1. Observations of volcanic ash by lidar, MODIS and surface air-quality measurements Robin Hogan University of Reading Last updated: 18 April 2010

2. 15 April: 1139 UTC NASA MODIS radiometer

3. 15 April: 1329 UTC NASA MODIS radiometer

4. 16 April: 1044 UTC NASA MODIS radiometer

5. 16 April: 1224 UTC NASA MODIS radiometer Stationary colours in the sea (sediment and algae) x Chilbolton x Cabauw Volcanic ash

6. Chilbolton Doppler lidar: 16 April Descending volcanic ash? Vertical velocity shows turbulence in boundary layer and also in ash layer Mixes into turbulent boundary layer Background aerosol particles in the boundary layer (0-1 km)

7. Chilbolton Doppler lidar: 16 April Descending volcanic ash? Mixes into turbulent boundary layer Spherical liquid droplets have very low depolarization Ash is non-spherical so strongly depolarizing Background aerosol particles in the boundary layer (0-1 km)

8. Chilbolton Doppler lidar: 17 April Further images at http://www.met.reading.ac.uk/radar/realtime/today.html Normal aerosol particles in the boundary layer: no further sign of volcanic ash…

9. Surface sulphur dioxide Spike due to volcanic ash? Much less that UK air quality objective (1 hr average exceeds 350  g m -3 less than 24 times per year)

10. Aerosol particles (PM10s) Much less clear sign of ash

11. Possible ozone chemistry at Reading (speculative!) Further data at http://www.airquality.co.uk/ Possible NO 2 source due to volcano? Converted to NO when sun comes up? NO 2 + sunlight  NO + O Large ozone depletion: O 3 + NO  NO 2 + O 2

12. Ultraviolet EZ-lidar, Cardington Bedfordshire, 16 th April http://www.metoffice.gov.uk/corporate/pressoffice/2010/volcano/lidar/ This plot was produced by the University of Manchester, NCAS and FGAM.

13. RIVM Caeli lidar, Netherlands, 16 th April Courtesy of Arnoud Apituley RIVM Caeli lidar, Netherlands, 16 th April Courtesy of Arnoud Apituley This lidar is not operated all the time but has Raman capability Further images here: http://cerberus.rivm.nl/lidar/Cabauw/2010/ Volcanic ash just above boundary-layer

14. Cabauw EZ-lidar, Netherlands, 16 th April Courtesy of David Donovan, KNMI Cabauw EZ-lidar, Netherlands, 16 th April Courtesy of David Donovan, KNMI Ash appears not to mix into the boundary layer as it did over Chilbolton… As over Chilbolton, ash much more depolarizing than ordinary boundary-layer aerosol

15. Cabauw EZ-lidar, Netherlands, 18 th April Courtesy of David Donovan, KNMI Cabauw EZ-lidar, Netherlands, 18 th April Courtesy of David Donovan, KNMI Is this volcanic ash too? Why does it not mix into the boundary layer? De Bilt radiosonde put midday boundary-layer top at ~1 km

16. Cabauw EZ-lidar, Netherlands, 18 th April Courtesy of David Donovan, KNMI Cabauw EZ-lidar, Netherlands, 18 th April Courtesy of David Donovan, KNMI Further images: http://www.knmi.nl/~knap/lidar_cabauw/ Another layer coming in?

17. Thursday 15 th, 1329 Summary from MODIS images Icelandic wind from northwest Further images: www.sat.dundee.ac.uk Volcanic ash

18. Friday 16 th, 1234 Volcano obscured by clouds Dilute volcanic ash measured over southern England and the Netherlands with lidar, signs of reaching the ground in England

19. Saturday 17 th, 1317 Wind at Iceland from the north Volcanic ash heading south behind a cold front Cold front Volcanic ash No depolarizing aerosol observed over Chilbolton or Cabauw

20. Sunday 18 th, 1222 Northerly winds weakening Is this the ash above the cloud? Weakening front Not much sign in the MODIS image of the depolarizing aerosol observed at Cabauw but could be optically thin