**1. Introduction**

272 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

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Large-scale forest fires in the tropics, emitting vast amounts of aerosols and trace gases, drew the attention of scientists around the world in the late 80s and early 90s. A number of international collaborative research projects, such as TRACE-A (Transport and Atmospheric Chemistry near the Equator-Atlantic, [1]) and SAFARI-92 (South African Fire-Atmosphere Research Initiative, [2]), were initiated under the auspices of the International Geosphere-Biosphere Programme to investigate biomass burning emissions and their longrange transport. One of the areas of great interest was the Amazon region (Figure 1), which later led to the creation of the international Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA, [3]) in Brazil in 1998. Several intense observation campaigns were dedicated, not only to rainfall measurements by radar and storm structure, but also to biomass burning, monitoring of emissions and transport of aerosols and their impact on the vegetation and population of the region. However, monitoring of background concentrations of aerosols, deploying stacked filter units, had already been initiated in 1990 at the "Sierra do Navio" site (Amapá, about 190 km north of the equator) and in Cuiabá (Mato Grosso), a town located in the Brazilian savannah [4]. The location of both sites is shown in Figure 1.

São Paulo is Brazil´s most populous State, with approximately 42 million inhabitants (21,5% of Brazil's total population) in an area of 249 000 km². The region is diverse in terms of its geography, natural environment and economy, and can be broadly classified into three main zones. In the southeast, the Atlantic coastal strip is separated from the remainder of the State by the scarp of the Serra do Mar, containing Brazil´s largest remaining areas of

© 2012 Held 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 Held 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.

Atlantic rainforest, a threatened ecosystem that has been largely eliminated in most of the Brazilian States bordering the Atlantic ocean. Located on a plateau above the scarp are the densely populated and heavily industrialized regions of metropolitan São Paulo (RMSP) and its satellite cities. Continuing inland, the largest fraction of the area of the State has an economy mostly based on agro industry. Here has been widespread conversion of natural ecosystems to agriculture. The most important single agricultural activity is sugar cane production, although there are also substantial cattle ranching, citrus cultivation and agro forestry for pulping and construction. In all regions, it is largely local emission sources that determine the chemical composition of the atmospheric aerosol, with a smaller influence of long-range transport of polluted air masses from elsewhere in Brazil.

Review of Aerosol Observations by Lidar and Chemical Analysis in the State of São Paulo, Brazil 275

requires burning of the crop in sectors of the plantations during the night prior to manual cutting to remove excess foliage. This practice results in large quantities of aerosols and trace gases being emitted into the atmosphere (Figure 2a), not only negatively affecting local towns, but also regions much further downwind [10-12], demonstrating the importance of

**Figure 2. (a)** Typical sugar cane fire in central São Paulo State. **(b)** Dust lifted from freshly cut sugar

(b)

(a)

Along the São Paulo coast, marine aerosols are modified by the inclusion of pollutants emitted from transport, urban, and industrial sources. There are some areas where levels of anthropogenic pollution are low, and where the aerosol composition can be mainly attributed to natural origins. However, compared to metropolitan São Paulo and the interior of the State, the coastal zone has been much less well studied, with the exception of

cane fields by the downdraft of an approaching storm.

Cubatão, a heavily industrialized town near the coast close to Santos.

monitoring aerosols throughout the State.

**Figure 1.** Brazil, showing the location of São Paulo State in relation to the Amazon region, as well as the background monitoring stations in Sierra do Navio (Amapá) and Cuiabá (Mato Grosso).

In terms of atmospheric quality, suspended aerosol particles are (together with ozone) probably the most important atmospheric pollutant in both São Paulo city and the largely agricultural hinterland of the State. Ozone is generated during reactions involving the nitrogen oxides (NOx) and volatile organic compounds (VOCs) emitted from vehicles, biomass burning and biogenic sources. The particulates are either emitted directly (in the form of primary aerosols), or are produced during reactions involving gaseous precursors (SO2, NOx and hydrocarbons). In large urban areas, such as the Metropolitan Region of São Paulo (RMSP), anthropogenic emissions from vehicles and industrial processes are the dominant contributors to elevated aerosol levels, while biomass burning [5-7] and dust lifted from barren fields (Figure 2) during the dry winter season constitute the principal sources of aerosols in the central and western sectors of the state. The State of São Paulo is the largest producer of sugar cane in Brazil, accounting for about 60% of Brazil's harvest [8], with more than 4,7 million hectares planted in 2010, of which 44% are burnt before harvesting [9]. The sugar cane is mostly harvested from April to November. Although progress is being made in mechanization, large areas are still harvested manually, which requires burning of the crop in sectors of the plantations during the night prior to manual cutting to remove excess foliage. This practice results in large quantities of aerosols and trace gases being emitted into the atmosphere (Figure 2a), not only negatively affecting local towns, but also regions much further downwind [10-12], demonstrating the importance of monitoring aerosols throughout the State.

274 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

long-range transport of polluted air masses from elsewhere in Brazil.

Atlantic rainforest, a threatened ecosystem that has been largely eliminated in most of the Brazilian States bordering the Atlantic ocean. Located on a plateau above the scarp are the densely populated and heavily industrialized regions of metropolitan São Paulo (RMSP) and its satellite cities. Continuing inland, the largest fraction of the area of the State has an economy mostly based on agro industry. Here has been widespread conversion of natural ecosystems to agriculture. The most important single agricultural activity is sugar cane production, although there are also substantial cattle ranching, citrus cultivation and agro forestry for pulping and construction. In all regions, it is largely local emission sources that determine the chemical composition of the atmospheric aerosol, with a smaller influence of

**Figure 1.** Brazil, showing the location of São Paulo State in relation to the Amazon region, as well as the

In terms of atmospheric quality, suspended aerosol particles are (together with ozone) probably the most important atmospheric pollutant in both São Paulo city and the largely agricultural hinterland of the State. Ozone is generated during reactions involving the nitrogen oxides (NOx) and volatile organic compounds (VOCs) emitted from vehicles, biomass burning and biogenic sources. The particulates are either emitted directly (in the form of primary aerosols), or are produced during reactions involving gaseous precursors (SO2, NOx and hydrocarbons). In large urban areas, such as the Metropolitan Region of São Paulo (RMSP), anthropogenic emissions from vehicles and industrial processes are the dominant contributors to elevated aerosol levels, while biomass burning [5-7] and dust lifted from barren fields (Figure 2) during the dry winter season constitute the principal sources of aerosols in the central and western sectors of the state. The State of São Paulo is the largest producer of sugar cane in Brazil, accounting for about 60% of Brazil's harvest [8], with more than 4,7 million hectares planted in 2010, of which 44% are burnt before harvesting [9]. The sugar cane is mostly harvested from April to November. Although progress is being made in mechanization, large areas are still harvested manually, which

background monitoring stations in Sierra do Navio (Amapá) and Cuiabá (Mato Grosso).

(a) (b)

**Figure 2. (a)** Typical sugar cane fire in central São Paulo State. **(b)** Dust lifted from freshly cut sugar cane fields by the downdraft of an approaching storm.

Along the São Paulo coast, marine aerosols are modified by the inclusion of pollutants emitted from transport, urban, and industrial sources. There are some areas where levels of anthropogenic pollution are low, and where the aerosol composition can be mainly attributed to natural origins. However, compared to metropolitan São Paulo and the interior of the State, the coastal zone has been much less well studied, with the exception of Cubatão, a heavily industrialized town near the coast close to Santos.

In the State of São Paulo, the first aerosol measurements began in Cubatão [13], and within the metropolitan area of São Paulo, notorious for its traffic emissions [14]. In terms of morphology, São Paulo is among the world's five largest cities, and is sixth largest in terms of population [15], with about 11,3 million inhabitants. The population of the Metropolitan Region of São Paulo (RMSP), which includes peripheral urban areas, reached an estimated 19,9 million persons in 2009 [16]. Human activities including road transport and industry now exert an enormous impact on air quality in the region, and therefore on the health of the population [17]. The total fleet of vehicles (cars, buses, trucks and motorcycles, powered by gasoline, ethanol and diesel) in the State of São Paulo exceeded 12,8 million in 2011, of which about 50% operate within the RMSP [9].

Review of Aerosol Observations by Lidar and Chemical Analysis in the State of São Paulo, Brazil 277

Sodar observations made during the period of June 2009 to December 2011 showed that strong nocturnal Low-Level-Jets (LLJs) develop on top of the surface radiation inversion, mostly during the relatively dry austral winter months (May – October), when stable conditions prevail [26, 27]. These LLJs generally form during the late evening at altitudes ranging from 250–500 m AGL, with maximum speeds of 12–20 m.s-1. They usually last until 08:00–09:00 Local Time (LT), when the inversion has been eroded by the solar radiation. The frequency of LLJs varied from 3 - 22 days per month, with higher frequencies and greater intensity generally during the winter months. Observations with a sodar were made at three different locations in the central region of the State, *viz.* in Bauru, Rio Claro and Ourinhos. Earlier measurements, deploying tethered balloons and radiosondes in the eastern region of the State, yielded similar results in terms of structure, dynamics, seasonality and development characteristics [28]. LLJs have been observed in many parts of the world and were found to have regional extent. The practical importance of the LLJ lies in the rapid transport of moisture

Regular monitoring of air pollutants under the auspices of the Companhia de Tecnologia de Saneamento Ambiental (CETESB), the air quality "watchdog" in the State of São Paulo, started in the 70s, but a fully automatic monitoring network was only installed in 2000. Since then, observations are available in real time [30]. In 2001, 29 automatic stations, the majority in the RMSP, were already in operation [31]. From 2008 onwards, the automatic monitoring network was significantly expanded. In 2011, 42 monitoring stations in 28 towns were in operation, 19 in the RMSP and 23 in the remaining parts of the State [9]. The majority of the stations monitor particulate matter (PM10), NO, NO2, NOx and O3, as well as meteorological parameters, while a few also measure PM2.5, SO2 and CO. The automatic air quality monitoring network is shown in Figure 3. Additionally, CETESB also maintained a network of 41 manual monitoring stations during 2011, where measurements are made of PM2.5, PM10, TSP (Total Suspended Particulates), black smoke and SO2, in various combinations [9]. Aerosol mass concentrations are determined using either β-attenuation instruments

(automatic stations) or gravimetric and reflectometric techniques (manual stations).

standards are defined in CONAMA Resolution No. 03/90 (Table 2 in [9]).

In accordance with recommendations of the World Health Organization [32], CETESB defines 5 levels of air quality: "Boa" (good), "Regular" (regular), "Inadequada" (insufficient), "Má" (bad) and "Péssimo" (extremely bad), the highest being invoked if one of the monitored pollutants exceeds the pre-defined threshold. The national air quality

PM10 and TSP measurements are available since 1984 and 1985, respectively [31], although initially only from very few stations in the interior of the State, but gradually increasing to 41 and 11, respectively, in 2011 [9]. Figure 4 shows the year-to-year variation of annual mean PM10 concentrations against the National Air Quality Standard (PQAr) for the RMSP and two sites in Cubatão (Figure 3, Nos. 24 and 25), which is one of the major industrial hubs in Brazil, where one site is located within the industrial suburb (No. 25) and the other in the

and pollutants in a narrow vertical band above the radiation inversion [29].

**3. Ground-level monitoring of particulates** 

Observations from the Brazilian Lightning Detection Networks (RINDAT [18] and BrasilDAT at ELAT/INPE [19]) have shown a significantly higher lightning frequency over the RMSP and other large urban complexes within the State since the inception of the RINDAT Lightning Network in 1999 [20, 21]. This prompted a study of the impact of anthropogenic emissions on the frequency of lightning [22], showing a distinct increase of cloud-to-ground flashes, not only over the RMSP, but also over other large cities and densely populated or industrialized regions in the State, correlated to the occurrence of heat islands and increased concentrations of PM10.
