Three stories about
aerosols
Marin Simić, 4.G
Gimnazija “Matija Mesić” Slav. Brod
Croatia
24th September 2012
I. STORY:
“There’s something sometimes
in our atmosphere”
Solar radiation in the Earth
atmosphere
Incoming solar radiation
i=io exp (- m ∙ (Φa+ Φg+ ΦNOx+ Φw+ ΦO3+ Φr))
i
io
m
Φ
- intensity that reaches Earth’s surface
- intensity at the top of the atmosphere
- atmosphere optical mass
- optical thickness (depth)
a
- aerosols / absorption and scattering
g
- atmospheric gases /absorption
NOx
- nitrogen oxides/ absorption
w
- water vapour / absorption
O3
- ozone /absorption
r - Rayley scattering on O2 and N2 molecules- “blue color of the
sky”
Atmosphere optical depth
i=io exp (- m ∙ (Φa+ Φg+ ΦNOx+ Φw+ ΦO3+ Φr))
iλ=i0,λexp(- m ∙ Φλ)
iλ the intensity of a narrow beam of sunlight of a
particular wavelength that reaches Earth's surface
I0 λ the intensity of sunlight just above Earth's
atmosphere
Φλ atmosphere optical thickness – extinction
coefficient of the incoming radiation due to
scattering and absorption on molecules and aerosols
m relative air mass
Φa aerosols optical thickness is the degree to which aerosols
prevent the transmission of light by absorption or scattering of
light.
- the integrated extinction coefficient over a vertical column of
unit cross section
Relative air mass
-
the path length relative to that at the zenith at
sea level
relative optical mass = S/D = 1/sinθ
for θ < 30o
II. STORY:
What we can do about it?



Aerosol measurements made carefully
according to the protocol with the GLOBE
sun photometer should be accurate to
within less than about 0,02 AOD units.
The accuracy of measurements made with
a GLOBE sun photometer is comparable to
measurements made with other types of
sun photometers.
In comparison even operational
“professional” sun photometers claim
accuracies of no better than 0,01 AOD.
Efforts of scientists…



The very first calibrations of LED sun
photometers were made at Seguin Texas, in
December 1998, and later at Mauna Loa
Observatory, Hawaii on several occasions.
The experiment made by Mims and his team, as
well as measurements performed by other
scientists show that AOD obtained from the LED
detector is consistent with data obtained from
Sun photometers with narrowband optical filters.
Langley’s calibration plot for GLOBE LED sun
photometers were presented in several papers
prepared by GLOBE scientific team and other
scientists (Brooks 2001, Mims III 1998) .
GLOBE Sun Photometer
The true is:

Students can reliably make the
required measurements and LED
based Sun photometers give results
that compare favourably with
conventional filter based instruments
even thought their optical properties
are significantly different.
Our efforts together…


More than 120 GLOBE schools
around world are conducting aerosol
measurements on daily basis and
have reported around 80.000 data
on AOD since the project started.
In 2010 there were four GLOBE sun
photometers operating in Croatia and
5000 measurements
Student’s project



Medicinska skola Zagreb and II Gimnazija
Zagreb prepared together very interesting
project on air quality in Zagreb.
They took measurements on the same
days and compare the AOD values. Beside
that they compare the official data on
suspended particles and also use bio
indicators as a measure of air quality.
High values of AOD, no matter what the
cause, may be linked to human health
through their influence on respiratory
system.
Atmosphere Transmission in
Zagreb
The connection with science…

Students are encouraged to compare
their measurements with other
ground and satellite based
measurements. Such comparison can
serve both as a check on GLOBE
measurements and on the
performance of other sun
photometers.
III. STORY:
How does it impacts our present,
our future?

Energy budget :
by directly scattering and absorbing radiation

Water cycle:
by serving as condensation nuclei during cloud
formation and by influencing precipitation

Biogeochemical cycle:
vulcanic eruptions, dust storms, erosion

Human health
impact the quality of the air that we breathe and
the health of all living organisms
Don’t forget…


Information about the concentration, size
distribution, and variability of aerosols in the
atmosphere and AOD is needed for climate
studies, for comparison with satellite data, to
track events that alter aerosol concentrations and
to understand the global distribution and
variability of aerosols.
Routine ground based AOD observations are of
outmost importance for the calibration and
validation of AOD retrievals from satellites. In
addition they are necessary to correct for aerosol
effects in the retrieval of other satellite products.
And we are not allone…



Today, several networks use handheld LED Sun
photometers as ground base instruments, and
determine AOD values and validate satellite data
according to measurements performed by LED
Sun photometers.
Besides networks operated by students and
volunteers, like GLOBE and The Haze network,
some are operated by national weather service
or Institutes like The Chinese Sun Haze meter
Network that started in 2004 as the very first
standard network established to measure AOD
through China (Xin 2007).
The networks are collaborating with Aerosol
Robotic network (AERONET) and the Moderate
Resolution Imaging Spectroradiometer (MODIS).
Literature I.
1. Aničić J. et al., 2010: Kakav zrak udišemo u
središnjem I zapadnom dijelu Zagreba?
(Proceedings of the 13 Annual Croatian GLOBE
Conferences, Zadar, available on
www.vnovak.hr/globe/smotra2010/zadar_10_proje
kti.html)
2. Boersma, K.F. and J.P. de Vroom, 2006:
Validation of MODIS aerosol observations over the
Netherlands with GLOBE student measurements,
Journal of Geophysical Research, 111, D20311,
doi:10.1029/2006JD007172
3. Brooks, D.R, and F.M. Mims III, 2001:
Development of an inexpensive hand held LEDbased Sun photometer for the GLOBE program,
Journal of Geophysical Research, 106, 4733-4740,
doi:10.1029/2000JD900545
Literature II.



4. Mims III, F. M., 1992: Sun Photometer with
Light-Emitting Diodes as Spectrally Selective
Detectors, Applied Optics, 31, 6965-6967
5. Mims III, F. M. , 1998: An Inexpensive and
Accurate Student Sun Photometer with LightEmitting Diodes as Spectrally Selective Detectors,
Proceedings of the Third Annual GLOBE
Conference, 232-239
6. Xin, J., et al., 2007: Aerosol optical depth
(AOD) and Ångström exponent of aerosols
observed by the Chinese Sun Hazemeter Network
from August 2004 to September 2005, Journal of
Geophysical Research, 112, D05203,
doi:10.1029/2006JD007075
Literature III
7. gaw.web.psi.ch
8. www.globe.gov