Abstract
Abstract. Atmospheric aerosols impact air quality and global climate. Space based measurements are the best way to observe their spatial and temporal distributions, and can also be used to gain better understanding of their chemical, physical and optical properties. Aerosol composition is the key parameter affecting the refractive index, which determines how much radiation is scattered and absorbed. Composition of aerosols is unfortunately not measured by state of the art satellite remote sounders. Here we use high resolution infrared measurements for aerosol type differentiation, exploiting, in that part of spectrum, the dependency of their refractive index on wavelength. We review existing detection methods and present a unified detection method based on linear discrimination analysis. We demonstrate this method on measurements of the Infrared Atmospheric Sounding Interferometer (IASI) and five different aerosol types, namely volcanic ash, windblown sand, sulfuric acid droplets, ammonium sulfate and smoke particles. We compare these with traditional MODIS AOD measurements. The detection of the last three types is unprecedented in the infrared in nadir mode, but is very promising, especially for sulfuric acid droplets which are detected in the lower troposphere and up to 6 months after injection in the upper troposphere/lower stratosphere.
Highlights
Atmospheric aerosols consist of primary and secondary
The advantage of the principal component analysis (PCA) method is that the Jacobian does not need to be known; while the advantage of the pseudo retrieval method is that it exploits better the full space and does not depend on ad-hoc choices such as the number of principal components
Comparison with the MODIS (Fig. 13) monthly aerosol optical depth (AOD) average for October shows a good similarity in the transport
Summary
Atmospheric aerosols consist of primary (sea spray, crustal material, smoke, and organic matter) and secondary POLDER (Tanreet al., 2011) is currently the most advanced aerosol sounder in orbit, measuring polarization and intensity in different spectral channels and in a multi-angle geometry. It was demonstrated (Dubovik et al, 2011) that this instrument can be used to derive aerosol (chemical) composition via retrieval of refractive indices. Using thermal infrared radiation for aerosol sounding has a number of appealing advantages such as (i) the possibility of measuring in absence of solar light, at night and in the winter at high latitudes (ii) less problems with retrieval over bright surfaces (iii) enhanced sensitivity to coarse mode aerosols and (iv) large sensitivity to aerosol composition (Clarisse et al, 2010a).
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