Tropospheric aerosol observations in São Paulo, Brazil using a compact lidar system

Abstract

A backscattering light detection and ranging (lidar) system, the first of this kind in the country, has been set up in a suburban area in the city of São Paulo, Brazil (23°33′ S, 46°44′ W) to provide the vertical profile of the aerosol backscatter and extinction coefficients at 532 nm and up to 4–5 km height above sea level (asl). The measurements have been carried out during the second half of the so‐called Brazilian dry season, September and October in the year of 2001. When possible, the lidar measurements were complemented with aerosol optical thickness measurements obtained by a CIMEL Sun‐tracking photometer in the visible spectral region, not only to validate the lidar data, but also to provide an input value of the so‐called extinction‐to‐backscatter ratio (lidar ratio). The lidar data were also used to retrieve the Planetary Boundary Layer (PBL) height and low troposphere structural features over the city of São Paulo. Three‐dimensional air mass back trajectory analysis was also conducted to determine the source regions of aerosols observed during this study. These first lidar measurements over the city of São Paulo during the second half of the dry season showed a significant variability of the aerosol optical thickness (AOT) in the lower troposphere (0.5–5 km) at 532 nm. It was also found that the aerosol load is maximized in the 1–3 km height region and this load represents about 20–25% of the lower tropospheric aerosol.