A study of the intense spring pollution events occurring between 2007 and 2016 on the Paris Area is presented using ground-based and spaceborne measurements. Emphasis is placed on 2011 where data included ground-based lidar measurements. This last period corresponds with the highest regional pollution levels of the past decade. The information threshold (daily average of (mass concentration of particles with aerodynamic diameter less than 10m) PM10>50gm(-3)) was exceeded 16 times, while the alert threshold (daily average of PM10>80gm(-3)) was exceeded twice. The information (alert) threshold exists to protect the most fragile people (the entire population). Ground-based and spaceborne measurements demonstrate the benefit of their synergy as each is representative of specific space and time scales. The operational products of the spaceborne instruments Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) and the Moderate Resolution Imaging Spectroradiometer are used. For 2011, CALIOP vertical profiles are inversed to assess the backscatter to extinction ratio, which is then successfully compared with similar results derived from the CALIOP operational products, a ground-based lidar and Sun photometers. The aerosols are identified to be polluted continental and polluted dust aerosols following the criteria used for the inversion of the CALIOP profiles. Aerosol typing is consistent between the ground-based and spaceborne lidars, demonstrating the importance of CALIOP for other years where the ground-based lidar was not in operation. The main pollution sources responsible for the spring aerosol pollution, occurring during anticyclonic meteorological conditions, are identified as coming from Western Europe: Benelux, Rhine-Ruhr area, and the Lorraine area.

The measurement range of a coherent wind Doppler lidar (CWDL) along a laser beam is the maximum distance from the lidar where wind speed data are accurately retrieved. It means that, at this distance, a sufficient number of emitted laser photons are backscattered and received by the lidar. Understanding of the propagation of the laser through the atmosphere, and particularly the backscattering and extinction processes from aerosols, is therefore important to estimate the metrological performances of a CWDL instrument. The range is directly related to specific instrument characteristics and atmospheric content, such as the aerosols type, size, and density distributions. Associated with the measurement range is the notion of data availability, which can be defined, at a given range and over a time period, as the percentage number of data retrieved correctly by the CWDL over the total number of measurement attempts.This paper proposes a new approach to predict the CWDL data availability and range of measurement using both instrumental simulation and atmospheric observations of aerosol optical properties from weather stations and simulations. This method is applied in several CWDL measurement campaigns during which estimated data availabilities and ranges are compared with the observations. It is shown that it is fairly possible to anticipate the data availability and the range coverage of CWDL technology at any site of interest where atmospheric data are available. The method also offers an additional way to diagnose the operation of the instrument and will help in the design of future instruments.

Le changement climatique récent est attribué entre autres à l'impact des particules atmosphériques d’origine naturelle ou des activités humaines d’après le dernier rapport du GIEC [IPCC, Climate Change 2014: Synthesis Report]. Les aérosols affectent également les propriétés des nuages et influencent le cycle de l'eau, pouvant intensifier les moussons. En avril 2010, le volcan Eyjafjallajökull a créé un panache de plusieurs milliers de kilomètres sur l’Europe et causé la fermeture de plusieurs aéroports internationaux, clouant au sol des millions de voyageurs et causant une perte économique globale de 1,7 milliard de dollars. Tous les jours, les aérosols transfrontaliers (panaches de sable du Sahara, résidus de combustion des forêts canadiennes) affectent la santé des populations habitant notamment en zones urbaines ainsi que les activités économiques.

Avec presque 1 million d’habitants sur le Grand Geneve, l’amelioration de la qualite de l’air constitue un enjeu sanitaire important, tout autant qu’une attente forte des populations. Ce constat est largement partage entre la France et la Confederation helvetique. Les actions des uns ayant des repercussions sur la qualite de l’air respire par les autres, il est par consequent indispensable qu’il existe une vision partagee, des outils communs puis une gestion coordonnee de la qualite de l’air a l’echelle des 212 communes de l’espace franco-suisse qu’est le Grand Geneve. Les elements du premier diagnostic de la qualite de l’air sur le Grand Geneve etabli en 2012 ont mis en evidence certains points de vigilance comme le centre-ville et l’aeroport de Geneve, ainsi que les secteurs residentiels. La region Rhone-Alpes est concernee par des depassements reguliers des normes de qualite de l’air definies au niveau europeen. Parmi les secteurs qui posent probleme figure l’agglomeration d’Annemasse, avec des depassements enregistres en poussieres fines. Cette agglomeration est situee entre deux zones particulierement concernees par la pollution atmospherique : d’un cote, le bassin genevois et, de l’autre, la vallee de l’Arve, faisant actuellement l’objet d’un Plan de Protection de l’Atmosphere (dont certaines communes font partie du Grand Geneve). L’objectif du projet G²AME (Grand Geneve Air Modele Emission) a ete de produire un outil commun et harmonise de diagnostic et d’aide a l’etablissement d’un plan d’actions a l’echelle du Grand Geneve. Cet outil a permis de mieux connaitre les emissions de polluants du territoire transfrontalier, de travailler de maniere prospective en identifiant les secteurs les plus emetteurs et de tester l’evaluation d’actions d’amenagement du territoire, d’infrastructure ou d’action d’amelioration de la qualite de l’air. Ainsi, le programme elabore sur 2 ans, de juin 2013 a l’ete 2015, a permis : - la mise en coherence des inventaires d’emissions en situation actuelle : cette action a permis de cartographier de part et d’autre de la frontiere les sources et polluants, et d’estimer quantitativement les differentes sources d’emissions du bassin. Ainsi, ce travail a permis de mettre en evidence les differences de parc roulant entre les pays, la predominance des emissions de PM10 du secteur residentiel cote francais, l’importance des emissions d’oxydes d’azote de Geneve et de la zone aeroportuaire ; - le developpement d’un modele transfrontalier commun pour la cartographie de la qualite de l’air et l’etude des scenarios : ce modele numerique permet de cartographier les concentrations et les depassements de normes de la qualite de l’air sur le bassin (selon les normes en vigueur dans chaque pays). Ce modele permet a la fois un calcul de la pollution de fond regional par WRF/Chimere en prenant en compte l’ensemble des stations de mesures francaises et suisses puis un calcul a l’echelle de la rue sur l’ensemble du reseau routier, a l’aide du modele SIRANE ; - le calcul prospectif de scenarios d’emissions : cette action a permis d’elaborer des scenarios realistes a l’echeance 2020 et 2030, afin de cartographier et estimer l’evolution des emissions et des concentrations associees, ainsi que les populations impactees a ces echeances (entre 50 et 75 % de la population encore impactee sur le Grand Geneve pour les PM10, suivant les normes suisses actuelles en 2030). G²AME est une operation realisee dans le cadre du programme de cooperation territoriale europeenne INTERREG IV A France-Suisse 2007-2013.

The accurate localization and characterization of aerosol and cloud layers is crucial for climate studies (aerosol indirect effect), meteorology (Planetary Boundary Layer PBL height), site monitoring (industrial emissions, mining,…) and natural hazards (thunderstorms, volcanic eruptions).LEOSPHERE has recently developed aerosol/cloud detection and characterization on WINDCUBE long range Coherent Wind Doppler Lidars (CWDL). These new features combine wind and backscatter intensity informations (Carrier-to-Noise Ratio CNR) in order to detect (aerosol/cloud base and top, PBL height) and to characterize atmospheric structures (attenuated backscatter, depolarization ratio). For each aerosol/cloud functionality the method is described, limitations are discussed and examples are given to illustrate the performances.

The great particulate pollution event that affected the Paris Megalopolis in March 2014 was due to long-range transport from the northern-northeastern Europe. Although this phenomenon has appeared as exceptional in the media, this is not an exception and similar events have already been observed by lidar measurements. Here we will briefly describe and illustrate the origin of this intense pollution obviously harmful to health.

The FENNEC program aims to improve our knowledge of both the role of the Saharan Heat Low (SHL) on the West African monsoon and the interactions between the African continent and the Mediterranean basin through the Saharan dust transport. The Saharan desert is the major source of mineral dust in the world and may significantly impact the air quality over the Western Europe by increasing the particular matter content. Two lidar systems were operated by the French component of the FENNEC project: an airborne lidar which was flown aboard the French Falcon 20 research aircraft and a ground-based lidar which was located in the southeastern part of Spain, close to Marbella. The presence of dust in the Saharan atmospheric boundary layer has been easily highlighted using the lidars and confirmed by ground-based sunphotometer and observations from both MODIS and SEVIRI spaceborne instruments. The simultaneous use of the sunphotometer-derived Angstrom exponent and the lidar-derived backscatter to extinction ratio is appeared to be a good approach to separate the optical contribution of dust from local aerosols for the coastal site. Over Spain, the dust layer was mainly located above the planetary boundary layer with several kilometers thick. Over the tropical Atlantic Ocean and the Mauritania the airborne lidar shows a high planetary boundary layer (~5 km above the mean sea level) associated to strong aerosol optical thickness (> 0.8 at 532 nm). The airborne lidar data have been inverted using both MODIS and SEVIRI-derived aerosol optical thickness. The differences between dust optical properties close to and remote from the sources will be discussed.

In the framework of the FENNEC experiment (6 to 30 June 2011) an effort has been dedicated to characterize Saharan dust plumes transported towards southern Europe. Hence, a multi instrumented field campaign has been conducted. Ground based nitrogen Raman LIDAR (GBNRL) has been deployed in southern Spain close to Marbella, simultaneously with airborne lidar (AL) performing measurements over both the tropical Atlantic Ocean and the western Africa (from 2 to 23 June). The GBNRL was equipped with co-polar and cross-polar channels to perform continuous measurements of the dust aerosols trapped in the troposphere. It was developed by LSCE with the support of the LEOSPHERE Company. The French FALCON 20 research aircraft operated by SAFIRE (Service des Avions Francais Instrumentes pour la Recherche en Environnement) carried the AL Leandre Nouvelle Generation (LNG) as well as a dropsonde releasing system and radiometers. A major, one week long, dust event has been sampled over Spain from 25 June to 1 July with high optical depth (>0.5 at 355nm) and particular depolarization ratios (15 to 25%). Backtrajectory studies suggest that the dust particles observed were from dust uplifts that occurred in Southern Morocco and Northern Mauritania. The event has been also documented 3 days before by the AL flying over Mauritania. AERONET sunphotometer measurements of aerosol properties, along the dust plume transport path appear to be coherent with both the lidar and the backtrajectory analysis. These analysis exhibit a likely major contribution from the Western Sahara sources to the Southern Europe. Such a contribution may impact the visibility and then the airtrafic, modify the tropospheric chemistry, and add nutrients to both the Mediterranean Sea and the continental surfaces. It can also affect the health of European populations. We will present strategy of the experiment and the case study built from measurements performed at the end of June.

Following the eruption of the Icelandic volcano Eyjafjallajökull on the 14 April 2010, ground‐based N2‐Raman lidar (GBL) measurements were used to trace the temporal evolution of the ash plume from 16 to 20 April 2010 above the southwestern suburb of Paris. The nighttime overpass of the Cloud‐Aerosol LIdar with Orthogonal Polarization onboard Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite (CALIPSO/CALIOP) on 17 April 2010 was an opportunity to complement GBL observations. The plume shape retrieved from GBL has been used to assess the size range of the particles size. The lidar‐derived aerosol mass concentrations (PM) have been compared with model‐derived PM concentrations held in the Eulerian model Polair3D transport model, driven by a source term inferred from the SEVIRI sensor onboard Meteosat satellite. The consistency between model and ground‐based wind lidar and CALIOP observations has been checked. The spatial and temporal structures of the ash plume as estimated by each instrument and by the Polair3D simulations are in agreement. The ash plume was associated with a mean aerosol optical thickness of 0.1 ± 0.06 and 0.055 ± 0.053 for GBL (355 nm) and CALIOP (532 nm), respectively. Such values correspond to ash mass concentrations of ∼400 ± 160 and ∼720 ± 670 μg m−3, respectively, within the ash plume, which was lower than 0.5 km in width. The relative uncertainty is ∼75% and mainly due to the assessment of the specific cross‐section assuming an aerosol density of 2.6 g cm−3. The simulated ash plume is smoother leading to integrated mass of the same order of magnitude (between 50 and 250 mg m−2).

This study shows an aerosol content survey in the low and middle troposphere over Paris with a compact and light Nitrogen-Raman lidar which has been recently developed by the Commissariat à l'Energie Atomique (CEA) and LEOSPHERE company. This eye-safe and wide field-of-view system (full overlap between 150 and 200 m) is particularly well-adapted to air pollution survey in the vicinity of Megalopolis. Extinction-to-backscatter coefficient (so-called Lidar Ratio LR) profiles obtained with a Tikhonov regularization scheme are presented for long-range transport events of aerosols (volcanic ash plume LR = 48 ± 10 sr, and desert dust, LR = 45 ± 8 sr) which may contribute to the local load of aerosols emitted by traffic and industries in Megalopolis. Due to an insufficient signal to noise ratio (SNR < 30), a new dichotomous algorithm has been developed to perform daytime inversions every hour which is in accordance with the typical time evolution of aerosols within the planetary boundary layer. This inversion scheme is based on the constraint of the elastic channel with the aerosol optical depth (between typically 0.2 and 0.7 km) determined with the N2-Raman channel and thus only gives access to an equivalent LR between 0.2 and 0.7 km with a relative uncertainty lower than 15%. This approach has been applied to retrieve diurnal cycle of LR for polluted continental aerosols over Paris and is compared with Tikhonov regularization applied during the night. We found a mean value of 85 ± 18 sr for polluted continental aerosols which is in agreement with other studies performed around the Paris urban area. Results for aerosol optical properties are presented and the error sources are discussed for each approach.

A field campaign was conducted in London between 15 and 23 June 2009 in order to study the influence of emissions from within the London orbital motorway (M25) in terms of aerosol concentrations within the planetary boundary layer (PBL). The instrumental set-up involves a compact aerosol backscatter lidar, onboard a mobile van, developed by the CEA/LSCE and commercialized by LEOSPHERE Company and in situ instrumentation onboard the British Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 research aircraft devoted to aerosol and gas measurements. For this experiment, the eye-safe lidar has been working at the wavelength of 355 nm. These observations represent the first application of this lidar around the London area. Thanks to the excellent manoeuvrability of the van, we monitored the particulate emissions from vehicles on the M25 by circling the M25. Coordinated FAAM flights and lidar-van circuits were carried out around the M25. The possibility for the aircraft to perform vertical profiles into and out of airports gave us the opportunity to compare in situ measurements with lidar vertical profiles in terms of aerosol extinction coefficient. The aerosol extinction coefficient values shows spatial heterogeneities around the M25 and strong discrepancies were noticed between nephelometer and lidar measurements at 760 m. Such a severe discrepancy needs further investigation: the impact of clouds might be stronger and the correction of nephelometer values from relative humidity may be different, as suggested by lidar polarization observations showing higher values when relative humidity is lower. This work presents the first results of the spatiotemporal variability of aerosol concentrations in the London area. The future work particularly focuses on the link between the height of the different aerosol layers (convective PBL, nocturnal layer, residual layers...) and the aerosol loading in the low tropospheric column. The research aircraft enables a more accurate characterization of the detected plumes in terms of aerosol microphysical and optical properties. The coupling between active remote sensing and in situ measurements will allow the retrieval of vertical profiles of mass concentrations (PM10) in this urban environment with a very high vertical resolution (30 m).