4 Flashcards
Effects of air pollution
Health
Acidification
Eutrophication
Climate change
PRIMARY SOURCES of AIR POLLUTION
These are emitted directly into the atmosphere.
- SO2
- CO
- NOx
- SOx
- Particulates
- Hydrocarbons
- Metals
SECONDARY SOURCES of AIR POLLUTION
These pollutants are formed in the atmosphere by chemical reactions either with water or by reaction with sunlight. These include:
- O3 (ozone)
- Other photochemical oxidants
- Oxidised hydrocarbons
UK Clean Air Strategy,
2019
Plans for dealing with all sources of air pollution, making our air healthier to breathe, protecting nature and boosting the economy
UK Clean Air Strategy Aim, Emission targets for 5 key pollutants:
Aim to cut harm to human health by half.
Emission targets for 5 key pollutants:
* Fine particulate matter (PM 2.5
* Ammonia (NH 3
* Nitrogen oxides (NO x
* Sulphur dioxide (SO 2
* Non methane volatile organic compounds (NMVOCs)
What can we do on a personal level?
Reduce vehicle usage
Turn off your engine when parked or in traffic
Switch to electric vehicle
Reduce how much you burn in your home and garden
Insulate your home
Reduce number of deliveries needed
Reduce exposure by:
Opening windows when cleaning or doing DIY
Choose quieter routes when walking or cycling
Air pollution categories
Primary: Emitted directly into the atmosphere
e.g. particles from diesel engines
Secondary: Formed by reaction with atmosphere
e.g. sulphuric acid from sulphur
dioxide
Sources of industrial emissions
- Continuous:
Stacks
Chimneys
General ventilation
Vacuum pumps - Routine:
Equipment cleaning
Start up /shutdown
Materials handling - Irregular:
(The most difficult to control!)
Plant failure
Spillages
Leaks
Demolition
CRITERIA POLLUTANTS identified by the EC and WHO are:
- CO
- NO2
- O3 (Ozone)
- SO2
- PM-10 (particulate matter with diameter <10μm)
- Lead
CLIMATE CHANGE
Climate change is the long-term change in average weather conditions, including temperature, precipitation and wind.
PARIS AGREEMENT, 2015
Key elements:
*To limit global temperature increase to 1.5 C
*To limit GHG emissions by humans to the same levels that
trees, soil and oceans can absorb naturally (Net
*Achieve this between 2050 and 2100
*Rich countries to help poor
IMPACT OF AIR POLLUTION – BHOPAL DISASTER
The Bhopal gas tragedy is considered the world’s worst industrial disaster.
Over 500,000 people were exposed to methyl isocyanate Methyl isocyanate and other chemicals Long term health effects
These gases caused long term health effects:
- Eye damage – cataracts, corneal opacities
- Respiratory issues
- Neurological impairments
- Children’s health – many children of parents exposed have birth defects
UK Net zero targets
Requires UK to bring all greenhouse gas emissions
to net zero by 2050
First
First major economy to pass net zero emissions law
Part of the Climate Change Act
net zero meaning
Net zero means any emissions balanced by schemes to off
set equivalent amount of GHG from atmosphere
E.g. by planting, more trees, carbon capture and storage
Waste minimisation hierarchy
air pollution
Reduction at source: Efficient design
Recycling/reuse: Collection & Recycling
Treatment:
- Incineration
- Adsorption
- Absorption
Disposal: to air
Characterisation
so the emissions should be fully characterised for:
- Concentration
- Flow and Variation
- Physical Properties
- Chemical Properties
- Temperature & Pressure
REDUCTION AT SOURCE
Changing or eliminating a process that produces air pollution is often easier than trying to trap the effluent.
Change process
Change raw materials
Containment
Housekeeping
Air pollution treatment methods
Cooling
Cyclones
Filtration
Scrubbers
ESP
Flaring
Specific contaminant removal
Collection
Big challenge for mobile
sources
Process emissions from
stacks easier to collect
Impact of fugitive emissions
Cooling
For gases too hot for treatment
Cooling may drop below condensation point
Removes some particulates and
gases
Can produce liquid effluent
Cyclones
Very common for pre-cleaning
Use centrifugal forces to remove particles
Cheap to install
No moving parts
Small
Work best on large particles
Fabric filters
Operate like a vacuum cleaner
Removes particulates
Filter elements collect the dust
Removed periodically
Not suitable for high temperatures or wet gases
Solid residue reuse/disposal
Explosion risk
Wet collection
scrubbers
Examples are spray towers, venturi scrubbers, packed scrubbers
Effectively remove particles >
5 µm and some gaseous pollutants using water
Use a large amount of liquid
Not ideal where water supplies are limited
Expensive to construct and operate
Alternative liquids can be used to collect gaseous pollutants (absorption)
ELECTROSTATIC PRECIPITATORS
Electrostatic precipitators (ESP) are widely used to trap fine particulate matter in applications where a large volume of gas needs treatment and where a wet scrubber is not appropriate.
Adsorption
Effective for low concentrations
Several different techniques
available
Activated carbon, alumina, silica gel
Adsorption material has finite
capacity so needs regeneration /disposal
Adsorption – gas is contacted with a solid
Absorption – gas is contacted with a liquid
Incineration or flaring
Used
Used when a pollutant can be oxidised to CO 2 and water, or in oxidising H 2 S to SO 2
Catalytic combustion can allow for lower temperature flare
Common in oil and gas
Can be designed with no visible flame
Control of sulphur oxides (SO x)
Before
*Low sulphur fuel
During
*Fluidised bed combustion
*Gasification
After
*Flue gas de sulphurisation
Flue gas desulphurisation
Common treatment methods:
Largest source of SO2 is burning fossil fuels
Common treatment methods:
*Wet scrubbing with an alkaline
*Wet sulphuric acid process
*Dry sorbent injection
FGD may remove 95 % or more of SO 2
Control of nitrogen oxides (NOx)
Burner design (low NOx burners)
Low excess air
Recirculate flue gas
Inject water into combustion
chamber
Staged combustion
Inject ammonia
Control of VOCs and odour
Incineration or combustion is common for low concentrations
Catalysts achieve 95-99 % destruction of VOCs
Condensation and absorption used for high concentrations of VOCs
Odour treatments:
-Biofilters
-Ozone treatment
-Masking/neutralising
Control of CO2
CO2 produced by oxidation of organic compounds
Combustion
Respiration
Oxidative decay
Substitute fossil fuels with other fuels or energy providers
Carbon capture and storage (CCS)
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