air and the atmosphere

• atmosphere: a sea of air that surrounds the earth

• divided into several layers, separated from each other by abrupt changes in temperature due to differences in absorption of solar energy

layers of the atmosphere

• troposphere

  • lowest layer, contains 75% of the mass of earth’s air

  • extends 10km/6mi up from sea level at the equator

  • temperature declines with altitude and then abruptly rises when entering the tropopause

    • tropopause: the boundary between the troposphere and upper layers

  • air composition

    • 78% nitrogen, 21% oxygen, 1% other eg. permanent gases and variable gases

• stratosphere

  • second layer, extends from 10-50km/6-30mi above earth’s surface

  • air is very calm

  • temperature increases with altitude until another reversal in the stratopause

    • stratopause: the boundary between the stratosphere and upper layers

  • air composition

    • similar to troposphere with two exceptions:

      • less water vapor

      • 1000x more ozone (O3)

      • ozone in troposphere = bad, in stratosphere = good

air pollution

• air pollution: the presence of chemicals in the air in quantities and durations that are harmful to the environment and human health

• some pollutants are natural

  • natural fires

  • terpenes (from forests)

  • pollen (allergen)

  • dust (from volcanos)

types of pollutants

• primary pollutants: harmful substances emitted directly in that form

  • may react with one another or with a basic air component to become secondary pollutants

• conventional pollutants + pollutant criteria

  • the EPA sets the National Ambient Air Quality Standards (NAAQS) which limits six major pollutants

    • particulate matter (PM)

      • classified based on diameter

        • PM10: 10 micrometers or smaller

        • PM2.5: 2.5 micrometers or smaller

      • comes from wildfires, industrial activities, motor vehicles, cooking, and fuel burning

      • particles can enter the lungs, and the smallest can enter the bloodstream

        • this can cause heart attacks, strokes, and negatively impact children’s nervous systems

      • associated with ~80,000 deaths in the US

    • ozone (ground level)

    • nitrogen oxides (NOx)

    • sulfur oxides (SOx)

    • carbon monoxide (CO)

    • lead

smog

• “smog” = fusion of words “smoke” and “fog”

• two types

  • industrial smog

  • photochemical smog

industrial smog

• important until the mid-1900’s in industrial cities (eg. London, Donora, Pittsburg, Chicago)

• now, rarely a problem in MDCs but still a problem in China, India, Eastern Europe

• caused by large amounts of heavy oil and coal burnt in homes for heat and in industrial work

  • generally worse in winter

• releases sulfur oxides (SOx) and particulate matter

• appears grey in color

the great smog

• took place in London in December 1952

• unusually cold → more coal burnt

• visibility fell to ~12 inches

• 100,000+ people treated for respiratory problems

• caused 3,000-4,000 extra deaths

  • extra death: a death caused by smog above the normal rates which are attributed to the abnormal smog conditions

  • mainly of cardiac and respiratory ailments

• asthma

  • disease which negatively effects lungs

  • more common among people alive/born during the great smog

• US equivalent: Donora, PA, October 1948

photochemical smog

• more pressing current problem in more developed countries

• composed of a mixture of primary and secondary pollutants

• formed when primary pollutants interact under the effect of sunlight and give origin to a mixture of 100 chemicals dominated by ozone

  • worse in summer

• primary pollutants involved and their sources

  • nitrogen oxides (NOx) mainly from vehicles

  • volatile organic compounds (VOCs) from vehicles, gas stations, dry cleaners, print shops, vegetation

• appears orange in color

ozone

• stratospheric → good

• ground level → bad

  • very irritating for the respiratory system

thermal inversions

• thermal inversion: a process which occurs when a layer of cold air temporarily trapped near the ground by a warmer, upper layer

  • pollutants do not get dispersed during thermal inversions

  • warm air is less dense than cold air

• normal conditions

  • during the day, sun warms up the air near the surface, which expands and rises, carrying low-lying pollutants higher

  • under normal conditions, there is a constant movement of air

• sometimes a layer of cold air is trapped beneath a warmer, less dense error

  • warm air prevents ascending air currents and the dispersion of pollutants

  • common in valleys and urban areas

urban heat islands

• structures eg. buildings, roads, and other infrastructure absorb and re-emit the sun’s heat more than natural landscapes such as forests and water bodies

• urban areas become islands of higher temperature relative to outlying areas

• result in thermal inversions and more thunderstorms

• dust domes: pollutants including soot trapped in urban air through thermal inversions

case study: mexico city

• megacity with over 22 million people in the metro area

  • more people, more industry, more cars

• located at a high altitude → solar radiation is intense

• surrounded by mountains, air can be stagnant with winter thermal invasions

• deforestation and construction have exposed soil to wind erosion