Anthropogenic and forest fire pollution aerosol transported to the Arctic: observations from the POLARCAT-France spring campaign

During the POLARCAT-France airborne measurement campaign in spring 2008, several pollution plumes transported from mid-latitude regions were encountered. The study presented here focuses on air masses from two different geographic origins (Europe and Asia) and from 2 different source types (anthropogenic pollution and forest fires). One case study analyses an European air mass, which was sampled during three consecutive day. Modelling of the aerosol particle ageing by coagulation suggests that coagulation cannot solely explain the evolution of the size distributions, which is particularly true for the accumulation mode. Analyses of the aerosol refractory size distributions indicate that the Aitken mode was mostly composed of volatile compounds, while accumulation mode particles desorbed to a refractory mode yielding a modal mean diameter evolving from 48 to 59 nm for the three consecutive days of sampling the same air mass. The single refractory mode suggests an internally mixed aerosol population which is supported from electron microscopy and subsequent EDX analyses of the accumulation mode particles. Another case study focuses on European air masses polluted by fire emissions and Asian air masses with contributions from both biomass burning and anthropogenic emissions. On the one hand, the aerosol size distributions of the European biomass burning plumes are almost mono-modal with most of the particles found in the aged accumulation mode which desorbed uniformly. On the other hand, Asian air masses were more complex because of the mixing of different source contributions related to more variable and multimodal ambient and refractory aerosol size distributions. Electron microscopy illustrated soot-like inclusions in several samples. Within samples attributed to forest fire sources, the chemical signature is highly associated with the presence of potassium, which is characteristic for biomass burning plumes. The particle images suggest an internal mixing of sampled aerosol particles

Overview of aerosol properties associated with air masses sampled by the ATR-42 during the EUCAARI campaign (2008)

International audienceWithin the frame of the European Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) project the Météo-France aircraft ATR-42 performed 22 research flights, over central Europe and the North Sea during the intensive observation period in May 2008. For the campaign, the ATR-42 was equipped in order to study aerosol physical, chemical and optical properties, as well as cloud microphysics. During the campaign, continental air masses from Eastern and Western Europe were encountered, along with polar and Scandinavian air masses. For the 22 research flights, retroplume analyses along the flight tracks were performed with FLEXPART in order to classify air masses into five sectors of origin which allows for a qualitative evaluation of emission influence on the respective air parcel. In the polluted boundary layer (BL), typical concentrations of particles with diameters larger than 10 nm (N10) are of the order of 5000-6000 cm−3, whereas N10 concentrations of clean air masses were lower than 1300 cm−3. The detection of the largest particle number concentrations occurred in air masses coming from Polar and Scandinavian regions for which an elevated number of nucleation mode (25-28 nm) particles was observed and attributed to new particle formation over open sea. In the free troposphere (FT), typical observed N10 are of the order of 900 cm−3 in polluted air masses and 400-600 cm−3 in clean air masses, respectively. In both layers, the chemical composition of submicron aerosol particles is dominated by organic matter and nitrate in polluted air masses, while, sulphate and ammonium followed by organics dominate the submicron aerosols in clean air masses. The highest CCN/CN ratios were observed within the polar air masses while the CCN concentration values are the highest within the polluted air masses. Within the five air mass sectors defined and the two layers (BL and FT), observations have been distinguished into anticyclonic (first half of May 2008) and cyclonic conditions (second half of May 2008). Strong relationships between meteorological conditions and physical, chemical as well as optical properties are found

Physical and optical properties of 2010 Eyjafjallajökull volcanic eruption aerosol: ground-based, Lidar and airborne measurements in France

International audienceDuring the Eyjafjallajökull eruption (14 April to 24 May 2010), the volcanic aerosol cloud was observed across Europe by several airborne in situ and ground-based remote-sensing instruments. On 18 and 19 May, layers of depolarizing particles (i.e. non-spherical particles) were detected in the free troposphere above the Puy de Dôme station, (PdD, France) with a Rayleigh-Mie LIDAR emitting at a wavelength of 355 nm, with parallel and crossed polarization channels. These layers in the free troposphere (FT) were also well captured by simulations with the Lagrangian particle dispersion model FLEXPART, which furthermore showed that the ash was eventually entrained into the planetary boundary layer (PBL). Indeed, the ash cloud was then detected and characterized with a comprehensive set of in situ instruments at the Puy de Dôme station (PdD). In agreement with the FLEXPART simulation, up to 65 μg m−3 of particle mass and 2.2 ppb of SO2 were measured at PdD, corresponding to concentrations higher than the 95 percentile of 2 yr of measurements at PdD. Moreover, the number concentration of particles increased to 24 000 cm−3, mainly in the submicronic mode, but a supermicronic mode was also detected with a modal diameter of 2 μm. The resulting optical properties of the ash aerosol were characterized by a low scattering Ångström exponent (0.98), showing the presence of supermicronic particles. For the first time to our knowledge, the combination of in situ optical and physical characterization of the volcanic ash allowed the calculation of the mass-to-extinction ratio (η) with no assumptions on the aerosol density. The mass-to-extinction ratio was found to be significantly different from the background boundary layer aerosol (max: 1.57 g m−2 as opposed to 0.33 ± 0.03 g m−2). Using this ratio, ash mass concentration in the volcanic plume derived from LIDAR measurements was found to be 655 ± 23 μg m−3 when the plume was located in the FT (3000 m above the sea level - a.s.l.). This ratio could also be used to retrieve an aerosol mass concentration of 579 ± 60 μg m−3 on 19 April, when LIDAR observations detected the ash cloud at 3000 m a.s.l. in correspondence with model simulations (FLEXPART). On 22 April, another ash plume entered the BL, and although it was more diluted than during the May episode, the French research aircraft ATR42 that passed over Clermont-Ferrand in the PBL confirmed the presence of particles with a supermicronic mode, again with a modal diameter at 2 μm. This data set combining airborne, ground-based and remote sensing observations with dispersion model simulations shows an overall very good coherence during the volcanic eruption period, which allows a good confidence in the characteristics of the ash particles that can be derived from this unique data set

Analysis of aerosol transported to the Arctic based on LaMP's airborne measurements (ATR-42) during the POLARCAT project

Ces travaux, effectués dans le cadre de la 4e année polaire internationale et à partir des mesures in-situ obtenues durant le projet POLARCAT-France, ont pour objectifs de fournir, dans un premier temps, une climatologie des panaches de pollution transportés depuis les continents sources (Amérique du Nord, Europe et Asie) vers l’Arctique. La climatologie contient des informations sur les propriétés physique, chimique et optique des particules d’aérosols, l’origine des panaches ayant été déterminée à l’aide du modèle lagrangien de rétro-trajectoire FLEXPART. Dans un second temps, les processus qui influent sur les propriétés des particules de pollution durant leur transport vers l’Arctique ont été étudiés. Si au cours de la campagne d’été au Groenland, il a été montré que la totalité des panaches rencontrés ont subit un processus de dépôt humide durant leur transport vers l’Arctique, la campagne de printemps au nord de la Suède a permis de mettre en avant l’évolution d’un même panache échantillonné lors de 3 vols consécutifs ainsi que des propriétés de mélange entre les contributions anthropiques et naturelles de deux panaches asiatiques.The aims of this thesis were, in a first step, to build a climatology of pollution plumes transported from source continents to the Arctic as measured during the POLARCAT-France campaigns performed in spring and summer 2008, in the frame of the 4th International Polar Year. The climatology is including informations on aerosol particle physical, chemical and optical properties and is organized as a function of pollution plume origins (determined with the Lagrangian transport model FLEXPART). In a second step, aerosol processes which influenced aerosol properties during transport to the Arctic were studied. During the summer campaign, the whole plumes encounter experienced wet scavenging processes on their pathway to Groenland. In spring, a plume was sampled during three consecutive days and thus, its ageing was characterised. Finally, two Asian plumes allowed us to highlight the external mixing between anthropogenic and biomass burning contributions transported to northern scandinavia

Analysis of aerosol transported to the Arctic based on LaMP's airborne measurements (ATR-42) during the POLARCAT project

Ces travaux, effectués dans le cadre de la 4e année polaire internationale et à partir des mesures in-situ obtenues durant le projet POLARCAT-France, ont pour objectifs de fournir, dans un premier temps, une climatologie des panaches de pollution transportés depuis les continents sources (Amérique du Nord, Europe et Asie) vers l’Arctique. La climatologie contient des informations sur les propriétés physique, chimique et optique des particules d’aérosols, l’origine des panaches ayant été déterminée à l’aide du modèle lagrangien de rétro-trajectoire FLEXPART. Dans un second temps, les processus qui influent sur les propriétés des particules de pollution durant leur transport vers l’Arctique ont été étudiés. Si au cours de la campagne d’été au Groenland, il a été montré que la totalité des panaches rencontrés ont subit un processus de dépôt humide durant leur transport vers l’Arctique, la campagne de printemps au nord de la Suède a permis de mettre en avant l’évolution d’un même panache échantillonné lors de 3 vols consécutifs ainsi que des propriétés de mélange entre les contributions anthropiques et naturelles de deux panaches asiatiques.The aims of this thesis were, in a first step, to build a climatology of pollution plumes transported from source continents to the Arctic as measured during the POLARCAT-France campaigns performed in spring and summer 2008, in the frame of the 4th International Polar Year. The climatology is including informations on aerosol particle physical, chemical and optical properties and is organized as a function of pollution plume origins (determined with the Lagrangian transport model FLEXPART). In a second step, aerosol processes which influenced aerosol properties during transport to the Arctic were studied. During the summer campaign, the whole plumes encounter experienced wet scavenging processes on their pathway to Groenland. In spring, a plume was sampled during three consecutive days and thus, its ageing was characterised. Finally, two Asian plumes allowed us to highlight the external mixing between anthropogenic and biomass burning contributions transported to northern scandinavia

Transport of anthropogenic and biomass burning aerosols from Europe to the Arctic during spring 2008

Aircraft measurements taken as part of the POLARCAT campaign (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) were aimed at investigating pollution transport and atmospheric chemistry in the Arctic. During this campaign, pollution plumes of anthropogenic and biomass burning origin were measured in the Arctic troposphere in spring 2008. We combine those aircraft measurements with simulations using the WRF-Chem model (Weather Research and Forecasting Model including aerosol and chemistry) to investigate cases of aerosol transport from Europe to the Arctic during spring 2008. We focus our work on the POLARCAT-France campaign in the Scandinavian Arctic in April 2008. We evaluate the model's ability to reproduce observations made during this campaign. Then, we assess with WRF-Chem the extent, vertical distribution and composition of the aerosol plumes by comparing model results with in situ observations of aerosols and CO, used as an anthropogenic and biomass burning tracer. We also use airborne aerosol LIDAR measurements to assess modelled aerosol vertical distributions in the Arctic. With the help of Lagrangian back-trajectories, we investigate in more detail the aerosol transport pathways from Europe to the Arctic, as well as the processes responsible for horizontal and vertical transport. By comparing model results with POLARCAT aircraft data from spring 2008, we provide a means for interpreting the POLARCAT aircraft data set with the goal of improving our understanding of aerosol transport to the Arctic