Ultrafine aerosol particles in aircraft plumes: Analysis of growth mechanisms

An analysis of in situ measurements of ultrafine volatile aerosols in the plume near field of the DLR aircraft ATTAS using low (0.02 g/kg) and high (2.7 g/kg) fuel sulfur contents (FSCs) is presented. The observed growth of nanoparticles (diameter 5 - 10 nm) is reproduced in detail by a microphysical simulation with chemi-ion emissions of 2.6 x 10¹⁷ /kg fuel. Volatile aerosol dynamics is controlled by sulfuric acid (H₂SO₄) for high FSC, consistent with a S to H₂SO₄ conversion of 1.8%. The very high conversion for low FSC (55%) prescribed in the model to match the observations contradicts direct in situ measurements of H₂SO₄ and suggests that species other than H₂SO₄, likely exhaust hydrocarbons, control particle growth in such cases.