On the contribution of natural Aeolian sources to particulate matter concentrations in Europe: Testing hypotheses with a modelling approach

The significance of natural sources in the concentrations of particles smaller than 10 μm (PM10) in Europe is addressed. When considering only European anthropogenic emissions, chemistry-transport model simulations underestimate the PM10 concentrations by 30-50%, using the current knowledge about aerosol physics and chemistry. Along this article we hypothesize that the missing mass originates from natural sources like erosion dust entrainment and resuspension. The methodology consists in testing these hypotheses in the CHIMERE regional chemistry-transport model, and comparing the results with long series of PM10 measurements in Europe. It is demonstrated that the introduction of background Saharan dust boundary conditions greatly improves the model simulation over Southern Europe, and to a smaller extent also over northern Europe. However to accurately simulate acute episodes of Saharan dust transport time-resolved boundary conditions need to be used. Local erosion occurring over European regions is also considered. The introduction of a simplified bulk scheme for online calculation of mineral dust emission makes the model skill improve everywhere in Europe, indicating that this process can be significant in Europe. We finally assume that resuspension of material available on the ground, explains most of the remaining part of the missing part of PM10 average load. A simplified scheme for the corresponding emission, which depends on turbulence near the ground, is proposed. It also makes the model improve substantially, especially over Northern Europe. However sensitivity tests show that such an improvement can also be obtained by simply increasing the model secondary organic matter in aerosols by a factor of 3. We conclude that our results are consistent with the existence of a strong biogenic resuspension aerosol source, but more experimental work is required to ascertain this hypothesis.