AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Validation of Long-term Observations Using Sample-air Dilution with Particle Soot Absorption Photometer
JOHN BACKMAN, Aki Virkkula, Ville Vakkari, Johan Paul Beukes, Pieter G. van Zyl, Miroslav Josipovic, Stuart Piketh, Petri Tiitta, Kgaugelo Chiloane, Gerhard Fourie, Alfred Wiedensohler, Thomas Tuch, Tuukka Petäjä, Markku Kulmala, Lauri Laakso, University of Helsinki
Abstract Number: 269 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract There is an increase in scientific interest with respect to the climatic effects of black carbon (BC), which is an absorber of insolation. Research suggests that BC is the second most prominent radiative forcing agent. Atmospheric BC absorbs solar radiation in the atmosphere, reduces insolation at the surface, and redistributes energy vertically in the atmosphere with climatic implications.
A variety of challenges in the remote sensing of BC aerosols promotes the importance of in-situ measurements. Filter-based absorption measurements techniques are an economical and widely used method to determine atmospheric BC concentrations. Primarily, the deposition of light-absorbing species onto a filter-matrix will reduce the amount of light transmitted through the filter. Light-absorption coefficients can then be calculated by measuring the attenuation of light through the filter-matrix. Eventually, the aerosol-laden filter need to be changed to a pristine one, therefore, the method relies on filter changes. There are commercially available instruments capable of changing filters automatically; the Radiance Research Particle Soot Absorption Photometer (PSAP) require manual filter changes.
The interval, by which the filter needs to be changed, can be extended by diluting the sample air. This decreases the amount of manual labour required for long-term observations. Thus, the applicability of the instrument can be improved. The comparison between a diluted sample measured with a particle soot absorption photometer (PSAP) and a non-diluted sample measured with a multi-angle absorption photometer (MAAP) provides a means of assessing this sampling method. The method, however, requires non-standard post-processing of the of the PSAP data. The post-processing of the data lowers the detection limit, which is necessary due to the low concentrations of the diluted sample. The data analysed comprise of 23 months of measurements conducted on the Mpumalanga Highveld in South Africa, ending in January 2011. Initial results show a correlating slope of 0.981.