Aerosol light absorption measurement techniques : a comparison of methods from field data and laboratory experimentation

Abstract: Popular science Currently, there is a global drive to better understand the influences behind our changing climate. With each passing decade, the world has observed dramatic changes in weather patterns, seasonal temperatures, and our surrounding natural environments. Within the heavily-studied climate sciences, the influence of atmospheric aerosols remains the most uncertain. As there is no instrument that offers reliable measurements, simplicity in use, and reasonable cost as a single entity, there remains a necessity for advancement in monitoring and measurement techniques. The aim of this investigation is to consider the current measurement techniques for aerosol absorption and compare instrument performance in a variety of conditions. Utilizing data from scientific flights in the California-based CalNex campaign (April-May 2010) and an experiment in the NOAA laboratories of Boulder, Colorado (April 1st, 2012- May 2nd, 2012), many conditions of aerosol absorption measurements are examined. Within this investigation, instruments for both short term field campaigns and long term monitoring are considered. Filter-based instruments are the most commonly used method for the measurements of absorption of radiation by atmospheric aerosol in a long term global network. With these, potential biases in measurement are scrutinized due to changes in conditions during sampling, high organic aerosol loading, and the application of potentially overestimating empirical corrections. The short term techniques for aerosol measurements are often considered to be references for the filter-based measurements. Here, photoacoustic techniques and the difference method, where absorption is derived from the difference in measurements of extinction and scattering, are compared with the filter-based instruments. The aim of this investigation is not to decide which of these instruments or methodologies for the quantification of absorption by atmospheric aerosols should be deemed “the best method”, but rather to provide real-world examples of their applications, capabilities, and limitations. Insights obtained from this study may provide further direction in the drive to reduce uncertainty in aerosol measurements, and furthermore, future climate predictions for all atmospheric components collectively.