1. LOAC (Light Optical Aerosol Counter): a new small balloon-borne aerosol counter/sizer with some particle characterization capabilities J.-B. Renard, G. Berthet, F. Jegou, M. Jeannot LPC2E-CNRS, Orléans, France F. Dulac, J. Sciare, J. Nicolas LSCE/CEA, Gif-sur-Yvette, France M. Mallet, P. Durand LA, Toulouse, France C. Thaury, S. Salles, J.-L. Mineau, T. Tonnelier Environnement-SA company, Poissy, France N. Verdier CNES, Toulouse, France P. Charpentier MeteoMODEM company, Ury, France J. Giacomoni Aerophile SA company H. Olafsson Iceland University

2. Different types of aerosols in the troposphere and the stratosphere, having different origins Interplanetary grains Pollution Volcanoes Transported sands Disintegrated meteorites Biomass burning (and pyroconvection)

3. How to study aerosols when not at ground?  From satellites (remote sensing of the atmosphere) - Estimation of aerosols size and nature (using some hypothesis for the data analysis)  Aerosols Lidar measurements from Calipso Extinction from GOMOS/envisat

4. From dedicated aircrafts and from (large) balloons:  - Collecting techniques, optical instruments Aerosol counter STAC operated in the middle atmosphere, below stratospheric balloons Vertical profiles and size distribution … assuming liquid particles (which is not always the case even in the stratosphere)

5. Only sparse in situ measurements and strong constraints:  - High costs (aircrafts and balloons)  - Technical limitations (how to fly during strong volcanic eruption?)  - Need of complex infrastructures (few launching bases in the world for the stratospheric balloons) There is a need for an aerosol counter that can be launched under all kinds of balloons (including meteo balloons) : - Low cost (the instrument can be lost after the flight) - Light instrument - Insensitive to the aerosols nature (accurate determination of size), which is not the case with the usual aerosol counters.

6. LOAC : Light Optical Aerosol Counter Measurements at 2 scattering angles : 12°, where the scattered light is ~ insensitive to the nature of the aerosols 60°, where the scattered light is very sensitive to the nature of the aerosols Combining the measurements => accurate determination of the size distribution => estimation of the main nature of the aerosols Aerosols Laser

7. Collaboration between French research institutes and private companies LOAC was design and tested in our institutes (CNRS and CNES) LOAC is build by Environnement-SA company Gondola and telemetry are build by MeteoMODEM company

8. - 20 size classes between 0.4 - 100  m - - Optical chamber and pump: weight < 500 g - Can work during 4 hours with 2 alkaline batteries of 4.5 V -Total weigh with gondola for flight under meteo balloon : 1 kg (using meteoMODEM telemetry) Large stratospheric balloon Long duration stratospheric balloon Meteo balloon Low altitude troposheric balloon

9. First version of LOAC (10 copies 2011-2012): 3 flights under large stratospheric balloons (Sweden and Brazil) 6 flights under meteo balloons (Iceland, France) 9 months onboard a tethered balloon (Touristic balloon “Air de Paris”) 4 LOAC are lost … Improved version of LOAC (20 copies at the end of 2012) 2 test flights under meteo balloon at the end of August 2012 (France)

10. Kiruna, Northern Sweden, 1 April 2011 (large stratospheric balloon, onboard German gondola TWIN, CNES launch) Strong variability of aerosol content

11. West Iceland, 20 July 2011 (meteo balloon, Iceland meteo office launch)  “clean stratosphere”

12. Comparison of the 2 measurements channels at scattering angles of 12° and 60° (size distributions) => identification of the main nature of the aerosols (by comparison to a laboratory data base) The 2 curves are close => liquid aerosols

13. Bauru (Brazil), 13 March 2012 (stratospheric balloon, Reims University “Tropico project”) Several enhancements of “large” particles around 10  m Soot particles ?

14. Sausset-les-Pins (France), 28 June 2012 (meteo balloon, CNES) 2 flights during an episode of sand above Mediterranean sea Size grains in the 5-30  m range

15. At ground, liquid aerosols (launch on the beach) On the middle troposphere, sand Data Carbon Mineral Droplets Data Carbon Mineral Droplets

16.  LOAC is involved in several projects: Mid-september 2012 : tests of the new version of LOAC during sand events, meteo balloon (Meteo France) Winter 2012-2013: ParisFog campaign, study of fog, tethered balloon (SIRTA – meteo France) Beginning of 2013: Tests onboard low altitude tropospheric balloons “BPCL” (CNES) Summer 2013: Charmex campaign, study of aerosols transport above Mediterranean sea, BPCL and meteo ballons (CNES) End of 2013: Aerowave campaign, stratospheric aerosols, large stratospheric balloons (CNES) … 2018 : Strateole phase 2, tens of long-duration stratospheric balloons above equatorial regions