Topic 19: Air Pollution

Part 1

What is air pollution?• Definition• Natural sources: dust from wind

storms, soot and carcinogenic materials from forest fires and volcanoes, VOCs released by some plants

• Anthropogenic sources: burning of fossil fuels (power plants, factories, motor vehicles, home heating systems)

Types of pollutantsTwo broad categories:•Primary•Secondary

Figure 19-3Figure 19-3

The Major Players• Carbon oxides• Nitrogen oxides• Sulfur dioxide• Particulates• Volatile organic compounds (VOCs)

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

Acid Deposition

• What it is: fallout of sulfuric (H2SO4) and nitric acid (HNO3) as precipitation, or sulfate (SO4

2-) and nitrate (NO3

-) salts as particulate matter.

• Effects: – Ecosystems: changes pH of

soil and aquatic systems– Stuff: erodes statues and

stone buildings

Open Source

Types of acid deposition

• Wet deposition= rain, snow, fog, cloud vapor of pH 5.6 or lower

• Dry deposition= acidic particles like sulfate and nitrate salts

• Together they are acid deposition, or more commonly called acid rain (pH <5.6)

• Wet deposition tends to travel farther than dry.

Acid deposition: in-depth• Sources: power plants,

factories, smelting plants, vehicles

• Tall smokestacks reduce local pollution, but increase downwind pollution, sometimes 1000s of miles away (eg New England, from mid-west)

• Eastern US has precipitation of pH 4.4-4.7 on average. This is due to wind borne acidic compounds and urban areas with lots of vehicles.

www.sourcewatch.org

© Cornell University

Regional effects

• Ecological– Leaches nutrient ions from the soil– Releases (toxic) heavy metal ions bound to soil

particles into aqueous solution in the soil– Increases acidity (decreases pH) of water bodies to

fatal levels for animal life

• Human– Chronic respiratory diseases– Leach heavy metals into drinking water sources

• Bioaccumulation

– Damage to buildings, statues, metal finishes

Factors That Limit Organisms

• Organisms have a “range of tolerance” for numerous factors• pH, temperature, salinity, UV radiation, heavy metal

concentrations, etc…Figure 3-11Figure 3-11

Aquatic organisms and pH

• Where in the world is the most acidic precipitation?

• How can we prevent acid rain?

Asia (particularly China)

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.