Plans to study horizontal NO2 distribution

Ankie Piters, Tim Vlemmix, KNMI

data from: INTA, IUPB, JAMSTEC, KNMI, Leicester, NASA

Objectives:

– Satellite pixel inhomogeneity

– 3D-field of view of MAXDOAS-like instruments

IUPB, INTA, JAMSTEC (287o) 10-25 July

NASA_P2 (66o) 14-20 July

Leicester (326o) 10-22 July

NASA_P3 (187o) 14-20 July

KNMI (253o) 14-25 July

more directions anticipated from: BIRA, IUPB, IUPH

Idea

• use different times and viewing directions

• transport each measurement with the current wind to satellite overpass time

• determine horizontal distribution of NO2 inside satellite pixel

What is the effective location of the measurement?

• Somewhere between top op PBL and surface?

? ? ?

20 July, between 6 and 10:

• average wind speed at 200m: 8.7 m/s

• average wind direction at 200m: 264o

• line IUPB – NASA_P2: 266.5o

similar air mass observed by IUPB

and NASA_P2, with time delay

DSCD*AMFgeom

• time delay is clearly visible

• calculate correlation as a

function of time delay

elevation 30o

elevation 15o

R

time delay (hour)

-0.11-0.20

time delay distance

• 0.11 hour at 8.7 m/s 3.4 km for 30o elevation

• 0.2 hour at 8.7 m/s 6.3 km for 15o elevation

• variations in NO2 signal originate at 1.8 km for 30o

elevation and 3.4 km for 15o elevation (for this day)

3.4 km (6.3 km)

1.8 km (3.4 km)139o

20.5o

distance altitude

• the variations in NO2 we see

on 20 July, 6-10h, are

originating at ~0.9-1 km

• BLH, cloud base?

• other examples?

3.4 km 1.8 km

1 km

0.9 km30o

15o

How can the data be combined?

• All data processed with same settings (semi-blind

intercomparison)

• Correct for known differences between instruments

• Subtract dscd at 90o, closest in time

• Use measured AOT, BLH

• Use correct AMFs

• measurements

transported to OMI

overpass time

Cabauw

latitude

latitude

long

itude

long

itude

OMI pixel

OMI pixel

30o elevation

4o elevation

dAMF, 8 UT

• AOT=0.2, BLH=1.0 km

• AOT=0.3, BLH=1.0 km

• AOT=0.2, BLH=0.9 km

NASA_P2

IUPB

summary

Effective measurement location for 20 July is near the

boundary layer height, how about other days/situations?

The lower elevation angles can be used to ‘fill up’ an OMI

pixel, 30/15o will give only one dimension

Trying to get overlapping data consistent will give more

insight in the validity of the AMFs and the assumptions

used in the calculation of the AMFs.

to do ….

• collect data:

– NO2 DSCD data for the period 10-25 July: BIRA, IUPB, IUPH

– reference data: NO2 lidar (RIVM), in-situ data (Bremen, RIVM, EMPA),

direct sun (BIRA, NASA) and zenith sky (CNRS)

– auxiliary data: aerosol, BLH, clouds

• study (in-)consistencies for same air mass observations

• determine horizontal gradients for selected days, possibly combined

with the mobile measurements (BIRA, CNRS, MPI)

• compare to satellite data

• make recommendations on observation strategies