Significant enhancement of aerosol optical depth in marine air under high wind conditions

The relationship between the AOD and wind speed (U), obtained at the Mace Head atmospheric research station, is determined for clean marine (Northeast Atlantic) conditions under steady-state wind speed scenarios. AOD measurements were made under much higher wind speed conditions (up to 18 m s^-1) than hitherto measured. The AOD is found to be approximately dependent on U², with a high correlation (r² = 0.97) determined at all measured wavelengths of 862 nm, 500 nm, 412 nm and 368 nm. A corresponding anti-correlation was observed between the Ångström exponent and wind speed (r² = 0.93). The results illustrate that under moderate-to-high wind conditions, sea-spray AOD can rival or even exceed that associated with pollution plumes over oceanic regions and can potentially contribute to radiative, dynamical and biogeochemical feedback processes associated with future climate change.