Developing models of aerosol representation to investigate composition, evolution, optical properties, and CCN spectra using measurements of size-resolved hygroscopicity

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Title: Developing models of aerosol representation to investigate composition, evolution, optical properties, and CCN spectra using measurements of size-resolved hygroscopicity
Author: Gasparini, Roberto
Abstract: A Differential Mobility Analyzer /Tandem Differential Mobility Analyzer (DMA /TDMA ) was used to measure size distributions , hygroscopicity , and volatility during the May 2003 Aerosol Intensive Operational Period at the Central Facility of the Atmospheric Radiation Measurement Southern Great Plains site . Hygroscopic growth factor distributions for particles at eight dry diameters ranging from 0 .012 ? ?m to 0 .600 ? ?m were measured . These measurements , along with backtrajectory clustering , were used to infer aerosol composition and evolution . The hygroscopic growth of the smallest and largest particles analyzed was typically less than that of particles with dry diameters of about 0 .100 ? ?m . Condensation of secondary organic aerosol on nucleation mode particles may be responsible for the minimal growth observed at the smallest sizes . Growth factor distributions of the largest particles typically contained a non -hygroscopic mode believed to be composed of dust . A model was developed to characterize the hygroscopic properties of particles within a size distribution mode through analysis of the fixed -size hygroscopic growth measurements . This model was used to examine three cases in which the sampled aerosol evolved over a period of hours or days . Additionally , size and hygroscopicity information were combined to model the aerosol as a population of multi -component particles . With this model , the aerosol hygroscopic growth factor f (RH ) , relating the submicron scattering at high RH to that at low RH , is predicted . The f (RH ) values predicted when the hygroscopic fraction of the aerosol is assumed to be metastable agree better with measurements than do those predicted under the assumption of crystalline aerosol . Agreement decreases at RH greater than 65 % . This multi -component aerosol model is used to derive cloud condensation nuclei (CCN ) spectra for comparison with spectra measured directly with two Desert Research Institute (DRI ) CCN spectrometers . Among the 1490 pairs of DMA /TDMA -predicted and DRI -measured CCN concentrations at various critical supersaturations from 0 .02 -1 .05 % , the sample number -weighted mean R2 value is 0 .74 . CCN concentrations are slightly overpredicted at both the lowest (0 .02 -0 .04 % ) and highest (0 .80 -1 .05 % ) supersaturations measured . Overall , this multi -component aerosol model based on size distributions and size -resolved hygroscopicity yields reasonable predictions of the humidity -dependent optical properties and CCN spectra of the aerosol .
URI: http : / /hdl .handle .net /1969 .1 /3878
Date: 2006-08-16

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Developing models of aerosol representation to investigate composition, evolution, optical properties, and CCN spectra using measurements of size-resolved hygroscopicity. Available electronically from http : / /hdl .handle .net /1969 .1 /3878 .

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