The investigator plans to make optical measurements of cloud droplet size spectra and liquid water content (LWC) with simultaneous measurements of cloud and rain water composition, aerosol size spectra, and three dimensional winds at a marine site on the NW coast of Washington State. By combining the droplet spectra and LWC with the other measurement the investigators will address both: 1) droplet and chemical eddy fluxes associated with interception of cloud water by vegetation and 2) the relationship between droplet and CCN number concentration in the marine boundary layer. Cloud droplet- cloud condensation nuclei (CCN) relationships will be studied by comparing CCN concentrations (inferred from aerosol size spectra) in clear air to cloud droplet concentrations. Vertical wind speed, LWC, and droplet concentration will be combined to produce eddy covariance estimates of integrated cloud droplet fluxes and the size dependence of droplet deposition velocity. The measured cloud water eddy fluxes will be compared to calculated droplet sedimentation fluxes and cloud water interception by an artificial tree. The chemical fluxes associated with rain will be compared to those associated with intercepted cloud water. Understanding droplet/chemical flux and CCN/droplet relationships is important for characterizing the chemical cycling of trace species between the atmosphere and the biosphere and for understanding the response of climate to CCN cycling in the marine atmospheric.
