**6.2. Impact of aerosols on rainfall**

306 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

The impact of anthropogenic aerosols on human health has been acknowledged in both metropolitan and rural regions [93, and references therein]. In general terms, as pointed out in [93], in recent years the population of São Paulo State has suffered from either acute (short-term, high concentration) or chronic (long-term, lower concentration) exposure to particulate air pollutants, depending on location. In rural regions, there is acute exposure to high concentrations of biomass burning particulates present in plumes, as well as chronic exposure to these aerosols on a regional basis throughout the dry season. In metropolitan São Paulo, there is chronic exposure to particulates derived from road transport and industrial emissions, together with periodic acute exposure to extremely high levels of

pollutants under conditions of thermal inversions and stationary air masses [94-96].

correlated with PM10 concentrations obtained for the preceding month [106].

There have been many studies of the correlation between aerosol concentrations and human health impacts in the metropolitan regions, especially in São Paulo city [97-102]. Typical effects include asthma and pneumonia, as well as other cardiovascular and respiratory symptoms. Increased levels of PM10 were associated with increases of 6,7% and 2,2% in hospital admissions of children due to respiratory illness [96, 103]. Increments of 10 g.m-3 in PM10 concentrations resulted in increases in hospital admissions of between 0,9% and 6,7% in Sao Paulo [97, 103-105]. In the elderly, a 5,4% increase in the number of deaths was linked to a 10 g.m-3 increase in PM10 [105]. Industrial emissions in Cubatão have been found to seriously affect the lung function of children, with respiratory airflow rates

Bourotte *et al.* [56] investigated the relationships between peak expiratory flow (PEF) measurements and soluble ions in fine and coarse aerosols, and found a negative correlation

and fine fraction Mg2+. The findings suggested that increased levels of coarse particles could

In these heavily polluted regions, atmospheric particles contain components known to be carcinogenic and mutagenic, including ketones, aldehydes, quinolines, carboxylic acids, polycyclic aromatic compounds (PAHs), and nitro-PAHs. These substances have been associated with exhaust emissions from road vehicles in southeast Brazil [69, 107-109]. Benzo[a]pyrene equivalent values suggest that the cancer risk is greater for the São Paulo city aerosol than elsewhere in the State, although concentrations may not exceed World

Biomass burning emissions in rural regions also have a recognized influence on human health, as well as environmental impacts including modification of nutrient cycling [10, 11, 47], and effects on climate including alterations of the radiative properties of the lower atmosphere, cloud formation and precipitation [110, 111]. For these reasons, as well as due to the need to meet certification requirements of importing countries, there has been

, Na+, Mg2+ and NH4+, as well as between PEF

**6.1. Impact of aerosols on human health** 

between PEF and the coarse fraction ions Cl-

Health Organization guidelines [65].

be of especial concern for asthmatic individuals.

**6. Impacts of aerosols** 

Aerosols derived from all of the sources described above are able to alter the radiative properties of the troposphere, and can modify the processes that lead to the development of cloud condensation nuclei, cloud droplets, and ultimately precipitation [118-120]. The magnitudes of these effects depend on the size distribution, number concentration and chemical composition of the particles, and can therefore vary widely within the same region.

Dufek and Ambrizzi [121] used daily precipitation data collected at 59 locations in São Paulo State to investigate rainfall trends for the period 1950-1999. Although some of the findings were contradictory, an overall trend towards a wetter climate was identified, with rainfall concentrated into a smaller number of more intense events. It was suggested that these changes could be related to the presence of biomass burning aerosols, as well as changes in land use. Evidence that the aerosols probably act as cloud condensation nuclei was provided in [122], where a relationship was identified between water-soluble organic carbon (WSOC) in the particles and dissolved organic carbon (DOC) in rainwater.

An important point is that sugar cane production in São Paulo State has increased over this period. Between the 1990/91 and 2000/01 seasons, the harvest increased from 132 Mt to 194 Mt [123]. It can therefore be supposed that there was also a large increase in emissions of aerosols from the burning of the crop, since manual harvesting of the cane (which requires prior burning) was the norm over the period. Mechanization of the crop (which does not involve burning) has only been introduced recently (from around 2005). The main conclusion to be drawn from this is that the trend towards a smaller number of more intense precipitation events, as reported in [121], could now be reversed in the interior of São Paulo State, as sugar cane burning is progressively phased out.

Review of Aerosol Observations by Lidar and Chemical Analysis in the State of São Paulo, Brazil 309

**Figure 25. (a)** Spatial distribution of the average maximum reflectivity (dBZ), during the period October 1998 to March 1999. TITAN storm threshold was defined as reflectivity >40 dBZ within the 240 km range of the Bauru Doppler radar (after [124]). **(b)** Flash density within the 450 km range of the Bauru radar (after [21]). The circle indicates the 240 km quantitative range as in the TITAN image

(b)

(a)

above.

The climatological characterization of storm properties, such as area, volume, maximum echo top and reflectivity during two summer seasons, *viz.,* 1998-1999 and 1999-2000, based on observations from the Bauru S-band Doppler radar, has for the first time shown the spatial distribution of these parameters in central São Paulo State. Gomes and Escobedo [124] showed that some preferential areas of precipitation, taking into account a precipitation envelope area defined by the 25 dBZ threshold, were located along the Tietê River valley. The mean maximum reflectivity field (>40 dBZ), representing the cores of convective precipitation systems, has highlighted some preferential regions for convection to develop over urban and industrialized areas, such as metropolitan Campinas (Figure 25a). A climatology of flash density (Figure 25b; [21]) also identified Campinas as one of three regions with a higher concentration of lightning discharges, attributed to the occurrence of heat islands due to anthropogenic activities. Thus, the spatial distribution of the reflectivity field exceeding 40 dBZ in the Campinas region reinforces results showing a strong correlation between the frequency of cloud-to-ground lightning strokes and precipitation intensity.

The influence of anthropogenic aerosols on precipitation patterns in the region is the subject of research currently in progress as part of a thematic climate change research programme sponsored by FAPESP (the São Paulo State Research Foundation). The quantitative evaluation of changes in the rainfall pattern, such as increases or decreases of area rainfall totals, number and volume of convective cells, duration of rain events, distribution of echo top heights, etc., is in progress for a 10-year period of integrated radar observations (Bauru and Presidente Prudente radars), using the TITAN Software.

## **6.3. Impact of aerosols on the frequency of lightning**

Westcott [125] documented for the first time an impact of large cities on the cloud-to-ground (CG) lightning frequency in the Midwest of the United States. This was followed up by various researchers around the world, including in Brazil [20] and ultimately summarized in [22], using 10 years of observations from the Brazilian Lightning Detection Networks (1999- 2008). This research confirmed the impact of anthropogenic activities on lightning, but it also highlighted the complexity of the correlation between urban heat islands, concentrations of PM10 and SO2 in terms of weekly cycles and meteorological conditions, such as CAPE (Convective Available Potential Energy) and other microphysical parameters. One of the most important findings was that the CG frequency increases with increasing concentrations of PM10 up to a certain threshold of PM10 concentration (saturation), after which it decreases with further increases of PM10 concentrations. As the CG frequency increases due to urban impacts, the percentage of positive strokes is reduced.

State, as sugar cane burning is progressively phased out.

and Presidente Prudente radars), using the TITAN Software.

**6.3. Impact of aerosols on the frequency of lightning** 

precipitation intensity.

prior burning) was the norm over the period. Mechanization of the crop (which does not involve burning) has only been introduced recently (from around 2005). The main conclusion to be drawn from this is that the trend towards a smaller number of more intense precipitation events, as reported in [121], could now be reversed in the interior of São Paulo

The climatological characterization of storm properties, such as area, volume, maximum echo top and reflectivity during two summer seasons, *viz.,* 1998-1999 and 1999-2000, based on observations from the Bauru S-band Doppler radar, has for the first time shown the spatial distribution of these parameters in central São Paulo State. Gomes and Escobedo [124] showed that some preferential areas of precipitation, taking into account a precipitation envelope area defined by the 25 dBZ threshold, were located along the Tietê River valley. The mean maximum reflectivity field (>40 dBZ), representing the cores of convective precipitation systems, has highlighted some preferential regions for convection to develop over urban and industrialized areas, such as metropolitan Campinas (Figure 25a). A climatology of flash density (Figure 25b; [21]) also identified Campinas as one of three regions with a higher concentration of lightning discharges, attributed to the occurrence of heat islands due to anthropogenic activities. Thus, the spatial distribution of the reflectivity field exceeding 40 dBZ in the Campinas region reinforces results showing a strong correlation between the frequency of cloud-to-ground lightning strokes and

The influence of anthropogenic aerosols on precipitation patterns in the region is the subject of research currently in progress as part of a thematic climate change research programme sponsored by FAPESP (the São Paulo State Research Foundation). The quantitative evaluation of changes in the rainfall pattern, such as increases or decreases of area rainfall totals, number and volume of convective cells, duration of rain events, distribution of echo top heights, etc., is in progress for a 10-year period of integrated radar observations (Bauru

Westcott [125] documented for the first time an impact of large cities on the cloud-to-ground (CG) lightning frequency in the Midwest of the United States. This was followed up by various researchers around the world, including in Brazil [20] and ultimately summarized in [22], using 10 years of observations from the Brazilian Lightning Detection Networks (1999- 2008). This research confirmed the impact of anthropogenic activities on lightning, but it also highlighted the complexity of the correlation between urban heat islands, concentrations of PM10 and SO2 in terms of weekly cycles and meteorological conditions, such as CAPE (Convective Available Potential Energy) and other microphysical parameters. One of the most important findings was that the CG frequency increases with increasing concentrations of PM10 up to a certain threshold of PM10 concentration (saturation), after which it decreases with further increases of PM10 concentrations. As the CG frequency

increases due to urban impacts, the percentage of positive strokes is reduced.

(a)

**Figure 25. (a)** Spatial distribution of the average maximum reflectivity (dBZ), during the period October 1998 to March 1999. TITAN storm threshold was defined as reflectivity >40 dBZ within the 240 km range of the Bauru Doppler radar (after [124]). **(b)** Flash density within the 450 km range of the Bauru radar (after [21]). The circle indicates the 240 km quantitative range as in the TITAN image above.

Review of Aerosol Observations by Lidar and Chemical Analysis in the State of São Paulo, Brazil 311

agreement between sugar cane producers and the State government has been reached, which involves elimination of burning in mechanizable areas by 2014, and in nonmechanizable areas by 2017 [9, 126]. This will have major environmental implications, including improvements in air quality and changes in the rates of deposition of nutrient species from the atmosphere to vegetation, soils and freshwater bodies [10]. Nonetheless, at present burning continues in 44% of the area planted with sugar cane [9]. Tsao *et al.* [127] suggest, using a life cycle analysis, that pollutant emissions in sugar cane regions are still increasing, due an expansion of the planted area, and that the burning step still contributes

Improvements in air quality in the metropolitan regions are likely to proceed at a slower pace than in the interior of the State, largely due to the dominant influence of emissions from the road transport sector. Nonetheless, emissions of aerosols and other pollutants are ultimately expected to be attenuated following progressive modernization of the vehicle fleet, and implementation of better controls on emissions from both vehicular and industrial

Examples of case studies presented have demonstrated the capability of weather radars to detect, track and quantify emissions from biomass fires in the absence of rain echoes, deploying a special elevation scanning procedure to generate Volume-Scans every 7,5 min. Furthermore, satellites orbiting with lidar systems on board (e.g., MODIS-AQUA, CALIPSO, CloudSat) also have the capability to detect and quantify optical properties of

With the gradual introduction of lidars in Brazil during recent years, it has also become possible to quantify in situ the vertical distribution and optical properties of suspended aerosols. However, in the State of São Paulo there are currently only three lidar systems available, *viz.*, one fixed lidar each in São Paulo city and in Cubatão, supplemented by the mobile lidar for periodic deployment in the interior of the State. Additional fixed lidar installations are therefore suggested for Campinas, Rio Claro, Bauru and São José do Rio Preto (situated in an important sugar cane production region in the north of the State) as a minimum configuration for a network, together with a second mobile system in São José dos

*Instituto de Pesquisas Meteorológicas, Universidade Estadual Paulista, Bauru, S.P., Brazil* 

*Instituto de Química, Universidade Estadual Paulista, Araraquara, S.P., Brazil* 

*Centro de Lasers e Aplicações, Instituto de Pesquisas Energéticas e Nucleares,* 

Campos to cover the industrial activities in the Paraiba Valley.

the largest fraction of the total emission.

sources.

aerosols.

**Author details** 

Gerhard Held and Ana Maria Gomes

Andrew G. Allen and Arnaldo A. Cardoso

*Universidade de São Paulo, São Paulo, S.P., Brazil* 

Fabio J.S. Lopes and Eduardo Landulfo

**Figure 26.** Lightning density (flashes per km2 per year) during the period 1999 - 2008 for the eastern part of the State of São Paulo, which includes the major urban complexes, as well as the highly industrialized Paraiba Valley (after [22]).
