Technical Booklet K Ventilation·Page 13
Surface Water Activity
A measure of water availability to micro-organisms, expressed as the ratio of water vapour pressure to that of pure water at the same temperature.
Surface water activity – a measure of the availability of water to micro-organisms and is determined from the ratio of the vapour pressure of the water in the substrate to that of pure water at the same temperature and pressure. This ratio is in steady-state conditions numerically equal to the equilibrium relative humidity of the air except that the latter is commonly expressed as a percentage.
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