ÓPTICA PURA Y APLICADA – Vol. 37, núm. 3 - 2004
Detection of Biomass Burning Aerosols in Córdoba, Argentina, using the
AERONET / NASA Data Base
Detección de Aerosoles de Quema de Biomasa en Córdoba, Argentina, usando la
Base de Datos de AERONET / NASA.
L. A. Otero
(1,4), P. R. Ristori
(2), B. Holben
(3), E. J. Quel
(1)1.
CEILAP (CITEFA-CONICET) - San Juan B. De La Salle 4397 - B1603ALO Villa
Martelli-Argentina.
2.
Laboratoire de Pollution de l'Air et du Sol, École Polytechnique Fédéral de Lausanne,
Suisse.
3.
.
NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A.
4.
Fellow of CONAE.
ABSTRACT:
Physical and optical properties of biomass burning aerosols in a continental
dry region in South America, Argentina, were analyzed using AERONET
measurements from Córdoba – CETT site. Due to the high frequency of
occurrences of biomass burning in the dry season, it is important to characterize
their optical properties to understand the atmospheric radiative processes in the
region. To evidence temporal variation of the microphysical aerosol properties,
the aerosol size distribution and Ångström wavelength exponent were calculated
for the days in study.
Key words:
Aerosols, biomass burning, AERONET
RESUMEN:
Se han analizado propiedades físicas y ópticas de aerosoles provenientes de la
quema de biomasa usando las mediciones de AERONET de la estación Córdoba
– CETT, ubicada en una región continental seca de la Argentina, en Sudamérica.
Debido a la gran cantidad de eventos de quema de biomasa durante la estación
seca, es importante caracterizar las propiedades ópticas con el fin de entender los
procesos radiativos en la región. Para evidenciar la evolución temporal de las
propiedades microfísicas de los aerosoles, se calculó la distribución en talla de
aerosoles y el coeficiente de Ångström en los días de estudio.
REFERENCES AND WEB LINKS.
[1] M. O. Andreae, “Climatic effects of changing atmospheric aerosol levels en World Survey of Climatology” vol 16, Future Climates of the World, A. Henderson-Sellers, 341-392 Elsevier, New York, (1995).
[2] S. K. Satheesh, V. Ramanathan, Xu Li-Jones, J. M. Lobert, I. A. Podgorny, J. M. Prospero, B. N. Holben, and N.G. Loeb, “A model fro the natural and anthropogenic aerosols over the tropical Indian Ocean derived from Indian Ocean Experiment data”, J. Geophys Res., vol 104, D22, 27.421-27.440 (1999).
[3] C. Pilinis, S. N. Pandis and J. H. Seifeld, “Sensitivity of direct climate forcing by atmospheric aerosols to aerosol size abd composition”, J. Geophys. Res., 100, 18.739-18.754, (1995)
[4] J. S. Schafer, T. F. Eck, B. N. Holben, P. Artaxo M. A. Yamasoe and A. S. Procopio et al. “Observed reductions of total solar irradiance by biomass-burning aerosols in the Brazilian Amazon and Zambian Savanna”, Geophys. Res. Lett., 29, 17, 1823, doi: 10.1029 / 2001GL014309, (2002).
[5] www.nps.gov
[6] B. Holben, T.F.Eck, I.Slutsker, D.Tanre, J.P.Buis, A.Setzer, E.Vermote, J.A.Reagan, Y.Kaufman, T.Nakajima, F.Lavenu, I.Jankowiak, and A.Smirnov, “AERONET- A federated instrument network and data achieve for aerosol characterization”, Remote Sens. 12, 1147-1163, (1991).
[7] M. Hess, P. Koepke, I. Schult, “ Optical Properties of Aerosols and Clouds: The Software Package OPAC” Bulletin of the American Meteorological Society 831 - 844 Vol. 79, No. 5, (1998).
[8] L. Otero, P. Ristori, J. Fochesatto, B. Holben, E. Quel. "Estadística de la evolución de los aerosoles medidos en las estaciones de la red AERONET en Argentina desde 1999". Accepted to be published Anales AFA (2003).
[9] www.conae.gov.ar
[10] L. Otero, P. Ristori, J. Fochesatto, E. Quel, B. Holben. “Detección De Procesos de Intrusión de Masas de Aire Utilizando un Análisis Estadístico de Series Temporales De Fotómetros Solares”. Anales AFA 2002 Vol. 14 ISBN/ISSN: 0327-358X, 289 – 293, (2003).
[11] O. Dubovik and M. King “A flexible inversion algorithm for retrieval of aerosol optical properties from Sun and sky radiance measurements”. J. Geophys. Res., Vol. 105, No. D16, Pages 20,673-20,696, 2000. [12] W.E. K Middleton, “Vision through the Atmosphere”,. University of Toronto Press, 1952.
[13] M Iqbal., “An Introduction to Solar Radiation”. Academic Press, (1983).
[11] T. F. Eck, B, N. Holben, J.S. Reud, O. Dubovik, A. Siminov, N. T. O’Neill, I. Slutsker and S. Kinne, “Wavelength dependence of the optical depth of biomass burning, urban and desert dust aerosols”. J. Geophys. Res. 104, 31, 333-349, (1999).
[12] L. A. Remer, y. J. Kaufman, “Dynamic aerosol model: Urban/Industrial aerosol”, J. Geophys. Res., 103, 13.859-13.871, (1998).
[13] J. S. Reid, P. V. Hobbs, “Physical and optical properties of young smoke from individual biomass fires in Brazil”, J. Geophys. Res., 103, 32.013-32.031, (1998)
1.- Introduction.
Aerosols are originated from different sources: sea salt from oceans, mineral dust from arid and semiarid locations, sulfate and nitrate from both natural and anthropogenic source and organic and carbonaceous aerosols from biomass burning and industrial combustion [1, 2]. Estimation of the effect of aerosols on climate is complicated by the fact that aerosols and their chemical composition, abundance and size distribution are highly variable, spatially and temporally [2, 3].
The study of biomass burning aerosols in these latitudes is important due to their direct, indirect, and semi-direct effects over climate. The lack of
information that we have for feeding global climate models on their absorption properties as well as their seasonal and inter-annual variability lead to important errors that have to be corrected [4].
Biomass burning is composed by small particles, water vapor and gases like carbon monoxide, carbon dioxide, nitrogen oxide, and volatile organic compounds.
All measurements in this study were made using a CIMEL radiometer from the AERONET research program. This instrument is described in detail in [6]. Analyzed data is Quality Assured at Level 2.0 (Pre – and post – field calibrated, automatically cloud screened and manually inspected)
The instrument which captured the episode mentioned in this article is located in Córdoba, Argentina, at the “Centro Espacial Teófilo Tabernera” (CETT) (31.5o S – 64.4o W) at 730
meters above sea level on the central part of the country.
The climate of the area is dry continental characterized for a dry season during winter. The aerosol climatology for this region is clean-dry continental and continental averaged, [7, 8].
2.- Case study.
2.a.- The episode.During August 22 to 27, 2002 a very important burning episode happened when a fire in the region of Molinari, in one of the most important National Park “La Quebrada del Condorito” at a distance approximately 30 km from CETT. There was a biomass burnt of 4650 ha. This event was detected also by satellite images [9].
2.b. Temporal series of Aerosol Optical Thickness.
Figure 1. Temporal evolution for aerosol optical thickness and precipitable water vapor. August 20 to 29, 2002 at
Córdoba AERONET Site.
Spatial and temporal variability of the aerosol optical thickness (AOT) [10] in the region can be used as a good indicator of the production and transport of biomass burning. The temporal evolution of AOT and precipitable water vapor (PWV) for nine days (August 20 to 29, 2002) is shown in Figure 1. A high correlation is observed between AOT and PWV time series due to aerosol
hygroscopic growth that characterize of smoke particles.
The steady increase in the aerosol optical thickness is stopped abruptly due to the washout of the atmosphere during the rain episode of the day 241.
2.c.- Size Distribution, Single scattering albedo and Aerosol Optical Thickness Extinction and Absorption.
The sky radiance almucantar and the direct sun measurements at 440, 670, 870 and 1020 nm were used to retrieve aerosol size distribution and single scattering albedo (SSA) following the methodology of Dubovik et al. [11].
In Figure 2 the aerosol size distribution is presented. It is possible to observe a typical dust aerosol size distribution during the day 233 (August 20, 2002), according with the season and the region in study.
For the days 236 and 237 the fine modal prevails. Finally for the day 240 a typical biomass burning aerosol size distribution is observed, characterized by a dominating fine accumulation mode.
Day 241, a 6 mm rain episode took place, (according to data base of Global Precipitation Climatology Project (GPCP)) cleaning the atmosphere of smoke particles by wet deposition. The following day (242) it can be seen a similar size distribution as the one at the beginning of the study.
Figure 2. Temporal evolution for size distribution. August 20 to 29, 2002 at Córdoba AERONET Site.
with high concentration of black carbon produced by combustion [4].
Figure 3. Single scattering albedo retrievals.
Figure 4 and 5 shows AOT extinction and AOT absorption total mode. The AOT extinction is derived from almucantar retrievals [11]. For calculating the absorption AOT the following equation is used (1).
(
)
abs ext
AOT = −1 SSA AOT (1)
Aerosol optical thickness extinction and absorption are calculated for the following channels: 1020, 870, 670 and 440 nm.
Figure 4. Aerosol Optical Thickness (Extinction ).
Figure 5. Aerosol Optical Thickness (Absorption).
Figure 6. Fine to Total AOT Extinction Ratio.
Figure 7. Fine to total AOT Absorption Ratio.
Figure 6 shows the AOT extinction ratio between the one calculated for fine particles to the total AOT. Figure 7 shows the same ratio but only for absorption. Again it is possible to see, in figure 7, the differentiation between air masses on day 238. It is interesting to see that in Figure 6 there is not a sharp differentiation.
Table I present the maximum difference between the AOT absorption and extinction curves. It is clearly seen a more important variability in AOT for absorption fine mode than AOT extinction fine mode.
TABLE I
Maximum percentage of increase between the curves of AOT absorption and extinction fine mode.
Percentage of increase
(%)
440 nm 670 nm 870 nm 1020 nm
AOT
absorption 55.9 87.0 108.2 122.4 AOT
extinction 11.7 24.1 38.6 49.7
2.d.- Ångström Exponent.
( )
( )
o o AOT−α λ λ = β λ
λ
(2)
where β is the turbidity parameter or optical thickness of aerosols at λ0 = 1 µm, proportional to
the aerosol concentration. The variability of β is between 0 and 0.5 reaching greater values in exceptional cases, and is related to the atmospheric visibility [12, 13]. The Ångström coefficient, α, is related to the quadratic distribution of the average radii of aerosols from the micrometric and sub-micrometric ranks. It varies from 0 to 4, from coarse to small particles respectively.
Figure 8. Ångström Exponent versus Aerosol Optical Thickness. August 20 to 29, 2002 at Córdoba AERONET
Site. (Y) 233; ({) 234; (¯) 235; (¼) 236; (¨) 237; (Z) 238; ( ) 239; () 240; (U) 242
The relationship between Ångström Exponent (α) and AOT is shown in Figure 8. There is a strong tendency for α to increase as AOT increase. The AOT increases from 0.2 to 1 during the episode. In the same way α increases changing from dust dominated to biomass burning dominated [11]. High values of α at high AOT is characteristic of small-particle smoke aerosols with typical accumulation modal radius values of 0.13 to 0.15 µm in a lognormal volume size distribution, [12, 13].
Conclusions.
This paper studies the temporal variability of aerosol optical properties during a period of intense biomass burning in Córdoba AERONET Site.
For doing this we use most of the AERONET product analyzing their sensibility to this episode clearly detected in situ and by satellite imagery.
Like this we propose a methodology to analyze similar events using part of the new products available from AERONET site.
In this case we can characterize the event for: 1. The aerosol size distribution retrieved
shows bimodal characteristic, with a fine mode dominated during August 26 to 27, 2002, about 0.2 µm3/µm2
, which is 40
higher than normal aerosol burden.
2. Ångström exponent coefficient near 1.7 and aerosol optical thickness for 500 nm near 0.85.
3. High variability of aerosols optical thickness absorption in the fine mode. 4. High values of single scattering albedo and
inverse dependency with the wavelength. To complete this study it would be useful additional information as, for example, aerosol biomass burning layer telemetry. A collocated LIDAR system would be useful for this purpose. In order to achieve this goal it will be important to develop compact and reliable systems with an affordable cost for research institutions.