1. © Crown copyright Met Office PCASP Dr. Phil Rosenberg

2. © Crown copyright Met Office Instrument Status PCASP1 (the first one we bought) has been upgraded by DMT to the SPP200 electronics. Originally damaged in transit on return from USA Returned for repair Faulty upon receipt – turned out to be a bad PCB New board fitted and first test flight in Oct Measured spectrum intermittently looked odd – very bimodal. Turned out to be a bad contact one of the PCBs. Flying today! PCASP2 (the one we’ve been flying for the past two years) is functioning okay. Struggling to get good reference voltage, could be the laser on its way out, could be contaminated cleaning solvent. New solvent just arrived and instrument will be recleaned and aligned this week

3. © Crown copyright Met Office Calibration Calibration is now performed covering the full range from ~ 0.1 to 3 microns diameter. Using oleic acid or DEHS oil up to ~ 0.5 microns. Using PSL beads above this size – Began just before Volcano. Users should be aware of increased uncertainty where the two methods meet.

4. © Crown copyright Met Office Calibration Using PSL Beads

5. © Crown copyright Met Office Calibration Results

6. © Crown copyright Met Office Calibration Results

7. © Crown copyright Met Office Calibration Accuracy and Variability Accuracy of calibrated bin boundaries generally better than approx 10 % absolute. Accuracy of the bin widths is better than 1 % Bin boundaries tend to drift by only a few percent during normal use over a few months. Bin boundaries can change by up to 20 % when the instrument is cleaned and realigned.

8. © Crown copyright Met Office How Do We Get Particle Sizes Although PCASP measures scattering cross section, particle diameter is a much more useful parameter. If we assume the particles are homogeneous and spherical we can use Mie theory to relate cross section to diameter. The solution is dependant upon the particles refractive index.

9. © Crown copyright Met Office Theoretical Mie Curves

10. © Crown copyright Met Office Zooming in... Derive bin widths by summing the widths of the sub-bins Derive bin centre by averaging the centres of the sub-bins weighted by their widths

11. © Crown copyright Met Office Software to do this for you

12. © Crown copyright Met Office How to provide you with cal data? Data files used Resulting bin boundaries Calculated fit params Particle sizes and times

13. © Crown copyright Met Office The Impact of Calibration and RI Correction on Volcanic Ash Measurements

14. © Crown copyright Met Office Low level mass distribution

15. © Crown copyright Met Office Inlet efficiencies Whenever streamlines are bent small particles tend to follow the airflow, large particles do not. Subisokinetic Superisokinetic Isokinetic Image from Aerosol sampling: science, standards, instrumentation and Applications by J. H. Vincent,

16. © Crown copyright Met Office Flow Simulation

17. © Crown copyright Met Office What Can We Do About the Sampling Efficiency? Modelling may give some insight but requires large amounts of computing power. Wind tunnel calibration can give comparison to another well calibrated (isokinetic?) inlet, but only at surface pressures. Comparison in flight with (well characterised?) Low Turbulence Inlet on Fennec. Any modelling must be linked with modelling and measurement of large scale flow round the aircraft – possible EPSRC bid led by Glasgow to do this work.

18. © Crown copyright Met Office Summary Steady improvement since last year. Do you want cal data in the netCDF or do you want it as a separate text file? Do you want counting stats errors in the netCDF?