Claire McConnell Ralf Toumi (Imperial College) EM25:

1. Aerosol Measurements in London using the OPAL Weather Station Network:Preliminary Results from the EM25 Campaign Claire McConnell Ralf Toumi (Imperial College) EM25: Jim Haywood (Met Office), Patrick Chazette (LSCE), Will Morgan (Manchester)

2. Motivation • Measurement of column aerosol load • Total column load important for radiative effect (SW and LW), interaction with clouds, long range transport • Spatial distribution of aerosol across London • Transport of London aerosol plume, input from outside London • Development of a cheap, automatic, freely available, educational network of measurements across London

3. OPAL Weather Station Network • Currently 38 Davis weather stations in London – a few more awaiting installation • Measure pressure, T, RH, precipitation, wind speed & direction, solar radiation, UV index • Data recorded every minute • Most located in schools • Locations not always optimal, data uncalibrated (so far)

4. LGfL Weather Website • Data publicly available at http://weather.lgfl.org.uk • Publicly available for previous month • Complete (secure) archive • All data • Requires registration • Allows csv downloads

5. Using Solar Radiation to Infer Aerosol Loading • Dense network of solar radiation measurements (low quality?) – probably only existing urban network • Simple method to capitalise on high density measurements: • Use change in solar radiation flux over time to infer amount of aerosol • → spatial distribution of aerosol • Sky must be clear! • Data available for every minute, presently using 30 minute averages

6. Technique: Langley Extrapolations Solar Radiation (I) • Plot ln(I) against air mass (1/cos(θ) ) • Calculate gradient of ln(I) and air mass • Magnitude of gradient indicates amount of aerosol present Time Clear sky AOD at 550nm = 1.0

7. Test Case: 23rd June 2009

8. Focus on Clear Times 1300Z 1400Z 1600Z 1500Z

9. Langley Extrapolation Results Wind E to NE

10. Comparison with Other Data PM10 OPAL solar radiation PM2.5 Met Office Aerosol Forecast MODIS 550nm AOD 1050Z MODIS 550nm AOD 1240Z

11. EM25 Campaign • 16th – 26th June 2009 • BAe145 aircraft • circuits around London and the UK coast • Vertical profiles at Farnborough, Northolt, Biggin Hill, Southend • Aerosol size distribution, scattering, absorption, composition • Chemistry (CO, Ozone, NOx...) • Met variables • Lidar (failed) • French Lidar van • circuits around M25, cross-sections from Reading to Imperial • Vertical profile of back scatter

12. Courtesy of P. Chazette, LSCE Daytime, 23 June (10:10-12:50 GMT) Flight 4 (1/2) Trip between Reading and Dover during the comeback to France. Cloud free condition. M25, Paris, 24/09/2009

13. Courtesy of P. Chazette, LSCE Daytime, 23 June (10:10-12:50 GMT) Flight 4 (2/2) Other area subjects to pollution! M25, Paris, 23/09/2009

14. Next Steps... • Look-up table to convert from measured Langley gradient to AOD • Switch to high resolution OPAL data (every minute) • Sensitivity tests • Calibration/instrument comparisons • Other clear days? • Longwave radiative effect of London aerosol • IR camera for EM25 campaign • Weather station data • Urban heat island?

15. c.mcconnell@imperial.ac.uk

16. PM2.5 in 2 hour intervals Note change in pattern throughout day from E-W split to NE-S split

17. Longwave Aerosol Effect AOD=1.0 AOD=0.0 Theoretical calculations with SBDART, 8-12um.