Prediction of ambient light scattering using a physical model responsive to relative humidity: Validation with measurements from detroit

Abstract

A model for the prediction of atmospheric light extinction from field measurements of airborne aerosol concentration, chemical speciation, and size distribution has been tested with field data from the Detroit, Michigan area. The amount of light scattered by airborne particulates in ambient conditions is accurately predicted by the model using measurements of accumulation mode sulfate, nitrate, volatile and nonvolatile carbon. Model predictions were compared with simultaneously measured light scattering. The model is unique amongst physical models in its simulation of the effect of relative humidity on visibility reduction and on the light scattering efficiency of specific chemical constituents of the airborne aerosol. A proven physical model offers an advantage over statistical models in that it should prove reliable for extrapolation of ambient conditions well outside conditions currently realized. Within the range of the available data, the physical model is shown to simulate the light scattering as well as statistical models. Calculations with the physical model indicate that on average sulfate compounds are less efficient scatterers of light in ambient settings than statistical analyses would indicate.