Quantification of gas, ash, and sulphate aerosols in volcanic plumes from open path Fourier transform infrared (OP-FTIR) emission measurements at Stromboli volcano, Italy by Smekens, J-F, Mather, TA, Burton, MR, La Spina, A, Kabbabe, K, Esse, B, Varnam, M, Grainger, RG