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 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 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 Solar Radiation ( I ) Clear sky AOD at 550nm = 1.0

7. Test Case: 23 rd June 2009

8. Focus on Clear Times 1300Z1400Z 1500Z 1600Z

9. Langley Extrapolation Results Wind E to NE

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

11. EM25 Campaign 16 th – 26 th 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. 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 Courtesy of P. Chazette, LSCE

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

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.