Urban Cloud Condensation Nuclei Spectral Flux

Abstract

The cloud condensation nuclei (CCN) spectral flux and the condensation nuclei (CN) flux from an urban area are determined from in situ aircraft measurements at Denver, Colorado. The concentration differences between upwind and downwind cross sections at several altitudes are used to estimate anthropogenic fluxes. The CCN and CN production rate estimates are consistently three times larger than a similar 1966 study by Squires, also at Denver. On a per capita basis, the present measurements are only a factor of 2 higher. This is probably within the seasonal and day-to-day variability and/or may be result of somewhat different measurement techniques. The instantaneous CCN spectra produced flux estimates over the range of critical supersaturation Sc of 0.04%–0.9%. Some of the estimated particle production rates for Denver are 1 × 1018 s−1 for CN, 1.7 × 1017 s−1 for CCN at 0.9% Sc, 1.16 × 1017 s−1 for CCN at 0.5% Sc, 3 × 1015 s−1 for CCN at 0.1% Sc, and 5 × 1014 s−1 for CCN at 0.04% Sc.