Wind-produced submicron particles in the marine atmosphere

The mean relationship between wind speed and the concentrations of condensation nuclei (CN) and cloud condensation nuclei (CCN) has been found from shipboard measurements between latitudes 50–54°S in the central south Indian Ocean through two winter months. It took the form: log C = a+bU, where C is the particle concentration (cm−3), U is the wind velocity in m s−1, a was 1.25 for CN (radius r> 1.5 nm) and 0.94 or 0.76 for CCN active at 0.6% or 0.1 % supersaturation respectively, while b was 0.037 for each. This value of b is too low for climatic regulation by wind-produced oceanic CCN to be very important and appears to be more consistent with earlier data than a recently found value of 0.1 for the North Atlantic. on microscope photographs of particles collected in very strong winds showed that sea salt could not account for increases in concentrations of particles with radii less than 50 nm although the CN and CCN measurements suggested a continued increase to smaller sizes. Diffusion battery measurements confirmed the presence of these small particles but their nature and origin is unknown.