**5. Aerosol detection in the burning region**

As mentioned before, some regions in the Brazilian territory suffers from intense anthropogenic biomass burning activities, such as forest and sugarcane plantation fires, during the so-called dry season. High concentrations of biomass burning aerosol particles, produced mainly in the Amazon basin and the Brazilian Mid-Western region, can be detected due to these fire activities in the tropical forest, savanna and pasture [35]. In this context, data from AERONET sunphotometer, MODIS sensor and CALIPSO satellite were employed in order to detect possible sources of biomass burning aerosols and map its transportation from Mid-Western to the Southeastern region in Brazil.

Initially the image data measured by the MODIS sensor aboard the Terra satellite were used to identify possible signs of smoke from biomass burning. In the image retrieved on 21 August 2007, presented in Figure 5, it can be clearly seen the presence of a dense smoke layer in the region South and Southeast of Campo Grande (CG - Lat: 20°26'16'' Long: 54°32'16''). The trajectories generated using the HYSPLIT model indicate the transport of air masses from the Midwestern region of Brazil to the Southeast, where the MSP-Lidar system and the AERONET sunphotometer are installed. Figure 5 also shows that the CALIOP sensor aboard the CALIPSO satellite overpass the region near of Campo Grande during the nighttime of 21 August 2007, as can be seen by the descending trajectory (in the left of Figure 5). Furthermore, the sensor made measurements during daytime on the same day, however, in a region between the cities of Campo Grande and São Paulo, which will be helpful in the monitoring processes of the aerosol transport from the region of CG to MASP.

Impacts of Biomass Burning in the Atmosphere of the Southeastern Region of Brazil Using Remote Sensing Systems 259

258 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

**5. Aerosol detection in the burning region** 

transportation from Mid-Western to the Southeastern region in Brazil.

Brazil

to MASP.

**Figure 4.** Days above the AOD 95th Percentile (maximum AOD by MODIS > 1.143) over southeast of

As mentioned before, some regions in the Brazilian territory suffers from intense anthropogenic biomass burning activities, such as forest and sugarcane plantation fires, during the so-called dry season. High concentrations of biomass burning aerosol particles, produced mainly in the Amazon basin and the Brazilian Mid-Western region, can be detected due to these fire activities in the tropical forest, savanna and pasture [35]. In this context, data from AERONET sunphotometer, MODIS sensor and CALIPSO satellite were employed in order to detect possible sources of biomass burning aerosols and map its

Initially the image data measured by the MODIS sensor aboard the Terra satellite were used to identify possible signs of smoke from biomass burning. In the image retrieved on 21 August 2007, presented in Figure 5, it can be clearly seen the presence of a dense smoke layer in the region South and Southeast of Campo Grande (CG - Lat: 20°26'16'' Long: 54°32'16''). The trajectories generated using the HYSPLIT model indicate the transport of air masses from the Midwestern region of Brazil to the Southeast, where the MSP-Lidar system and the AERONET sunphotometer are installed. Figure 5 also shows that the CALIOP sensor aboard the CALIPSO satellite overpass the region near of Campo Grande during the nighttime of 21 August 2007, as can be seen by the descending trajectory (in the left of Figure 5). Furthermore, the sensor made measurements during daytime on the same day, however, in a region between the cities of Campo Grande and São Paulo, which will be helpful in the monitoring processes of the aerosol transport from the region of CG

**Figure 5.** Image of the MODIS sensor aboard the Terra satellite showing a dense smoke layer in the South and Southwest region of Mato Grosso State (Campo Grande) on 21 August 2007. The green arrows show the nighttime (descending) and daytime (ascending) trajectories of the CALIPSO satellite for the same day. The trajectories generated by the HYSPLIT model show that aerosol masses were transported from the Midwestern region of Brazilian territory to the Southeastern region where the MSP-Lidar system and AERONET sunphotometer are installed.

After identifying the presence of a dense smoke layer through the MODIS image, some optical properties of the atmospheric aerosol retrieved by the AERONET sunphotometer installed in CG site were analyzed. The AOD and AE products can provide information about the absorption and extinction characteristics and the size distribution of the aerosol in the atmosphere. In general, high values of AOD are associated to high extinction (absorption) of radiation, and in the same reasoning, high values of AE are associated to the fine mode size distribution of aerosols. These two characteristics are considered a signature of biomass burning aerosol. Figure 6 shows the scatter plot of Ångström Exponent as a function of the Aerosol Optical Depth for the month of August 2007 and case previously selected at Campo Grande (points in red), the grey filled lines are the AOD and AE median values for all data and the dashed lines are the respective median standard deviation. The AE values below the horizontal line corresponding to the median, AE=1.46±0.09, are an indication that most of the aerosol load is in the coarse mode size distribution. Those values above the median line belong to the fine mode size type of aerosols. The AE indicates a small sized particle distribution similar to those found in the presence of biomass burning aerosols as shown by [36]. Making the same interpretation to the AOD median vertical line, AOD = 0.198±0.078, the values in the left side of the AOD median corresponding to low extinction and absorption of radiation aerosol types, and the right side is related to the high extinction and absorption radiation types. The median values were assumed as a better statistical evaluator since it was found using a skewness test that the AOD vs. AE distribution is rather asymmetrical, and instead of the standard deviation it has been used the median standard deviation as the measure of the variability or dispersion of the data set, according to [02]. The scatterplot in Figure 6 was divided into four distinctive sectors, I, II, III and IV. Each of them represents different types and sizes of aerosol according to the AOD and AE values. This study should be focusing mainly on regions II and IV, which correspond to fine mode size distribution and high absorption and extinction aerosol types, and coarse mode and high absorption and extinction aerosol types, respectively. In sector II there is a strong indication of the predominance of biomass burning aerosols in the atmosphere as the large AE corresponds to small sized particles and the large AOD for a strong absorbing type of aerosols. The same reasoning can be applied to sector IV, although the values below the AE median values can be associated to particle growth during the long-range transport [37]. As can be seen in Figure 6, the most AOD and AE values of aerosol measured during 21 August 2007 (red points) are inside the region II, representing biomass burning aerosol types.

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daytime on the same day the satellite made measurements in an area between Campo Grande and São Paulo, as can be seen in Figure 5. The AOD and LR retrieved by the CALIOP sensor were obtained using the Level 2 Aerosol Layer products Version 3.0 for both trajectories during 21 August 2007. Figure 7 shows the AOD (left panel) and LR values (right panel) according to the latitude for the nighttime trajectory (21 Aug 2007 –

In the left panel of figure 7 it can be observed the values of AOD retrieved by CALIOP sensor spanning from 0.65 to 0.30. Such values are higher compared with those measured by the AERONET sunphotometer installed at CG site, represented by the red points in Figure 6. The high values of AOD measured by CALIOP sensor are a strong indication that highly absorbent aerosols are present in the atmosphere; in addition, it is a strong indication that these particles are from biomass burning aerosols [38]. Such evidence is confirmed analyzing the Lidar Ratio values, which can indicate the most likely type of aerosol detected, as shown at the right panel of Figure 7. The CALIOP sensor signed LR values of 70 sr. According to [39, 40], the LR value of 70 sr corresponds to the aerosol type from biomass burning or continental polluted air. However, biomass burning aerosol types differ according to their detection altitude. Generally, such layers are detected above the PBL, localized approximately between 3 to 5 km and more [41,42]. In the case of the CALIOP nighttime measures on 21 August 2007 in the region of the CG's AERONET site, the detected layers correspondent to the AOD and LR values presented in Figure 7 were localized between 2.5 and 4 km, which is Above the PBL, demonstrating that the detected layers are mostly loaded by biomass burning aerosols. The 532 nm Total Attenuated Backscatter profile presented in Figure 8 shows an intense backscatter signal from an aerosol layer at high altitude, localized above the PBL approximately between 2.5 and 4 km, which is the biomass burning layer detected near the AERONET sunphotometer site at CG pointed by the dashed line in red. Such aerosol type is confirmed by the Vertical Feature Mask (VFM) product presented in Figure 9, which identifies the subtype of each aerosol in the

**Figure 7.** AOD and LR distribution as function of latitude (21 Aug 2007 – NT trajectory in figure 5) measured by the CALIOP sensor on 21 August 2007 during the nighttime. The star marks the point of the satellite closest approach to the AERONET site installed at CG. The red triangle represents the value

of AOD measured by the AERONET sunphotometer during the closest approximation time.

NT in figure 5).

atmosphere [43].

**Figure 6.** Scatterplot of the Ångström Exponent versus Aerosol Optical Depth at 532 nm for the case study selected (21 August 2007) and for the complete period of the August 2007. The four distinctive sectors represent different types and sizes of aerosol according to the AOD and AE values. The region II represents aerosols with biomass burning products characteristics, with high values of AOD and AE. The calculated median and median standard deviation values are AOD = 0.1980.078 and AE = 1.460.09, respectively.

On 21 August 2007, the CALIPSO satellite overpasses the region near the AERONET site in CG during the nighttime (descending trajectory), with the closest approach to the AERONET site of 126 km (horizontal distance) at 05:00 UTC approximately. During the daytime on the same day the satellite made measurements in an area between Campo Grande and São Paulo, as can be seen in Figure 5. The AOD and LR retrieved by the CALIOP sensor were obtained using the Level 2 Aerosol Layer products Version 3.0 for both trajectories during 21 August 2007. Figure 7 shows the AOD (left panel) and LR values (right panel) according to the latitude for the nighttime trajectory (21 Aug 2007 – NT in figure 5).

260 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

biomass burning aerosol types.

1.460.09, respectively.

AOD = 0.198±0.078, the values in the left side of the AOD median corresponding to low extinction and absorption of radiation aerosol types, and the right side is related to the high extinction and absorption radiation types. The median values were assumed as a better statistical evaluator since it was found using a skewness test that the AOD vs. AE distribution is rather asymmetrical, and instead of the standard deviation it has been used the median standard deviation as the measure of the variability or dispersion of the data set, according to [02]. The scatterplot in Figure 6 was divided into four distinctive sectors, I, II, III and IV. Each of them represents different types and sizes of aerosol according to the AOD and AE values. This study should be focusing mainly on regions II and IV, which correspond to fine mode size distribution and high absorption and extinction aerosol types, and coarse mode and high absorption and extinction aerosol types, respectively. In sector II there is a strong indication of the predominance of biomass burning aerosols in the atmosphere as the large AE corresponds to small sized particles and the large AOD for a strong absorbing type of aerosols. The same reasoning can be applied to sector IV, although the values below the AE median values can be associated to particle growth during the long-range transport [37]. As can be seen in Figure 6, the most AOD and AE values of aerosol measured during 21 August 2007 (red points) are inside the region II, representing

**Figure 6.** Scatterplot of the Ångström Exponent versus Aerosol Optical Depth at 532 nm for the case study selected (21 August 2007) and for the complete period of the August 2007. The four distinctive sectors represent different types and sizes of aerosol according to the AOD and AE values. The region II represents aerosols with biomass burning products characteristics, with high values of AOD and AE. The calculated median and median standard deviation values are AOD = 0.1980.078 and AE =

On 21 August 2007, the CALIPSO satellite overpasses the region near the AERONET site in CG during the nighttime (descending trajectory), with the closest approach to the AERONET site of 126 km (horizontal distance) at 05:00 UTC approximately. During the In the left panel of figure 7 it can be observed the values of AOD retrieved by CALIOP sensor spanning from 0.65 to 0.30. Such values are higher compared with those measured by the AERONET sunphotometer installed at CG site, represented by the red points in Figure 6. The high values of AOD measured by CALIOP sensor are a strong indication that highly absorbent aerosols are present in the atmosphere; in addition, it is a strong indication that these particles are from biomass burning aerosols [38]. Such evidence is confirmed analyzing the Lidar Ratio values, which can indicate the most likely type of aerosol detected, as shown at the right panel of Figure 7. The CALIOP sensor signed LR values of 70 sr. According to [39, 40], the LR value of 70 sr corresponds to the aerosol type from biomass burning or continental polluted air. However, biomass burning aerosol types differ according to their detection altitude. Generally, such layers are detected above the PBL, localized approximately between 3 to 5 km and more [41,42]. In the case of the CALIOP nighttime measures on 21 August 2007 in the region of the CG's AERONET site, the detected layers correspondent to the AOD and LR values presented in Figure 7 were localized between 2.5 and 4 km, which is Above the PBL, demonstrating that the detected layers are mostly loaded by biomass burning aerosols. The 532 nm Total Attenuated Backscatter profile presented in Figure 8 shows an intense backscatter signal from an aerosol layer at high altitude, localized above the PBL approximately between 2.5 and 4 km, which is the biomass burning layer detected near the AERONET sunphotometer site at CG pointed by the dashed line in red. Such aerosol type is confirmed by the Vertical Feature Mask (VFM) product presented in Figure 9, which identifies the subtype of each aerosol in the atmosphere [43].

**Figure 7.** AOD and LR distribution as function of latitude (21 Aug 2007 – NT trajectory in figure 5) measured by the CALIOP sensor on 21 August 2007 during the nighttime. The star marks the point of the satellite closest approach to the AERONET site installed at CG. The red triangle represents the value of AOD measured by the AERONET sunphotometer during the closest approximation time.

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**6. Transport and detection of biomass burning aerosols** 

installed at CG site, represented by the red points.

For the days when the presence of aerosols from biomass burning were detected by the sensors onboard CALIPSO and TERRA satellites, and also by the sunphotometer on CG site, air mass trajectories were generated using the HYSPLIT model, that is a complete system for computing simple trajectories to complex dispersion and deposition simulations using either puff or particle approaches [44]. The HYSPLIT trajectories are computed based on the Global Data Assimilation System (GDAS), an operational system from the National Weather Service of the National Centers for Environmental Prediction (NCEP) and it was used to investigate if the air mass parcels in the Midwestern have been dislocated towards the Southeastern region where the MSP-Lidar system is installed. The purpose to use this trajectory model is to constrain the direction of the air masses to improve the correlation between the optical properties (i.e., AOD and Lidar ratio) measured by two different instruments spatially separated, i.e., CALIOP sensor and ground-based AERONET sunphotometer and MSP-Lidar system. According to Figure 5, the HYSPLIT trajectories show that there were transportation of biomass burning aerosols generated in the Midwestern region of Brazil, i.e. Campo Grande region, to the Southeastern, where the MSP-Lidar system is installed, as well as an AERONET sunphotometer system. The same analysis presented in the previous section was performed to the daytime measurement made by the CALIOP sensor in its trajectory in the region between the cities of CG and SP (Figure 5), using the AOD and LR retrieved using the Level 2 Aerosol Layer products Version 3.0. Figure 10 shows the AOD (left panel) and LR values (right panel) as function of the latitude for the daytime trajectory (21 Aug 2007 – DT in Figure 5). It can be seen that in this region the CALIOP sensor obtained not so high AOD values, being around 0.10. The LR values varied around 40‐55 sr, representing the dust aerosol type or a mixture of dust and pollution (polluted dust) [39,40]. In the left panel of Figure 10 low values of AOD can be observed, around 0.10. Such values are lower compared to those measured by the AERONET sunphotometer

**Figure 10.** AOD and LR distribution as function of latitude (21 Aug 2007 – DT trajectory in figure 5) measured by the CALIOP sensor on 21 August 2007 during the daytime. The star marks the point of the satellite closest approach to the AERONET site installed at CG. The red triangle represents the value of

AOD measured by the AERONET sunphotometer during the closest approach time.

**Figure 8.** CALIOP 532 nm Total Attenuated Backscatter profile along with the orbit track in the graphic embedded in the upper left. The dashed line in red represents the closest approach to the region of Campo Grande on 21 August 2007 around 05:00 (UTC). It can be noticed an intense aerosol layer detached above the PBL, localized approximately between 2.5 and 4.0 km of altitude.

**Figure 9.** CALIOP Vertical Feature Mask of aerosol layers measured in the region of the CG's AERONET sunphotometer on 21 August 2007 around 05:00 (UTC). It can be seen an aerosol layer above the PBL localized approximately between 2.5 and 4.0 km altitude and classified as biomass burning aerosol type (6 = smoke). The layer immediately below, within the PBL, is classified as a mixture of dust and pollution (5 = polluted dust aerosol type).

## **6. Transport and detection of biomass burning aerosols**

262 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

**Figure 8.** CALIOP 532 nm Total Attenuated Backscatter profile along with the orbit track in the graphic embedded in the upper left. The dashed line in red represents the closest approach to the region of Campo Grande on 21 August 2007 around 05:00 (UTC). It can be noticed an intense aerosol layer

detached above the PBL, localized approximately between 2.5 and 4.0 km of altitude.

**Figure 9.** CALIOP Vertical Feature Mask of aerosol layers measured in the region of the CG's

and pollution (5 = polluted dust aerosol type).

AERONET sunphotometer on 21 August 2007 around 05:00 (UTC). It can be seen an aerosol layer above the PBL localized approximately between 2.5 and 4.0 km altitude and classified as biomass burning aerosol type (6 = smoke). The layer immediately below, within the PBL, is classified as a mixture of dust

For the days when the presence of aerosols from biomass burning were detected by the sensors onboard CALIPSO and TERRA satellites, and also by the sunphotometer on CG site, air mass trajectories were generated using the HYSPLIT model, that is a complete system for computing simple trajectories to complex dispersion and deposition simulations using either puff or particle approaches [44]. The HYSPLIT trajectories are computed based on the Global Data Assimilation System (GDAS), an operational system from the National Weather Service of the National Centers for Environmental Prediction (NCEP) and it was used to investigate if the air mass parcels in the Midwestern have been dislocated towards the Southeastern region where the MSP-Lidar system is installed. The purpose to use this trajectory model is to constrain the direction of the air masses to improve the correlation between the optical properties (i.e., AOD and Lidar ratio) measured by two different instruments spatially separated, i.e., CALIOP sensor and ground-based AERONET sunphotometer and MSP-Lidar system. According to Figure 5, the HYSPLIT trajectories show that there were transportation of biomass burning aerosols generated in the Midwestern region of Brazil, i.e. Campo Grande region, to the Southeastern, where the MSP-Lidar system is installed, as well as an AERONET sunphotometer system. The same analysis presented in the previous section was performed to the daytime measurement made by the CALIOP sensor in its trajectory in the region between the cities of CG and SP (Figure 5), using the AOD and LR retrieved using the Level 2 Aerosol Layer products Version 3.0. Figure 10 shows the AOD (left panel) and LR values (right panel) as function of the latitude for the daytime trajectory (21 Aug 2007 – DT in Figure 5). It can be seen that in this region the CALIOP sensor obtained not so high AOD values, being around 0.10. The LR values varied around 40‐55 sr, representing the dust aerosol type or a mixture of dust and pollution (polluted dust) [39,40]. In the left panel of Figure 10 low values of AOD can be observed, around 0.10. Such values are lower compared to those measured by the AERONET sunphotometer installed at CG site, represented by the red points.

**Figure 10.** AOD and LR distribution as function of latitude (21 Aug 2007 – DT trajectory in figure 5) measured by the CALIOP sensor on 21 August 2007 during the daytime. The star marks the point of the satellite closest approach to the AERONET site installed at CG. The red triangle represents the value of AOD measured by the AERONET sunphotometer during the closest approach time.

Two possible reasons can explain the detection of different values of AOD and LR from those values retrieved on the nighttime measurements (Figure 7). The first one is that the detected aerosols have their optical properties changed due to long-range transport, mixing with other aerosol types or absorbing moisture from the atmosphere, undergoing aging processes. The low value of the Lidar ratio (40 to 55 sr) also indicates the aging processes of the aerosols; such lower values may be linked to an increase of particle size by moisture absorption and/or a reduction of the light absorption capability of the particles [37]. However, the second reason can be the fact of the transported aerosol masses only reaches the region measured by the CALIOP sensor on 22 August 2007, a day after the CALIPSO satellite overpasses.

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and 5.0 km range altitude, which represent the dust aerosol type [45]. Such values of LR are not consistent with those values for biomass burning; however, it should be kept in mind that the Klett's inversion method only provide a constant LR value for the whole atmosphere column; in addition, the MASP is considered one of the most polluted cities in the world, having several different aerosol types loaded in its atmosphere, which can turn the retrieval of the LR value and the confidence of the aerosol type classification very difficult tasks. Furthermore**,** the HYSPLIT backtrajectories leads to a strong indication that the detached layer between 3.5 and 5 km is the biomass burning aerosol transported from the Midwestern region of Brazil. Backscatter profile analyses performed in posterior time period (around 20:00 UTC) presents LR values of 60 sr, consistent to the biomass burning

**Figure 11.** Air mass trajectories generated by the HYSPLIT model. Such trajectories identify the transport of aerosols from the Midwestern region of Brazilian territory on 21 August 2007 for the

Southeast region of Brazil, reaching the MASP on 23 August 2007.

aerosol type according to [45].
