Continued development of a fixed-frequency Albedometer

Date

2011-05

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Abstract

Atmospheric aerosols have both direct and indirect effects on climate change. Being able to completely describe the effects will allow scientists to accurately model climate change. This thesis will describe some improvements on the aerosol albedometer, an instrument previously described in the literature. Here, we report on the status of these improvements and the accuracy and precision of the measurements made of the scattering and extinction coefficients (bscat and bext) with this instrument. We were able to drastically improve the temporal response time, through the use of a glass tube to reduce the sample volume. By comparing optical results to particle concentrations using a condensation particle counter (CPC), we were able to calculate the values of the scattering and extinction cross section (σscat and σext) and compare these to the accepted values calculated from Mie theory. These values agreed within one measurement standard deviation of the accepted values in 13 out of 16 trials. We were also able to observe the increase in relative standard deviations as particle number densities (# particles/cm3) decreased, giving an idea of how precision scales with concentration of particles. The precision for the measured albedo was shown to be better than that predicted by propagating the uncertainty from bscat and bext values and associated precisions. Lastly, the effect of light absorbing gases on the measurements was studied in order to understand any potential systematic errors caused by the presence of these gases. It was found that while ozone is of minimal concern, the contribution from NO2 is of significance and needs to be subtracted out of the measurement.

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Keywords

Albedometer, Atmospheric aerosols

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