**1. Introduction**

246 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

salts, J. Aerosol Sci., Vol 7, 361 – 371.

Sci., 34, 1664–1669.

Tang I. N., 1976, Phase tranformation and growth of aerosol particles composed of mixed

Tang I. N., Munkelwitz H. R., 1977, Aerosol growth studies-III; Ammonium Bisulfate

Wallace J. M. and Hobbs P. V., 1977, Atmospheric Science, An introductory survey, 467 pp. Wang, P. K. and H. R. Pruppacher, 1977: An experimental determination of the efficiency with which aerosol particles are collected by water drops in subsaturated air, J. Atmos.

Weller, B., B. Albrecht, S. Esbensen, C. Eriksen, A. Kumar, R. Mechoso, D. Raymond, D. Rogers, D. Rudnick, 1999: A science and implementation plan for EPIC: An eastern Pacific investigation of climate processes in the coupled ocean-atmosphere system.

Twomey, S., 1974: Pollution and the planetary albedo, Atmos. Environ, 8, 1251-1256. Twomey, S. 1991, Aerosols Clouds and Radiation, Atmos. Environ., 25A, 2435-2442.

[Available online from http://wwwatmos.washintong.edu/gcg/EPIC/].

Aerosols in a moist atmosphere, J. Aerosol Sci., Vol 8, 321 – 330.

Usually, both for the scientific community and to the general public, there is a tendency to associate air pollution with large urban centers (mainly coming from motor vehicles or factory chimneys). However, large areas, especially tropical regions, live with another source of pollution: the biomass burning. According to the Intergovernmental Panel on Climate Change (IPCC) report, biomass burning is the major source of air pollution and is considered an important environmental problem with several impacts on local, regional and global levels [1]. Biomass burning includes burning of forests, grasslands, and croplands. Large quantities of gases and materials, besides trace elements, are emitted into the atmosphere by this action. This can affect both the regional and global climate through the interaction with solar radiation and the chemical and physical processes in the atmosphere. A large amount of these burning points occurred in the southern part of the Amazon basin during the dry season and the product of these emissions can be transported to some cities in the southeast of the country, a highly polluted region, and with cities with serious air pollution problems at the urban environment. Moreover, with the growing demand for biofuels in Brazil, the cultivation of sugarcane has been expanding considerably in southeastern Brazil, being a strong contribution to poor air quality in the region due to the burning of that culture, aiming to facilitate its harvest.

A very useful tool in studies of the effects of burning in the atmosphere is the Lidar (Light Detection and Ranging) technique, which gives vertical profiles of aerosols and allows the monitoring of the temporal evolution of the atmospheric structure, as well as to obtain values of backscattering coefficient. This technique is characterized by high spatial and temporal resolution, allowing the measurement of small concentrations of different gases (mainly water vapor), aerosols and local meteorological parameters such as wind direction

© 2012 Lopes et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Lopes et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and temperature, depending, however, on the type of Lidar system and the wavelength used.

Impacts of Biomass Burning in the Atmosphere

of the Southeastern Region of Brazil Using Remote Sensing Systems 249

**2.1. Moderate Resolution Imaging Spectroradiometer (MODIS) Sensor** 

Resolution Imaging Spectroradiometer) is highlighted.

of aerosol and clouds and CloudSat (2006) to study the clouds.

sensor (AQUA satellite) between 2003 and 2010 were used.

or absorption during its passage through any given element [6].

wavelength used).

found in Barnes et al. (1998) [4].

equivalent to the median [5].

Through the EOS (Earth Observing System) program, initiated in 1980 with the main objective to allow continuous observations for a period of at least 15 years of global changes, various sensors have been launched, and among them the MODIS in 1999 (Moderate

The MODIS sensor is on board the polar orbiting satellites TERRA and AQUA launched in 1999 and 2002, respectively. The sensor was the first designed to obtain global observations of aerosols with moderate resolution (between 250m and 1000m depending on the

The AQUA satellite is part of the so-called A-Train constellation [3], which also contains the Aura satellite (launched in 2004) to study the atmospheric chemistry and dynamics with emphasis on the sensor for ozone monitoring OMI - Ozone Monitoring Instrument, PARASOL (2004) to study the water and carbon cycle, CALIPSO (2006) to study the profile

MODIS has 36 spectral bands between 0.4 and 14.5 μm, allowing the generation of several products related to aerosol, such as aerosol optical depth over the ocean and land with a resolution of 10x10 km (at nadir), and the size and type distribution over oceans and type of aerosol over the continent. General and operational characteristics of the sensor can be

The MODIS aerosol data analyzed consist of the aerosol product level 3, MOD08. This level of data is generated daily for the entire globe offering several properties related to aerosols such as optical depth over ocean/continent and Ångström Exponent over the continent. The spatial resolution of the data is 1.0° for level 3. In this chapter, data from the AOD MODIS

Any given set of data, ordered from the lowest to the highest value, have a central value which is called a median. Likewise, it is possible to think of the values dividing the set of data in four equal parts, that is, the quartiles, Q1, Q2 and Q3, with Q2 being equal to the median. The values dividing the set in 10 equal parts are the deciles, and the values which divide the set in 100 equal parts are the percentiles. A percentile is the value of a data set below which a certain amount of the observations are. For instance, the 90th percentile represents the number below which 90% of the data is found. The 50th percentile is

The AOD is a dimensionless coefficient, indicating the amount and efficiency of solar radiation extinction by optically active material for a given wavelength. The optical depth may be defined as an attenuation coefficient of a beam of light which undergoes scattering

Higher values of optical depth lead to lower values for the optical transmittance of the air column, with the intensity of solar radiation on the surface also being smaller. Consequently, the temporal and spatial evolution of this radiation depends on the

A Lidar system operates on the same physical principle of Radar, but using a laser beam as emission source; the detection components are composed by a telescope and an optical analyzer system. In the case of Lidar, a light pulse is directed into the atmosphere. The light beam interacts with the atmospheric compounds and is scattered in all directions by particles and molecules. A portion of the light is absorbed and other portion is scattered back towards the Lidar system. The backscatter light is collected by a telescope and focused upon a photo detector capable to measure the signal intensity as function of the distance from the system.

Lidar systems, both aboard of satellites and ground-based, have been used in synergy with sunphotometer systems to detect and track the transport of aerosol from the MidWestern portion of the Brazilian territory to the Southeastern region, mainly the São Paulo city, where a ground-based elastic backscatter Lidar system is installed [2]. Here, some results obtained using a methodology developed to detect biomass burning aerosol loaded in the atmosphere at specific locations of the Brazilian territory will be presented, mainly in the Midwestern and Northern portion, considered to be one of the biggest producers of biomass burning in South America due to the vast quantities of forest, pasture and plantations, and track the transport trajectories of the aerosol plumes into the areas located at the Southeastern portion of Brazil, in the city of São Paulo, where it is possible to identify such plumes using the AERONET sunphotometer and the elastic backscatter Lidar system. Initially, Ångström Exponent (AE) and Aerosol Optical Depth (AOD) values retrieved from the AERONET sunphotometer network and the MODIS satellite, combined with AOD and Lidar ratio (LR) products from the CALIOP measurements are used in order to identify biomass burning aerosols loaded in the atmosphere in the MidWestern and Northern portion of the Brazilian territory. Attenuated backscatter profile images and aerosol optical properties values from CALIOP are used to monitor and track such aerosol plumes to the Southeastern region. If the transportation of biomass burning to São Paulo city is confirmed using the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model) backtrajectories, the backscatter Lidar and the sunphotometer data are used to analyze the presence of those plumes at the São Paulo atmosphere. Such results can be a strong indication that the city of São Paulo, one of the most polluted cities in the world, is affected not only by the presence of aerosol from local sources but also by aerosols produced in remote sources.

## **2. Instrumentation**

This study has the aim of analyzing the biomass burning aerosol optical properties using data from the CALIOP sensor installed on board the satellite CALIPSO and MODIS sensor aboard the TERRA and AQUA satellite. In addition, ground-based data measurements such as an elastic backscatter Lidar system and the AERONET sun photometer data will be used. In this section some details of each instrument will be presented.

## **2.1. Moderate Resolution Imaging Spectroradiometer (MODIS) Sensor**

248 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

but also by aerosols produced in remote sources.

In this section some details of each instrument will be presented.

**2. Instrumentation** 

used.

from the system.

and temperature, depending, however, on the type of Lidar system and the wavelength

A Lidar system operates on the same physical principle of Radar, but using a laser beam as emission source; the detection components are composed by a telescope and an optical analyzer system. In the case of Lidar, a light pulse is directed into the atmosphere. The light beam interacts with the atmospheric compounds and is scattered in all directions by particles and molecules. A portion of the light is absorbed and other portion is scattered back towards the Lidar system. The backscatter light is collected by a telescope and focused upon a photo detector capable to measure the signal intensity as function of the distance

Lidar systems, both aboard of satellites and ground-based, have been used in synergy with sunphotometer systems to detect and track the transport of aerosol from the MidWestern portion of the Brazilian territory to the Southeastern region, mainly the São Paulo city, where a ground-based elastic backscatter Lidar system is installed [2]. Here, some results obtained using a methodology developed to detect biomass burning aerosol loaded in the atmosphere at specific locations of the Brazilian territory will be presented, mainly in the Midwestern and Northern portion, considered to be one of the biggest producers of biomass burning in South America due to the vast quantities of forest, pasture and plantations, and track the transport trajectories of the aerosol plumes into the areas located at the Southeastern portion of Brazil, in the city of São Paulo, where it is possible to identify such plumes using the AERONET sunphotometer and the elastic backscatter Lidar system. Initially, Ångström Exponent (AE) and Aerosol Optical Depth (AOD) values retrieved from the AERONET sunphotometer network and the MODIS satellite, combined with AOD and Lidar ratio (LR) products from the CALIOP measurements are used in order to identify biomass burning aerosols loaded in the atmosphere in the MidWestern and Northern portion of the Brazilian territory. Attenuated backscatter profile images and aerosol optical properties values from CALIOP are used to monitor and track such aerosol plumes to the Southeastern region. If the transportation of biomass burning to São Paulo city is confirmed using the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model) backtrajectories, the backscatter Lidar and the sunphotometer data are used to analyze the presence of those plumes at the São Paulo atmosphere. Such results can be a strong indication that the city of São Paulo, one of the most polluted cities in the world, is affected not only by the presence of aerosol from local sources

This study has the aim of analyzing the biomass burning aerosol optical properties using data from the CALIOP sensor installed on board the satellite CALIPSO and MODIS sensor aboard the TERRA and AQUA satellite. In addition, ground-based data measurements such as an elastic backscatter Lidar system and the AERONET sun photometer data will be used. Through the EOS (Earth Observing System) program, initiated in 1980 with the main objective to allow continuous observations for a period of at least 15 years of global changes, various sensors have been launched, and among them the MODIS in 1999 (Moderate Resolution Imaging Spectroradiometer) is highlighted.

The MODIS sensor is on board the polar orbiting satellites TERRA and AQUA launched in 1999 and 2002, respectively. The sensor was the first designed to obtain global observations of aerosols with moderate resolution (between 250m and 1000m depending on the wavelength used).

The AQUA satellite is part of the so-called A-Train constellation [3], which also contains the Aura satellite (launched in 2004) to study the atmospheric chemistry and dynamics with emphasis on the sensor for ozone monitoring OMI - Ozone Monitoring Instrument, PARASOL (2004) to study the water and carbon cycle, CALIPSO (2006) to study the profile of aerosol and clouds and CloudSat (2006) to study the clouds.

MODIS has 36 spectral bands between 0.4 and 14.5 μm, allowing the generation of several products related to aerosol, such as aerosol optical depth over the ocean and land with a resolution of 10x10 km (at nadir), and the size and type distribution over oceans and type of aerosol over the continent. General and operational characteristics of the sensor can be found in Barnes et al. (1998) [4].

The MODIS aerosol data analyzed consist of the aerosol product level 3, MOD08. This level of data is generated daily for the entire globe offering several properties related to aerosols such as optical depth over ocean/continent and Ångström Exponent over the continent. The spatial resolution of the data is 1.0° for level 3. In this chapter, data from the AOD MODIS sensor (AQUA satellite) between 2003 and 2010 were used.

Any given set of data, ordered from the lowest to the highest value, have a central value which is called a median. Likewise, it is possible to think of the values dividing the set of data in four equal parts, that is, the quartiles, Q1, Q2 and Q3, with Q2 being equal to the median. The values dividing the set in 10 equal parts are the deciles, and the values which divide the set in 100 equal parts are the percentiles. A percentile is the value of a data set below which a certain amount of the observations are. For instance, the 90th percentile represents the number below which 90% of the data is found. The 50th percentile is equivalent to the median [5].

The AOD is a dimensionless coefficient, indicating the amount and efficiency of solar radiation extinction by optically active material for a given wavelength. The optical depth may be defined as an attenuation coefficient of a beam of light which undergoes scattering or absorption during its passage through any given element [6].

Higher values of optical depth lead to lower values for the optical transmittance of the air column, with the intensity of solar radiation on the surface also being smaller. Consequently, the temporal and spatial evolution of this radiation depends on the

atmospheric optical depth, which will depend on local factors, since these cause variations in how the solar radiation in the electromagnetic spectrum and the direction of propagation is distributed.

The AOD can be divided into some components, due to Rayleigh and Mie scattering, as well as the absorption by atmospheric particles. Therefore, the optical depth is a measure of transparency, being defined as the fraction of radiation (or light) that is scattered or absorbed in a path. An easy example is that of a fog. The fog between an observer and an object immediately in front of him has an optical depth tending to zero. If the object is moving away from the observer's, the optical depth will increase until it reaches a large value where the object is no longer visible.

The optical depth indicates the amount of absorbing and scattering optically active material found in the path of a beam of radiation. It is defined as the integral over the optical path of the product of the total quantity of molecules present in the medium and the cross section of extinction for each wavelength. The optical depth is expressed by:

$$
\pi\_{\lambda} = \int \sigma\_{\lambda} N(\mathbf{x}) d\mathbf{x} \tag{1}
$$

Impacts of Biomass Burning in the Atmosphere

of the Southeastern Region of Brazil Using Remote Sensing Systems 251

operate autonomously and continuously. Two of them are passive sensors and can provide a view of the atmosphere surrounding the Lidar curtain, namely, a wide field camera with a spatial resolution of 125 m for pixels and a three-channel infrared imaging radiometer instrument at each of the two wavelengths [9]. The lasers are Q-Switched to provide a pulse length of about 20 ns. The receiver subsystems measure the attenuated backscattering signal intensity at 1064 nm and the two orthogonal polarization components at 532 nm. From the backscattering signal measured by the receiver system, the CALIOP data products are assembled and separated in two categories: Level 1 and 2 products. Level 1 products are composed of calibrated and geolocated profiles of the attenuated backscatter returned signal, and are separated in three types, the total attenuated backscatter profile at 1064 nm, total attenuated backscatter profile (the sum of parallel and perpendicular signals) and the perpendicular backscatter signal, both at 532 nm [8, 10]. The level 2 products are derived from level 1 products and are classified in three types: layer products, profile products and vertical feature mask (VFM). Layer products provide the optical properties of aerosol and clouds integrated or averaged in the layers detected in the atmosphere. The profile products provide retrieved backscatter and extinction profiles within the detected layers. The VFM provide information of the cloud and aerosol location, and also their types. The level 2 data of aerosol layers provide information about values of the AOD, LR, and information from

the heights of top and bottom of the layers detected by the CALIOP sensor.

AERONET is a global network of optical monitoring of atmospheric aerosols, maintained by NASA and expanded throughout various research institutions around the world. This network has more than 200 measuring points, 22 in South America. The sunphotometer system from the AERONET network is a remote sensing instrument very useful not only to work in synergy with Lidar but also to retrieve several optical properties from aerosol

The CIMEL 318A spectral radiometer is a solar-powered weather-hardy robotically pointed Sun and sky instrument. This instrument is installed on the roof of the Physics Department at the University of São Paulo (USP). The CIMEL photometer performs measurements of the AOD at several wavelengths in the visible and the near-infrared spectral region to enable the assessment also of the Ångström Exponent [11]. The principle of operation of this system is to acquire aureole and sky radiances observations using a great number of scattering angles from the Sun, through a constant aerosol profile to retrieve the aerosol size distribution, the phase function and the AOD. For this study, the channels used are centered at 340, 440, 500, 670, 870, 940 and 1020 nm, with a 1.2 m full FOV (field of view) angle. The measurements are taken pointed directly to the Sun (four sequences) or to the sky (five sequences) in nine different pre-programmed sequences [11]. The inversion of the solar radiances measured by the CIMEL sunphotometer to retrieve the aerosol optical depth values is based on the Beer-Bouguer-Lambert equation, assuming that the contribution of multiple scattering within the small FOV of the sunphotometer is negligible. The aerosol

**2.3. AERONET sunphotometer** 

optical depth at 532 nm was determined by the relation:

loaded in the atmosphere.

Where �� is the extinction cross section, dx the path of integration and N(x) the volume number density of optically active atoms or molecules [particles cm-2] [6]. It expresses the amount of light removed from a beam by scattering or absorption during its path in any means. Being I0 the intensity of the radiation source and I the intensity observed after a certain path, the optical depth may be defined by the following equation:

$$\frac{d}{d\_0} = e^{-\tau} \tag{2}$$

In the atmospheric sciences, the atmospheric optical depth is commonly referred as the vertical path from the surface of the earth or the altitude of the observer into space. Since it regards the vertical path, the optical depth of a sloping path is �� � ��, which is called the air mass factor, which to that atmosphere is usually defined as � � � ���Θ ⁄ where Θ is a zenith angle corresponding to a certain path. Thus:

$$\frac{l}{l\_0} = e^{-\mu r} \tag{3}$$

### **2.2. CALIPSO satellite**

Ground-based systems are very useful for monitoring local and regional aerosol properties in the atmosphere, playing an important role in the estimation of the aerosol influence on the radiation budget. However, in order to cover the cloud and aerosol vertical distribution in a global range, NASA and CNES agencies has launched a satellite with a Lidar system as a main operational instrument on board [7]. The CALIPSO satellite was launched in April 2006, and since then is part of the NASA's A-Train satellite constellation as mentioned before. CALIPSO is flying in a 705 km sun-synchronous polar orbit with an equator-crossing time of about 13:30 in local time, covering the whole globe in a repeat cycle of 16 days [8]. The CALIPSO payload consists of three co-aligned nadir-pointing instruments designed to operate autonomously and continuously. Two of them are passive sensors and can provide a view of the atmosphere surrounding the Lidar curtain, namely, a wide field camera with a spatial resolution of 125 m for pixels and a three-channel infrared imaging radiometer instrument at each of the two wavelengths [9]. The lasers are Q-Switched to provide a pulse length of about 20 ns. The receiver subsystems measure the attenuated backscattering signal intensity at 1064 nm and the two orthogonal polarization components at 532 nm. From the backscattering signal measured by the receiver system, the CALIOP data products are assembled and separated in two categories: Level 1 and 2 products. Level 1 products are composed of calibrated and geolocated profiles of the attenuated backscatter returned signal, and are separated in three types, the total attenuated backscatter profile at 1064 nm, total attenuated backscatter profile (the sum of parallel and perpendicular signals) and the perpendicular backscatter signal, both at 532 nm [8, 10]. The level 2 products are derived from level 1 products and are classified in three types: layer products, profile products and vertical feature mask (VFM). Layer products provide the optical properties of aerosol and clouds integrated or averaged in the layers detected in the atmosphere. The profile products provide retrieved backscatter and extinction profiles within the detected layers. The VFM provide information of the cloud and aerosol location, and also their types. The level 2 data of aerosol layers provide information about values of the AOD, LR, and information from the heights of top and bottom of the layers detected by the CALIOP sensor.

## **2.3. AERONET sunphotometer**

250 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

value where the object is no longer visible.

angle corresponding to a certain path. Thus:

�

**2.2. CALIPSO satellite** 

extinction for each wavelength. The optical depth is expressed by:

certain path, the optical depth may be defined by the following equation:

� ��

��

Ground-based systems are very useful for monitoring local and regional aerosol properties in the atmosphere, playing an important role in the estimation of the aerosol influence on the radiation budget. However, in order to cover the cloud and aerosol vertical distribution in a global range, NASA and CNES agencies has launched a satellite with a Lidar system as a main operational instrument on board [7]. The CALIPSO satellite was launched in April 2006, and since then is part of the NASA's A-Train satellite constellation as mentioned before. CALIPSO is flying in a 705 km sun-synchronous polar orbit with an equator-crossing time of about 13:30 in local time, covering the whole globe in a repeat cycle of 16 days [8]. The CALIPSO payload consists of three co-aligned nadir-pointing instruments designed to

In the atmospheric sciences, the atmospheric optical depth is commonly referred as the vertical path from the surface of the earth or the altitude of the observer into space. Since it regards the vertical path, the optical depth of a sloping path is �� � ��, which is called the air mass factor, which to that atmosphere is usually defined as � � � ���Θ ⁄ where Θ is a zenith

is distributed.

atmospheric optical depth, which will depend on local factors, since these cause variations in how the solar radiation in the electromagnetic spectrum and the direction of propagation

The AOD can be divided into some components, due to Rayleigh and Mie scattering, as well as the absorption by atmospheric particles. Therefore, the optical depth is a measure of transparency, being defined as the fraction of radiation (or light) that is scattered or absorbed in a path. An easy example is that of a fog. The fog between an observer and an object immediately in front of him has an optical depth tending to zero. If the object is moving away from the observer's, the optical depth will increase until it reaches a large

The optical depth indicates the amount of absorbing and scattering optically active material found in the path of a beam of radiation. It is defined as the integral over the optical path of the product of the total quantity of molecules present in the medium and the cross section of

 �� � � �������� (1) Where �� is the extinction cross section, dx the path of integration and N(x) the volume number density of optically active atoms or molecules [particles cm-2] [6]. It expresses the amount of light removed from a beam by scattering or absorption during its path in any means. Being I0 the intensity of the radiation source and I the intensity observed after a

� ��� (2)

� ���� (3)

AERONET is a global network of optical monitoring of atmospheric aerosols, maintained by NASA and expanded throughout various research institutions around the world. This network has more than 200 measuring points, 22 in South America. The sunphotometer system from the AERONET network is a remote sensing instrument very useful not only to work in synergy with Lidar but also to retrieve several optical properties from aerosol loaded in the atmosphere.

The CIMEL 318A spectral radiometer is a solar-powered weather-hardy robotically pointed Sun and sky instrument. This instrument is installed on the roof of the Physics Department at the University of São Paulo (USP). The CIMEL photometer performs measurements of the AOD at several wavelengths in the visible and the near-infrared spectral region to enable the assessment also of the Ångström Exponent [11]. The principle of operation of this system is to acquire aureole and sky radiances observations using a great number of scattering angles from the Sun, through a constant aerosol profile to retrieve the aerosol size distribution, the phase function and the AOD. For this study, the channels used are centered at 340, 440, 500, 670, 870, 940 and 1020 nm, with a 1.2 m full FOV (field of view) angle. The measurements are taken pointed directly to the Sun (four sequences) or to the sky (five sequences) in nine different pre-programmed sequences [11]. The inversion of the solar radiances measured by the CIMEL sunphotometer to retrieve the aerosol optical depth values is based on the Beer-Bouguer-Lambert equation, assuming that the contribution of multiple scattering within the small FOV of the sunphotometer is negligible. The aerosol optical depth at 532 nm was determined by the relation:

$$\frac{\tau\_{\text{g32}}^{aer}}{\tau\_{\text{g00}}^{aer}} = \left(\frac{532}{500}\right)^{-a} \tag{4}$$

Impacts of Biomass Burning in the Atmosphere

<sup>൧</sup> (6)

*, z)* are the atmospheric volume backscatter

ఉೌሺఒǡ௭ሻ (7)

ሻ݀ݖ<sup>ᇱ</sup> <sup>௭</sup>

*, z)* is the Lidar

*, z)* is the

of the Southeastern Region of Brazil Using Remote Sensing Systems 253

**Figure 1.** Metropolitan Area of São Paulo (MASP) map with the sampling locations indicated: (1) São Paulo University Campus (USP), site of the Lidar and AERONET sunphotometer, in the point L.

In the present stage, the inversion of the Lidar profile is based on the solution of the basic Lidar equation taking into account the atmospheric solar background radiation correction

signal received from a distance z at the wavelength , P0 is the emitted laser power, is all

The retrieval of the aerosol optical properties is based on the measurements of the aerosol backscatter coefficient aer at 532 nm, up to an altitude of 5 to 8 km. The determination of the vertical profile of the aerosol backscatter and extinction coefficients relies on the Lidar inversion technique following a modified Klett's algorithm [23, 24] under the assumption of the single scattering approximation. One has, however, to bear in mind that this inversion technique is an ill-posed problem in the mathematical sense, leading to errors as large as 30% when applied [22]. To make the Lidar equation solvable it is necessary to establish a relation between (, z) and (, z). This is achieved assuming the backscatter-to-extinction

ܮܴ ൌ ఈೌሺఒǡ௭ሻ

<sup>௭</sup><sup>మ</sup> ቃ ൈ ݁ݔൣെʹ ߙሺߣǡ ݖ<sup>ᇱ</sup>

[22]. The Lidar equation is presented according to equation (6), where *P(*

*, z)* and aer*(*

coefficients for the molecular and aerosol contribution, respectively; and aer*(*

ܲሺߣǡ ݖሻ ൌ ܲߦ ቂఉሺఒǡ௭ሻାఉೌሺఒǡ௭ሻ

Lidar system parameters, m*(*

ratio (LR) as:

volume extinction coefficient at range z.

Where the Ångström Exponent [12] was derived from the measured optical depth in the blue and red channels (440nm and 670 nm):

$$a = -\frac{\log\left(\frac{\tau\_{440}^{4w}}{\tau\_{670}^{4w}}\right)}{\log\left(\frac{440}{a\tau\_0}\right)}\tag{5}$$

The AE is also an indirect mean to retrieve the particle size distribution [13] and its possible composition [14, 15]. Concerning the uncertainty, the major source of error would be in the calibration procedure, which is proportional to the associated uncertainty of the AOD at a given wavelength [16].

### **2.4. Elastic backscatter Lidar system (MSP-Lidar)**

A ground-based elastic backscatter Lidar system is in operation since 2001 in the Environmental Laser Applications Laboratory at the Centre for Laser and Applications (CLA) at the Nuclear Energy Research Institute (IPEN). The MASP and instrument locations in this area are depicted in Figure 1 (point L).

The Lidar technique is based on the emission of a collimated laser beam through the atmosphere and on the detection of the backscattered laser light by the suspended atmospheric aerosols and molecules. A backscattering Lidar can thus provide information on the Planetary Boundary Layer (PBL) mixed depth, entrainment zones and convective cell structure, aerosol distribution, clear air layering, cloud-top altitudes, cloud statistics, atmospheric transport processes and other inferences of air motion [17-20]. The Lidar system is a single-wavelength backscatter system pointing vertically to the zenith and operating in the coaxial mode. The light source is based on a commercial Nd:YAG laser (Brilliant by Quantel SA) operating at the second harmonic frequency (SHF), namely at 532 nm, with a fixed repetition rate of 20 Hz. The average emitted power can be selected up to values as high as 3.3 W. The emitted laser pulses have a divergence of less than 0.5 mrad. A 30 cm diameter telescope (focal length f=1.5 m) is used to collect the backscattered laser light. The telescope's FOV is variable (1–2 mrad) by using a small diaphragm. Lidar is currently used with a fixed FOV of the order of 1 mrad, which according to geometrical calculations [21] permits a full overlap between the telescope FOV and the laser beam at heights around 300 m above the Lidar system. This FOV value, in accordance with the detection electronics, permits the probing of the atmosphere up to the free troposphere (12- 15 km asl). The backscattered laser radiation is then sent to a photomultiplier tube (PMT) coupled to a narrowband (1 nm full width at half maximum - FWHM) interference filter to assure the reduction of the solar background during daytime operation and to improve the signal-to-noise ratio (SNR) at altitudes greater than 3 km. The PMT output signal is recorded by a Transient Recorder in both analog and photon counting modes. Data are averaged between 2 and 5 min and then summed up over a period of about 1 h, with a typical spatial resolution of 15 m, which corresponds to a 100 ns temporal resolution.

**2.4. Elastic backscatter Lidar system (MSP-Lidar)** 

resolution of 15 m, which corresponds to a 100 ns temporal resolution.

in this area are depicted in Figure 1 (point L).

blue and red channels (440nm and 670 nm):

given wavelength [16].

ఛఱయమ ೌ ఛఱబబ ೌ ൌ ቀହଷଶ ହቁ ି

ܽൌെ

Where the Ångström Exponent [12] was derived from the measured optical depth in the

୪୭൬ ഓరరబ ೌ ഓలళబ ೌ൰

୪୭ቀ రరబ లళబ<sup>ቁ</sup>

The AE is also an indirect mean to retrieve the particle size distribution [13] and its possible composition [14, 15]. Concerning the uncertainty, the major source of error would be in the calibration procedure, which is proportional to the associated uncertainty of the AOD at a

A ground-based elastic backscatter Lidar system is in operation since 2001 in the Environmental Laser Applications Laboratory at the Centre for Laser and Applications (CLA) at the Nuclear Energy Research Institute (IPEN). The MASP and instrument locations

The Lidar technique is based on the emission of a collimated laser beam through the atmosphere and on the detection of the backscattered laser light by the suspended atmospheric aerosols and molecules. A backscattering Lidar can thus provide information on the Planetary Boundary Layer (PBL) mixed depth, entrainment zones and convective cell structure, aerosol distribution, clear air layering, cloud-top altitudes, cloud statistics, atmospheric transport processes and other inferences of air motion [17-20]. The Lidar system is a single-wavelength backscatter system pointing vertically to the zenith and operating in the coaxial mode. The light source is based on a commercial Nd:YAG laser (Brilliant by Quantel SA) operating at the second harmonic frequency (SHF), namely at 532 nm, with a fixed repetition rate of 20 Hz. The average emitted power can be selected up to values as high as 3.3 W. The emitted laser pulses have a divergence of less than 0.5 mrad. A 30 cm diameter telescope (focal length f=1.5 m) is used to collect the backscattered laser light. The telescope's FOV is variable (1–2 mrad) by using a small diaphragm. Lidar is currently used with a fixed FOV of the order of 1 mrad, which according to geometrical calculations [21] permits a full overlap between the telescope FOV and the laser beam at heights around 300 m above the Lidar system. This FOV value, in accordance with the detection electronics, permits the probing of the atmosphere up to the free troposphere (12- 15 km asl). The backscattered laser radiation is then sent to a photomultiplier tube (PMT) coupled to a narrowband (1 nm full width at half maximum - FWHM) interference filter to assure the reduction of the solar background during daytime operation and to improve the signal-to-noise ratio (SNR) at altitudes greater than 3 km. The PMT output signal is recorded by a Transient Recorder in both analog and photon counting modes. Data are averaged between 2 and 5 min and then summed up over a period of about 1 h, with a typical spatial

(4)

(5)

**Figure 1.** Metropolitan Area of São Paulo (MASP) map with the sampling locations indicated: (1) São Paulo University Campus (USP), site of the Lidar and AERONET sunphotometer, in the point L.

In the present stage, the inversion of the Lidar profile is based on the solution of the basic Lidar equation taking into account the atmospheric solar background radiation correction [22]. The Lidar equation is presented according to equation (6), where *P(, z)* is the Lidar signal received from a distance z at the wavelength , P0 is the emitted laser power, is all Lidar system parameters, m*(, z)* and aer*(, z)* are the atmospheric volume backscatter coefficients for the molecular and aerosol contribution, respectively; and aer*(, z)* is the volume extinction coefficient at range z.

$$P(\lambda, \mathbf{z}) \;= P\_0 \xi \left[ \frac{\beta\_m(\lambda, \mathbf{z}) + \beta\_{air}(\lambda, \mathbf{z})}{\mathbf{z}^2} \right] \times \exp\left[-2 \int\_0^\mathbf{z} a(\lambda, \mathbf{z}') d\mathbf{z}'\right] \tag{6}$$

The retrieval of the aerosol optical properties is based on the measurements of the aerosol backscatter coefficient aer at 532 nm, up to an altitude of 5 to 8 km. The determination of the vertical profile of the aerosol backscatter and extinction coefficients relies on the Lidar inversion technique following a modified Klett's algorithm [23, 24] under the assumption of the single scattering approximation. One has, however, to bear in mind that this inversion technique is an ill-posed problem in the mathematical sense, leading to errors as large as 30% when applied [22]. To make the Lidar equation solvable it is necessary to establish a relation between (, z) and (, z). This is achieved assuming the backscatter-to-extinction ratio (LR) as:

$$LR = \frac{a\_{aar}(\lambda, x)}{\beta\_{aar}(\lambda, x)}\tag{7}$$

However, it is known that the LR depends on several physical-chemical parameters inherent to the aerosols being inspected, such as the aerosol refractive index, size and shape distribution of the aerosol particles [25]. To derive the appropriate "correct" values of the vertical profile of aerosol backscatter coefficient in the lower troposphere an iterative inversion approach was used (by "tuning" the LR values), based on the intercomparison of the AOD values derived by the Lidar and a collocated AERONET sunphotometer [26], assuming the absence of stratospheric aerosols and that the PBL is homogeneously mixed between ground and the altitude of 300 m, where the Lidar overlap factor is close to 1. Once the correct values of the vertical profile of the aerosol backscatter coefficient were derived (when the difference between the AODs derived by sunphotometer and Lidar was less than 10%), the Klett's inversion technique was reapplied, using the appropriate LR values, to retrieve the final values of the vertical profiles of the backscatter and extinction coefficient at 532 nm. The vertical profiles of pressure and temperature measured by radiosoundings launched twice a day, at 12 UTC and 00 UTC in a distance about 10 km from the place where the MSP-Lidar system is located, are used in order to obtain the molecular contribution based in the Bucholtz's approach [27].

Impacts of Biomass Burning in the Atmosphere

of the Southeastern Region of Brazil Using Remote Sensing Systems 255

state of São Paulo. The number of fire outbreaks tends to increase from the month of March, achieving its maximum in the trimester July-August-September. The peak of the burning season (August) coincides with the least amount of precipitation in the region, while the reverse is also found, burning minimum in the months with maximum

**Figure 2.** Outbreaks of fire during the period from January, 1999 to July, 2007: (a) summer; (b) autumn;

(c) (d)

(a) (b)

The great quantity of active fires during the dry season, combined with low humidity in the region, can cause several health problems in the people living near the plantations and burnings of sugarcane. The association between internal and external exposure to the biomass smoke and its effects on health has been reported in some areas of Asia and India [30, 31]. Carbon deposition in the lungs occurred consistently in patients exposed to biomass burning [32]. Unlike most regions where external biomass burning is sporadic, the biomass burning in the region of São Paulo is a common and scheduled activity, due to the areas

The seasonal and interannual variation of the active fires in the State of São Paulo can be analyzed in Table 1. Through this table it can be noticed that the highest value of active fires occurred in 1999 followed by a decrease until 2001. From this year on, a slightly constant tendency of decrease in numbers of forest fires was noticed, except for the two last measured years (2005 and 2006). It is important to highlight that the measurements and monitoring in 2007 only goes until July, before the burning maximum period – August, September and October (as seen on Figure 2), probably due to technical problems with the satellite acquisitions. Besides the annual active total fires, the seasonal variation of the

precipitation (December and January).

(c) winter and (d) spring.

with sugarcane crops.
