Simulation of the Planetary Boundary Layer characteristics and its relation to air quality in the Metropolitan Area of Rio de Janeiro, Brazil

Abstract

Frequently in the Metropolitan Area of Rio de Janeiro (MARJ), air quality monitoring stations record concentrations of particulate matter (PM10) and ozone (O3) above the reference values proposed by the World Health Organization. In this region, weather conditions combined with high atmospheric pollutant emissions and complex topography favor the occurrence of high concentrations of pollutants such as PM10 and O3 for several consecutive days. Hence, this study evaluated 1) the Planetary Boundary Layer (PBL) conditions simulated by the Weather Research and Forecasting (WRF) model and b) its relation to the air quality recorded during days with high concentrations of O3 and PM10 in the MARJ. Two episodes, one during summertime when high O3 concentrations were registered and one during the winter with high PM10 concentrations, were considered. The study used the WRF model to simulate conditions during those periods. Upper air and surface observations, synoptic charts, and satellite images were used to verify WRF results. In both periods, it was possible to identify the influence of the South Atlantic Subtropical Anticyclone associated with clear sky conditions, slight air subsidence, and weaker winds. The comparison with observations showed the model simulated coherently local weather conditions. Weaker winds and the performance of the sea breeze during the afternoon favored the maintenance of pollutants and their transport to the northeast/northwest of the region. In general, WRF consistently represented the height of the PBL and atmospheric stability. Therefore, this study shows that WRF results can be used to simulate PBL conditions and could be used as a source of upper air information in the MARJ.