Development of an automated sampling system to measure ambient aerosol properties relevant to climate
Conference
·
OSTI ID:166536
- Univ. of Illinois, Urbana, IL (United States); and others
Global radiative models have shown that sulfate aerosol particles exert radiative forcing comparable in magnitude but opposite in sign to the estimated effect of greenhouse gases. Uncertainties in key parameters such as back-scatter ratio (b), mass scattering efficiency ({alpha}), and effect of hygroscopic growth on light scattering (f(RH)) are 30%, 40%, and 20% respectively. To reduce such uncertainties, accurate regional measurements of the above parameters need to be undertaken. For this purpose, a controlled relative humidity (RE) nephelometry system (humidograph) has been developed. The system employs a three wavelength nephelometer that measures total-scatter and back-scatter coefficients. Alternate use of 10 {mu}m and 1 {mu}m impactors upstream of the humidograph allows investigation of the contributions to light scattering from particles in the fine and coarse modes or fine mode respectively. Description of the development, the hardware, and the software that have lead to a fully automated, reliable ambient aerosol sampling system will be presented. The humidograph has been tested with laboratory aerosols of known composition. The system measured deliquescence at RH values in agreement with literature values. Test results show that the change in light scattering upon deliquescence depends on particle size (d{sub p}), composition, and the wavelength of light ({lambda}). Measured f(RH) values were 1.99 at 450 nm to 2.14 at 700 nm for (NH{sub 4}){sub 2}SO{sub 4} particles, 2.90 to 3.69 respectively for Na{sub 2}SO{sub 4}, and 2.97 to 3.99 respectively for NaCl. Hysteresis has been observed for (NH{sub 4}){sub 2}SO{sub 4} particles. These results demonstrate that if metastable particles are ignored, light scattering coefficients may be underestimated by 42% at 450nm to 67% at 700nm. Ambient aerosol samples exhibited f(RH) values between 1.6 and 2.5 and demonstrated dependence upon d{sub p} and {lambda}.
- OSTI ID:
- 166536
- Report Number(s):
- CONF-9510126--
- Country of Publication:
- United States
- Language:
- English
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