Atmospheric Science and Air Pollution

Atmospheric Science and Air Pollution

• The atmosphere is a thin layer of gases surrounding Earth. It absorbs radiation, moderates climate and transports water and nutrients.
• Earth's atmosphere is composed of 78% nitrogen, 21% oxygen and 1% other gases.
• The four layers of the atmosphere differ in temperature, density and composition.
• Human activities significantly impact variable gases in the atmosphere.
• The troposphere is the lowest layer and is where weather occurs. Air is denser here than in upper layers. Temperature decreases with altitude and weather/vertical mixing of air occurs here. The tropopause acts as a cap limiting mixing between the troposphere and the layer above.
• The stratosphere is located above the troposphere at 11-50 km (approximately 7-31 mi) above sea level. It is drier and less dense and colder in the lower region. Little vertical mixing occurs here. The stratosphere contains ozone, which absorbs UV radiation.
• The mesosphere is above the stratosphere (50-80 km or 31-56 mi) above sea level. It has extremely low air pressure and temperatures.
• The thermosphere is the top layer that extends upward to 500 km (300 mi). Temperatures are warmer with increasing elevation.
• Atmospheric pressure is force per unit area produced by a column of air; directly related to density.
• Relative humidity is a measure of water vapor content in air (based on a ratio).
• Solar energy striking Earth (and temperature) is determined by earth's spatial relationship with the sun. Energy heats and moves air, thus influencing weather and climate.
• 70% of incoming solar energy is absorbed by the atmosphere and Earth's surface; remaining is reflected back to space. Solar radiation is greatest near the equator.
• Convective circulation: less dense, warmer air rises creating vertical currents. Rising air expands and cools. Cooler, denser air descends, replacing warmer air. This influences weather and climate.
• Large-scale circulation systems produce global climate patterns via Hadley and Ferrel cells and Polar cells.
• Thermal inversion: a layer of cool air beneath warmer air resists mixing. A common occurrence in valleys, impacting urban areas by trapping pollutants (e.g., Los Angeles, Okanagan and other mountain valleys).
• Urban heat island effect: Buildings, cars and pavements absorb and concentrate heat.

Central Case: "Apocalypse" in Beijing

• Beijing and other industrializing regions experience significant air quality concerns.
• Emission regulations still catch up with industrial and economic expansion (e.g., coal-fired power plants and more cars).
• Natural wind-blown dust from agricultural practices in neighboring areas worsens air quality.
• Wood-burning stoves contribute to air pollution.

Outdoor Air Pollution

• Air pollutants are gases and particulate material added to the atmosphere, affecting climate and harming people.
• Outdoor (ambient) air pollution has recently decreased in developed countries due to government policy and improved technologies. Developing countries still have significant problems.
• Natural sources include dust storms (westward across the Atlantic by trade winds), unsustainable agriculture, erosion, desertification, volcanoes and burning vegetation (forests).
• Point sources are specific locations where large quantities of pollutants are discharged (e.g., power plants, factories).
• Nonpoint sources are more diffuse, consisting of many small sources (e.g., automobiles).
• Primary pollutants are directly harmful and can react to form harmful substances (e.g., soot, carbon dioxide).
• Secondary pollutants form when primary pollutants react with constituents of the atmosphere (e.g., tropospheric ozone, sulfuric acid).

Environmental Legislation

• The Canadian Environmental Protection Act categorizes pollutants based on their potential threat to human health (criteria air contaminants).
• Persistent organic pollutants last a long time in the environment.
• Heavy metals, like mercury and lead, are harmful even in low concentrations.
• Toxic air pollutants cause cancer or neurological problems.

Government Agencies

• Federal agencies (e.g., Ministry of Environment & Climate Change) are responsible for international agreements (e.g., Montreal Protocol, Kyoto Protocol) and transboundary agreements.
• Provincial/territorial agencies manage air pollution through environmental ministries.
• Municipalities (e.g., Montreal and Greater Vancouver) may directly regulate pollution sources or raise public awareness.

Monitoring Pollution Trends

• Cleaner-burning vehicles, catalytic converters, permit-trading programs, clean coal technologies and scrubbers have reduced many forms of air pollution.
• Phaseout of leaded gasoline has also reduced pollution.

Smog

• Smog is unhealthy mixtures of air pollutants that often form over urban areas.
• Industrial smog is from coal and oil combustion. Photochemical smog is from light-driven reactions of primary pollutants and normal atmospheric compounds (reactions involve nitrogen oxide, hydrocarbons, water vapor, oxygen, nitrogen, oxygen atoms in presence of UV light). Morning traffic contributes to photochemical smog, sunlight promotes ozone production.

Acid Deposition

• Acid deposition is the deposition of acid or acid-forming pollutants from the atmosphere onto Earth's surface (e.g., acid rain).
• Acid rain originates from combustion of fossil fuels, releasing sulfur dioxide and nitrogen oxides.
• These react with water to form sulfuric and nitric acids.
• Acid deposition has wide-ranging effects on ecosystems and built environments including leaching nutrients from topsoil, altering soil chemistry harming plants, damaging forests in proximity to deposition sites, mobilizing toxic metal ions, running off into surface waters, and corroding structures.
• The historic Inco superstack helped reduce SO2 emissions by 90%, but nitrate emissions and acidic nitrate precipitation remain high.

Stratospheric Ozone Depletion

• Ozone (O3) in the lower stratosphere blocks incoming damaging UV radiation.
• Chlorofluorocarbons (CFCs) attack stratospheric ozone.
• CFCs were used in refrigerators and aerosols during the 1970s.
• Ozone depletion created a hole over Antarctica.
• The Montreal Protocol (1987) cut CFC production in half and follow-up agreements reduced CFC production by 95%, leading to a recovery of the ozone layer.

Indoor Air Pollution

• Indoor air contains higher concentrations of pollutants than outdoor air.
• Indoor air pollution is a significant health threat, causing 11,000 deaths per day (North America, at least 90% of time indoors, exposed to synthetic materials, cleaning fluids, plastics and chemically treated wood).
• In developing countries, indoor air pollution arises from burning wood, charcoal, dung and crop wastes (for cooking and eating), and leads to health issues. Radon gas is the second leading cause of lung cancer in industrializes countries.
• Reducing indoor air pollution involves using low-toxicity materials, monitoring air quality, keeping rooms clean and limiting chemical exposure in developed countries. In developing countries, improved methods are needed.

Overall Conclusions

• Some success has been achieved in addressing outdoor air pollution, especially in developed countries.
• There is still work required in developing nations and for better control of acidic deposition, photochemical smog.
• The long lifespan of some contaminants means the full scope of impact is not yet understood. The precautionary principle is essential.
• Both outdoor and indoor air pollution pose serious health threats.