Understanding the formation of natural particles in the atmosphere, and their growth to radiatively active sizes, is critical to quantifying the role of anthropogenic emissions on cloud formation, climate change and public health. Only a few regions have been identified as strong natural sources of aerosols in the boundary layer: in particular, the coastal region seems to be the strongest natural source of these new particles. The PARFORCE programme was designed to elucidate and understand the underlying processes leading to observed coastal nucleation and to quantify the factors promoting coastal nucleation. Initial results indicate that nucleation rates in the coastal environment are of the order of 10(7) cm(-3) s(-1) and can be explained by ternary nucleation of sulphuric acid, water vapour and ammonia; however, growth to detectable sizes can only be explained by additional condensation of, probably, organic vapour - otherwise these new stable embryos are lost due to coagulation. The primary biogenic condensing species leading to the observed particle concentrations is thought to be a halocarbon derivative. Peak concentration of particles at sizes >3 nm can reach 1,000,000 cm(-3) after a coastal nucleation event and these events occur almost on a daily basis over considerable spatial scales.
