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This study is aimed to qualitatively analyze the impact of remote sources on air pollution in the Metropolitan Area of São Paulo (MASP). Air-mass back trajectories from June to August of 1999 were calculated using a three-dimensional kinematic trajectory model and grouped into trajectory clusters. Correlations of individual trajectory clusters with O3, CO and PM10 concentrations were determined. In this model, trajectories were obtained using the means of the three wind velocity components (U, V and W). The three-dimensional wind field was derived from the Regional Atmospheric Modeling System, and downscaling was employed. Coarse and fine nested grids (64-km and 16-km horizontal resolution, respectively) were used. Every 12 h (at 00 and 12 UTC), a back-trajectory ensemble, using the 64-km grid, was calculated for five defined endpoints at intervals of 0.5° N, S, E and W of the MASP (λ = 23° 33′S, ϕ = 46° 45′W), that last endpoint being centered in the MASP. To analyze cluster trajectories, the five trajectory ensembles from each day were allocated into one of four clusters (northeast, southeast, southwest or northwest quadrant) based on the origin of the trajectory over 4 days. Days on which all five trajectories originated from the same quadrant were classified as “core” days. Core day concentrations of CO, O3 and PM10 during the study period were evaluated. The results show that, during the study period, air-mass back trajectories in the MASP originated from all four quadrants: northeast (32%), southeast (12%), southwest (19%) and northwest (37%). Our analysis of back-trajectory clusters in the MASP suggests a transport to ambient air of O3 precursors and O3 from the northeast region, which is associated with agricultural activities involving biomass burning. [ABSTRACT FROM AUTHOR]

A backscattering tight 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-backscatler 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. [ABSTRACT FROM AUTHOR]

Examination of the Doppler SODAR data from Sao Paulo, Brazil, has given valuable information on the coupling between planetary boundary layer (PBL) and the free atmosphere above, which is reported here. In this communication a case study, on the dynamics of the urban boundary layer over the Metropolitan Area of Sao Paulo (MASP), Brazil, is examined for July 27, 1999 when a multiple gravity wave (GW), a low-level jet (LLJ) and a cold front (CF) all occurred in one single day in succession, making use of data from Doppler SODAR, surface meteorological instruments, satellite imageries and model derived values. The experimental findings are compared to provide validations of ground troth with the model-derived profiles based on the mesoscale analysis of Regional Atmospheric Modelling System (RAMS). It is seen that the multiple GW, the LLJ and the CF have different types of nonlinear coupling between the PBL and the free atmosphere. However, there is convincing matching between Doppler SODAR derived features, those of mesoscale analysis from RAMS and satellite view of cloud dynamics. The study provided valuable information on (i) the very nature of these events, (ii) the nonlinear hydrodynamical coupling between the PBL and the free atmosphere above, during such events, and (iii) the possible mechanism of CF influencing the formation of GW and LLJ. [ABSTRACT FROM AUTHOR]