AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Black Carbon in Dust and Geological Material: Reconciling Thermal/Optical and Spectral Quantification Methods
L.-W. ANTONY CHEN, Yongming Han, Jerome Robles, Judith Chow, Junji Cao, John Watson, Desert Research Institute
Abstract Number: 212 Working Group: Instrumentation and Methods
Abstract Atmospheric black carbon (BC) aerosol affects the Earth’s climate. Through sequestration of carbon and nutrients in the pedosphere, BC plays an important role in the global carbon cycle. BC in sedimentary rocks also keeps long-term records of paleoenvironmental changes. Quantifying BC in samples dominated by geological material (GM), such as fugitive dust, surface soil, and sediment, is however challenging, since GM interferes BC measurement with commonly used thermal/optical methods by changing organic matter charring behaviour and promoting BC evolution at lower temperatures. Pure optical methods that quantify BC based on light absorption can be interfered by iron-rich GM showing substantial light absorption in the visible region. In this study, improvements in BC quantification were made by introducing acid pre-treatment for thermal/optical methods and spectral detection for optical methods. Surface soil samples with relatively low BC contents and street dust samples with relatively high BC contents were collected from central China. The acid pre-treatment reduces most of the GM interference and concentrates BC levels in the samples. Thermal/optical reflectance (TOR) analysis shows that the pre-treatment preserves most BC and improves the measurement precision and detection limit, allowing <0.1 wt% of BC in the samples to be detected. Parts of the samples were resuspended onto Teflon and quartz-fiber filters and examined with an integrating-sphere-based spectrometer. The measured BC after acid pre-treatment correlates better with light absorption at 900 nm, at which absorption by organic matter and GM is expected to be minor. Further validations with standards and reference materials are carried out and will be presented. The light absorption efficiency/absorption Ångström exponent of BC and GM from spectral measurements will also be discussed.