Optimization of a counterflow virtual impactor (CVI) for studying aerosol effects on cloud droplet number

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7266015

Anderson, T L

This dissertation considers the problem of collecting cloud droplets in order to study the relatioship between droplet-nucleating particles and cloud droplet number concentration. Aerosol-induced modulation of cloud droplet number is potentially significant to global climate. The key activity was optimization of a Counterflow Virtual Impactor (CVI) for performing the cloud droplet collection. This involved numerical modeling of the collection process, construction and calibration of a new version of the CVI,and deployment of the new CVI in a field experiment. Numerical modeling revealed, with one cavent, that CVI measurements will not be significantly distorted either by droplet evaporation ahead of the collection plane or by droplet collisions during collection. The cavent is that if large (drizzle-size) droplets shatter upon collisions with smaller droplets, the measurement of droplet number could be distorted upwards. Laboratory calibration activities showed the new version to perform its size selection as predicted by theory and to have excellent cut sharpness. In addition, evidence of droplet shattering in the presence of large droplets was obtained. Thus, both laboratory and modeling evidence regarding large droplets lead to the suggestion that these be excluded from the inlet in field applications. The field experiment studying coastal stratiform clouds showed the CVI to perform well and to provide a large and unique data set relevant to examining the relationship between aerosol loading (number or volume) and cloud droplet number. Key resutls were (1) the majority of cloud droplet residue particles were smaller than one-tenth micrometer (diameter) in both clean and continentally influenced conditions, (2) total particle number variations were not correlated to cloud droplet number variations on any time scale, and (3) dominant sources of cloud variation, which tended to obscure the detection of aerosol effects, were meterology and cloud patchiness.

• Research Organization: Washington Univ., Seattle, WA (United States)
• OSTI ID: 7266015
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540120* -- Environment
Atmospheric-- Chemicals Monitoring & Transport-- (1990-)
AEROSOLS
ATMOSPHERIC CHEMISTRY
CHEMISTRY
CLIMATIC CHANGE
CLOUDS
COLLOIDS
CONDENSATION NUCLEI
DISPERSIONS
MATHEMATICAL MODELS
METEOROLOGY
PARTICLE SIZE
SIZE
SOLS