Term Paper on the Troposphere | Atmosphere | Earth | Geography

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Term Paper on the Troposphere

Term Paper Contents:

1. Term Paper on the Introduction to Troposphere
2. Term Paper on the Troposphere and Temperature
3. Term Paper on the Troposphere and Weather
4. Term Paper on Tropospheric Ozone
5. Term Paper on the Formation of Troposphere
6. Term Paper on the Effects of Troposphere

Term Paper # 1. Introduction to the Troposphere:

The troposphere is the lowest portion of Earth’s atmosphere. It contains approximately 75% of the atmosphere’s mass and 99% of its water vapour and aerosols.

The average depth of the troposphere is approximately 17 km (11 mi) in the middle latitudes. It is deeper in the tropical regions, up to 20 km (12 mi), and shallower near the poles, at 7 km (4.3 mi) in summer, and indistinct in winter. The lowest part of the troposphere, where friction with the Earth’s surface influences air flow, is the planetary boundary layer. This layer is typically a few hundred meters to 2 km (1.2 mi) deep depending on the landform and time of day. The border between the troposphere and stratosphere, called the tropopause, is a temperature inversion.

The word troposphere derives from the Greek – tropos for “turning” or “mixing,” reflecting the fact that turbulent mixing plays an important we associate with day-to-day weather occur in the troposphere.

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Term Paper # 2. The Troposphere and Temperature:

The Earth’s surface – rocks, water, and vegetation – is heated by solar energy. This energy radiates back into the atmosphere as heat causing the air to be warmest at the Earth’s surface. The temperature of the air in the troposphere decreases with increasing distance from the Earth’s surface. The Earth’s surface acts like a heater in a cold room.

The further you get from the heater, the more the air temperature drops. The fact that air temperature decreases with an increase in altitude is most obvious in mountainous regions. On wet days it may be raining at the base of a mountain but snowing on top. This accounts for the fact that snow and ice persists on mountain peaks year round.

In fact, the air temperature decreases by an average of 6.5°C per km (3.6°F per 1,000 ft) above the Earth’s surface and temperatures as low as –60°C (–76°F) occur at the top of the troposphere.

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Term Paper # 3. The Troposphere and Weather:

The term troposphere is derived from the Greek, tropos, meaning “to mix” or “turn.” This is an accurate term in that the troposphere is the layer of the atmosphere in which atmospheric circulation occurs.

As warm air rises, it is replaced by denser, cooler air which in turn is heated by the warmth of the Earth’s surface and the cycle continues. As a result, the lowermost portion of the troposphere is in constant motion and it is this air motion that is responsible for the changing patterns of weather.

The uppermost part of the troposphere, however, is very stable and free of clouds. This makes it the perfect place for large commercial aircraft to fly. Frequent flyers know that air turbulence is most commonly felt during takeoff and climb to cruising altitude or during descent from cruising altitude for landing.

The fact of decreasing temperature with altitude is fundamental not only to weather patterns but also ensures the maintenance of water on our planet. As warm air rises, it cools and condenses to form clouds. The condensing water droplets within clouds grow larger until they reach a critical size and fall back to Earth as precipitation.

The cycle of condensation and precipitation prevents evaporating water from escaping the planet altogether.

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Term Paper # 4. Tropospheric Ozone:

Ozone (O₃) is a constituent of the troposphere (it is also an important constituent of certain regions of the stratosphere commonly known as the Ozone layer). Photochemical and chemical reactions involving it drive many of the chemical processes that occur in the atmosphere by day and by night. At abnormally high concentrations brought about by human activities (largely the combustion of fossil fuels, such as gasoline, diesel, etc.), it is a pollutant, and a constituent of smog.

Many highly energetic reactions produce it, ranging from combustion to photocopying. Often laser printers will have a smell of ozone, which in high concentrations is toxic. Ozone is a powerful oxidizing agent readily reacting with other chemical compounds to make many possibly toxic oxides.

The troposphere extends between 10 and 18 kilometers above the surface of the Earth and consists of many layers. Ozone is more concentrated above the mixing layer, or ground layer. Ground-level ozone, though less concentrated than ozone aloft, is more of a problem because of its health effects. Tropospheric ozone is a greenhouse gas and initiates the chemical removal of methane and other hydrocarbons from the atmosphere. Thus, its concentration affects how long these compounds remain in the air.

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Term Paper # 5. Formation of the Troposphere:

The majority of tropospheric ozone formation occurs when nitrogen oxides (NO_x), carbon monoxide (CO) and volatile organic compounds (VOCs), such as xylene, react in the atmosphere in the presence of sunlight. NO_x, CO, and VOCs are called ozone precursors. Motor vehicle exhaust, industrial emissions, and chemical solvents are the major anthropogenic sources of these chemicals. Another source is windshield washer fluid.

Although these precursors often originate in urban areas, winds can carry NO_x hundreds of kilometers, causing ozone formation to occur in less populated regions as well. Methane, a VOC whose atmospheric concentration has increased tremendously during the last century, contributes to ozone formation but on a global scale rather than in local or regional photochemical smog episodes. In situations where this exclusion of methane from the VOC group of substances is not obvious, the term Non-Methane VOC (NMVOC) is often used.

The chemical reactions involved in tropospheric ozone formation are a series of complex cycles in which carbon monoxide and VOCs are oxidised to water vapour and carbon dioxide. The reactions involved in this process are illustrated here with CO but similar reactions occur for VOC as well. Oxidation begins with the reaction of CO with the hydroxyl radical. The hydrogen atom formed by this reacts rapidly with oxygen to give a peroxy radical HO₂

OH + CO → H + CO₂

H + O₂ → HO₂

Peroxy radicals then go on to react with NO to give NO₂ which is photolysed to give atomic oxygen and through reaction with oxygen a molecule of ozone:

HO₂ + NO →  OH + NO₂

NO₂ + hi → NO + O

O + O₂ → O₃

The net effect of these reactions is:

CO + 2O₂ → CO₂ + O₃

This cycle involving HO_x and NO_x is terminated by the reaction of OH with NO₂ to form nitric acid or by the reaction of peroxy radicals with each other to form peroxides. The chemistry involving VOCs is much more complex but the same reaction of peroxy radicals oxidizing NO to NO₂ is the critical step leading to ozone formation.

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Term Paper # 6. Effects of the Troposphere:

Ozone is known to have the following health effects at concentrations common in urban air:

i. Irritation of the respiratory system, causing coughing, throat irritation, and/or an uncomfortable sensation in the chest.

ii. Reduced lung function, making it more difficult to breathe deeply and vigorously. Breathing may become more rapid and more shallow than normal, and a person’s ability to engage in vigorous activities may be limited.

iii. Aggravation of asthma. When ozone levels are high, more people with asthma have attacks that require a doctor’s attention or use of medication. One reason this happens is that ozone makes people more sensitive to allergens, which in turn trigger asthma attacks.

iv. Increased susceptibility to respiratory infections.

v. Inflammation and damage the lining of the lungs. Within a few days, the damaged cells are shed and replaced much like the skin peels after sunburn. Animal studies suggest that if this type of inflammation happens repeatedly over a long time period (months, years, a lifetime), lung tissue may become permanently scarred, resulting in permanent loss of lung function and a lower quality of life.

A statistical study of 95 large urban communities in the United States found significant association between ozone levels and premature death. The study estimated that a one-third reduction in urban ozone concentrations would save roughly 4000 lives per year.

Problem Areas:

The United States Environmental Protection Agency has developed an Air Quality index to help explain air pollution levels to the general public. 8-hour average ozone concentrations of 85 to 104 ppbv are described as “Unhealthy for Sensitive Groups”, 105 ppbv to 124 ppbv as “unhealthy” and 125 ppb to 404 ppb as “very unhealthy”. The EPA has designated over 300 counties of the United States, clustered around the most heavily populated areas (especially in California and the Northeast), as failing to comply with the National Ambient Air Quality Standards.