Unit 7 Beta

Atmospheric Pollution: the one-page sheet

7.1 Introduction to Air Pollution

Air pollutants are primary (released directly: CO, NOx, SO2, particulates, VOCs) or secondary (formed in the air: ozone near the ground, sulfuric and nitric acid). Coal burning is the main source of SO2 and mercury; hot combustion makes NOx; CO starves the blood of oxygen; PM2.5 reaches deep into the lungs. The Clean Air Act sets limits on six criteria pollutants.

A primary pollutant is released directly by a source (CO from a tailpipe). A secondary pollutant forms in the air from primary ones (ozone near the ground, sulfuric acid).
Coal burning releases CO2, SO2, particulates and metals such as mercury. Burning any fossil fuel at high temperature also makes NOx from nitrogen in the air.
CO keeps blood from carrying oxygen. PM2.5 reaches deep into the lungs. VOCs come from gasoline vapor, paints and solvents.
The Clean Air Act lets the EPA set limits for six criteria pollutants: CO, lead, NO2, ozone, particulate matter and SO2. Taking lead out of gasoline cut airborne lead sharply.

primary pollutants (CO, NOx, SO2, particulates, VOCs) leave the tailpipe or smokestack they react with one another and with oxygen and water secondary pollutants form: ozone near the ground, and sulfuric and nitric acid lungs, heart and blood are harmed, so the Clean Air Act sets limits on six criteria pollutants

primary pollutant: A pollutant released directly into the air by its source, such as carbon monoxide from a tailpipe or sulfur dioxide from a coal plant's smokestack.
secondary pollutant: A pollutant that forms in the air when primary pollutants react with each other, with oxygen, water or sunlight. Ozone near the ground and sulfuric acid are examples.
criteria pollutant: One of six common air pollutants the EPA sets national limits for under the Clean Air Act: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter and sulfur dioxide.
Clean Air Act: The main United States law on air pollution (1970, with later amendments). It lets the EPA set air quality standards for the criteria pollutants and limit what cars, power plants and factories release.
nitrogen oxides: NO and NO2, together written NOx. They form when nitrogen and oxygen in the air combine at the high temperatures of engines and power plants. NO2 is a brownish gas.
sulfur dioxide: SO2, a gas released mainly when coal and other sulfur-containing fuels burn. It irritates the airways and reacts in the air to form sulfuric acid.
carbon monoxide: CO, a colorless, odorless gas from incomplete burning of fuel. It binds to hemoglobin in the blood and reduces the oxygen the blood can carry.
particulate matter: Tiny solid or liquid particles in the air, such as soot, dust and smoke. PM10 are 10 micrometers or smaller; PM2.5 are 2.5 micrometers or smaller and reach deepest into the lungs.
volatile organic compound: A volatile organic compound: a carbon-based chemical that evaporates easily, such as gasoline vapor, paint fumes and solvents. Trees also release some VOCs.

7.2 Photochemical Smog

Photochemical smog is a mix of secondary pollutants, mainly ground-level ozone, made when nitrogen oxides and VOCs react in sunlight. NO from morning traffic becomes NO2; sunlight splits NO2, and the freed oxygen atom forms ozone, which VOCs help build up. Ozone peaks in the early afternoon on hot, sunny days, irritates lungs and damages plants, and falls after dark.

Photochemical smog forms when NOx and VOCs react in sunlight. Its main part is ground-level ozone, a secondary pollutant.
Through a day: NO peaks with morning traffic, NO2 about an hour later, and ozone in the early afternoon. Ozone falls after dark.
Smog is worst on hot, sunny, still days in cities with heavy traffic, and often downwind of them.
Ozone up in the stratosphere absorbs UV radiation. Ground-level ozone, the same molecule, harms lungs and plants.

NO and VOCs are released into the city air NO2 builds up, peaking about an hour after the rush the oxygen atom joins O2 to form ozone (O3) ozone accumulates and peaks in mid-afternoon airways are irritated, asthma attacks rise, and crops and leaves are damaged

photochemical smog: A brownish mix of secondary pollutants, mainly ground-level ozone, formed when nitrogen oxides and volatile organic compounds react in sunlight. It is worst on hot, sunny afternoons in cities with heavy traffic.
ground-level ozone: Ozone (O3) in the lowest layer of the atmosphere, where people breathe. It forms when sunlight splits NO2 and the freed oxygen atom joins O2. It irritates lungs and damages plants.

7.3 Thermal Inversion

A thermal inversion is a layer of warm air over cooler air near the ground, the reverse of the normal pattern. The cool, dense air cannot rise through the warm layer, so smoke, exhaust and particles build up near the ground. Inversions form on clear, calm nights and winter mornings and in valleys and basins, and they break when the sun warms the ground or wind mixes the air.

Normally the lowest air is warmest near the ground and cools with height, so warm, polluted air can rise and spread out.
In a thermal inversion, a warm layer sits on top of cooler air near the ground. The cool, dense air cannot rise through it, so pollutants are trapped.
Inversions are most common on clear, calm nights and winter mornings, and in valleys and basins ringed by mountains.
Inversions do not make new pollution; they hold the pollution a place already makes. Deadly episodes such as London in 1952 combined an inversion with heavy coal smoke.

the air touching the ground cools, and in a valley cold air pools at the bottom temperature rises with height instead of falling: a thermal inversion it cannot rise, so smoke, exhaust and particles stay near the ground pollutant concentrations rise, and breathing problems increase the lowest air rises and mixes, and the inversion breaks up

thermal inversion: A layer of warm air sitting above cooler air near the ground, the reverse of the normal pattern in which air cools with height. The cool, dense air cannot rise through the warm layer, so pollutants are trapped near the ground.

7.4 Atmospheric CO2 and Particulates

Carbon dioxide and particulate matter have natural sources as well as human ones. Volcanoes, wildfires, respiration and decomposition release CO2, though human emissions are now about 100 times volcanic ones. Volcanic ash, wildfire smoke, desert dust, sea spray and pollen add particles. Particles scatter and absorb light, causing haze, and fine particles harm the lungs whatever their source.

Natural emissions of CO2 come from volcanoes, wildfires, respiration and decomposition. Today human activities release roughly 100 times more CO2 each year than volcanoes.
Natural particulate matter comes from volcanic ash, wildfire smoke, desert dust, sea salt spray and pollen. Human sources include burning fuel, construction and plowing.
Particles scatter and absorb light, which makes haze and lowers visibility.
PM2.5 harms the lungs and heart whatever its source, so smoke from a wildfire started by lightning is as dangerous as smoke from a fire people set.

CO2 enters the atmosphere without any human help natural particulate matter enters the air visibility falls and the sky looks hazy lung and heart problems rise, whether the particles are natural or human

natural emissions: Pollutants released by natural processes rather than people: CO2 from volcanoes, wildfires, respiration and decomposition, and particles from volcanic ash, desert dust, sea spray, pollen and smoke.
haze: A hazy, low-visibility sky caused by tiny particles in the air that scatter and absorb sunlight. Smoke, dust and pollution particles all cause haze.

7.5 Indoor Air Pollutants

Indoor air pollutants include radon from uranium in rock, formaldehyde and other VOCs off-gassed by new materials, carbon monoxide from poorly burning stoves and furnaces, asbestos fibers from disturbed old insulation, and smoke from cooking over open fires. Tight buildings trap them. Testing, ventilation, removing the source and CO detectors reduce the harm.

Radon is a radioactive gas from uranium decaying in rock and soil. It seeps through foundation cracks and is a leading cause of lung cancer. Test, then vent soil gas outside.
Formaldehyde and other VOCs off-gas from pressed wood, glues, carpets and paints, most strongly when new. Asbestos is dangerous when old insulation or tiles are disturbed.
Carbon monoxide comes from stoves, furnaces and generators that burn fuel incompletely; detectors save lives. Smoke from indoor cooking fires harms the most people worldwide.
Sick building syndrome: symptoms that ease when people leave a poorly ventilated building. Ventilation and source control are the main fixes.

less outdoor air comes in to dilute indoor pollutants radon, formaldehyde and other VOCs, carbon monoxide and asbestos fibers build up indoors exposure is long and steady lung cancer from radon and asbestos, poisoning from CO, irritation and sick building syndrome from VOCs

indoor air pollutant: A pollutant in the air inside a building, such as radon, formaldehyde, carbon monoxide, asbestos fibers or smoke from indoor stoves. Tight, poorly ventilated buildings let them build up.
radon: A colorless, odorless radioactive gas formed when uranium in rock and soil decays. It seeps into buildings through foundation cracks and is a leading cause of lung cancer.
asbestos: A fibrous mineral once used in insulation, tiles and pipe wrap. When it is damaged, its fibers get into the air and can cause lung disease and cancer if breathed in.
formaldehyde: A VOC given off by pressed-wood furniture, cabinets, glues and some fabrics, especially when new. It irritates the eyes, nose and throat and can cause cancer.
sick building syndrome: Sick building syndrome: headaches, eye irritation, coughing and tiredness that people feel in a particular building and that ease when they leave, usually from VOCs and poor ventilation.

7.6 Reduction of Air Pollutants

Air pollutants are cut by using cleaner fuel, burning it better, or capturing pollutants after burning. Scrubbers remove SO2; electrostatic precipitators and baghouse filters remove particles; catalytic converters change CO, NOx and hydrocarbons into less harmful gases; vapor recovery nozzles capture gasoline vapor. Laws such as emission caps and cap-and-trade programs make these cuts happen. None of the devices removes CO2.

Coal plants: scrubbers (wet or dry, often limestone) remove SO2; electrostatic precipitators and baghouse filters remove particles. Low-sulfur coal and fluidized bed combustion also cut SO2; cooler burning cuts NOx.
Cars: catalytic converters turn CO into CO2, NOx into N2, and hydrocarbons into CO2 and water. Vapor recovery nozzles capture gasoline vapor (VOCs) at the pump, not exhaust.
Policies: emission limits, cap-and-trade permits, fuel standards, tax credits for clean energy, and transit that cuts driving. A policy is a rule; a device is a technology.
None of these devices removes CO2. Cutting CO2 means burning less fossil fuel.

a plant or carmaker must cut its emissions the pollutant is prevented, changed, or captured less of each pollutant leaves the stack or tailpipe less smog, fewer acid-forming gases and fewer lung and heart problems

scrubber: A device on a smokestack that removes sulfur dioxide (and some particles) from exhaust. A wet scrubber sprays a mixture of water and limestone; the SO2 reacts and is captured as a solid.
catalytic converter: A device in a vehicle's exhaust system that uses metal catalysts to change carbon monoxide into CO2, nitrogen oxides into nitrogen gas, and unburned hydrocarbons into CO2 and water.
electrostatic precipitator: A device that removes particles from smokestack gas by giving them an electric charge and collecting them on plates with the opposite charge.
baghouse filter: A baghouse filter: a set of large fabric bags that smokestack gas is forced through, trapping particles the way a vacuum cleaner bag does.
vapor recovery nozzle: A vapor recovery nozzle: a gas pump nozzle that captures gasoline vapor (VOCs) pushed out of a car's tank during refueling and returns it to the station's storage tank.

7.7 Acid Rain

Acid deposition forms when sulfur dioxide and nitrogen oxides from power plants and vehicles react in the air to make sulfuric and nitric acid, which fall in rain, snow and fog or as dry particles, often far downwind. Each drop of 1 in pH is ten times more acidic. It acidifies lakes, harms fish and forests, and dissolves stone; limestone buffers it. Cutting SO2 and NOx raised rain pH.

Acid deposition forms from SO2 and NOx, not CO2, VOCs or particles. It falls as wet deposition (rain, snow, fog) and dry deposition (particles and gases).
Clean rain is about pH 5.6; acid rain is lower. Each drop of 1 in pH is 10 times more acidic.
Effects: acidic lakes with fewer fish, leached forest soils with toxic aluminum, and stone buildings (limestone, marble) that dissolve.
Buffering capacity: limestone soils and rock neutralize acid, so lakes on granite suffer most. Fixes: cut SO2 and NOx (scrubbers, cleaner fuels, cap and trade) and, short term, lime lakes.

the gases rise and travel with the wind, often hundreds of kilometers they form sulfuric acid and nitric acid, secondary pollutants acid deposition lowers the pH of soils and lakes trees weaken and aluminum washes into streams, where it harms fish gills fish eggs fail and many species disappear, unless limestone buffers the water

acid deposition: Acids that fall from the air in rain, snow or fog (wet deposition) or as dry particles and gases (dry deposition). It forms when sulfur dioxide and nitrogen oxides react in the air to make sulfuric and nitric acid. Often called acid rain.
buffering capacity: Buffering capacity: the ability of soil, rock or water to neutralize acid and resist a change in pH. Limestone gives lakes and soils a high buffering capacity; granite gives little.

7.8 Noise Pollution

Noise pollution is sound that harms people or wildlife because of its level or timing. It is measured in decibels, a logarithmic scale where each 10 dB is 10 times the intensity, and long exposure above about 85 dB damages hearing. Noise also raises stress in people and masks the sounds animals use to mate, feed and migrate. Barriers, quieter machines, slower ships, hearing protection and rules reduce it.

Noise pollution is sound at levels or times that harm people or wildlife. Sources: traffic, aircraft, construction, industry, ships and seismic surveys.
Sound is measured in decibels (dB), a logarithmic scale: each 10 dB is 10 times the intensity. Long exposure at or above 85 dB can damage hearing.
People: hearing loss, stress, poor sleep, high blood pressure. Wildlife: masked mating calls, disrupted migration and hunting, and stress, on land and in water.
Solutions: barrier walls, quieter equipment and pavement, slower ships, hearing protection, and rules on hours and zones.

noise reaches people and wildlife at high levels or at the wrong times hearing is damaged in people and animals mating, feeding and migration are disrupted populations near roads, airports and shipping lanes fall

noise pollution: Sound at levels or times that harm people or wildlife, for example from traffic, aircraft, construction, industry or ships. It can damage hearing, raise stress and disrupt animal communication and migration.
decibel: The unit (dB) for sound level. The scale is logarithmic: each increase of 10 dB is 10 times the sound intensity. Long exposure at or above about 85 dB can damage hearing.