Variability of Urban Aerosols over Santiago, Chile: Comparison of Surface PM10 Concentrations and Remote Sensing with Ceilometer and Lidar

Abstract

Lidar instruments have proven useful for characterizing the structure and dynamics of aerosol layers. We compare here the diurnal, seasonal and vertical variability of urban aerosols as described by a lidar ceilometer and surface particulate matter (PM10) concentrations using 4 years of observations available at Santiago, Chile, a city having a serious PM10 air pollution problem. Large diurnal variation of ceilometer backscatter values is observed on average up to 600 m (400 m) above the surface in spring and summer (fall and winter). The diurnal cycles of near-surface ceilometer backscatter and PM10 concentrations show prominent morning peaks. The large PM10 evening peak is less marked in the ceilometer backscatter values, suggesting that this significant feature of Santiago's air pollution is constrained to a shallow atmospheric layer. Daily averages of PM10 concentrations and ceilometer backscatter have correlations of 0.5 for the full data set, and a maximum of 0.75 for April. Results are supplemented with recently available observations gathered with a 355 nm elastic lidar. While the smaller blind region of the ceilometer provides a more complete picture of the aerosol layer dynamics, the higher resolution of the lidar allows a better definition of the aerosol layer structure. Both instruments suggest the frequent development of complex aerosol layers appearing over Santiago during the evening transition. The lidar shows also frequent occurrence of buoyancy oscillations in the stable basin's air mass.