Abstract
Determining size-resolved chemical composition of aerosols is important for modelling the aerosols’ direct and indirect climate impact, for source–receptor modelling, and for understanding adverse health effects of particulate pollutants. Obtaining this kind of information from optical remote sensing observations is an ill-posed inverse problem. It can be solved by variational data assimilation in conjunction with an aerosol transport model. One important question is how much information about the particles’ physical and chemical properties is contained in the observations. We perform a numerical experiment to test the observability of size-dependent aerosol composition by remote sensing observations. An aerosol transport model is employed to produce a reference and a perturbed aerosol field. The perturbed field is taken as a proxy for a background estimate subject to uncertainties. The reference result represents the ‘true’ state of the system. Optical properties are computed from the reference results and are assimilated into the perturbed model. The assimilation results reveal that inverse modelling of optical observations significantly improves the background estimate. However, the optical observations alone do not contain sufficient information for producing a faithful retrieval of the size-resolved aerosol composition. The total mass mixing ratios, on the other hand, are retrieved with remarkable accuracy.
Highlights
Mapping and forecasting aerosol fields on regional and global scales is a problem with high relevance for air pollution monitoring as well as for climate research
Obtaining reliable information on size-resolved aerosol composition is an essential step in constraining current estimates of the aerosol climate forcing effect, in understanding physical and chemical aerosol formation and transformation processes, and in studying the causes for adverse health effects related to particulate matter in ambient air
There appears to be a great potential for improving model results by assimilating lidar and aerosol optical depth (AOD) observations
Summary
Mapping and forecasting aerosol fields on regional and global scales is a problem with high relevance for air pollution monitoring as well as for climate research. To understand the complex interplay of meteorological, chemical and physical processes that determine the aerosols’ formation, transport, transformation and deposition processes, one needs to analyse both size and chemical composition of the aerosol phase (Matta et al, 2003; Eleftheriadis et al, 2006). This will help to better understand the relation between ambient aerosol concentrations and emission sources, which is an important prerequisite for formulating effective abatement strategies. Obtaining reliable information on size-resolved aerosol composition is an essential step in constraining current estimates of the aerosol climate forcing effect, in understanding physical and chemical aerosol formation and transformation processes, and in studying the causes for adverse health effects related to particulate matter in ambient air
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