Production of Cloud Condensation Nuclei in Mexico City

Abstract

As the first step in a long-term program oriented toward understanding the influence of air pollution on weather and climate in Mexico City, we measured the hourly variation of the atmospheric aerosol concentration active as cloud condensation nuclei (CCN) at supersaturation of 0.75%. The tests were performed at ground level using a horizontal thermal diffusion chamber during 1–5 April 1984. The results showed a pattern characterized by a maxima CCN concentration with values between 6500 and 3500 CCN cm⁻³ during the first hours of sunlight, until the concentration reaches values fluctuating between 2000 and 600 CCN cm⁻³ during the afternoon. Analysis of the results shows how the interplay of anthropogenic sources and local meteorological conditions determine a characteristic pattern of the CCN concentration.