Synergetic measurements of aerosols over São Paulo, Brazil using LIDAR, sunphotometer and satellite data during the dry season

[摘要] A backscattering LIDAR system, the first of this kind in Brazil, has been set-up in asuburban area in the city of São Paulo (23º33' S, 46º44' W) to provide the verticalprofile of the aerosol backscatter coefficient at 532 nm up to an altitude of4-6 km above sea level (asl). The measurements have been carried out during the second half of theso-called Brazilian dry season, September and October 2001 and during the first half of thedry season in August and September 2002. The LIDAR data are presented and analysed insynergy with aerosol optical thickness (AOT) measurements obtained by a CIMELsun-tracking photometer in the visible spectral region and with satellite measurementsobtained by the MODIS sensor. This synergetic approach has been used, not only tovalidate the LIDAR data, but also to derive a typical value (45 sr) of the so-calledextinction-to-backscatter ratio (LIDAR ratio) during the dry season. The satellite dataanalysis offers additional information on the spatial distribution of aerosols over Brazilincluding the determination of aerosol source regions over the country. The LIDAR datawere also used to retrieve the Planetary Boundary Layer (PBL) height, aerosol layeringand the structure of the lower troposphere over the city of São Paulo. These first LIDARmeasurements over the city of São Paulo during the dry season showed a significantvariability of the AOT in the lower troposphere (0.5-5 km) at 532 nm. It was also foundthat the aerosol load is maximized in the 1-3 km height region, although up to3 km thick aerosol layers were also detected in the 2.5-5.5 km region in certain cases.Three-dimensional 96-hours air mass back-trajectory analysis was also performed in selectedcases to determine the source regions of aerosols around São Paulo during the dry season.

[学科分类] 大气科学