Exploring the relationship between monitored ground-based and satellite aerosol measurements over the City of Johannesburg

Abstract

This project studied the relationship between aerosol optical depth (AOD) from the Multi-angle Imaging SpectroRadiometer (MISR) instrument on the Terra satellite, and ground-based monitored particulate matter (PM) mass concentrations measured at the City of Johannesburg monitoring sites. AOD is the vertical integral of the extinction coefficient (sext) at a specific wavelength in a column of air from the surface to the top of the atmosphere. In general, higher AOD values indicate a larger aerosol load in the column of air. However as sext is dependent upon the optical properties of the aerosols, which in turn can be impacted by factors such as refractive index, size and shape, the AOD of a column of aerosol particles is dependent upon more than just the aerosol load. These parameters can be impacted by meteorological factors as well. Thus, the PM-AOD relationship may be complex.