On the spatial extent and evolution of coastal aerosol plumes

Abstract

Airborne mapping and pseudo-Lagrangian experiments were conducted in coastal and tidal-induced nucleation plumes along the west coast of Ireland in June 1999. The mapping flights confirmed that the source of the previously reported coastal nucleation events is indeed the tidal zone around the coastline. Additionally, the mapping flights also confirmed that coastal nucleation is typically ubiquitous along the coastline, at least on the Irish coast. Along with the large horizontal extent of coastal nucleation events, these new particles were observed to be mixed up to >1000 m in the vertical despite slightly stable meteorological conditions. On the clean air mapping flight the background particle concentration (r > 1.5 nm) was observed to increase from <1000 cm -3 to > 100,000 cm -3, while accumulation mode (r > 50 nm) particle concentration remained constant at approximately 50 cm -3. During a semipolluted mapping flight, concentrations increased from 3000 to >100,000 cm -3 in places. The enhancement in particle concentration was confirmed to be in the size range 1.5-5 nm radius at the start of the nucleation event, while growth into larger sizes was observed later. During this semipolluted event, owing to favorable wind conditions, it was possible to perform a pseudo-Lagrangian experiment in a coastal plume advecting out over the northeast Atlantic. This plume was observed to be >60 km in width and >1000 m in the vertical and was encountered for >250 km off the coast. During this plume evolution the growth of the new particle mode at sizes <5 nm up to sizes >40 nm was observed. After the plume had evolved for 3 hours, increases in scattering coefficients were observed along with significant increases in cloud condensation nuclei concentrations. These results confirm that the spatial extent of tidal-related particle production is regionally significant, and after a few hours, the growth of these recently formed coastal aerosols significantly increase the concentration of radiatively active aerosol particles. Copyright 2002 by the American Geophysical Union.