Coastal CCN measurements at Mace Head with enhanced concentrations in strong winds

Abstract

Surface measurements of cloud condensation nuclei (CCN) number concentration (cm −3) are presented for unmodified marine air and for polluted air at Mace Head, for the years 1994 and 1995. The CCN number concentration active at 0.5% supersaturation is found to be approximately log-normal for marine and polluted air at the site. Values of geometric mean, median and arithmetic mean of CCN number concentration (cm −3) for marine air are in the range 124–135, 140–150 and 130–157 for the two years of data. Analysis of CCN number concentration for high wind speed, U, up to 20 m s −1 show enhanced CCN production for U in excess of about 10–12 m s −1. Approximately 7% increase in CCN per 1 m s −1 increase in wind speed is found, up to 17 m s −1. A relationship of the form log 10CCN= a+ b U is obtained for the periods March 1994 and January, February 1995 for marine air yielding values a of 1.70; 1.90 and b of 0.035 for both periods.