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)

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

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)

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

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

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

Test Case: 23rd June 2009

Focus on Clear Times1300Z 1400Z

1500Z 1600Z

Langley Extrapolation Results

Wind E to NE

Comparison with Other DataOPAL solar radiation PM10 PM2.5

Met Office Aerosol ForecastMODIS 550nm AOD 1050Z MODIS 550nm AOD 1240Z

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

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

Daytime, 23 June (10:10-12:50 GMT)Flight 4 (2/2)

Other area subjectsto pollution!

M25, Paris, 23/09/2009

Courtesy of P. Chazette, LSCE

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?

c.mcconnell@imperial.ac.uk

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

Longwave Aerosol Effect

AOD=1.0AOD=0.0

Theoretical calculations with SBDART, 8-12um.