Measurements of particle number density and Fuchs surface area, together with a range of gaseous pollutant concentrations, have been made in June 1995 at a coastal site in eastern England which receives air from a range of polluted and less polluted origins. Periods of enhanced local particle production were identified and found to be associated predominantly with relatively polluted air sectors. An examination of the factors contributing to homogeneous nucleation and hence new particle production suggests that those most important at this location are probably the production of hydroxyl radicals and the availability of ammonia. A numerical modeling study calculating characteristic timescales for new particle production and for condensation onto existing aerosol surfaces is able to predict periods of new particle production. The model suggests that oxidation of dimethyl sulphide and sulphur dioxide and homogeneous nucleation of sulphuric acid and water, probably in combination with ammonia, are the source of new particles at this site.