Air Pollution

Part 1

What is air pollution?• Air pollution the concentration of

chemicals in the troposphere at high levels that harm organisms, degrade solid materials, or alter climate.

• Natural sources: dust from wind storms, soot and carcinogenic materials from forest fires and volcanoes, VOCs released by some plants– These are usually quickly

dispersed.• Anthropogenic sources: burning of

fossil fuels (power plants, factories, motor vehicles, home heating systems)

Types of pollutants• We classify air pollutants as primary or secondary.• Primary: chemicals emitted directly into the atmosphere• Secondary: primary pollutants may interact with each other

and form different harmful chemicals

Figure 19-3Figure 19-3

The Major Players• Carbon oxides: CO, CO2

• Nitrogen oxides: NO, NO2

• Sulfur dioxide: SO2

• Particulates: Suspended particulate matter (SPM)• Volatile organic compounds (VOCs): methane, terpenes,

benzene, vinyl chloride, etc.

Carbon oxides

• CO (carbon monoxide) results from incomplete combustion of carbon containing substances– Sources: vehicle exhaust, clearing & burning of

forests/grasslands, tobacco smoke, cooking with fire or gas stoves

– Effects: reacts with hemoglobin, reducing ability to carry oxygen

• CO2 (carbon dioxide) – Sources: 93% natural carbon cycle, 7% human activities

(burning fossil fuels, clearing & burning forests/grasslands)– Effects: increases greenhouse effect

Nitrogen oxides• NO (nitrogen oxide)

– Source: reaction of atmospheric O2 and N2 at very high temperatures (car engines, coal-burning power plants)

– Effects: creates secondary pollutants

• NO2 (nitrogen dioxide)

– Source: 2NO + O2 2NO2

– Effect: Aggravate respiratory systems, suppress plant growth; creates more secondary pollutants

• Both contribute to the formation of photochemical smog

• NO2reacts with water vapor to form nitric acid and nitrate salts which are forms of acid deposition

Sulfur compounds

• SO2 (sulfur dioxide)

– Sources: 2/3 from human activities (burning of S containing coal; oil refining; smelting of sulfide ores)

– Effects: Combines with water vapor in the atmosphere to make sulfuric acid, and sulfate (SO4

2-) particles• Acid deposition • Aggravate asthma• Reduce visibility

Particulates

• Suspended particulate matter (SPM)

• Sources: 38% from human activities (plowing, construction, unpaved roads, tobacco smoke, burning of coal, vehicle exhaust)

• Categories:– Fine (PM-10): diameter< 10μm– Ultrafine (PM-2.5): diameter< 2.5μm

• Effects: respiratory system aggravation; mutations, reproductive problems, cancer…

Tropospheric Ozone

• O3

• Source: VOCs + NOx + UV + heat O3 (and other stuff…to be discussed later)

• Major component of photochemical smog

• Effects: irritates respiratory system, aggravates diseases such as asthma and heart-related, damages plants, rubber, paint, and fabrics

Volatile organic compounds

• VOCs• Include methane (rice paddies, cows, landfills,

oil and natural gas wells), benzene, vinyl chloride, trichlorethylene (TCE) come from gasoline, plastics, industrial solvents, synthetic rubber, tobacco smoke

• Volatile because they spontaneously evaporate• Effects: long-term exposure can cause cancer,

short-term high dose exposure can cause dizziness, unconsciousness, and death

Urban special cases: smogs• Industrial smog

– Combo of sulfur dioxide, sulfuric acid droplets, ammonium sulfate salts (combo of sulfuric acid and ammonia), and carbon particulates.

• Photochemical smog– Mix of primary and secondary

pollutants formed when UV light catalyzes reactants between nitrous oxides and VOCs. One secondary pollutant is ozone.

www.climatechange.org

Photochemical smog details • Formation requires vehicles and sunlight• Morning commuter traffic releases large amounts of NOx and VOCs• UV radiation promotes a series of reactions, that result in more than 100 chemicals• Ozone is the most abundant• Warmer temperatures increase the rate of reaction• Amount of smog peaks at noon when the sun rays are strongest. They dissipate and fall to low/zero

after midnight. Cycle starts over again in the morning.• Cities exacerbate the problem due to the heat island effect.

Factors Influencing Levels of Outdoor Air Pollution

• Reductions occur due to:– settling out, precipitation, sea spray, winds, and

chemical reactions.

• Increases occur due to:– urban buildings (slow wind dispersal of pollutants)– mountains (trap polluted air)– high temperatures (promote photochemical

reactions)

Lichens: Atmospheric canaries in a coal mine

• Absorb air for photosynthesis and respiration.

• Are stationary and long-lived.• Different species are sensitive to

different pollutants.• May store pollutants in their tissues or

die if pollution is severe.• Old man’s beard: sicken or die in the

presence of too much SO2. Scientists can monitor the health as an inexpensive way to monitor pollution levels.

Not so fun fact: lichens in Scandinavia absorbed lots of radioactive outfall from the Chernobyl disaster. 70,000 reindeer that ate the lichens had to be euthanized due to radioactive poisoning.