**1. Introduction**

In Brazil, there are four lidar systems dedicated to the study of aerosols in the troposphere. Installed at Embrapa in Manaus (Western Amazon), there is a lidar system coordinated by the Atmospheric Physics Laboratory (LFA) of the Institute of Physics at the University of São Paulo [1]. In São Paulo, there are two other systems, the SPU Lidar Station, installed at the Institute of Energy and Nuclear Research (IPEN/CNEN) and coordinated by the Laboratory of Environmental Applications of Lasers (LEAL) hosted in the Center for Lasers and Applications (CELAP) of the referred institute, and the scanning lidar system located at CEPEMA (Centre for Training and Research in Environment) in Cubatão (State of São Paulo) [2–5]. **Figure 1** shows an example of the aerosol profile retrieved at SPU Station.

The DUSTER Lidar system, situated at the Department of Atmospheric and Climate Sciences (DCAC) at the Federal University of Rio Grande do Norte (UFRN), can measure marine aerosols' physical and optical properties. It can also measure aerosols (mineral dust) that cross the Atlantic Ocean and come from the desert Sahara, and aerosols originated from fires in the African continent [6, 7]. The lidar system's design and installation in Natal result from a technical and scientific collaboration among UFRN and IPEN. The DUSTER Lidar system is a biaxial monostatic lidar with a typical spatial resolution of 7.5 m. Brazil is a country with continental dimensions where different aerosols are generated, whether by natural or anthropogenic sources. The two systems mentioned above, SPU Lidar Station in São Paulo and DUSTER Lidar system in Natal, can measure different aerosols types.

Quality assurance and quality control programs developed by the European Aerosol Research Lidar Network (EARLINET) [8] are being implemented at the LALINET stations of São Paulo, Manaus, and Natal. This implementation intends to increase the capability to provide a reliable dataset in collaboration with three EARLINET stations (Bucharest, Granada, and Munich) in the framework of the project APEL (Assessment of atmospheric optical Properties during biomass burning Events and Long-range transport of desert dust) [9, 10]. The main objective is

#### **Figure 1.**

*Quick-look of the Lidar Range Corrected Signal (RCS) at 532 nm measured at SPU Lidar Station on 02 July 2019. The signal between 10 and 14 km indicates cirrus clouds.*

#### *Lidar Observations in South America. Part II - Troposphere DOI: http://dx.doi.org/10.5772/intechopen.95451*

to make the final data products from the two networks comparable and study the similarities and differences in aerosol loads, transport heights, types, and properties [11]. The evaluation will be done at the hardware and software levels. At the hardware level, the quality of the signals will be checked using the specific EARLINET procedures, and, at the software level, the LALINET data processing algorithms will be compared with the EARLINET Single Calculus Chain [12–14]. The last is a fully automatic evaluation process that can be used for virtually any lidar configuration and was validated for several EARLINET lidar stations, being a powerful tool that allows lidar stations to retrieve the aerosol backscatter and extinction profiles from the raw lidar data (**Figure 2**).

In Bolivia's case, the Laboratory for Atmospheric Physics of Universidad Mayor de San Andrés (LFA for its acronym in Spanish) is carrying out some studies related to urban aerosols and pollution monitoring in the metropolitan region of La Paz and El Alto. This region is one of the fastest-growing urban settlements in South America, with the particularity of being located in very complex terrain at a high altitude over the Andes. With a total population of around 1.8 million inhabitants is the second most populous urban area in Bolivia. La Paz city is located in a stepped valley, whose height starts at 3200 m a.s.l. (southern area), going up to 4000 m a.s.l. (in the north). The metropolitan area includes El Alto city (4100 m a.s.l), adjacent to the west's valley, and is extended over the Altiplano plateau. The valley has many basins that converge in the lower part of the city generating complex air fluxes.

An elastic lidar system was installed in the Science Campus of the Universidad Mayor de San Andrés (16.5333 S, 68.0667 W, 3420 m a.s.l.) in 2007 to study the boundary layer's behavior in this complex terrain. The lidar system was developed by improving an old system donated by the European Space Agency to the LFA and an essential collaboration of the Raman Lidar Laboratory of NASA's Goddard Space Flight Center. The instrument regularly worked for some years collecting data every Monday. These ancillary data were used for different short-term studies [15].

In 2011, this lidar acquired an additional relevance when a new Global Atmosphere Watch (GAW) station was set up near the metropolitan area at Mount

#### **Figure 2.**

*Particle backscatter (Mm−1 sr−1) and extinction (Mm−1) coefficients and Lidar Ratio (sr), measured at SPU Lidar Station on 14 July 2019. Smoothed retrievals, obtained at 355 nm and 532 nm, using the Single Calculus Chain Algorithm.*

Chacaltaya (16.3502 S, 68.1314 W, 5240 m a.s.l.). This station was set up to study aerosols' physical and chemical properties, measure atmospheric gas concentrations, study the aerosols injected into the free troposphere, besides the effect of aerosols deposition onto the Andean glaciers. In this sense, the main task of the lidar system was to help with the study of the air fluxes that go from the metropolitan area to the Chacaltaya GAW station and vice versa and the behavior of the local atmospheric boundary layer, especially in connection with atmospheric pollution in the urban area.

Besides, in 2018 and thanks to a collaboration of the Andalusian Institute for Earth System Research, Granada, Spain, a Lufft CHM 15 k ceilometer was installed in the northern part of La Paz city, closer to the Chacaltaya GAW station than the LFA. The goal was to characterize the boundary layer height's seasonal behavior through continuous measurements for at least one year. The Wavelet Covariance Transform (WCT) was used to estimate this behavior using both the ceilometer and the university campus's lidar. Although we gained knowledge about the local ABL's temporal behavior, it is clear that due to the complexity of topography in this region, extending this work's main conclusions is not straightforward. More measurements and modeling are needed for this purpose.
