ICE FOG - LOW TEMPERATURE AIR POLLUTION
STABLE PRESSURE SYSTEMS OVER INTERIOR ALASKA SOMETIMES PRODUCE PROLONGED, EXTREME (BELOW -40 C) COLD SPELLS AT THE SURFACE. THE RATE OF RADIATIVE COOLING OF THE AIR IS ENHANCED BY SUSPENDED ICE CRYSTALS WHICH ARE THEMSELVES A RESULT OF THE INITIAL COOLING. RADIATION FOGS FORMED DURING THE ONSET OF COLD SPELLS ARE GENERALLY OF SHORT DURATION BECAUSE THE AIR SOON BECOMES DESICCATED. THESE FOGS CONSIST OF SUPERCOOLED WATER DROPLETS UNTIL THE AIR TEMPERATURE GOES BELOW THE "SPONTANEOUS FREEZING POINT" FOR WATER DROPLETS (ABOUT -40 C); THE FOG THEN BECOMES AN ICE CRYSTAL FOG, OR SIMPLY "ICE FOG." DURING THE COOLING CYCLE WATER IS GRADUALLY CONDENSED OUT OF THE AIR UNTIL THE DROPLETS FREEZE. THE PERSISTENCE OF FAIRBANKS ICE FOG DEPENDS ON A CONTINUAL SOURCE OF MOISTURE FROM HUMAN ACTIVITIES WITHIN THE FOG. MOST OF THE ICE FOG CRYSTALS HAVE SETTLING RATES WHICH ARE SLOWER THAN THE UPWARD VELOCITY OF AIR OVER THE CITY CENTER. THE UPWARD AIR MOVEMENT IS CAUSED BY CONVECTION CELLS DRIVEN BY THE 60 C "HEAT ISLAND" OVER FAIRBANKS. THIS CAUSES A REDUCED PRECIPITATION RATE WHICH PERMITS THE DENSITY OF ICE FOG IN THE CITY CENTER TO BE THREE TIMES GREATER THAN THAT IN THE OUTLYING AREAS. THE INVERSIONS WHICH OCCUR DURING COLD SPELLS OVER FAIRBANKS BEGIN AT GROUND LEVEL AND ARE AMONG THE STRONGEST AND MOST PERSISTENT IN THE WORLD. THEY ARE THREE TIMES STRONGER THAN THOSE IN THE INVERSION LAYER OVER LOS ANGELES. THUS, THE LOW-LYING AIR OVER FAIRBANKS STAGNATES AND BECOMES EFFECTIVELY DECOUPLED FROM THE ATMOSPHERE ABOVE, PERMITTING HIGH CONCENTRATIONS OF ALL POLLUTANTS. /AUTHOR/
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Supplemental Notes:
- Rr 121, 118 PP 35 FIGS, 9 TABS, 3 PHOTS, 81 REFS, 2 APP
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Authors:
- Benson, C S
- Publication Date: 1970-6
Media Info
Subject/Index Terms
- TRT Terms: Air pollution; Atmospheric temperature; Freezing; Ice; Ice fog; Water vapor
- Old TRIS Terms: Ice crystals; Temperature inversions
- Subject Areas: Economics; Highways; Maintenance and Preservation; Society;
Filing Info
- Accession Number: 00218699
- Record Type: Publication
- Files: TRIS
- Created Date: Jan 18 1971 12:00AM