Week 4 - Air Pollution

Question 1

Definition of air pollution?

Answer 1

Air pollution is when a substance (an air pollutant) is present
in the atmosphere at higher than ambient (clean) levels and
produces significant effects on humans, animals, vegetation or
materials

Question 2

Typical effects of air pollution?

Answer 2

Foul odours, irritation of senses, sickness,
death, vegetation damage, damage to materials, obscuration of
visibility, adverse weather or climate changes

Question 3

What is an aerosol?

Answer 3

A liquid or solid particle (clump
of many molecules) suspended/dispersed in air- often a mixture of many components e.g. ammonium sulphate

Question 4

At what rate is CO2 rising ppm/year?

Answer 4

2.5ppm/year

Question 5

What are primary pollutants?

Answer 5

Pollutants that are directly emitted e.g.Soot, SO2

Question 6

What are secondary pollutants?

Answer 6

Form in-situ from precursors via chemical transformation

Question 7

Example of toxic aerosols linked to cancer?

Answer 7

Asbestos, mercury vapour

Question 8

Examples of aerosols that become toxic at sufficiently high levels?

Answer 8

CO and CO2

Question 9

What is the equation for ideal gas law?

Answer 9

pV=nRt or pV=NkT

Question 10

What is the Boltzmann constant (k)

Answer 10

The proportionality factor that relates the average relative thermal energy of particles in a gas with the
thermodynamic temperature of the gas.
k = 1.380649 × 10−23 J K−1

Question 11

What is the Avogadro constant (Na)

Answer 11

The number of constituent particles (usually molecules, atoms, — in general, entities) in a mole.
NA = 6.022 × 1023 molecules mol−1

Question 12

What is the Universal gas constant (R)

Answer 12

R = 8.314 J K−1 mol−1

Question 13

Equation for Mole Fraction (Cx)

Answer 13

Cx=moles of X/moles of air

Question 14

Equation for absolute concentration [X]

Answer 14

Cx=Molecules of X/Molecules of air

Question 15

Equation for mass fraction (wx)

Answer 15

Cx* molecular mass of X/molecular mass of dry (air)

Question 16

Equation of Mass concentration (μx)

Answer 16

μx= Wx* air density

Question 17

How do we analyse air samples taken directly?

Answer 17

• mass spectrometry – ionize and measure mass/charge ratio of fragments
• Fluorescence – e.g., excite sample with laser/UV and measure emitted photons
• Chemiluminescence – react sample with substance and measure fluorescence of products
• Gas chromatography – separate different molecules in air, then
• Electron capture detector – measure electronegativity of component
• Flame ionisation detector – add to flame and measure ionization

Question 18

How do we analyse air samples taken indirectly?

Answer 18

Expose something to air, that either responds to or absorbs the
air pollutant – diffusion tubes; lichens

Question 19

How do we analyse samples through remove sensing ?

Answer 19

Some AP molecules absorb solar/terrestrial radiation at
specific wavelengths – can use Sun/Earth as source

Question 20

3 stages of mass spectrometry

Answer 20

1. Ionisation
2. Quadruople filtration
3. Detector (Faraday cup)

Question 21

What happens during mass spectrometry- ionisation phase?

Answer 21

A heated filament accelerates electrons
towards analyte prior to source slit

Question 22

What happens during mass spectrometry- quadrupole filtration?

Answer 22

Each analyte should have a unique mass/charge ratio allowing it to be filtered by the quadrupole

Question 23

What happens during mass spectrometry- detector?

Answer 23

Each analyte should have a unique mass/charge ratio allowing it to be filtered by the quadrupole

Question 24

Process of gas chromatography?

Answer 24

Separates out different constituents of a gas mixture

Question 25

What is ECD- electron capture- useful for?

Answer 25

Good for detecting halogens (strong electronegativity)- CFCs

Question 26

What are FID (flame ionisation detectors) good for ?

Answer 26

Good for detecting organic compounds

Question 27

What is Chemiluminescence

Answer 27

Describes the process of fluorescence resulting from a chemical reaction. The chemiluminescent sampler for the measurement of NO2 relies on the reaction of NO with O3 to produce an ‘excited’ form of NO2. As the excited molecule returns to its ground state, fluorescent radiation is emitted, the intensity of which is proportional to the concentration of NO.

Question 28

Process of integrated sampling techniques

Answer 28

*Open plastic tubes – typically installed on a lamp-post * One end has reagent that absorbs NO2 * Amount absorbed depends on exposure time and amount of NO2 present. * Typically leave up for weeks/months – measures integrated (average) exposure * Cheap – can map area & trends over time * But low time resolution

Question 29

What is Wien’s displacement law?

Answer 29

Peak in emission from a blackbody with temperature T is at wavelength λ= 2897 / T

Question 30

What is the emissivity for a black body?

Answer 30

1 (1 for Sun and Earth)

Question 31

What radiation do most molecules possessing a charge asymmetry or dipole moment absorb?

Answer 31

IR radiation

Question 32

Beer-Lambert Law (Intensity)

Answer 32

I (λ)=Io(λ) exp(-α(λ)NL)

Question 33

Why are methane measurements useful?

Answer 33

The fine-line structure of methane absorption makes it ideally suited to specific measurements

Question 34

How do we resolve interference (e.e.g other gases- water vapour) during methane measurements?

Answer 34

High resolution to get high sensitivity measurements

Question 35

What defines the viewing geometry of a satellite measurement?

Answer 35

The solar zenith angle (𝜃) and the satellite viewing angle (𝜃v) determine the geometric air mass factor for the slant column path.

Question 36

What is the air mass factor in satellite methane retrievals?

Answer 36

It accounts for the slant column path of light traveling through the atmosphere and helps convert slant column measurements into vertical column values.

Question 37

How is the slant column converted to the vertical column in satellite measurements?

Answer 37

By dividing the slant column by the air mass factor, assuming uniform sampling of gas concentrations in the incident and reflected solar beams.

Question 38

Why is the assumption of uniform gas concentration valid for small pixel sizes?

Answer 38

Because variations in methane concentration within the pixel are minimal, reducing retrieval errors.

Question 39

What factors reduce the success rate of methane retrievals from satellites?

Answer 39

Cloud cover & aerosols Surface reflectivity variations Large pixel sizes causing methane concentration variability

Question 40

What are balloon platforms?

Answer 40

High-altitude observational systems used for scientific reseach, atmospheric monitoring and remote sensing

Question 41

Time scale- boundary layer mixing?

Answer 41

Minutes

Question 42

Mixing timescale - transport around mid-latitudes?

Answer 42

~ 2 weeks

Question 43

Mixing timescale - transport between hemispheres?

Answer 43

~1 year

Question 44

Mixing timescale- transport from surface to upper stratosphere ?

Answer 44

~5 years

Question 45

What are aerosols in atmospheric science?

Answer 45

Aerosols are tiny solid or liquid particles suspended in the air. They can be natural (like dust, sea salt, or pollen) or anthropogenic (like soot or sulfates from burning fossil fuels).

Question 46

What are secondary aerosols?

Answer 46

Formed in the atmosphere through chemical reactions of primary pollutants. Examples: Ozone (O₃), smog, peroxyacetyl nitrate (PAN), and acid rain (from SO₂ + NOx reactions).

Question 46

What are primary air pollutants?

Answer 46

rimary pollutants are directly emitted into the atmosphere from a source. Examples: Carbon monoxide (CO), sulfur dioxide (SO₂), soot

Question 46

What is meant by a species with a constant source and a first-order sink?

Answer 46

Continuously produced at a constant rate (e.g., from human emissions or natural sources), And removed from the atmosphere at a rate proportional to its concentration (a first-order sink).

Question 46

What is the mass balance equation in atmospheric chemistry?

Answer 46

dt/dC=S−kC

Question 47

What does the equation 𝜏=𝑚/𝐹out+𝐿+𝐷 represent?

Answer 47

t gives the characteristic lifetime (𝜏) of a species in a system with multiple sinks.