Aerosol counting measurements with the LOAC light instrument using weather balloons Gwenael BERTHET, Damien VIGNELLES, Jean-Baptiste RENARD, Fabrice JEGOU, Thibaut LURTON, Matthieu JEANNOT, Benoît COUTE, Vincent DUVERGER LPC2E-CNRS, Orléans, France François DULAC LSCE-CEA / IPSL, CEA Saclay 701, 91191 Gif-sur-Yvette, France MeteoModem, Environnement SA and Aerophile private companies

Sources of aerosols in the upper troposphere and lower stratosphere +organics? Need for observations of aerosol size distributions to assess Chemistry Climate Models or estimate their radiative/chemical impacts Only a few in situ aerosol instruments (e.g. counters) mounted onboard aircrafts or balloon platforms

stratospheric sulfate aerosols SPARC Aerosol Assessment, 2006 Gaseous precursors: SO2 and OCS (carbonyl sulfide) 

Light Optical Aerosol Counter ● Collaboration between national research laboratory, 2 private companies, and the French Space Agency More than 90 copies produced at mid-2015 (now a commercial instrument sold by the MeteoModem company) ● Technical details: Instrument and pump: 300 g Electric consumption: ~3 W Concentrations for 19 size classes between 0.2 and ~50 mm (diameters) Automatic check every 10 minutes and electronic recalibration if necessary (ex. strong changes in temperature) Uncertainties: 60% for concentrations <10-2 cm-3, 20% for 10-1 cm-3, 6% for concentrations > 1 cm-3

Principle of measurements 2 scattering angles measurements (field of view of few degrees) ~12°, insensitive to the refractive index of the particles (mainly diffraction) => accurate size determination and counting ~60°, strongly sensitive to the refractive index of the particles => indication of the nature of the particles Detection of the maximum of intensity for particles that cross the laser beam Real-time stray light correction

The 12°/60° ratio is compared to charts obtained in laboratory for different families of particles: - Liquid droplets - Minerals - Carbons This is an open data base and other natures of particles can be considered (no more than 3 or 4 different natures) Speciation index

Pollution carbonaceous particles Saharan sand plume Pollution carbonaceous particles Size distribution Size distribution 12° angle 12° angle topology topology

Light => high reactivity of use LOAC is used at ground and under all kinds of balloons for scientific purposes tethered, weather, low troposphere, stratosphere + On-board Unmanned Airborne Vehicles (Fly-N-Sense Society)

In the Boundary Layer: fog events south suburbs of Paris 12° angle Size distribution End of the fog Welas and Fog Monitor : optical counters topology

In the Boundary Layer: pollution events Counting measurements can be converted to PM 2.5 and PM10 mass (mg/m3) Comparison with microbalance measurements from Airparif ambient air network

In the Boundary Layer: pollution events Strong pollution event of 11 December 2013 At 200m, carbonaceous particles

In the free troposphere: Mediterranean aerosols (CHARMEX campaign) Comparison with lidar and sunphotometer measurements LOAC data converted to extinction and to integrated volume concentrations

Tropospheric volcanic particles Weather Balloon flights in Iceland, one inside the Holuhraun volcano plume

lower stratosphere: Volcanic plume in the tropics Flight performed from the Réunion Island On may 19th 2015 (Morgane campaign) Calbuco Chilean volcano plume The balloon has crossed two volcanic plumes - the Piton de la Fournaise plume around 3 km - the Calbuco plume around 18 km Piton de la Fournaise plume LOAC concentration aerosols and LIDAR profiles Preliminary results

Stratosphere: example of mid-latitude profiles (44°N 0°E) Recurrent launches (2 per week) from a mid-latitude site (44°N, 0°E) to explore stratospheric aerosol variability 11 March 2015 12 January 2015 ALTITUDE (km) ALTITUDE (km) dN/dLogD (cm-3) dN/dLogD (cm-3)

Application of this aerosol sounding strategy to the study of the Asian Tropopause Aerosol Layer (ATAL) Formation of an aerosol layer in the tropopause region in the Asian monsoon anticyclone Connection with deep convective processes over the Indian subcontinent Indication of production of secondary aerosol formation Aerosol composition in the lower part of the ATAL: carbonaceous and sulfate material Vernier et al., GRL, 2011; JGR, 2015

Application of this aerosol sounding strategy to the study of the Asian Tropopause Aerosol Layer (ATAL) BATAL 2015 campaign Managed by Jean-Paul Vernier Expected launches of LOAC from Varanasi in August 2015 1 kg LOAC version for weather balloons The instrument must fly alone because electronics in this configuration are sensitive to electromagnetic radiation

Application of this aerosol sounding strategy to the study of the Asian Tropopause Aerosol Layer (ATAL) BATAL 2015 campaign Expected results: Size distributions of aerosols in the ATAL for diameters in the 0.2-50 µm range Information about their type, e.g. signature carbonaceous material confirmed ? Possible detection of cirrus clouds if any Example of size distributions recorded in the troposphere

Future - Improved version of LOAC in development - Flight of several hours in the stratosphere (large stratospheric balloons, Canada) - Detection of charged aerosols - Flights on alert in case of strong (Icelandic) volcano eruption, in the tropics (La Réunion site) - STRATEOLE, balloon flights of several months in the lower equatorial stratosphere - Space application : Studies of planetary atmospheres (at present, participation to a proposal for the Saturn atmosphere)

SUMMARY ● LOAC instrument ● Campaigns - Can provide size distribution (0.2 - 50 µm) and information on main type of aerosols - Light instrument for ground and airborne measurements, high reactivity for launching - Development between the CNRS National institute and private companies but now a commercial instrument - Many ground-based comparisons with other instruments (other counters, microbalances, lidars) – paper in revision in AMTD ● Campaigns - Pollution and fog studies in urban areas (ground, tethered balloons), transport of Saharian sand particles - ~25 flights per year at different latitudes (France, Iceland, Indian Ocean) for the in situ monitoring of the stratosphere (as done from Univ. of Wyoming) using weather balloons (similar strategy as done for ozone soundings throughout the world) Short-term: BATAL 2015: next August from Varanasi for the study of the ATAL Regular flights from La Réunion Island Longer term: - Improved version in development (better signal-to-noise ratio, electronics, more scattering angles) - Flights on alert in case of volcanic eruptions - Balloon flights of several months in the lower equatorial stratosphere (STRATEOLE2 project) - Space application : Studies of planetary atmospheres