Among the chemical and physical processes involved in the transformation of pollutants between their sources and their ultimate deposition, those associated with clouds, aerosols and precipitation must be rated as the most difficult both to study and to understand. This book presents a variety of recent advances in this field, including the properties and composition of aerosol particles, chemical transformation and scavenging processes, the relationship between liquid-phase chemistry and cloud micro-physics, entrainment, evaporation and deposition, trends in high Alpine pollution, transport processes, and developments in instrumentation. This book is Volume 5 in the ten-volume series on Transport and Chemical Transformation of Pollutants in the Troposphere.

Among the chemical and physical processes involved in the transformation of pollutants between their sources and their ultimate deposition, those associated with clouds, aerosols and precipitation must be rated as the most difficult both to study and to understand. This book presents a variety of recent advances in this field, including the properties and composition of aerosol particles, chemical transformation and scavenging processes, the relationship between liquid-phase chemistry and cloud micro-physics, entrainment, evaporation and deposition, trends in high Alpine pollution, transport processes, and developments in instrumentation. This book is Volume 5 in the ten-volume series on Transport and Chemical Transformation of Pollutants in the Troposphere.

The physical and chemical properties and processes of clouds are of great interest from a variety of perspectives, such as acid deposition, oxidant chemistry, and radiative transfer in the atmosphere. The Kleiner Feldberg Cloud Experiment was conducted in October--November 1990 at the field observatory of Kleiner Feldberg near Frankfurt, Germany, in the Taunus Highlands. The experiment was planned and organized within the EUROTRAC sub- project GCE (Ground-Based Cloud Experiment). The general aim of this project is to experimentally investigate physical and chemical processes occurring in ground-based clouds, to provide the basic information needed to understand the incorporation and transformation of trace atmospheric constituents within the multiphase cloud system. This book reports the results of the Kleiner Feldberg Cloud Experiment, addressing the main scientific questions related to the properties of clouds and the processes taking place in the cloud multiphase system. How are the different atmospheric trace species partitioned between gas phase, interstitial aerosols, cloud droplets? What kind of physical and chemical processes cause changes in the phase partitioning of trace species within clouds? Which interactions can be found between the microphysical and dynamical processes in clouds and the chemical composition of cloud droplets? Is the chemical composition of cloud droplets size-dependent, as can be expected by the different scavenging processes? Which influence do chemical reactions have on cloud water chemical composition? Does the gas/liquid partitioning in cloud obey Henry's law? How important is the deposition of atmospheric trace substances due to cloud dropletinterception with the Earth's surface? Are the sampling techniques for aerosols and cloud droplets reliable with respect to their chemical composition? This book provides updated information on cloud research to scientists involved in other fields of atmospheric sciences and also useful reference material for graduate students enrolled in atmospheric chemistry programmes.

The eleven papers presented in this issue are intended to provide a comprehen sive description of the cloud systems studied during the Kleiner Feldberg experi ment. The first paper provides a general overview of the experiment and a summa ry of the main accomplishments. The following three papers then describe the cloud systems from the meteorological, microphysical and chemical perspectives. Another four papers address more specifically the issues of incorporation of aerosol particles and trace gases within cloud droplets. A synthesis of the Kleiner Feldberg cloud properties and a comparison with experimental data is then provided by a paper which models the airflow and cloud mycrophysics and chemistry for selected cloud episodes during the experiment. Deposition of trace substances via cloud interception with the vegetation is the subject of the next paper, which integrates experimental data in a deposition resistance model. A technical paper at the end of the issue reports on a newly developed holographic technique to measure cloud droplet size distribution, which was tested for the first time during this experiment. The collaborative nature of the work accomplished within GCE is emphasized by the large authorship of most papers presented in this issue. This should not be regarded with surprise, but rather as an indication of the interdisciplinary efforts of the GCE scientific community for the accomplishment of this study. SANDRO FUZZI Coordinator, EUROTRAC sub-project GCE Journal of Atmospheric Chemistry 19: 3-35, 1994. 3 (c) 1994 Kluwer Academic Publishers. The Kleiner Feldberg Cloud Experiment 1990."