hygroscopic nucleus Microscopic particle (e.g. of sulphur dioxide, salt, dust, or smoke) in the free air, on which water vapour may condense to form droplets. Aerosols that are soluble in water (e.g. salt or sulphuric acid) can induce condensation in unsaturated air, e.g. salt nuclei can induce it at a relative humidity of less than 80%. The size of nuclei may be from 0.001 μm to more than 10 μm (i.e. ‘giant’ nuclei such as particles of sea-salt). See also AITKEN NUCLEI; and NUCLEUS.

hygroscopic nucleus A microscopic particle (e.g. of sulphur dioxide, salt, dust, or smoke) in the free air, on to which water vapour may condense to form droplets. Aerosols that are soluble in water (e.g. salt or sulphuric acid) can induce condensation in unsaturated air (e.g. salt nuclei can induce it at a relative humidity of less than 80 per cent. The size of nuclei may be from 0.001 μm to more than 10 μm (i.e. ‘giant’ nuclei such as particles of sea salt)). See also Aitken nucleus.