Photochemical Smog - Mrs. Reed Fresno High school · PDF file 2018. 4. 23. ·...

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Transcript of Photochemical Smog - Mrs. Reed Fresno High school · PDF file 2018. 4. 23. ·...

  • Photochemical Smog 6.3

  • This is the big idea for the next slides write it down. • The combustion of fossil fuels produces primary pollutants which may

    generate secondary pollutants and lead to photochemical smog, whose levels can very by topography, population density and climate.

  • Facts

    • 1 billion people exposed to outdoor air pollution per year

    • 1 million die prematurely due to air pollution

  • Primary Pollutants

    • Carbon Dioxide

    • a colorless, odorless, gas,

    • There are both natural and human sources of carbon dioxide emissions.

    • Natural sources include decomposition of organic matter, ocean releases, volcanic eruptions and respiration.

    • Human sources come from activities like deforestation as well as the burning of fossil fuels like coal, oil and natural gas.

  • Primary Pollutants

    • Carbon monoxide from incomplete combustion of fossil fuel.

    • Carbon monoxide CO, unlike CO2, is a bad poison. CO is produced by incomplete combustion, i.e. when there isn't enough oxygen to make CO2, you get CO.

    • Carbon monoxide binds very strongly to the iron in the hemoglobin in the blood. Once carbon monoxide attaches, it is very difficult to release. So if you breath in carbon monoxide, it sticks to your hemoglobin and takes up all of the oxygen binding sites Your blood loses all of its ability to transport oxygen, and you suffocate.

  • Primary Pollutants

    • Nitrogen oxides-especially nitrogen dioxide, a brown gas, but also nitrous oxides and nitric oxide

    • Combustion of oil and gas in cars and factory

    • Bacteria in soil

    • Forest fire

    • Volcanoes

    • Lightning

  • Northern hemisphere highest levels in May and September and occur highest at noon to early evening. Much comes from car exhaust

  • Nitrogen dioxide around the world

  • Nitrogen dioxide in china

  • Primary Pollutants

    • Sulphur dioxide- from coal with high sulfur content

  • Primary Pollutants • Particulates/particulate matter – EX: black carbon or soot fine particles of solid

    or liquid suspended in air, dangerous as they are taken into the lungs when breathing and cause lung diseases or cancer

    These striking archive pictures show Manchester's dark history - when the city's grandest buildings were blackened with soot.

  • London during heavy chimney burning creating massive soot particulates.

  • Through evolution moths in England changed colors from white to black to match the newly blackened trees do to heavy soot.

  • Primary Pollutants

    • Unburned hydrocarbons- when petroleum is burned in an engine some of it is not burned this is when hydrocarbons are emitted

    • When unburned fuel is emitted from a combustor the emission is caused by fuel "avoiding" the flame zones.

    • For example, in piston engines, some of the fuel-air mixture "hides" from the flame in the crevices provided by the piston rings grooves.

  • Please take careful notes pausing the video when necessary. This explains tropospheric ozone, nitrogen oxides, and unburned hydrocarbons

    • ozone&&view=detail&mid=107946FA17FC4EE6E596107946FA17FC4E E6E596&FORM=VRDGAR

  • Diagram how ozone is formed. Pause video as needed •

    ozone&&view=detail&mid=3C92AC03C57B5E7F92B73C92AC03C57B5 E7F92B7&rvsmid=9BB2F66E488656B64A8F9BB2F66E488656B64A8F &fsscr=0&FORM=VDFSRV

  • Secondary pollutants

    • Formed when primary pollutants undergo a variety of reactions with other chemicals already present in the atmosphere. Sometimes this is a photochemical reaction in the presence of sunlight.

  • Secondary pollutants

    • Tropospheric ozone

    • Ozone is also a greenhouse gas with a global warming potential 2,000 times that of carbon dioxide.

  • Formation of tropospheric ozone


    When fossil fuels are burned, two of the pollutants emitted are hydrocarbons (from unburned fuel) and nitrogen monoxide (nitric

    oxide, NO).

    Nitrogen monoxide reacts with oxygen to form nitrogen

    dioxide (NO2), a brown gas that contributes to urban haze. Nitrogen

    dioxide can also absorb sunlight and break up to release oxygen atoms

    that combine with oxygen in the air to form ozone.

  • We will get to this next

    Diagram this

  • Volatile organic compounds

    • Evaporation of solvents

    • Evaporation of fuels

    • Incomplete combustion of fossil fuels

    • Occurs naturally in terpenes in trees

  • How is photochemical smog formed

    • On warm sunny days with lots of traffic, photochemical smog can be formed over cities.

    • Although usually associated w/ combustion of fossil fuels deforestation can contribute: In Indonesia smog levels get extremely high do to this problem

  • Indonesia has revoked the license of a timber supplier and suspended the operations of three palm oil plantation operators over fires.

  • How is photochemical smog formed

    • It is mainly nitrogen dioxide and ozone but is a complex mixture of about one hundred different primary and secondary air pollutants

    • Biggest contributor: motor vehicles exhaust formed when ozone, nitrogen oxides and gaseous hydrocarbons from vehicle exhausts interact w/ strong sunlight

  • Glue this into your notebooks

  • The frequency and severity of photochemical smog in an area depend on local topography, climate, population density and fossil fuel use. Precipitation cleans the air and winds disperse the smog.

    Fresno under smog

  • • Photochemical smog first caused problems in Los Angeles it is often called Los Angeles type smog.

    • Other cities that frequently suffer are Santiago, Mexico City, Rio de Janeiro, and Beijing.

    • These areas have special geography that makes smog worse.

    • (we will get to this next)

  • Smog became a serious problem in Los Angeles after World War II. On Christmas Eve, 1948, traffic was clear; unfortunately, the air wasn’t.

  • Los Angeles

  • Los Angeles

  • All of the images that follow are from China

  • State the effect of tropospheric ozone.


    Ozone is a toxic gas and an oxidizing agent.

    It damages crops and forests- ozone degrades chlorophyll so photosynthesis and productivity lowers

    irritates eyes, can cause breathing difficulties in humans and may increase susceptibility to infection.

    It is highly reactive and can attack fabrics and rubber materials.

  • Los Angeles

    Thermal inversions trap the smog in valleys (for example, Los Angeles, Santiago, Mexico City, Rio de Janeiro, São Paulo, Beijing) and concentrations of air pollutants can build to harmful and even lethal levels.

  • Read pages 290 and 291. diagram both the normal pattern and the thermal inversion. Write down how a thermal inversion traps smog

  • Describe and evaluate pollution management strategies for urban air pollution.

    • How do we reduce this pollution?

    Copy the chart on page 291