic up to 30 km height at latitudes mostly between 85?N and 88.5? N. The lidar was integrated in a complex remote sensing infrastructure aboard Polarstern. Modern aerosol lidar methods and new lidar techniques and concepts to explore aerosol-cloud interaction were applied for the first time in the Central Arctic. The aim of this introductory article is to provide an overview of the observational spectrum of the lidar products for representative measurement cases. The highlight of the lidar measurements was the detection of a 10 km deep wildfire smoke layer over the North Pole area from, on average, 7 km to 17 km height with an aerosol optical thickness (AOT) at 532 nm around 0.1 (in October-November 2019) and 0.05 from December to mid of March 2020. The wildfire smoke was trapped within the extraordinarily strong polar vortex and remained detectable until the beginning of May 2020. Arctic haze was also monitored and characterized in terms of backscatter, extinction, and extinction-to-backscatter ratio at 355 and 532 nm. High lidar ratios from 60-100 sr in lofted mixed haze and smoke plumes are indicative for the presence of strongly light-absorbing fine-mode particles. The AOT at 532 nm was of the order of 0.025 for the tropospheric haze layers. In addition, so-called cloud closure experiments were applied to Arctic mixed-phase cloud and cirrus observations. The good match between cloud condensation nucleus concentration (CCNC) and cloud droplet number concentration (CDNC) and, on the other hand, between ice-nucleating particle concentration (INPC) and ice crystal number concentration (ICNC) indicated a clear influence of aerosol particles on the evolution of the cloud systems. CDNC was mostly between 20 and 100 cm-3 in the liquid-water dominated cloud top layer. ICNC was of the order of 0.1-1 L-1. The study of the impact of wildfire smoke particles on cirrus formation revealed that heterogeneous ice formation with smoke particles (organic aerosol particles) as INPs may have prevailed. ICNC values of 10-40 L-1 were clearly below ICNC levels that would indicate homogeneous freezing. [ABSTRACT FROM AUTHOR]

We present retrievals of tropospheric and stratospheric height profiles of particle mass, volume, and surface area concentrations in the case of wildfire smoke layers as well as estimates of smoke-related cloud condensation nucleus (CCN) and ice-nucleating particle (INP) concentrations from single-wavelength backscatter lidar measurements at ground and in space. A central role in the data analysis play conversion factors to convert the measured optical into microphysical properties. The set of needed conversion parameters for wildfire smoke are derived from AERONET observations of major smoke events caused by record-breaking wildfires in western Canada in August 2017 and southeastern Australia in January-February 2020. The new smoke analysis scheme is applied to stratospheric CALIPSO observations of fresh smoke plumes over northern Canada in 2017 and New Zealand in January 2020 and to ground-based lidar observation in southern Chile in aged Australian smoke layers in January 2020. These case studies show the potential of spaceborne and ground-based lidars to document large-scale and long-lasting wildfire smoke events in large detail and thus to provide valuable information for climate-, cloud-, and air chemistry modeling efforts performed to investigate the role of wildfire smoke in the atmospheric system. [ABSTRACT FROM AUTHOR]

The Taklamakan desert is an important dust source for the global atmospheric dust budget and a cause of the dust weather in Eastern Asia. The characterization of the properties and vertical distributions of Taklamakan dust in the source region is still very limited. To fill this gap, the DAO (Dust Aerosol Observation) was conducted in Kashi, China in 2019. Kashi site is about 150 km to the west rim of the Taklamakan desert and is strongly impacted by desert dust aerosols, especially in spring time, i.e. April and May. Apart from dust, fine particles coming from local anthropogenic emissions or/and transported aerosols are also a non-negligible aerosol component. In this study, we provide the first profiling of the 2α + 3β + 3δ lidar profiles of Taklamakan dust based on a multi-wavelength Raman polarization lidar. Four cases, including two Taklamakan dust events (Case 1 and 2) and two polluted dust events (Case 3 and 4) are presented. The lidar ratio in the Taklamakan dust outbreak is found to be 51±8-56±8 sr at 355 nm and 45±7 sr at 532 nm. The particle linear depolarization ratios are about 0.28±0.04-0.32±0.05 at 355 nm, 0.35±0.05 at 532 nm and 0.31±0.05 at 1064 nm. The observed polluted dust is commonly featured with reduced particle linear depolarization ratio and enhanced extinction and backscatter Angstrom exponent. In Case 3, the lidar ratio of polluted dust is about 42±6 sr at 355 nm and 40±6 sr at 532 nm. The particles linear depolarization ratios decrease to about 0.25, with a weak spectral dependence. In Case 4, the variability of lidar ratio and particle linear depolarization ratio is higher than in Case 3, which reflects the complexity of the nature of mixed pollutant and the mixing state. The results provide the first reference for the characteristics of Taklamakan dust measured by Raman lidar. The data could contribute to complementing the dust model and improving the accuracy of climate modeling. [ABSTRACT FROM AUTHOR]

Measurements performed in Western Africa (Senegal) during the SHADOW-2 field campaign are analyzed to show that spectral dependence of the imaginary part of the complex refractive index (CRI) of dust can be revealed by lidar-measured particle parameters. Observations in April 2015 provide good opportunity for such study, because, due to high optical depth of the dust, exceeding 0.5, the extinction coefficient could be derived from lidar measurements with high accuracy and contribution of other aerosol types, such as biomass burning, was negligible. For instance, in the second half of April 2015, AERONET observations demonstrated a temporal decrease of the imaginary part of CRI at 440 nm from approximately 0.0045 to 0.0025. This decrease is in line with a change in relationship between lidar ratios (the extinction-to-backscattering ratio) at 355 nm and 532 nm (S355 and S532). In the first half of April, S355 / S532 is as high as 1.5 and the backscatter Angstrom exponent Aβ, is as low as −0.75, while after 15 April S355 / S532 = 1.0 and Aβ is close to zero. The aerosol depolarization ratio δ532 for the whole April exceeded 30 % in the height range considered, implying that no other aerosol, except dust, occurred. The performed modeling confirmed that the observed S355 / S532 and Aβ values match the spectrally dependent imaginary part of the refractive index as can be expected for mineral dust containing iron oxides. West Africa is also known for significant biomass burning aerosol emissions during the dry season in the Sahel region. The second phase of the SHADOW-2 campaign was focused on evaluation of lidar ratio of smoke and estimates of its dependence on relative humidity (RH). For considered five smoke episodes the lidar ratio increases from 44 ± 5 sr to 66 ± 7 sr at 532 nm and from 62 ± 6 sr to 80 ± 8 sr at 355 nm, when RH varied from 25 % to 85 %. Performed numerical simulations demonstrate, that observed ratio S355 / S532, exceeding 1.0 in the smoke plumes, can indicate to increase of the imaginary part of the smoke particles in UV. [ABSTRACT FROM AUTHOR]

Long-range transported smoke aerosols in the UTLS (Upper Troposphere/Lower Stratosphere) over Europe were detected in Summer 2017. The measurements of ground-based instruments and satellite sensors indicate that the UTLS aerosol layers were originated from Canadian wildfires and were transported to Europe by UTLS advection. In this study, the observations of two multi-wavelength Raman Lidar systems in northern France (Lille and Palaiseau) are used to derive aerosol properties, such as optical depth of the UTLS layer, Lidar ratios at 355 and 532nm and particle linear depolarization ratios at 355, 532 and 1064nm. The optical depth of the UTLS layers at 532nm varies from 0.05 to above 0.20, with very weak spectral dependence between 355 and 532nm. Lidar ratios at 355nm are in 31±15sr to 45±9sr range and at 532nm, the Lidar ratios are in the range of 54±12sr to 58±9sr. Such spectral dependence of Lidar ratio is known to be a characteristic feature of aged smoke. The typical particle depolarization ratios in the UTLS smoke layer are 25±4% at 355nm, 19±3% at 532nm and 4.5±0.8% at 1064nm. The relatively high depolarization ratios and such spectral dependence are an indication of a complicated morphology of aged smoke particles. We found an increase of depolarization ratio versus transport time. The depolarization ratio at 532nm increases from below 2–5% for fresh smoke to over 20% for smoke aged more than 20 days. The 3β+2α observations of two cases at Palaiseau and Lille sites were inverted to the aerosol microphysical properties using regularization algorithm. The particles distribute in the 0.1–1.0μm range with effective radius of 0.33±0.10μm for both cases. The derived complex refractive indices are 1.52(±0.05)+i0.021(±0.010) and 1.55(±0.05)+i0.028(±0.014) for Palaiseau and Lille data. The retrieved aerosol properties were used to calculate the direct radiative forcing (DRF) effect specific to the UTLS aerosol layers. The simulations derive daily net DRF efficiency of −79.6Wm−2τ−1 at the bottom of the atmosphere for Lille observations. At the top of the atmosphere, the net DRF efficiency is −7.9Wm−2τ−1. The results indicate that the UTLS aerosols strongly reduce the radiation reaching the terrestrial surface by absorption. The heating rate of the UTLS layers is estimated to be 3.7Kday−1. The inversion of Palaiseau data leads to similar results. The heating rate predicts a temperature increase within the UTLS aerosol layer, which has been observed by the radiosonde temperature measurements. [ABSTRACT FROM AUTHOR]

Light extinction coefficients of 500 Mm−1, about 20 times higher than after the Pinatubo volcanic eruptions in 1991, were observed with lidar in the stratosphere over Leipzig, Germany, on 22 August 2017. A pronounced smoke layer extended from 14–16 km height and was 3–4 km above the local tropopause. Optically dense layers of Canadian wildfire smoke reached central Europe 10 days after injection into the lower stratosphere caused by rather strong pyrocumulonimbus activity over western Canada. The smoke-related aerosol optical thickness (AOT) was close to 1.0 at 532 nm over Leipzig during the noon hours. We present detailed observations of this record-breaking smoke event in a series of two articles. In part 1, we provide an overview of Aerosol Robotic Network (AERONET) sun photometer observations and Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals of AOT and show lidar measurements documenting the aerosol layering and the very high particle extinction coefficients. In part 2 (Haarig et al., 2018), observations with three polarization/Raman lidars are presented, performed at Leipzig after sunset on 22 August to elucidate the optical and microphysical properties of the aged smoke. As shown in this part 1, smoke particles were found throughout the free troposphere (532 nm AOT of 0.3). A pronounced 2-km thick stratospheric smoke layer occurred from 14–16 km height (AOT of 0.6). AERONET and lidar observations indicate peak mass concentrations of 70–100 μg m−3 in the stratosphere around noon and a well-defined (accumulation mode) smoke particle size distribution characterized by a large effective radius of 0.3–0.4 μm and the absence of a particle coarse mode. [ABSTRACT FROM AUTHOR]

Extremely high particle extinction coefficients, an order of magnitude higher than after the Mt. Pinatubo eruption in 1991, were measured in the stratosphere over Leipzig, Germany, on 22 August 2017. In a series of two articles, we present our observations of this record-breaking smoke event. In part 1 (Ansmann et al., 2018), we provide an overview of the smoke situation. The particle extinction coefficients reached 500 Mm−1 at 532 nm in the lower stratosphere around 15 km height and the smoke-related aerosol optical thickness (AOT) was close to 1.0 around noon. In part 2, we present the optical and microphysical properties of the fire smoke observed in a tropospheric layer from 5–6.5 km height and in a stratospheric layer from 15–16 km height. Three Raman lidars were run at Leipzig after sunset on 22 August. As a highlight, triple-wavelength polarization/Raman lidar measurements of the particle depolarization ratio and extinction-to-backscatter ratio (lidar ratio) at all three important lidar wavelengths of 355, 532, and 1064 nm could be performed. Very different particle depolarization ratios were found in the troposphere and in the stratosphere. The obviously compact and spherical tropospheric smoke particles caused almost no depolarization of backscattered laser radiation at all three wavelength (< 3 %), whereas the particles in the stratosphere lead to high depolarization ratios of 22 % at 355 nm and 18 % at 532 nm and a comparably low value of 4 % at 1064 nm in the stratosphere. The observed strong wavelength dependence is probably attributed to the narrow size distribution (accumulation mode) of irregularly shaped soot particles and the absence of a smoke coarse mode. The layer mean particle lidar ratios, on the other hand, were 40–45 sr (355 nm), and 65–80 sr (532 nm), and 80–95 sr (1064 nm) in both, the tropospheric and stratospheric layers indicating similar scattering and absorption properties. The 532 nm single scattering albedo was 0.8 in the stratospheric layer. The smoke particles were rather small (effective radius of 0.17 μm) in the tropospheric layer and much larger (effective radius of 0.32 μm) in the very dry stratosphere. [ABSTRACT FROM AUTHOR]