Aerosol-cloud interactions on a mountain peak in Puerto Rico

Here we present measurements of aerosol and cloud particles that were made during a 10 day period in December, 2004 at two locations in Puerto Rico. The concentration, size and optical properties of aerosol particles were measured at the El Faro lighthouse, located on the most northeast point of the coast of Puerto Rico and at the East Peak mountain observatory, 1000 m ASL and 20 km to the SW of the lighthouse. The primary objective of the project was to characterize aerosol properties along a quasi-Lagrangian trajectory in order to evaluate the transformation and removal of particles by clouds and precipitation.

At the mountain site the particles were sampled from three types of inlets: 1) total, i.e. interstitial and evaporated cloud droplets, 2) interstitial, and 3) within cloud droplets. The physical, chemical and optical properties of the particles that entered via these three inlets were measured with condensation nuclei counters, size spectrometers, an aerosol mass spectrometer (AMS), nephelometer, soot photometers and a cloud condensation nuclei counter. Cloud and rainwater samples were analyzed for inorganic ions, conductivity and PH.

An analysis of the aerosol properties at the mountain site when in cloud and cloud-free air, in comparison with similar properties measured at the light house, shows that the clouds are removing the majority of sulfate containing aerosols. The majority of the interstitial aerosols were less than 0.1 um in diameter. Given that the soot photometers shows little difference in the mass concentration of light absorbing material, i.e. black carbon, we conclude that the majority of interstitial particles were BC.