Aerosol chemical species contributions to the extinction coefficient

Citation

Ouimette, James Richard (1981) Aerosol chemical species contributions to the extinction coefficient. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/s1we-wc48. https://resolver.caltech.edu/CaltechETD:etd-08092005-093436

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

A model was developed for determining the contributions of aerosol chemical species to the extinction coefficient. The model assumes that the suspended particles are spherical and that particle volume is conserved with condensation and coagulation.

In general, the diameter, refractive index, and chemical composition of each particle must be known to rigorously calculate each species contribution. It is shown that species mass distributions with respect to particle diameter are sufficient to determine the species contributions exactly for some simple aerosols. Requirements were derived for each of the simple aerosols in which linear regression analysis could be legitimately applied to historical species mass concentrations data in order to estimate species contributions to light extinction.

The model was field tested at two remote arid locations in the southwestern United States where aerosol water content was ofsumed to be negligible. A low pressure impactor (LPI) was used in this research to size segregate aerosol from 0.05 to 4 [...] aerodynamic diameter for elemental analysis. Two new techniques were developed for analysis of aerosol deposits collected with the LPI. Nanogram sensitivities were achieved for soot and many elements.

A three-week experiment was conducted in remote northeastern Arizona to calculate the contributions of fine aerosol species to the extinction coefficient. Theoretical mass extinction efficiencies were calculated and numerically integrated with measured mass distributions to determine the contribution of each species to the extinction coefficient. The measured chemical species could account for 94 [plus or minus] 19% of the fine aerosol mass concentration and 85 [plus or minus] 34% of the measured particle extinction coefficient. All important species balances were met, both in total and with respect to size. The satisfactory agreement between the calculated and measured extinction coefficient indicates that the model and experimental technique are useful for determining the contributions to various aerosol species to visibility degradation at an arid site.

A one-year experiment was conducted at China Lake, California. Multiple regression analysis was applied to the measured particle scattering coefficient and fine aerosol species mass concentrations from 61 filter samples collected during 1979. Contributions of various aerosol species to the particle scattering coefficient, [...], were estimated. The statistically estimated contributions were compared with those determined theoretically using measured aerosol mass distributions. It was found that the statistically inferred species contributions to [...] agreed qualitatively with those calculated theoretically using measured aerosol distributions. Regression analysis overestimated the contribution of sulfate relative to that calculated theoretically. Using measured 1979 values, a light extinction budget was calculated for China Lake. Measured mass extinction coefficients were used to predict the reduction in visibility at China Lake which would occur by increasing the concentrations of various aerosol species.

Thesis Files