1) We have tested a new fluorination method which converts H2S gas to SF6, the latter is necessary for precise analysis of all four sulphur isotopes (32S, 33S, 34S and 36S) in order to determine S-MIF. This new method used CoF3 as the fluorination agent, which avoids the use of extremely dangerous gas F2 and thus is safer. Unfortunately, the reactivity of CoF3 and H2S turned to be very erratic, and even became inactive by time. We have also tested the possibility of fluorinating Ag2S to SF6 using use CoF3.
2) We have developed a new protocol that converts sulphate to sulphide, which is the first step of precise analysis of all four sulphur isotopes (32S, 33S, 34S and 36S) in order to determine S-MIF. The new protocol is easy to handle and allows to process multiple samples at a time, and is demonstrated with good reproducibility in terms of H2S yield and for further isotope analysis. It is thus a good alternative to the manual conventional method which suffers from a cumbersome distillation apparatus system, long reaction time and large volume of the reducing solution. The new protocol is especially useful for samples with limited amount of sulphate available.
3) We have also compiled S-MIF data of home-made S-33 enriched sulphate standards measured by 5 different laboratories cross the world. The standards were made by the host and distributed to the 5 laboratories, in order to compare the precision of the S-MIF analysis by different laboratories, and to seek the possibility to provide the first S-MIF standard reference material. An manuscript on this topic is drafted.
4) We have done 3 campaigns (totally 5 weeks) of lab experiments using the stainless-steel chamber (CESAM) in Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA) to simulate atmospheric sulphate production under designed conditions. These experiments were used to study O-MIF and S-MIF of sulphate produced under atmospheric conditions with different UV exposure, relative humility and with or without O3 present. In total, we have collected 91 sulphate samples for O-MIF and S-MIF analysis and 6 nitrate samples for O-MIF analysis in order to quantify the magnitude of O-MIF in O3 which is ultimate source of O-MIF.
5) We have completed the oxygen isotopic composition analysis of all samples at IGE, Grenoble, as well as sulphur isotopic composition analysis of all sulphate samples at IPGP, Paris. The S-MIF results, specifically, the systematics of δ34S, ∆33S and ∆36S, comparing with previous published data in the literature, suggesting that the S-MIF in stratospheric sulphate after explosive volcanic eruptions probably originates from the absorption cross section difference between 240-340 nm of different SO2 isotopologues. At high SO2 concentrations (>1 ppm), or in the air without O2, the effects of self-shielding or intersystem crossing may arise, respectively.
