 Normally, air temperature decreases with increasing altitude, resulting in cooler air on top of warmer air.

◦ The ground heats up, and heats air above it. The warm air rises, expands, and cools. ◦ This rising air carries pollutants up and away from where humans breathe and dilutes the pollutants in more air space.

 Sometimes, a layer of warm air in a high- pressure system moves in and pushes down on cooler air.  When this happens at lower altitudes, the cooler air mass is trapped near the ground, and it cannot rise as it becomes heated. Thereby, the air near the ground is kept humid and often polluted.

 Effect: In over-populated areas, breathing becomes difficult, even hazardous, for some people. Pollution levels rise.  Do? Listen for air quality advisory or warnings.

 Inversions are extremely stable.  They stop air (and anything in it) from mixing.

 Situations where inversions are likely to occur: ◦ clear, calm nights ◦ long nights (winter) ◦ snow cover ◦ topographic forcing (valleys)

 Pollution is anything that negatively affects the health, survival, or activities of humans or other living organisms.

 Human Health ◦ ACUTE: short duration exposure and/or immediate effects

 Human Health Acute Effects Examples: irritation of eyes, nose, and throat upper respiratory infections (bronchitis, pneumonia) headaches nausea allergic reactions, etc.

 Human Health ◦ CHRONIC: long duration exposure and/or long term effects

 Human Health Chronic Effects: Examples: lung cancer heart disease damage to brain, nerves, liver, kidneys, etc.

 Chemical Nature ◦ How active and harmful  Concentration ◦ See temperature inversions  Persistence ◦ How long pollutant stays around

 Temperature inversions break when: ◦ The Sun comes out and heats the ground, which heats the air above the ground to warmer than the layer above it. ◦ During cloudy weather, the Sun may not be strong enough to break up the inversion for several hours or days.

 Temperature inversions are harmful because: ◦ Air pollution concentrates in the layer that we breathe. ◦ In 1963, 300 people in NY City died due to a temperature inversion.

 Temperature inversions: ◦ Occur almost every night ◦ Occur more dramatically in cities near mountains ◦ This is why we have smokestacks.

 Smog - This is the brownish, gray haze that covers many of the world’s largest cities and is a result of dust, auto exhaust, and industrial manufacturing.

 Smog is impacted by the inversion layer because it is capped when the warm air mass moves over an area.  This happens because the warmer air layer sits over a city and prevents the normal mixing of cooler, denser air.  The air, instead, becomes still, and over time, the lack of mixing causes pollutants to become trapped under the inversion, developing significant amounts of smog.

 Thunderstorms and tornados can form due to the intense energy that is released after an inversion blocks an area’s normal convection patterns.

 Extreme Weather ◦ Freezing Rain – develops with a temperature inversion in a cold area because snow melts as it moves through the warm inversion layer ◦ The precipitation then continues to fall and passes through the cold layer of air near the ground and becomes "super-cooled" (cooled below freezing without becoming solid). ◦ The super-cooled drops then become ice when they fall on items, such as cars and trees, and the result is freezing rain or an ice storm.