Barbara Trost/Bob Morgan Alaska Department of Environmental Conservation Temperature Inversions in Alaska ITEP Air Quality Training Kodiak 2015

2 The Atmosphere as seen by Alan Shepard May 5, 1961 – US 1 st Manned Space Flight

3 Lavers of the Atmosphere as seen from Space

4 Temperature in the Atmosphere

5 Normal Circulation in the Atmosphere in the Daylight  Warm air rises | cold air sinks  Temperature decreases as you go higher in atmosphere  Warmer near ground, colder aloft  Mixing between air at low and high levels

6 Winter Day, with Good Mixing in the Atmosphere

7 Temperature Inversion  After sunset, ground loses heat quickly  Air above ground stays warmer  Colder air at surface is trapped under warmer layer  Temperature profile of atmosphere is inverted  A barrier is formed between the lower cold air and the upper warm air  Trapping pollution close to ground level  Inversion dissipates after sun heats up ground & wind mixes air between ground and above surface

8 Temperature Inversions (cont.)  Occurs in early morning hours after earth has lost all heat from sun  Calm winds, clear skies  Cold air will sink into the lowest points, such as basins or valleys or frozen rivers beds  Cold air can flow down off of hillsides

9 Temperature in the Atmosphere with a Temperature Inversion

10 Winter Day in Fairbanks with a Strong Temperature Inversion (View from the Hillside)

11 Winter Day in Fairbanks with a Strong Temperature Inversion (View from Ground Level)

12 Seasonal Factors  Occur year-round, but strongest in winter  Alaska experiences extreme winter inversions compared to lower 48  Can be very shallow - ~20 feet  Temperature difference of 20 ° over 100 feet of elevation Stack is above inversion Stack is below inversion inversion

13 Health Impacts  Can impact public health  Steam/smoke from smokestack rises and flattens out, trapping pollution in shallow layer above surface  Traps other pollutants, such as Carbon monoxide from vehicle exhaust or particulate matter from residential wood burning  Very cold air makes it difficult to breathe  Ice fog