ON THE RETRIEVAL OF URBAN AEROSOL MASS CONCENTRATION BY A 532 AND 1064 nm LIDAR |
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Authors: | Massimo Del Guasta Stefano Marini |
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Affiliation: | a Istituto di Ricerca sulle Onde Elettromagnetiche (IROE) - CNR, Via Panciatichi 64, 50127 Firenze, Italy;b ELIOWATT S.r.l. Via della Pieve in Piano 105, 53034 Colle di val d'Elsa Siena, Italy |
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Abstract: | Based on the hypothesis of a monomodal, lognormal size distribution, the uncertainty affecting the humid-mass retrieval from LIDAR data was estimated by considering our ignorance of the distribution width to be a source of error. The mass to backscatter ratio and its uncertainty were computed for six accumulation-mode aerosol models as a function of the backscatter angstrom coefficient (α) and of the relative humidity (RH). A mass to backscatter uncertainty of less than ±30% was obtained for all six models. We computed the mass and simulated the expected LIDAR backscatter at 532 and 1064 nm for a test data set of 14 “real-world” multimodal size distributions obtained from the literature. The possible presence of 0–20%–50% water-insoluble compounds in each aerosol mode was assumed. An urban-type accumulation mode and 10 different coarse mode compositions were considered, including dust-like aerosols. The aerosol mass concentration was derived by fitting the simulated LIDAR data at 532 and 1064 nm with a monomodal distribution of urban aerosols of “unknown” width. The relative over- or underestimation of the mass with respect to the real aerosol mass was expressed in terms of α and RH for the 10 coarse aerosol types. The LIDAR-derived mass turned out to be underestimated by 0 – 15% in the case of (NH4)2SO4, NaCl, maritime, and H2SO4 coarse aerosols. In the case coarse dust aerosols, the range of underestimation was wider (0–30%). Absorbing aerosols showed a maximum underestimation of 40–50%. |
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