The adsorption mechanisms of hazardous gas molecules such as NH3, H2S and SO2 on sepiolite have not yet been elucidated. Therefore, molecular dynamics (MD) simulations were employed to investigate the adsorption behaviour of sepiolite towards NH3, H2S and SO2. A calculation model for sepiolite containing structural and zeolitic water molecules was constructed in this study. The adsorption sites and molecular configurations of the hazardous gases in the sepiolite channels were studied. The radial distribution function was employed to evaluate the interactions between the gas molecules and sepiolite. The results show that the order of adsorption capacity of sepiolite for the gases is as follows: SO2 > H2S > NH3. These three types of gas molecules absorbed in the channel nanopores of sepiolite exhibit different atomic configurations. The diffusion coefficients of the gas molecules in the channels decreased in the following order: NH3 > H2S > SO2. In addition, the diffusion coefficients were affected significantly by the ratio of the number of gas/water molecules. This study provides new perspectives for understanding the molecular processes responsible for the adsorption properties of sepiolite.

The crustose lichen Lecanora conizaeoides has declined markedly around London with progressively diminishing sulphur dioxide pollution of the air since the 1960s. To identify the immediate causes of its decline, we applied S in the form of bisulphite (0·2 & 2 mM) and sulphate (2 mM), and N as nitrate (2 mM) to relict colonies of the lichen on beech trunks in a plantation in Windsor Forest. Growth of the lichen was monitored by estimating changes in percentage cover. By the end of a 25-month period of two-weekly treatments, all the chemical treatments had resulted in significant decreases in cover of L. conizaeoides compared to distilled water controls, with the 2 mM bisulphite causing the greatest loss. Bark surface pH was also lowered by the chemical treatments, but most by the 2 mM bisulphite applications. Similar results were obtained in two laboratory experiments where the nutrient applications were repeated under a controlled environment and thallus area monitored photographically. No evidence was obtained to support the hypothesis that growth of L. conizaeoides is stimulated by an elevated sulphur supply. We conclude that the disappearance of the lichen is linked to gradual increase in bark pH caused by the combined effects of a marked reduction in SO2 emissions and rising emissions of NH3.