New Particle Formation and Fate in the Coastal Environment (PARFORCE)

Homogeneous heteromolecular nucleation of natural atmospheric aerosols has been observed in the coastal environment more than 100 years ago. Aitken [1897] first reported elevated condensation nuclei (CN) concentrations close to the shore line on the west Scottish coast where he observed particle concentrations to rise from a background level of » 300 cm-3 to » 150,000 cm-3 during clean marine air flow under sunny conditions. The cause of these new particles was thought to be photochemical breakdown of gases released from the shore biota although the nucleating species were never identified. These ‘nucleation ’ events were also observed at various other coastal sites around western Europe, including the Mace Head Atmospheric Research Station in Ireland where these new particle events were found to be tidal-related [O’Dowd et al., 1998]. The coastal environment is a strong, and frequently active, source of natural atmospheric aerosol particles and consequently, this environment provides an excellent choice of a natural laboratory to study the conditions under-which natural particle formation occurs. In an effort to further elucidate new particle formation, the PARFORCE consortium and programme was set up to specifically focus on the processes and conditions which promote and control homogeneous heteromolecular nucleation in the coastal boundary layer. These aims are being achieved through running a long-term continuous aerosol monitoring programme at Mace Head along with two intensive field campaigns (September 1998 & June 1999) comprising detailed atmospheric chemistry measurements. In parallel to the experimental programme, aerosol nucleation and growth models are being further developed for use in close conjunction with the experimental data to identify the primary mechanisms involved. Primary objectives (1) Determine the environmental conditions and the rates under which homogeneous heteromolecular nucleation occurs in the coastal boundary layer (i.e. pre-existing aerosol surface area; precursor gas concentration; micro- and macro-scale meteorology). (2) Examine whether these nucleation events can be explained by binary or ternary heteromolecular nucleation of the following schemes: H2SO4-H2O o