1.
Instrumentation
The C-130 was equipped with the standard instrumentation fit
detailed in Johnson et al. (2000). In addition to the standard instrumentation,
the following equipment was fitted specifically to achieve the objectives of
SAFARI-2000. Table 1 shows the specialized additional instruments fitted to the
C-130 and the status of each during each flight.
1.1 Aerosol and cloud measurements
Aerosol size distributions
between 0.05-1.5 mm radius were
determined with a Particle Measuring System (PMS) Passive Cavity Aerosol
Spectrometer Probe (PCASP). A Fast Forward Scattering Spectrometer Probe
(FFSSP) developed from a PMS FSSP was used to measure aerosol and cloud
particles between 2-47 mm diameter,
while a PMS two-dimensional cloud probe (2-DC) measured drizzle-sized drops
between 25-800 mm diameter. The Small
Ice Detector (SID), developed jointly by the Met Office and the University of
Hertfordshire (Hirst et al., 2001),
was also fitted. SID was originally designed to measures particle shape, size
and concentration to discriminate between super-cooled water drops and ice
crystals in the diameter range 1-25 mm. However, coarse mode aerosol particles
are also detectable and may be sized. Total aerosol concentrations down to a
nominal 3 nm in diameter were measured with a TSI condensation particle (CP)
counter model 3025. Cloud condensation nuclei (CCN) supersaturation spectra
were measured with a Met Office CCN counter which is based on the thermal
gradient diffusion chamber design (Saxena et
al., 1970). The operating supersaturation range was normally between 0.1
and 1.2 % with respect to liquid water. The CCN counter builds up a spectrum by
subjecting individual samples of air drawn from a large bag sample to (usually)
5 supersaturations within the above range. Aerosol chemistry was determined
from isokinetic sampling onto filter substrates. Two filter packs were used:
quartz filter packs for black and organic carbon analysis, and Teflon packs for
major cation and anion chromatography.
Each of these packs had a Nuclepore filters mounted in front of them to
fractionate the particles into a coarse (onto the Nuclepore) and fine (onto the
Teflon or quartz) fraction, the approximate cut between coarse and fine
particles being 1.3mm diameter. These
filters were subsequently used with an electron microscope to determine the
shape of the aerosol particles. Chemical speciation was performed for inorganic
soluble ions using ion chromatography (Andreae et al., 2000). Inorganic soluble
and insoluble ions were determined using Particle Induced X-Ray Emission and
Instrumental Ion Activation Analysis (Maenhaut and Zoller, 1977). Black carbon
was determined using a light transmission technique (Andreae, 1983), and
organic carbon was determined using a thermal-optical transmission technique
(Birch and Cary, 1996). Particulate absorption of radiation of wavelength 0.567
mm was measured with a Radiance
Research Particle Soot Absorption Photometer (PSAP). Aerosol scattering was
determined at 3 wavelengths (0.45, 0.55, 0.70 mm)
with a TSI 3563 nephelometer. Corrections were applied to the data from the
PSAP to account for inaccuracies in the flow rate, area of exposure of the
filter, and absorption artifacts following the analysis of Bond et al. (1999). Corrections to the
nephelometer to account for the truncation of forward-scattered radiation were
applied following the results of Anderson and Ogren (1998). In addition to the
FFSSP and 2-DC for measuring droplet sizes, cloud liquid water content was
measured with two hot wire probes: the Johnson-Williams and the Nevzerov. Total
water content was measured with a Met Office Lyman-Alpha absorption hygrometer.
1.2 Radiation measurements
The C-130 was
equipped with upward and downward facing Eppley broad-band radiometers (BBRs)
fitted with clear and red domes with aft mounted obscurers which cover the
0.3-3.0mm and 0.7-3.0mm spectral regions respectively (see Haywood
et al., 2001). Upward and downward facing pyrgeometers are also mounted
adjacent to the pyranometers, which detect down-welling and upwelling
irradiances respectively over the 3.0-50mm
spectral range. A new narrow field-of-view (approximately 1.5o half
angle) nadir-viewing Short Wave Spectrometer (SWS) manufactured by Zeiss was
fitted to the aircraft to determine the upwelling solar radiance over the
spectral region 0.3-1.7mm in 324
continuous spectral bands. The nominal width of the spectral bands is
approximately 3.3nm in the 0.4-0.96mm
spectral region and 6nm in the 0.96-1.7mm
spectral region. The Met Office Scanning Airborne Filter Radiometer (SAFIRE)
measures radiances in 16 bands across the visible and near-infrared region of
the spectrum and was mounted in a pod on the port wing of the C-130. It was
operated almost exclusively in either nadir or zenith viewing modes. The
Airborne Research Interferometer Evaluation System (ARIES) measured terrestrial
radiances over the wavelengths 3.33-16.7mm
(3000-600cm-1 wavenumbers) at 1cm-1 wavenumber
resolution, and was mounted in a pod on the starboard wing of the C-130. While
capable of scanning, ARIES was operated almost exclusively in either nadir or
zenith viewing modes.
1.3. Chemistry measurements
Continuous measurements of ozone (TECO 49, UV absorption
technique) and carbon monoxide (resonance-fluorescence technique, developed by
fz-Juelich) were made throughout the SAFARI campaign. Sequential measurements
of NO and NOx (10 second averages) were also made for flights (TECO 42,
chemiluminescent technique). Measurements of acetonitrile, a unique tracer of
biomass burning, and acetone were obtained at a high resolution by Mass
Spectrometry (University of Mainz). It is hoped that a plume age can be obtained
from measurements of a range of C2-C7 non-methane hydrocarbons from bottle
samples and from benzene and toulene measurements from an on-board gas
chromatograph (University of Leeds). It is also envisaged that using the
hydrocarbon concentrations obtained photochemical production rates of acetone
can be estimated using a simple lagrangian model. Bag samples were also
obtained, in order to investigate emissions of carbon monoxide, nitrous oxide and methane from the biomass burning
plumes.
2. Flight patterns
The C-130 of the UK Met Office performed 8
dedicated flights from Windhoek, Namibia during the period 5-16 September 2000,
with two additional scientific transit flights Windhoek-Ascension Island on 2
September and 18 September, 2000, for a
total of approximately 80.5 hours. Table 1 shows the dates, duration, operating
region and objectives of the flights, and Figure 1 shows the flight tracks of
the C-130. Back trajectories suggest that the C-130 was generally operating
downwind of the significant sources of the biomass aerosol and that the aerosol
was typically a few days old. The majority of the flights were performed over
the ocean where the surface is relatively well-characterised, but two flights
were performed over the Etosha CIMELS sites with co-incident MODIS, MOPPITT and
MISR swaths from the TERRA satellite. Additionally, on September 13 the
aircraft operated in a fresh biomass plume over an anthropogenically induced
biomass fire near the agricultural town of Otavi in northern Namibia.
The dedicated
flight patterns typically consisted of straight and level runs (SLRs) within,
below and above the aerosol layer, with profiles in between. The SLRs within
the aerosol layer concentrated on in-situ sampling of the aerosol size
distributions with the PMS probes and SID, collection of filter samples to
determine aerosol chemistry, and in-situ measurements of the scattering,
back-scattering and absorption coefficients with the nephelometer and PSAP. The
SLRs below the aerosol layer typically consisted of a pair of into- and
down-sun legs performed at 30m ASL to enable determination of the direct and
diffuse components of irradiance and the aerosol optical depth (Hignett et al.,
1999). At low levels, SAFIRE and ARIES typically performed zenith views looking
up through the aerosol layer to determine the spectrally resolved downward
radiances. Orbits were also performed at low-levels to determine the spectrally
resolved angular distribution of the radiances from the SAFIRE instrument
(Francis et al., 1999). The SLRs above the aerosol layer enabled determination
of the aerosol optical depth from the upwelling irradiances from the BBRs over
ocean surfaces (Haywood et al., 2001a; 2001b). At high levels, SWS, ARIES and
SAFIRE typically performed nadir views to determine the spectrally resolved
upwelling radiances looking down through the aerosol layer.
3.Vertical profiles of CO
and aerosol concentrations.
Vertical profiles of
aerosol particle concentration, nephelometer scattering coefficient and carbon
monoxide were found to be well correlated. Two distinct types of aerosol
profile were observed, corresponding to over land and over ocean.
3.1. Vertical profiles over land
Figures 2 and 3 shows the
vertical profile of the CO (ppbv), nephelometer 0.55mm scattering coefficient (m-1), and PCASP number
concentration (cm-3) over the Etosha CIMELS site on 6 September
2000. At 10:00GMT (Figure 2), the decoupling of the boundary layer is
discernable, with the largest concentrations of CO and aerosol and scattering
coefficients in an elevated layer between approximately 3000-5250m ASL. By
12:00 GMT (Figure 3), the concentrations of CO and aerosol become well mixed
from the surface to 5250m in response to the strong surface heating and
associated dry convection.
3.2 Vertical profiles over ocean
Figure 4 shows
typical profiles of CO, aerosol scattering coefficient and aerosol number
concentration over the ocean. The main aerosol layer is at 3000-5000m ASL with
elevated aerosol concentrations down to 1500m. There is a distinct ‘clean slot’
where the aerosol concentrations, aerosol scattering and CO concentrations are
much reduced to pristine conditions above the Sc cloud which is capped by a
strong (10K) inversion. These conditions were found almost universally between
flights indicating that aerosol/cloud interaction was insignificant thus an
indirect effect in the Sc sheets appears unlikely. The implications of this
finding are far reaching – if the absorbing aerosol exists above the cloud
layer and there will be no indirect effect, and the net radiative forcing of
the aerosol may be positive rather than negative as suggested by the recent
IPCC (2001) report. Investigations using the observed optical properties of
biomass aerosols detailed in section 6 together with observed cloud fields
suggests that this may indeed be the case. Further investigation is required
before this result is generally accepted.
4.
Aerosol size distributions
Size distributions
from the PMS probes were measured during the duration of the campaign. Because
the C-130 was operating a significant distance downstream of the main areas of
biomass burning, the aerosol size distributions measured were representative of
aged biomass aerosol. The size distributions presented here represent the
flight average of aerosol size distributions measured during straight and level
runs, each of which was of at least 10 minutes duration. The size distributions
therefore represent typical aerosol size distributions encountered for each
day. An exception is for flight a790 on Sept 13 when the aircraft operated over
a large biomass fire in agricultural land spanning an area in excess of 8km2
near the town of Otavi. These measurements are taken from three straight and
level runs at mean altitudes of between 980ft and 693ft AGL, which was as low
as the aircraft could safely operate because of the proximity of the Otavi
mountains on either side of the biomass plume. A particle threshold of greater
than 5000particles/cm3 was applied so that these aerosol
distributions are representative of fresh biomass burning aerosol which is a
few minutes old.
The average
normalised number and normalised volume distributions obtained for each flight
during the campaign from the PMS probes are shown in Figures 5a and 5b. Figure
5a shows that the aged aerosol number-distribution shows a similar shape for
each day, with a mode radius of 0.14mm,
and evidence of another mode close to 1.13mm.
The most significant variations for different days is in the super-micron
particles measured by the FFSSP. Figure 1b shows the same measurements plotted
as volume distributions. The two modes at 0.14mm
and 1.13mm are both clearly visible.
Furthermore, some of the distributions (e.g. a790) show a further mode at a
radius of approximately 10mm, this mode
of coarse particles is particularly noticeable in the measurements made in the
biomass plume at Otavi.
Additional
measurements with the PMS probes were performed at 100ft ASL to determine the
size distribution of marine aerosol. The resulting size distributions are shown
in Figure 6. These aerosol distributions should be applied to the marine
boundary layer (generally the lowest 1-2km) in radiative transfer calculations
in closure studies/satellite retrieval algorithms.
5.
Aerosol chemical composition
Aerosol chemical composition analyses have not yet
been fully completed. However, BC has been determined using the light
transmission technique, and OC has been determined using the thermal-optical
transmission technique. These analyses are summarised in Figures 7 and 8. The
mean BC/OC mass fraction for aged aerosol is 0.08. These results are similar to
the results of Ferek et al. (1998) who reported BC/OC mass ratios of 0.08 for
smoldering fires during SCAR-B and Reullan et al. (1999) who reported BC/OC
ratios of 0.08 for savanna haze. This ratio of BC/OC is used in deriving the
aerosol optical properties in section 7.
6. CCN measurements
Figure 9 shows three CCN curves representing relatively young
biomass aerosol (~12 h over the sea) from 7 September, aged biomass aerosol (~4
days over the sea) from 16 September, and one spectrum from just above the
subsidence inversion within the 'clean slot' from 7 September (see Figure 4).
Concentrations of CCN are lower across the whole supersaturation range in the
aged aerosol compared to both the younger aerosol and the clean layer. The
differences between the young and the aged biomass aerosol CCN spectra may be
due to a combination of dilution and homogeneous aerosol processing.
Interaction of the biomass aerosol with boundary layer cloud is very unlikely
and so cloud processing (including washout) is unlikely. Calculations reveal
sedimentation is unlikely to significantly affect aerosol concentrations for
particles of the order of 0.1 mm and
smaller. The reasonable levels of Aitken particles (and CCN) in the clean slot
relative to the aged biomass probably arose through secondary particle
formation. The low concentrations of Aitken particles in the aged biomass
probably resulted from coagulation of these particles and hence growth into the
accumulation mode.
The gradients of all three curves are similar at
supersaturations greater than 0.4 % and was typical for all observations of the
biomass aerosol over sea and land. Although the aged curve contains lower
aerosol concentrations, the shape and chemistry of the aerosol size spectrum
has probably changed little. The gradient of the curves below 0.4 % are quite
different, with a much steeper gradient in the younger aerosol while the aged aerosol
has an approximately linear relationship. These results are consistent with
previous studies of CCN curve gradients (Desalmand, 1985).
The CCN to total CN ratio at 1.0 % supersaturation does not
change between the young aerosol in A787 and the aged aerosol in A792 i.e.
0.37 +/- 0.06 (one S.D.) and 0.36 +/-
0.20, respectively. Again, this indicates very little processing of the aerosol
in terms of the size spectrum and chemistry, apart from dilution. The CCN to CN
ratios within the clean slot were higher 0.80 +/- 0.06 at 1.0 %
supersaturation.
7. Determination of optical properties
Two methods for
determining the optical parameters are investigated here. The first uses PMS
measurements of the size distributions of aerosols and Mie scattering theory,
while the second provides independent measurements of the scattering and
absorption coefficients with the PSAP and nephelometer.
7.1 Determination of the optical properties from in-situ measurements of
the size distribution and assumed refractive indices
The optical
properties of the aerosol size distributions shown in Figures 5a and 5b are
determined using Mie scattering theory and the real part of refractive indices
of Yamasoe et al. (1998), and a wavelength independent imaginary refractive
index of 0.018i (similar to the 0.02i assumed by Gleason et al. (1998)). A
density of 1.35gcm-3 is assumed for the density of biomass aerosol
(Reid and Hobbs, 1998). Kotchenruther and Hobbs (1998) measured the effect of
relative humidity upon biomass aerosol scattering coefficients in Brazil. For
aged biomass aerosol the scattering coefficient increased by a factor of just
6% at a relative humidity of 80%. Similarly, Ross et al. (1998) reports an
increase in scattering coefficient of 10% at a relative humidity of 85%. The
ambient relative humidity measured by the aircraft on the runs making up the
size distributions shown in Figure 1 are considerably less than this, (mean
relative humidity 34% and standard deviation 16%), thus the effects of relative
humidity are neglected. Note that at present, no account has been made for
crustal mineral material that is likely to be present in the coarse mode of the
aerosol. However, neglect of the crustal material will not influence the
derived single scattering albedo significantly for wavelengths of 0.55mm. There may be a considerable effect upon
the specific extinction coefficient and is the subject of ongoing work. The
results are summarised in Table 2.
For the aged plume at a wavelength of
0.55mm the specific extinction
coefficient, kel=0.55, ranges from 2.5m2g-1
to 4.8m2g-1 while the asymmetry factor, gl=0.55, ranges from 0.56 to 0.61,
and wol=0.55 is in the narrow range
0.89-0.91. The mean optical parameters at 0.55mm
determined from the mean size distribution are kel=0.55=4.0m2g-1,
g l=0.55=0.58, and wo l=0.55=0.90.
7.2 Determination of the optical properties from in-situ measurements with
the nephelometer and PSAP
Measurements were
performed using the PSAP and nephelometer over periods identical to those used
in calculating the PMS mean aerosol size distributions shown in Figure 5. The
nephelometer was corrected for variations from STP, for truncation of the
forward-scattered radiation, and for deficiencies in the illumination source
(Anderson and Ogren, 1998). The PSAP was corrected for variations in the area
of the exposed filter, inaccuracies in the flow rate measured by the
instrument, for scattering being mis-interpreted as absorption, and for
multiple scattering (Bond et al., 1999). Both of these sets of corrections tend
to decrease the absorption coefficient while increasing the scattering
coefficient hence raising wo
(see Haywood and Osborne, 2000). While the nephelometer measures at three
wavelengths (0.45, 0.55, and 0.70mm),
the PSAP measures the absorption at 0.567mm.
This enables determination of wo l=0.55 to a
reasonable accuracy, but assumptions have to be made about the wavelength
dependence of the absorption coefficient to enable estimation of wo l=0.45 and wo l=0.70. Here we make the
assumption that the absorption coefficient is proportional to 1/l (Reid and Hobbs, 1998). The model
calculations suggest this is a more realistic assumption than a wavelength
independent absorption coefficient. The results are summarised in Table 2.
The single
scattering albedo from the PSAP and nephelometer is in good agreement overall
with those derived from measurements of the size distribution, which supports
the use of an imaginary refractive index of 0.018i.
8. Effects of non-sphericity
In addition to the PMS probes, the C-130 was
equipped with the SID probe that determines the degree of non-sphericity of
super-micron radius particles (smallest detectable radius ~1.0mm). The operating principles of the SID
probes is straightforward and is similar to the PMS probes. Radiation of a
single frequency is emitted from a laser, is incident upon a particle and is
scattered. For the PMS probes, the scattered radiation is collected over a
particular range of scattering angles by use of e.g. a parabolic mirror and is
focussed upon a photo-detector which converts the intensity of the collected
scattered radiation into a voltage. The SID probe uses a series of 7 individual
detectors to determine whether the scattering pattern resembles that expected
from spherical particles. A ‘asphericity factor’, af, is hence defined wich determines the degree of non-sphericity.
Experience in mixed phase clouds indicates that an af of around 11 is the interface between a particle exhibiting
spherical scattering with an afs
higher than 11 exhibiting increasingly non-spherical scattering.
Figure 10 shows an example of af for three different types of particle namely sea-salt, biomass
plume from SAFARI-2000, and mineral dust. Sea-salt particles were sampled
during straight and level runs (SLRs) at 100ft over ocean during SAFARI-2000.
Biomass particles are from SLRs during flight a787 on 7 September, 2000 when
the C-130 was operating in an aged biomass plume. Mineral dust measurements are
taken from SLRs during an outbreak of Saharan dust during the SaHAran Dust
Experiment (SHADE) based in Sal, Cape Verde Islands from 21-29 September, 2000.
Figure 10 shows that the scattering of radiation by sea-salt particles is well
represented by spherical particles (mean af
4.5 stdev 1.8). The af for mineral
dust shows that the particles are almost exclusively non-spherical (mean af 22.6 stdev 10.4). The results for the
biomass aerosol shows that the scattering is somewhere between the sea-salt and
the mineral dust (mean af 15.9 stdev
10.7) and hence the majority of super-micron particles must be considered
non-spherical. The implications of these findings are that for the aerosol
measured in SAFARI-2000, the FFSSP measurements may be affected by
non-spherical scattering effects that may influence the derived super-micron
particle size distributions. These results may also have implications for the
sun-photometer derived size distributions that rely on measurements of the sky
radiances (e.g. Dubovik et al., 2000) because non-spherical particles generally
scatter more radiation in the backward direction and may therefore lead to
erroneous inclusion of a larger number of small particles.
9. Comparison of C-130
measurements of size distributions and optical depths and optical properties
with those from the Etosha CIMELS site.
9.1Optical depths
The broad-band
optical depths were calculated using the method of Hignett et al. (1999) for
flights a786 and a790 on 6 and 13 September, 2000. The 0.3-0.7mm optical depths were found to be 0.40 and
0.64. These values compare reasonably with the 0.51 and 0.61 optical depths
measured at the CIMELS site. The C-130 measurements of optical depth may be
subject to change as more sophisticated treatment of the obscurer corrections
is necessary. These calculations are underway.
9.2 In situ size distributions & optical parameters
The size
distributions measured by the PMS probes of the C-130 may be compared directly
to those derived from the Etosha Pan CIMELS site. Two retrieval algorithms are
used in deriving the size distributions namely those of Dubovik and King (2000)
and Nakajima et al. (1996). The retrieval algorithm of Dubovik and King (2000)
also produces estimates of the refractive index of the aerosol particles and
the imaginary part of the refractive index. The flights that were performed
over the Etosha CIMELS site were a786 and a790 on 6 and 13 September 2000. A
comparison of the size distributions is shown in Figure 11. The agreement between
the size distributions derived using the retrieval algorithm of Dubovik and
King (2000) is in significantly better agreement with the in-situ PMS probe
measurements made by the C-130 than the retrieval algorithm of Nakajima et al.
(1996). Indeed, on 13 September, the agreement between the size distributions
is excellent, considering that the measurements are totally independent, thus
providing evidence that the retrieval algorithm of Dubovik and King (2000) is
accurate for biomass aerosols.
The real (re) and imaginary (im) part of the refractive indices and the single scattering albedo
from the Dubovik and King (2000) retrievals may also be compared against the
C-130 measurements/ modelling efforts summarised in Table 2. In the C-130
calculations, re is assumed to be
1.53, 1.55, 1.59, and 1.58 at wavelengths of
0.44, 0.67, 0.87, and 1.02mm,
and im is assumed to be 0.018i over
all these wavelengths.
For 6 September, re from the Dubovik and King (2000)
retrievals is 1.57, 1.58, 1.59, and 1.59 and im is 0.018i which is entirely consistent with the C-130
measurements/modelling assumptions when the variability in the retrievals is
considered. The single scattering albedo at 0.55mm
is 0.90 for the Dubovik and King (2000) retrieval and 0.89 and 0.86 when derived
from the PMS distributions and from the nephelometer and PSAP on the C-130
(Table 2).
For 13 September, re from the Dubovik and King (2000) retrievals is 1.56, 1.57, 1.59,
and 1.60 and im is 0.019i which is
entirely consistent with the C-130 measurements/modelling assumptions when the
variability in the retrievals is considered. The single scattering albedo at
0.55mm is 0.87 for the Dubovik and King
(2000) retrieval and 0.87 and 0.88 when derived from the PMS distributions and
from the nephelometer and PSAP on the C-130 (Table 2).
9.3 Derivation of size distributions from C-130 orbits
The size
distributions and optical depths of the aerosol may also be derived from
multi-spectral SAFIRE radiance measurements from low-level orbits over the
Etosha site. These orbits were performed by matching the angle of bank of the
aircraft to the solar zenith angle, q,
thus enabling radiance measurements ranging from zero to 2q. An example of the radiance measurements is
shown in Figure 12. The results show the expected lower radiances at longer
wavelengths, although there still some calibration issues that need rectifying
as indicated by the
10. Discussion and conclusions
The chemical
composition analysis suggests that the mass ratio of BC/OC for the aged aerosol
measured over and around Namibia is approximately 0.08. By applying reasonable
assumptions about the refractive indices and density of BC and OC, an imaginary
part of the refractive index of 0.018i is deduced. Application of this
imaginary part of the refractive index leads to agreement between the single
scattering albedo measured using the PSAP and nephelometer, and those derived
from the in-situ measured size distributions.
The range in the
mass scattering efficiency, ks l=0.55,
of 2.5-4.3m2g-1 is similar to the 2.9-4.6m2g‑1
determined by Ross et al. (1998) for
biomass burning aerosol in S. America. The g l=0.45 of 0.64 from the measured
size distribution is in good agreement with the g l=0.44 of 0.65
derived by Remer et al. (1998). wo l=0.55 is in
reasonable agreement with the results of Remer et al. (1998), Kaufman et al. (1992), and von Hoyningen-Huene et al. (1998). However, wo l=0.55 is
higher than the 0.83 derived by Hobbs et al. (1997) and Reid et al. (1998) with implications on the
global mean estimates of the radiative forcing due to biomass aerosols.
The agreement
between the sun-photometer measurements of size distribution, real and
imaginary part of the refractive index, and single scattering albedo is
excellent, and justifies further work and collaboration.
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J.M
Haywood, S.R. Osborne, P.N. Francis, A. Keil: Met Office, Y46 Bldg, DERA,
Farnborough, Hants, GU14 0LX, UK.
P. Formenti:
Departemento de Fisica, Universidade de Evora, Rua R. Ramalho, 59, P-7000-532
Evora, Portugal
M.O. Andreae,
Max_planck Institute for Chemistry, Mainz, Germany
B. N. Holben, O.
Dubovik: NASA GSFC, Code 923, Greenbelt, MD 20771, USA
(jim.haywood@metoffice.com;simon.osborne@metoffice.com;pete.francis@metoffice.com;andreas.keil@metoffice.com;
pfo@uevora.pt;moa@mpch-mainz.mpg.de;
brent@aeronet.gsfc.nasa.gov; dubovik@aeronet.gsfc.nasa.gov)
