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CivE221 > CivE221: Topic 6-Air Pollution > Flashcards

CivE221: Topic 6-Air Pollution Flashcards

(66 cards)

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1
Q

3 scales of air pollution

A

microscale, mesoscale, macroscale

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2
Q

microscale air pollution + examples

A

indoor/in the house:
- construction materials, wood, coal, gas buring
- bioaerosols (pathogens)
- inadequate ventilation
- radioactive materials (radon)

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3
Q

mesoscale air pollution + examples
- industrial and mobile sources

A

city scale/industrial

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4
Q

macroscale air pollution + examples

A

global:
- acid rain
- ozone depletion
- global warming

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5
Q

air pollution

A

chemicals added to the atmosphere by natural events or human activities in high enough concentrations to be harmful

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6
Q

types of air pollution

A

primary air pollution, secondary air pollution

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7
Q

primary air pollution + examples (3)

A

a harmful substance that is emitted directly into the atmosphere
- CO
- NOx
- SO2

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8
Q

secondary air pollution + examples (2)

A

a harmful substance that is formed in the atmosphere when a primary pollutant reacts with substances normally found in the atmosphere
- O3
- acid rain

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9
Q

Major Air pollutants (8)

A
  • CO
  • HAPs
  • Pb
  • NOx
  • Photochemical Oxidants
  • SOx
  • PM10
  • PM2.5
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10
Q

Carbon monoxide (CO) + why its bad + source

A

colourless, odorless gas. Lethal to humans.

Hemoglobin has greater affinity for CO than it does for oxygen, forming Carboxyhemoglobin. This deprives the body of oxygen.

incomplete oxidation of carbon

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11
Q

HAPs (hazardous air pollutants) dangers + examples + source

A

Knowledge comes from studies on the effects of chemicals on industrial workers. Often cause disease.

asbestos and arsenic cause cancer

industries, atmosphere (photolysis)

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12
Q

Lead (Pb) pollution dangers + source

A

accumulative pollutant which causes anemia and brain damage. Occurs as a particulate

automobile fuels (historically), volcanic activity, airborne soil, smelters and refining processes, incineration of lead containing wastes

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13
Q

NOx + source

A

responsible for the yellowish colour in air surrounding large cities

causes cough and irritation, as well as edema (fluid in lung)

bacterial activities in soil
combustion reaction in cars, power plants, and industrial sources

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14
Q

Photochemical oxidants + source + examples (2)

A

results in eye irritation and respiratory issues

secondary pollutant. The production rate depends on sunlight.

  • photochemical smog or O3 (ozone)
  • PANs
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15
Q

SOx + source

A

worsens respiratory symptoms for patients with bronchitis, asthma, lung irritation

natural: biological deay, volcanoes, oceans
anthropogenic: power plants, industries, oil refiners

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16
Q

anthropogenic

A

human

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17
Q

photochemical smog + chemicals contained within (4)

A

a type of smog produced when the sun’s UV rays react with NOx and VOCs in the atmosphere

  • HNO3
  • PANs
  • Aldehydes
  • Ozone
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18
Q

Most abundent chemical in photochemical smog + what it does

A

peroxyacetyl nitrates (PANs)

powerful respiratory and eye irritant

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19
Q

NAAQOs

A

advisory regulations for National Ambient Air Quality Objectives

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20
Q

CAAQS

A

legally binding regulations for ambient air quality standards

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21
Q

Most common micro air pollution (7) + source

A
  • CO: improperly operating furnaces, cigarettes
  • Radon: natural geologic or construction material
  • VOCs: paints, spirits, cleansers, pressed wood product
  • NO2: range-top burner, oven, pilot light, space heaters, gas dryer, cigarettes
  • Formaldehyde: pressed wood, insulation, textiles and combustion sources
  • Heavy metal: paint
  • Bioaerosol: bacteria, viruses, fungi, mites, pollen
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22
Q

Ozone context

A

located in upper atmosphere
protects Earth from 95% of UV radiation

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23
Q

Ozone depletion effects

A

issues with: human health, crop yieds, forest productivity, climate change, wildlife populations, air pollution, degredation of outdoor materials

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24
Q

Causes of Ozone depletion

A

CFCs - persistent chemicals that destroy the ozone layer

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25
Acid rain causes
SO2, NOx, and VOC react with water vapor and forms acid that returns to the surface as either dry or wet dposition
26
pH cutoff between regular rain and acid rain
5.6
27
Effects of acid rain
Natural world: depletes soil nutrients, forest decline and ecosystem damage anthrpogenic: accelerates concrete and metal corrosion, weakens infrastructure
28
Greenhouse gasses purpose
Greenhouse gasses trap some infrared radtion in the atmoshpher - if all heat escaped, Earth would be too cold - if too much is trapped, we get climate change
29
Global warming results (4)
- stronger infrastructre: designs must withstand extreme weather and flooding - material durability: heat affects concrete, steel and asphalt - rising water levels: roads and buildings need flood-resistant solutions - urban heat: require smarts designs to cool cities
30
Fundamental processes to remove or neutralize air pollution
- absorption - adsorption - combustion - selective Catalystic Reduction
31
absorption + most effective at removing what? + devices that utilize absorption
mass transfer from gas to liquid. 1. the contaminant gets dissolved into liquid using countercurrent flow 2. the liquid with the dissolved gasses is then treated or disposed of most effective at removing highly soluble gasses and particulates Scrubbers
32
scrubber tower types (3)
Plate tower, packed tower, spray chamber
33
plate tower vs. packed tower
- trays with froth enhance gas-liquid contact - effective for high gas flow rates with good mixing - higher pressure drop - uses packing material to increase surface area - more efficient with lower pressure drop - risk of channeling
34
adsorption + most effective at removing? + examples (4)
mass transfer from gas to solid contaminant is bonded to solid through either chemical (stronger chemical bonds) or physical (diffusion) interactions the absorbent may be regenerated (treated to remove contaminants and used again) most effective at removing organic gasses examples: - activated carbon - silica gel - activated alumina - molecular sieves
35
adsorption wave
the changing region where the majority of pollutant removal is take place. the waves leading edge moves as material close to the inlet becomes saturated
36
breakthrough curve + breakpoint
graphed curve of the adsorption wave. breakpoint: point at which conc. of pollutant in solid begins to rise steeply. Indicates adsorbent is approaching saturation
37
combustion methods to remove air pollution (2)
thermal combustion, catalytic combustion
38
thermal combustion + most effective at removing? + examples (3)
burn pollutants at high temp. in a direct flame most effective at removing organic gases (C and H - like CH3, C6H6, etc.) varnish cooking, meat smokehouses, paint-bake oven
39
catalytic combustion + most effect at removing? + examples (3)
a catalyst is place in beds the catalyst speeds up oxidation at a lower temperature most effective at removing organic gases printing-press, varnish cooking, asphalt oxidation
40
common catalysts for catalytic combustion
platinum or palladium
41
what do we need to watch out for with catalytic combustion
catalysts can be "poisoned" (deactivated) by sulfer or lead
42
when to use catalystic combustion vs. thermal
we use thermal when the self energy concentration of the pollutant if greater than 3.7MJ/m^3 and we use catalytic when the self energy concentration of the pollutant is less than 3.7 MJ/m^3
43
Selective Catalytic Control + used to remove? + examples (2)
Used to remove NOx. 1. anhydrous ammonia (reducing agent) is injected into the exhaust, upstream of a catalyst bed 2. in the presence of the catalyst bed, NOx is reduced to N2 power plants, industrial boilers
44
Specific technology used to remove particulate matter from air pollution sources (5_
- spray chamber - venturi scrubber - cyclone -filter/baghouse - electrostatic precipitator (ESP)
45
spray chamber + collection mechanism + process
(type of scrubber) mechanically removes particles through collision collection mechanism: inertial impaction of particles into water droplet Process: 1. polluted gas enters a chamber 2. nozzle spray a fine mist of liquid into chamber 3. inertia causes particulates to collide with water droplets 4. particle is captured by the water and removed from the gas 5. the water particles containing the pollutant settle and are drained from the spray chamber
46
spray chamber limitations
limitation water droplets are large enough to capture bigger aerosols but not fine ones
47
spray chamber applications
applications - sticky, wet, corrosive, or liquid particles explosive or combustible particles -simultaneous particle/gas remov
48
venturi scrubber process
1. polluted air is accelerated through a narrow throat where liquid is ontroduced 2. fine particles collide with atomitized (due to high speeds) water droplets and become trapped 3. gas stream then enters diverging section and speed decreases 4. the now polluted water droplets separate from the gas stream due to a cyclone (centrifugal force)
49
venturi scrubber collection method
inertial impaction of particles into water droplets
50
venturi scrubbers appplications
- phosphoric acid mist - open hearth steel (metal fume) - ferro-silicon furnace
51
cyclone
- can be used with or without scrubber - can use multiple in parallel for high gas volumes or for higher efficiency
52
cyclone collection method + most effective for?
centrifugal force carries particles to wall most effective for coarse dusts
53
cyclone applications
wood dust, paper fibers, buffing fibers
54
Filter types (2)
deep bed filter, bag house
55
deep bag filter purpose + example
for relatively clean gases and low volumes - filter in air conditioner
56
bag house materials
natural - cotton, wool synthetic - acetates, acrylics fiberglass - for higher temperatures
57
bag house process
as air enters the bag house, the air can easily pass through the fine holes, but the particulates cannot and either fall into the hopper of accumulate on the outside of the bags
58
methods to clean bag house + description
shaker - mechanically shake off dust cake reverse air - clean air is forced back through the bags in revers. the bags collapses slightly and release the dust pulse jet - bursts of compressed air cause a shockwave that travels dow nthe bags and dislodges dust
59
dust cake
build up of particulates on the outside of filters
60
bag house filter applications
- carbon black industry - cement crushing - feed and grain handling
61
electrostatic precipitator collection method
electrostatic forces
62
ESP cleaning methods
rapping plates - vibrations dislodge collected particles which then fall into a hopper
63
fly ash resistivity
the resistance to current flow
64
ESP applications
non-explosive: -fly ash - cement dust - iron/steel splinter possibly explosive: -electric power plant -portland cement kilns - blast furnace gas from metallugical processes - mist from acid production facilities
65
ESP process
1. a current is established between plates and wires (electrodes) 2. as the polluted gas passes through the wire and plate, it gets in the way of the electron path. This causes the ions to attach to the particulates, giving them a negative charge 3. the now negatively charged particles are attracted to the positively charged collecting electrode
66
regenerated
cleaned to be used again - particularly for adsorption

CivE221 (3 decks)

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