1. Page 1 © Crown copyright 2004 Aircraft observations of Biomass burning aerosol Ben Johnson, Simon Osborne & Jim Haywood AMMA SOP0 Meeting, Exeter, 15 th May 2007

2. Page 2 © Crown copyright 2004 DABEX – Aircraft obs of BB aerosol MODIS Fire counts 13 th Jan – 3 rd Feb, 2006 Aircraft Run locations

3. Page 3 © Crown copyright 2004 Fresh smoke plumes  Smoke plumes: Aerosol concentration > 5000 cm -3 Mixing with mineral dust Smoke plume

4. Page 4 © Crown copyright 2004 Aerosol size distributions PCASP (0.05 - 1.5μm)

5. Page 5 © Crown copyright 2004 Absorption of solar radiation Dust Biomass aerosol Not absorbing Highly absorbing Aircraft Mean BB Aircraft mean dust

6. Page 6 © Crown copyright 2004 Vertical distribution Dust BB aerosol -------- 0.45  m ---------- 0.55  m ---------- 0.70  m Nephelometer wavelengths Dust BB aerosol Dust Biomass aerosol Mixture

7. Page 7 © Crown copyright 2004 Aerosol optical properties (@ 550nm) from Mie theory Aerosol typeSingle-scattering albedo (ω) Extinction coefficient K ext (m 2 g -1 ) Asymmetry parameter (g) Angstrom parameter (Å) Fresh BB0.803.70.492.4 Aged BB0.835.10.591.9 DUST0.98 +/- 0.02 0.330.75-0.1 n dust = 1.53 + 0.0004i, ρ dust = 2.65 g cm -3, n BB = 1.54 + 0.035i, ρ BB = 1.35 g cm -3

8. Page 8 © Crown copyright 2004 Aerosol direct radiative forcing (Solar only)  Edward & Slingo (1996) 2-stream radiation model with 220 bands.  Surface albedo = 0.28.  Solar parameters based on January 15th and latitude of 13.5N (Niamey). TOA forcing close to zero !! “hides” large surface and atmospheric changes.

9. Page 9 © Crown copyright 2004 Comparison with remote sensing data? AERONET/PHOTONS sunphotometers: AOD, size distribution, absorption, angstrom. MODIS Aerosol optical depth MISR Aerosol optical depth

10. Page 10 © Crown copyright 2004 Remote sensing vs aircraft: Optical depth MISRMODIS Good mean value but underestimates high AODs Not too bad, but only 4 data points!

11. Page 11 © Crown copyright 2004 Summary  Biomass-burning aerosol had very high SW absorption (x2 SAFARI), whereas dust was virtually non-absorbing.  Huge variation in size distributions and optical parameters, due to variable proportions of dust and biomass aerosol.

12. Page 12 © Crown copyright 2004 Collaborations / comparisons  More independent estimates of single- scattering albedo.  Obs of size distributions, optical and chemical properties and mixing state.  Radiative effect / forcing of aerosols.  Lidar vertical profiles – aircraft nephelometer

13. Page 13 (a)(b) Back trajectories from Niamey Origin of low-level dust at 0.5kmOrigin of BB aerosol at 3km

14. Page 14 © Crown copyright 2004 Remote sensing vs aircraft: Optical depth Aircraft uses profile of Neph+PSAP AERONET slightly lower than aircraft or Microtops Simon Osborne Aircraft