Molecular dynamics simulations and stabilization energy calculations are performed in this work in order to understand the stability of CH(4) hydrate, CO(2) hydrate, and CH(4)-CO(2) mixed hydrate. The model systems of fully occupied type SI CH(4) hydrate, CO(2) hydrate, and CH(4)-CO(2) mixed hydrate are prepared in a simulation box of 2 x 2 x 2 unit cell with periodic boundary conditions. The MD simulation results reveal that the CH(4)-CO(2) mixed hydrate is the most stable one in above three hydrates. The stabilization energy calculations of small and large cavities occupied by CH(4) and CO(2) show that the CO(2) molecule is less suitable for the small cavity because of its larger size compared with the CH(4) molecule but is more suitable for the large cavity. The results in this work can also explain the possibility of CH(4) molecule in reoccupying the small cavity during the replacement of CH(4) hydrate by CO(2), from the hydrate stability point of view.

The exchange rates of carbonyl sulfide (COS) and dimethyl sulfide (DMS) between 19 tree species and the atmosphere were investigated under natural field conditions using a static enclosure. Most of the investigated trees acted as sinks for atmospheric COS and a few trees, such as Salix matsudana Koidz. and Ulmus pumila L. could emit COS. The distinct diurnal variations of COS uptake for the investigated trees indicated that COS uptake strongly depended on photosynthetically active radiation (PAR). The average COS uptake rates for most species were much higher in summer than in autumn, indicating leaf age and temperature also might be the important influencing factors for COS uptake. Platanus orientalis L., Sophara japonica var. P. loud., Magnolia denudata Desr. and Sophora japonica L. were capable of continuously absorbing COS in daytime as well as in nighttime. For Platanus orientalis L., the maximal COS uptake rate and DMS emission rate on a single leaf area basis were À15.29 and 0.42 pmol m À2 s À1, respectively. The COS exchange fluxes for the investigated tree species depended strongly on the ambient COS mixing ratios. Significant correlation between DMS emissions and temperature was observed in summer. r

[1] Precipitation samples (rain and snow) from 10 provinces in China were collected during the winter season. The concentration of initial dissolved carbonyl sulfide (COS) and its photochemical production rates by natural sunlight were measured. All investigated precipitation samples were found to be supersaturated with COS, and the initial dissolved COS concentrations were in the range from 17.7 to 48.2 ng L À1 . The COS saturation ratios (SR) for the investigated samples were in the range from 15.8 to 60.4. The COS photochemical production rates depended strongly on sunlight intensity and were independent of microbial activity as well as dissolved O 2 . The amount of COS produced photochemically by sunlight irradiation for 14 to 50 days was $1-2 orders of magnitude greater than that of initial dissolved COS.