Cloud Condensation Nuclei Measurements Research Articles

Particle Emissions From a Large Kraft Paper Mill and Their Effects on the Microstructure of Warm Clouds

Airborne measurements of cloud condensation nuclei (CCN), total particle counts, the size distribution of particles, and the microstructure of warm clouds have been made in the vicinity of a large Kraft pulp and paper mill. The plume of CCN and total particles from the mill is well-defined at distances up to 40 km downwind and the concentrations of these particles reach values which exceed those in the ambient air by a factor of about 4. A large peak in the concentrations of CCN was measured in the plume at a distance downwind of the mill corresponding to a travel time of about 4 hr. The total particle count in the plume peaked after about 2 hr of travel time downwind. The particles in the plume were measured over the size range 0.3 to 8 μm; their concentrations were much higher than in the ambient air, particularly those with diameters <1 μm. At points downwind in the plume corresponding to travel times ≳6 min, a secondary peak appeared in the concentration of particles with diameters just in excess of 0.3 μm and it persisted for travel times up to about 4 hr. The rates of production of CCN and particles >0.3 μm in diameter in the plume is estimated to be about 0.05 cm−3 sec−1. It is suggested that this is due to gas-to-particle conversions.Clouds that form in the plume from the paper mill had a much broader spectrum of droplet sizes than those which form in the ambient air. Since the former clouds contain a significant number of droplets with diameters >30 μm, as well as a large number of smaller droplets, precipitable drops should form in them very efficiently by the coalescence mechanism. These observations support the suggestion made by Hobbs et al. that the effluents from paper mills are probably responsible for the anomalously high annual precipitation amounts which have occurred in the vicinity of such mills in Washington State in recent years.

Experimental Investigation of Transient Supersaturations in a Thermal Diffusion Chamber

Abstract The effect of transient supersaturations on the concentration of cloud condensation nuclei (CCN) in a conventional parallel-plate type thermal diffusion chamber is experimentally investigated by controlling the relative humidity of the sample and the temperature of the top and bottom plates individually. It is found that the error in CCN counts is quite significant around 90% relative humidity and might be dominant at cloud bases where the relative humidity approaches 100%. The error is a combined result of thermal and hydrodynamical transients. It is suggested that a chamber having a continuous and laminar inflow of the sample which has the steady-state temperature profile already existing in it is but suited for reliable CCN measurements. The calculations based on the theory of Saxena, Burford and Kassner help explain the obtained results which also support the earlier theoretical predictions of Fitzgerald. The results seem to disagree with recent experimental observations reported by Radke and...

Cloud condensation nuclei and visible pollution in Los Angeles

Simultaneous measurements of cloud condensation nuclei and light scattering in Los Angeles down to a visibility of 7.5 miles are presented. It is shown that, in Los Angeles, air pollution is a good source of nuclei. Their concentration increases with decrease in visibility.

Inadvertent weather modification and Los Angeles smog

The potential mechanisms for inadvertent weather modification by anthropogenic aerosols are reviewed briefly. Within this framework, limited measurements of cloud condensation nuclei and ice nuclei taken during the 1969 Pasadena experiment are discussed. The condensation nuclei observations were made with an MRI thermal diffusion counter and the ice nuclei were made using a Millipore filter technique. The results suggest that the cloud condensation nuclei counts are in the range of 10 3cm −3 at 0.5% water vapor supersaturation, and they increase during the day in rough correspondence with the second moment of the aerosol distribution. On the other hand, the ice nuclei counts are in the range of 200 m −3 at 18°C, and appear to decrease during the day. Such diurnal behavior may be related to the “poisoning” of otherwise active nuclei in the presence of organic material in the Los Angeles atmosphere.

Simultaneous airborne measurements of cloud condensation nuclei and sodium‐containing particles over the ocean

AbstractSimultaneous airborne measurements have been made over the Pacific Ocean of the concentrations of cloud condensation nuclei (CCN) active at 0.5 per cent supersaturation and the concentrations and size‐spectra of sodium‐containing particles (SCP) over a wide range of sizes. The concentrations of SCP decreased sharply with increasing height above the ocean and it is likely that most of them originated from the ocean. However, even at altitudes as low as 50 ft above the surface of the ocean, and over surf, the measured concentrations of SCP were only a few per cent of the concentrations of CCN at G.5 per cent supersaturation. Also the average concentrations of CCN did not change significantly with altitude up to at least 10,000 ft. These observations indicate that sea‐salt particles were not the major source of the CCN.It is suggested that the production of sulphates in cloud droplets, followed by the release of these particles when the droplets evaporate, is an important mechanism for increasing the efficiency of CCN in the air.

Cloud Condensation Nuclei and their Possible Influence on Precipitation

Abstract Measurements of cloud condensation nuclei (CCN) conducted both from the ground and from an instrumented aircraft during two winter seasons, utilizing a thermal diffusion chamber, suggest that. CCN spectra prove to always have, in both rainy and dry weather, continental-like characteristics. Their concentrations were shown to depend on wind direction and found to be surprisingly high, even in air masses with a partial maritime trajectory. The existence of local sources appears to have a limited and a generally minor effect on the characteristics of CCN spectra. On the average, CCN concentrations tend to decrease by a factor of 2 during the first three days of a rainy spell. Consequently, cloud droplet concentrations, computed for cumulus clouds assumed to have base updraft velocities of 250 cm sec−1, seem to show a similar trend but are always within the range of 180–950 cm−2. Since these variations do not seem to correlate with rainfall, they are not dominant in their effect on the relative effic...