2013•HAL (Le Centre pour la Communication Scientifique Directe)Requires access
Indication of aerosol aging by optical absorption properties
Luka Drinovec, Griša Močnik, Jean‐Eudes Petit, Jean Sciare, Olivier Favez, Peter Zotter, Robert Wolf, Andrê S. H. Prévôt, A. D. A. Hansen
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Abstract
The ability to discriminate between local and regional air pollution is important for aerosol monitoring and control. Aging by atmospheric processing can change the aerosol's chemical and physical characteristics. Here we present a new method for indicating aerosol age using optical absorption parameters measured by the dual-spot Aethalometer (Magee Scientific, Model AE33). This instrument provides a real-time determination of a sample-on-filter loading effect, based on the linear model similar to Virkkula (2007) and Park (2010): BC_measured = BC_ambient (1- k*ATN). The compensation parameter k is determined in real-time for each of the operational wavelengths from 370 nm to 950 nm. The wavelength dependence of absorption and the compensation parameter both provide a highly time-resolved specific spectral fingerprint that may be interpreted in terms of aerosol composition in terms of aerosol sources and age. Optical and chemical properties of aerosols were measured with high time resolution during summer and winter EMEP campaigns in Paris (France) and Payerne (Switzerland). An Aerosol Chemical Speciation Monitor (Aerodyne, ACSM) and an High Resolution Time-of-Flight Aerosol Mass Spectrometer (Aerodyne, AMS) were used to measure quantitative chemical composition for non-refractory aerosol particles. During summer we observed complex temporal variation of k, where k(880 nm) changed from approximately 0.006 for fresh aerosols to near zero for aged aerosols as shown using Potential Source Contribution Function (PSCF) back trajectory analysis method. We have combined the Aethalometer and ACSM/AMS measurements, and normalized the sum of inorganic secondary and organic aerosol mass to BC. Values of this ratio are expected to be high for air parcels containing aged aerosols. The ratio correlates well with the loading compensation parameter k measured by the Aethalometer at 880 nm. This indicates that the compensation parameter k can be used for discrimination between local (fresh) and regional (aged) air pollution aerosols.