Investigation of carbon monoxide time evolution over the city of São Paulo during the nighttime using LES model

The main objective of this work is to investigate the role play by the inversion layer and low level jet on the carbon monoxide (CO) time evolution at the surface in the city of Sao Paulo, Brazil. This investigation is based on numerical simulations of the stable PBL using the large-eddy simulation model (LES). The computations were applied over a one kilometer square flat terrain and homogeneous land use area located in the city of Sao Paulo. The surface emission of CO is estimated from inventory of annual emission of 7 million vehicles, assuming that the CO is mainly originated from incomplete fuel burning. With a population of about 11 million inhabitants, the city of Sao Paulo is characterized by air pollution events with high concentrations of CO at the surface during wintertime, mainly during nighttime period, associated to the intense surface inversion. The numerical simulations, using a prescribed surface flux of CO and sensible heat, indicated that the CO concentration at the surface of Sao Paulo is mainly modulated by the inversion layer intensity and the low level jet position. The vertical distributions of the second order statistic moments for CO and temperature are also strongly regulated by the low level jet main features.