**4. MODIS aerosol optical depth**

Figure 3 shows the maximum values of AOD for the southeastern region of Brazil from 2003-2010 (latitude between 14°S and 25°S and longitude between 54.1°W and 38.1°W). This region is known for having main urban centers, especially the metropolitan area of São Paulo and Rio de Janeiro, with large amounts of industries. In addition, the city of Cubatão is located at this region (50 km from MASP), in the state of São Paulo, known in the 1980s and 1990s as one of the most polluted cities in the world [33].

Despite the known major sources of pollution in the southeastern region of Brazil, it is possible to notice high maximum AOD values only during spring and winter. Except for these periods, and for one day in 2003 and other in 2010, both at summer, the maximum AOD over the Southeastern region was always below 1.0. The average of the maximum AOD between 2003 and 2010 was 0.492±0.505, indicating the high variability of the maximum AOD over the region.

The 95th percentile calculated using data on maximum daily AOD for the southeastern region of Brazil was 1.143. This means that 95% of the daily data (MOD08) from the MODIS sensor (from a total of 2921 measurements spanning from 2003 to 2010) have lower values than 1.143. At first, this value can be considered low, but aspects of the sensor used must be taken into account, such as a spatial resolution of 1 km and that the maximum concentration of aerosols tends to be found near the surface, hindering the use of remote sensing for this task.

256 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

periods.

number of fires for each year can also be observed in the Table 1, where it can be clearly seen that the maximum active fires seasons are winter and spring, followed by autumn and summer in almost every analyzed year, except for the years of 2000 and 2004, where the total active fires detected were greater in spring and summer than in winter and autumn, respectively. For the year of 2004, it was observed that the rain rates for these two periods were normal according to the climatology, without an obvious reason for that variation. It can also be seen the difference between the number of fires during the maximum fires season (winter) and the minimum (summer), reaching a value 3 times higher at some

**Year/ Season Summer Autumn Winter Spring Total**  57 924 2633 2401 6090 598 451 2202 1288 4489 78 277 1658 1026 3091 120 670 1657 1416 3829 97 519 1759 1065 3420 74 387 1118 1484 3171 215 680 1912 1498 4174 53 933 1889 1490 4398 108 602 306 - 983 **Total 993 5443 15134 11668 33645** 

**Table 1.** Active fires measured by the NOAA-12 satellite for the State of São Paulo – Brazil

Figure 3 shows the maximum values of AOD for the southeastern region of Brazil from 2003-2010 (latitude between 14°S and 25°S and longitude between 54.1°W and 38.1°W). This region is known for having main urban centers, especially the metropolitan area of São Paulo and Rio de Janeiro, with large amounts of industries. In addition, the city of Cubatão is located at this region (50 km from MASP), in the state of São Paulo, known in the 1980s

Despite the known major sources of pollution in the southeastern region of Brazil, it is possible to notice high maximum AOD values only during spring and winter. Except for these periods, and for one day in 2003 and other in 2010, both at summer, the maximum AOD over the Southeastern region was always below 1.0. The average of the maximum AOD between 2003 and 2010 was 0.492±0.505, indicating the high variability of the

The 95th percentile calculated using data on maximum daily AOD for the southeastern region of Brazil was 1.143. This means that 95% of the daily data (MOD08) from the MODIS sensor (from a total of 2921 measurements spanning from 2003 to 2010) have lower values than 1.143. At first, this value can be considered low, but aspects of the sensor used must be taken into account, such as a spatial resolution of 1 km and that the

**4. MODIS aerosol optical depth** 

maximum AOD over the region.

and 1990s as one of the most polluted cities in the world [33].

**Figure 3.** MODIS Maximum Aerosol Optical Depth over southeast of Brazil (a) 2003-2006 and (b) 2007- 2010. Years: (a) 2003 (orange); 2004 (blue); 2005 (green); 2006 (red) and (b) 2007 (orange); 2008 (blue); 2009 (green); 2010 (red)

Both the Amazon and Midwestern Brazil are great sources of aerosols into the atmosphere, and the maximum daily value of AOD found on the Southeastern region can be compared to these areas. In all of these regions the largest occurrences of elevated AOD are during the winter and spring in the Southern Hemisphere. The occurrence of higher AOD levels during this period for the Northern and Central region is basically due to the highest amount of biomass burning in the region (dry season). In Brazil, biomass burning in the Amazon region occurs with greater intensity during the dry season (July - October) and primarily affects the ecosystems of forest, pasture and Cerrado [34]. The small amount of precipitation and the increased atmospheric stability at this period contributes to the persistence of aerosols in the atmosphere, as well as a higher transport of biomass burning aerosols from the Amazon region (Section 6).

Analyzing the 146 days with maximum AOD higher than the 95th percentile (1.143) found between 2003-2010 it is observed that approximately 82% of the cases occurred during the spring in the Southeastern hemisphere (Figure 4). When considering the period corresponding for spring and winter, the same has 144 days with values above the 95th percentile (99% approximately). The emissions from these fires have significant impacts on the concentration of gases and aerosols. The results presented here emphasize the importance of monitoring the aerosols for the period between June and October. The values recorded during summer and fall may be related, among other reasons, with burning events in the Southeastern region and transport of biomass burning aerosols from distant regions, such as the Amazon and MidWestern region of Brazil regions, Bolivia, the Northern portion of Argentina and the North region of South America. Another possible explanation for the values found are the urban aerosols emitted into the studied area.

Impacts of Biomass Burning in the Atmosphere

of the Southeastern Region of Brazil Using Remote Sensing Systems 259

**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

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,

MSP-Lidar system and AERONET sunphotometer are installed.

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