METR 3513: Section 1: Atmospheric Composition and Air Pollution

Comprehensive review flashcards covering major atmospheric components, light-air radiation interactions, primary and secondary air pollutants, atmospheric sinks, criteria EPA pollutants, and atmospheric layer structure.

What are the three main molecular gases that make up Earth's atmosphere, and what are their approximate volume percentages?

Nitrogen ($N_2$) at $78\%$, Oxygen ($O_2$) at $\sim 21\%$, and Argon ($Ar$) at $\sim 1\%$.

What are the primary sources and key processes responsible for atmospheric Nitrogen ($N_2$)?

Primary sources are volcanic outgassing and biological cycling. Early volcanoes released $NH_3$ and $N_2$, with UV radiation breaking down ammonia to leave stable $N_2$. Denitrifying bacteria in the nitrogen cycle continually return $N_2$ to the atmosphere.

What is the primary origin of atmospheric Argon ($^{40}Ar$)?

Radioactive decay of Potassium-40 ($^{40}K$) in Earth's crust and mantle, released through outgassing over geologic time.

How do molecular air gases ($N_2$, $O_2$) interact with sunlight, and what visible phenomenon does this produce?

They scatter ultraviolet and visible light through Rayleigh scattering, which causes the sky to appear blue.

What is the mathematical relationship between the intensity of Rayleigh scattering and the wavelength of light?

The amount of Rayleigh scattering is inversely proportional to the fourth power of the wavelength ($\lambda^{-4}$).

What is the definition of a trace gas in Earth's atmosphere?

Gases present in very small concentrations, making up less than $1\%$ of the atmosphere (excluding water vapor).

How do trace gases differ from greenhouse gases?

Trace gases are classified strictly by their low abundance ($<1\%$), whereas greenhouse gases are classified by their physical ability to absorb and re-emit infrared (thermal) radiation. Not all trace gases are greenhouse gases (e.g., Argon is a trace gas but not a greenhouse gas).

How do bright aerosols and dark aerosols differ in their main interaction with sunlight and their climate impact?

Bright aerosols (dust, ash, sea salt) primarily scatter sunlight, producing a net cooling effect. Dark aerosols (black carbon or soot) strongly absorb sunlight, producing a net warming effect.

What is the difference between primary pollutants and secondary pollutants?

Primary pollutants are emitted directly from a source into the air (e.g., $CO$, $SO_2$), whereas secondary pollutants form in the atmosphere through physical or chemical reactions (e.g., $O_3$, sulfates).

How are mobile sources of air pollution distinguished from stationary sources?

Mobile sources move from one location to another (e.g., cars, trucks, buses, aircraft), while stationary sources remain in a fixed location (e.g., power plants, factories, refineries).

What is the distinction between point sources and nonpoint sources of air pollution?

Point sources release emissions from a single, identifiable location (e.g., a factory smokestack or refinery flare), whereas nonpoint sources release emissions over a broad area without a single discharge point (e.g., urban traffic or agricultural fields).

What are the three main types of atmospheric sinks for removing pollutants?

1. Dry Deposition (direct transfer of gases or particles to surfaces)

2. Wet Deposition (removal by precipitation like rain, snow, or fog)

3. Chemical Sinks (chemical reactions transforming pollutants into other species)

Why is Carbon Monoxide ($CO$) toxic to human health?

$CO$ binds to hemoglobin approximately $200$ times more strongly than oxygen, reducing oxygen delivery throughout the body.

What chemical reaction represents the primary atmospheric sink for Carbon Monoxide ($CO$)?

Reaction with hydroxyl ($OH$) radicals: $CO + OH \rightarrow CO_2 + H$.

What is Nitrogen Dioxide ($NO_2$), and what are its primary sources?

It is a reddish-brown reactive gas in the $NO_x$ family produced mainly during high-temperature combustion in vehicles, power plants, and industrial operations.

What are the major environmental impacts of Sulfur Dioxide ($SO_2$) emissions?

Acid rain formation, damage to forests and vegetation, visibility reduction (haze), and acidification of lakes and streams.

What three components are required to form ground-level (tropospheric) ozone ($O_3$)?

Nitrogen oxides ($NO_x$), Volatile Organic Compounds ($VOCs$), and sunlight.

What are the primary human sources and main health impacts of Lead ($Pb$) pollution?

Primary sources include metal smelters, battery manufacturing, mining, and aviation gasoline; main health impacts include nervous system damage, developmental delays, and reduced IQ in children.

What is Particulate Matter ($PM_{2.5}$ and $PM_{10}$), and why is particle size critical for health?

Particulate matter consists of solid particles and liquid droplets suspended in air ($PM_{2.5} < 2.5\,\mu m$, $PM_{10} < 10\,\mu m$). Finer particles ($PM_{2.5}$) penetrate deeper into the lungs and bloodstream, causing cardiovascular disease, respiratory damage, and premature mortality.

What are the four reactions in the Chapman Mechanism (1930) for stratospheric ozone?

1. $O_2 + h\nu \rightarrow O + O$ ($\lambda < 240\,nm$)
2. $O + O_2 + M \rightarrow O_3 + M$
3. $O_3 + h\nu \rightarrow O_2 + O$ ($\lambda < 320\,nm$)
4. $O_3 + O \rightarrow 2O_2$

What are the key physical characteristics of the troposphere?

It contains $75\text{-}80\%$ of atmospheric mass, most water vapor, and nearly all weather. Temperature decreases with altitude, strong vertical mixing occurs, and it extends from $\sim 8\,km$ at the poles to $\sim 18\,km$ at the equator.

Why does temperature increase with altitude in the stratosphere?

Because stratospheric ozone absorbs harmful solar ultraviolet (UV) radiation, which heats the layer and creates a temperature inversion.

How is ozone distributed between the stratosphere and troposphere?

Approximately $90\%$ of atmospheric ozone resides in the stratosphere ('good ozone'), while approximately $10\%$ is located in the troposphere ('bad ozone').

How does Earth's atmospheric gas composition compare to Jupiter's?

Earth's atmosphere is composed primarily of Nitrogen ($78\%$) and Oxygen ($21\%$), whereas Jupiter's atmosphere is dominated by Hydrogen ($90\%$) and Helium ($10\%$).

A researcher observes a blue sky, infrared absorption by atmospheric gases, and reduced visibility caused by airborne particles. Which classification correctly links each observation to its dominant atmospheric component?

Molecular air scatters sunlight, trace gases absorb it, and aerosols scatter and absorb it

A monitoring team is evaluating atmospheric substances and finds elevated ozone and particulate matter alongside abundant nitrogen and oxygen. Which interpretation best applies?

A gas or particle becomes an air pollutant when its concentration becomes sufficiently high to cause harm

Point vs. Nonpoint sources

Point sources you can easily point at, nonpoint sources are many small sources spread out over an area

What’s a sink?

Any process that removes pollutants from the atmosphere

Dry Deposition

Direct transfer of particles or pollutants from the atmosphere to surfaces

Wet Deposition

Removal via precipitation

Chemical Sinks

Chemical reactions transform pollutants into other species

Transport

Movement of particles by wind or atmospheric circulations

What are the six major air pollutants per EPA criteria?

CO, NO2, SO2. O3, PM2.5 & PM10, Pb

Ground-level ozone concentrations are typically highest during:

Warm Sunny Afternoons

Draw and label nitrogen (N2)

2 nitrogen atoms connected with a single bond

Draw and label oxgyen (O2)

2 oxygen atoms connected with a double bond

Draw and label ozone (O3)

3 oxygen atoms, one in the middle connected to the other two with single bonds

Draw and label carbon dioxide (CO2)

one carbon atom bonded to two oxygen atoms with double bonds

Draw and label water vapor (H2O)

2 hydrogen atoms single-bonded to an oxygen atom in a bent shape

Draw and label methane (CH4)

one carbon atom in the center of 4 hydrogen atoms connected with single bonds

Greenhouse gas examples

Co2, CH4, H2O, and O3

Main sources of carbon dioxide (CO2)

respiration and fossil fuel combustion

Main sources of methane (CH4)

wetlands and livestock

Main source of ozone (O3)

photochemical reactions involving sunlight

main sources of dust

wind blown soil and deserts

Rayleigh scattering contributes to the blue color of the sky

True, air molecules preferentially scatter shorter wavelengths of visible light, especially blue light

Light extinction occurs through absorption and scattering.

True, light extinction occurs when light is removed from its original direction by absorption and scattering

most atmospheric aerosols interact through Mie scattering

True, aerosols are generally much larger than atmospheric molecules, so Mie scattering is an important way they interact with light

Black carbon doesn't absorb sunlight very strongly

False, black carbon strongly absorbs incoming solar radiation and can produce a warming effect

visible light spans

400-700nm

UVB wavelengths span

280-315nm

UVA wavelengths span

215-400nm

UVC wavelengths span

100-280nm

Aerosols interact with light through ___ and ___

scattering and absorption

Describe one warming effect of black carbon

Black carbon absorbs sunlight, converting the radiation into heat and warming the atmosphere.

what reaction forms ozone?

O + O2 -> O3

Why are trace gases important even though they occur in small concentrations?

Trace gases can have large effects on Earth's radiation balance and atmospheric chemistry even at low concentrations. Greenhouse gases such as CO₂, CH₄, H₂O, and O₃ absorb radiation and influence Earth's temperature. Some trace gases also participate in important chemical reactions.

How would Earth look different without atmospheric scattering?

Without atmospheric scattering, the sky would appear dark/black even during the daytime, because sunlight would not be scattered throughout the atmosphere into our line of sight. The Sun would still appear bright, but there would be no blue sky.

Ozone (O3) is a secondary pollutant

True, Ground-level ozone is formed through chemical reactions in the atmosphere, especially photochemical reactions involving sunlight.

What is an air pollutant?

An air pollutant is a substance in the atmosphere that can harm human health, ecosystems, materials, or the environment.

How is ground-level ozone formed?

Through photochemical reactions involving sunlight and precursor pollutants such as NOₓ and VOCs.

Water vapor is a greenhouse gas

True, water vapor absorbs infrared radiation and contributes significantly to the greenhouse effect

Photodissociation occurs when two molecules combine

False, photodissociation is when light energy breaks a molecule apart into smaller molecules or atoms

Rayleigh scattering is strongest when particles are much ___ than the wavelength of light

smaller

water vapor and carbon dioxide absorb ___ radiation

IR radiation

The process that breaks molecules apart using light is ___

photodissociation/photolysis

what is molecular air's main interaction with light?

rayleigh scattering

what is trace gases main interaction with light

primarily absorption of specific wavelengths

what is aerosols main interation with light

both scattering and absorption

Why is water vapor a greenhouse gas but oxygen isn't

Water vapor is a greenhouse gas because it absorbs infrared radiation emitted by Earth's surface. Oxygen (O₂) does not significantly absorb infrared radiation, so it is not a greenhouse gas.

Describe one cooling effect of bright aerosols

Bright aerosols can scatter incoming sunlight back to space, reducing the amount of solar energy reaching Earth's surface and producing a cooling effect.

What role does NO2 play in ozone formation?

NO₂ absorbs sunlight and photodissociates: NO₂ + sunlight → NO + O. The O atom then reacts with O₂ to form O₃: O + O₂ → O₃.

Compare Rayleigh and MIe scattering

Rayleigh → very small particles → molecules → blue sky
Mie → larger particles → aerosols → less wavelength-dependent scattering

What oxidant is often called the detergent of the atmosphere and removes CO and CH₄?

Hydroxyl radical (OH) which is a highly reactive atmospheric oxidant that helps remove pollutants and gases such as carbon monoxide (CO) and methane (CH₄).

How high does the troposphere extend at the poles?

8km

How high does the troposphere extend at the equator?

Approximately 18 km

What percentage of the atmosphere's mass is contained in the troposphere?

75-80%

What percentage of ozone is in the stratosphere

90%, 10% in troposphere