One year of Raman lidar observations of free tropospheric aerosol layers over South Africa

Giannakaki, E.; Komppula, Mika; Pfüller, A.; Korhonen, Kimmo; Mielonen, Tero; Laakso, Lauri; Vakkari, Ville; Baars, Holger; Engelmann, Ronny; Beukes, Paul; Zyl, P. G. van; Josipovic, Micky; Tiitta, Petri; Chiloane, K.; Lihavainen, Heikki; Lehtinen, K. E. J.

doi:10.5194/acpd-15-1343-2015

Cited by 6 publications

(10 citation statements)

References 66 publications

(81 reference statements)

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“…The mean values of the LPDR and AE ( Figure 6 c,d) indicate changes in the shape and size of the aerosols due to the transforming processes that smoke aerosols went through, during their long-range transport, as mentioned before. The LPDR values, that ranged between 0.04 to 0.15 and those of AE greater than 1 (not exceeding 1.9), are representative for smoke aerosols [ 33 , 34 ]. On the other hand, LPDR values, greater than 0.20 and AE values close to zero, indicate the presence of dust aerosols [ 1 , 19 ].…”

Section: Resultsmentioning

confidence: 99%

Canadian Biomass Burning Aerosol Properties Modification during a Long-Ranged Event on August 2018

Papanikolaou

Giannakaki

Papayannis

et al. 2020

Sensors

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The aim of this paper is to study the spatio-temporal evolution of a long-lasting Canadian biomass burning event that affected Europe in August 2018. The event produced biomass burning aerosol layers which were observed during their transport from Canada to Europe from the 16 to the 26 August 2018 using active remote sensing data from the space-borne system Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). The total number of aerosol layers detected was 745 of which 42% were identified as pure biomass burning. The remaining 58% were attributed to smoke mixed with: polluted dust (34%), clean continental (10%), polluted continental (5%), desert dust (6%) or marine aerosols (3%). In this study, smoke layers, pure and mixed ones, were observed by the CALIPSO satellite from 0.8 and up to 9.6 km height above mean sea level (amsl.). The mean altitude of these layers was found between 2.1 and 5.2 km amsl. The Ångström exponent, relevant to the aerosol backscatter coefficient (532/1064 nm), ranged between 0.9 and 1.5, indicating aerosols of different sizes. The mean linear particle depolarization ratio at 532 nm for pure biomass burning aerosols was found equal to 0.05 ± 0.04, indicating near spherical aerosols. We also observed that, in case of no aerosol mixing, the sphericity of pure smoke aerosols does not change during the air mass transportation (0.05–0.06). On the contrary, when the smoke is mixed with dessert dust the mean linear particle depolarization ratio may reach values up to 0.20 ± 0.04, especially close to the African continent (Region 4).

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Section: Resultsmentioning

confidence: 99%

Canadian Biomass Burning Aerosol Properties Modification during a Long-Ranged Event on August 2018

Papanikolaou

Giannakaki

Papayannis

et al. 2020

Sensors

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“…At Marikana and Elandsfontein the largest observed AODs are not related to largest CS, which could be due to the presence of elevated aerosol layers. In a recent study by Giannakaki et al (2015) data from a ground-based lidar at Elandsfontein are analyzed and the results show that the mean contribution of elevated aerosol layers to the AOD is 46 %. To estimate the effect of elevated aerosol layers on the CS-AOD comparison at Marikana, CALIPSO observations of aerosol vertical extinction profiles are used.…”

Section: Comparison Of Condensation Sink and Aerosol Optical Depthmentioning

confidence: 99%

“…Laakso et al (2008) and Vakkari et al (2011) have studied new particle formation over moderately polluted savannah ecosystems in South Africa and found that nucleation takes place in the boundary layer almost every sunny day throughout the year with a frequency of as high as 69 % of all analyzed days (Vakkari et al, 2011). Hirsikko et al (2012) extended the studies in South Africa to a polluted measurement site and found an even higher frequency for the nucleation event days (86 %), which is among the highest event frequencies reported in the literature so far. Hirsikko et al (2013) also studied the causes for two or three consecutive daytime nucleation events, followed by subsequent particle growth during the same day.…”

Section: Introductionmentioning

confidence: 99%

Characterization of satellite based proxies for estimating nucleation mode particles over South Africa

Sundström¹,

Franck²,

Tabakova³

et al. 2014

Preprint

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Abstract. In this work satellite observations from the NASA's A-Train constellation were used to derive the values of primary emission and regional nucleation proxies over South Africa to estimate the potential for new particle formation. As derived in Kulmala et al. (2011), the satellite based proxies consist of source terms (NO2, SO2 and UV-B radiation), and a sink term describing the pre-existing aerosols. The first goal of this work was to study in detail the use of satellite aerosol optical depth (AOD) as a substitute to the in situ based condensation sink (CS). One of the major factors affecting the agreement of CS and AOD was the elevated aerosol layers that increased the value of column integrated AOD but not affected the in situ CS. However, when the AOD in the proxy sink was replaced by an estimate from linear bivariate fit between AOD and CS, the agreement with the actual nucleation mode number concentration improved somewhat. The second goal of the work was to estimate how well the satellite based proxies can predict the potential for new particle formation. For each proxy the highest potential for new particle formation were observed over the Highveld industrial area, where the emissions were high but the sink due to pre-existing aerosols was relatively low. Best agreement between the satellite and in situ based proxies were obtained for NO2/AOD and UV-B/AOD2, whereas proxies including SO2 in the source term had lower correlation. Even though the OMI SO2 boundary layer product showed reasonable spatial pattern and detected the major sources over the study area, some of the known minor point sources were not detected. When defining the satellite proxies only for days when new particle formation event was observed, it was seen that for all the satellite based proxies the event day medians were higher than the entire measurement period median.

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“…In principle, the emitted linearly polarised light is backscattered, mainly with the same linear polarisation and partly depolarised, upon interaction with atmospheric targets which are non-spherical and randomly oriented (Mishchenko and Hovenier, 1995). The polarisation-sensitive detection of the collected backscattered signal is usually performed by separating the signal into two optical paths; the first (parallel or co-polar) contains the backscattered light with the original polarisation and half of the depolarised light, and the second (cross or cross-polar) contains the other half of the depolarised light (Gimmestad, 2008). There are also systems that rely on the detection of the total and cross-backscattered signals instead (Engelmann et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

The eVe reference polarisation lidar system for the calibration and validation of the Aeolus L2A product

et al. 2022

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Abstract. The eVe dual-laser/dual-telescope lidar system is introduced here, focusing on the optical and mechanical parts of the system's emission and receiver units. The compact design of the linear–circular emission unit along with the linear–circular analyser in the receiver unit allows eVe to simultaneously reproduce the operation of the ALADIN lidar on board Aeolus as well as to operate it as a traditional ground-based polarisation lidar system with linear emission. As such, the eVe lidar aims to provide (a) ground reference measurements for the validation of the Aeolus L2A aerosol products and (b) the conditions for which linear polarisation lidar systems can be considered for Aeolus L2A validation, by identifying any possible biases arising from the different polarisation state in the emission between ALADIN and these systems, and the detection of only the co-polar component of the returned signal from ALADIN for the L2A products' retrieval. In addition, a brief description is given concerning the polarisation calibration techniques that are applied in the system, as well as the developed software for the analysis of the collected signals and the retrieval of the optical products. More specifically, the system's dual configuration enables the retrieval of the optical properties of particle backscatter and extinction coefficients originating from the two different polarisation states of the emission and the linear and circular depolarisation ratios, as well as the direct calculation of the Aeolus-like backscatter coefficient, i.e. the backscatter coefficient that Aeolus would measure from the ground. Two cases, one with slightly depolarising particles and one with moderately depolarising particles, were selected from the first conducted measurements of eVe in Athens in September 2020, in order to demonstrate the system's capabilities. In the slightly depolarising scene, the Aeolus-like backscatter coefficient agrees well with the actual backscatter coefficient, which is also true when non-depolarising particles are present. The agreement however fades out for strongly depolarising scenes, where an underestimation of ∼18 % of the Aeolus like backscatter coefficient is observed when moderately depolarising particles are probed.

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One year of Raman lidar observations of free tropospheric aerosol layers over South Africa

Cited by 6 publications

References 66 publications

Canadian Biomass Burning Aerosol Properties Modification during a Long-Ranged Event on August 2018

Canadian Biomass Burning Aerosol Properties Modification during a Long-Ranged Event on August 2018

Characterization of satellite based proxies for estimating nucleation mode particles over South Africa

The eVe reference polarisation lidar system for the calibration and validation of the Aeolus L2A product

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