Air Quality and Source Apportionment Flashcards
Meterorology plays a big part in air quality, which is shown by the 1950s smog in London
What caused the 1950s London ‘pea-souper’ Smog
There was calm conditions /low wind speed and low relative humidity
This resulted in SO₂ condensing onto clouds (only can happen at low humidity)
The SO₂ came from coal combustion (resulted in 4000 extra deaths)
From the deaths caused by the 1950s London smog, how did policy change
- clean air acts in 1956, 1963 and 1993
- Introduced smokeless zones, which resulted in decreased coal for domestic use and reduced use of coal containing SO₂
Was the 1956 Clean Air Act successful?
- Yes
- Concentrations of SO₂ and black smoke levels have continually decreased from the introduction of this policy
- New acts like NECD commitment 2010-2019 and NECD/Gothenburg commitment 2020-2029 have been implimented to keep SO₂levels low
SO₂ is found within diseal fuels
How is has regulation since 1994 onwards caused levels to decrease in these products?
- 1994: Sulphur limit of 500ppm (for on-road transport)
- 2006: Sulphur limit of 15ppm (for on-road trasport) known as ultra-low sulphur diseal
- 2007: Sulphur limit of 500ppm (for off-road functions) known as low sulphur diseal
Some shipping vessel still use bunker fuels (some as high as 50,000ppm of S)
How are they regulated?
There is a emission control area around international boarders, where smaller boats will trasport good to land
They are called Emission Control Areas (ECA) some extend 200 miles from international shores
A UK sulphur emission NAEI study in 2020 saw which activity to be the biggest contributor to sulphur emissions
Shipping trails to be the highest
Then followed by non-industrial combustion plants are second highest
How to UK levels of CO and SO₂ compare to levels recommended by EU limits
UK levels are hugely higher than recommended by EU limits
But the UK levels are relative low on a international scale
What has the trend of NO₂ levels looked like in the UK between 1990 and 2020
There has been a general decrease
There are multiple different types of Smog, for example the 1940s LA Smog
Describe how it occured?
- Driven by photochemical driven ozone formation due to vehicle emission
- Due to high emissions of VOCs and NO₂
- This resulted in lots of ozone forming in the troposphere
- (is an issue for lots of developing countries now)
Globally, how manny death a year are thought to be caused by air pollution
Up to 8 million deaths/yr
What effect can air pollution have on agriculture
- Reduces crop (wheat, rice, maize, soy) yeilds (up to 12% per yr globally)
- With an estimated cost of around £20 billion/yr
DEFRA is the UK government board for Environment, Food and Rural Affairs
What are the main 10 air pollutants they have identified
- SO₂
- NOx
- CO
- Ozone
- Particulate matter
- Lead
- Benzene
- 1,3-butadiene
- Polycyclic aromatic hydrocarbons (PAH)
- Ammonia
How is NO₂ formed and what is its lifetime
- Formed from high-temperature combustion in air (burning fuel) - vehicle engines, power generation etc
- Lifetime around 12hrs
NOx gases and ozone are highly related together, how?
- NO + O₃ → NO₂ + O₂
- NO₂ + sunlight → NO + O
- O + O₂ → O₃
What is the issue with NO₂ exposure
NO₂ exposure drives respiratory health effect
As we know, if a car was emitting NO from its exhaust, it would react with ozone to form NO₂
Which side of the road would you be least exposed to air pollution?
The air is circulated between the two buildings, so neither side of the road are you better off
What is the biggest source of NO₂ emissions in the UK
- Local road traffic (60%)
- With Car (diesel) being the biggest contributor to this (35%)
- Even though one may assume these emissions would be higher during rush hours, there is very little difference in concentrations across a day
What is the annual mean concentration of NO₂ within the UK and does this fall within UK and WHO guidlines
Average annual mean NO₂ concentration is 40μg/m³
This is below UK guidelines, however several roads have exceeded this, and local authorities get fined
UK limits however are almost 4x as high as WHO guidlines of 10μg/m³ annual mean
Across a 12hr mean, what does the typical profile for NO₂ look like for Roadside, Urban Background and Rural Background
Peaks at rush hour times
Urban background follows similar trend as roadside
In march 2020 the UK went into a national lockdown which was the removed in 2021
What effect did this have on the atmospheric levels of NO₂
In 2020 (red) there was a large decrease from the average annual mean of NO₂
In 2021, when lockdown was removed, levels stayed below the average for the previous 2 years
These graphs show research data from 3 different field campaigns in London, Beijing and Delhi, with London being the only place where NO₂ meets UK and EU guidlines
Why are NO levels low during the day time?
Typcially there is a decrease in NO during the day which then rises at night
This is because during the day sunlight and ozone react with NO in the daytime which for NO₂
BUT there is no sharp rise in NO₂ as it is destructed to form more ozone
What is the difference in size between PM10, PM2.5 and PM0.1?
- PM10: 10μm = coarse particles
- PM2.5: 2.5μm = fine particles
- PM0.1: 0.1μm = ultrafine particle
Which is the most common size for particulate matter (not by weight)
PM0.1
Contribution to mass is small but >90% of particles in air is in UFP region
PM has a lifecycle and from it we can gain information from the size of the PM
What is the main stages of the lifecycle
- Dispersion, dilution (and cooling) (sec/min)
- Through nucleation and coagulation the particle will grow
- The majority of particles will end up staying in the accumulation mode
- The heavier a particle is however the more likely it is, to be depositied
What are some primary sources of PM
Natural: Marine, aerosol, volcanic, forest fires
Anthropogenic: transport, industry and power plants, agriculture, cooking
What are some secondary soruces of PM
NPF - photochemical reactions and condensation of semi-volatile organic compounds
There are now signals of health care products in the atmosphere
Why are they easier to identify
because their emissions are relatively low
What is the annual average mean PM10 and PM2.5 concentration in the UK, and it is within WHO guidlines
PM10 = 40μg/m³
PM2.5 = 20μg/m³
signficantly above WHO guidlines of 15μg/m³ and 5μg/m³ (these values are pretty much unachiveable)
Here is a graph for PM2.5 concentration
Explain the shape of the graph
- Urban back ground has a slight delay due to domestic emissions
Air from roadside being push to urban background via wind
Domestic emissions e.g. cooking etc
Here is a graph for PM2.5 pollution highlighting the impact of covid
Describe why in 2020 (purple) there was not a large decrease from 2017-2019 averages, like there was for NO₂
In 2020 there was a lot of pollution pushed from Eastern Europe due to parts of their industry still running during lockdown
This is why levels where higher in 2020 compared to 2021
Indicating solving air pollution is not just a national problem
Modelling result indicate the >90% of the global population is exposed to PM2.5 concentrations that exceed that 5μg/m³ guidelines
Why is this not potentially that bad?
Not all PM2.5 are harmful, could be due to saltwater, sand etc
However the quality of air in some places like Delhi is so bad it can shortern people lives
Is ozone a primary or secondary pollutant
Secondary pollutant
Formed in the atmosphere (not directly emitted)
Why is the formation of Ozone driven by meterology
clear weather can increase formation as the reaction is driven by sunlight
Volatile Organic Compounds (VOC) + NOx + Sunlight → Ozone
Why is tropospheric ozone levels hard to control
Because it is a secondary, transboundary pollutant
This means ozone can move about in the atmosphere, so no one nation could be responsible for its levels
(Hence the UK and WHO guildlines don’t really mean much and are high to reflect this)
If we had a really hot summer, what would happen to Ozone and NO levels?
The level of ozone should increase slightly, as it formation is catalysed by sunlight
Ozone can then go on to react with NO which will reduce the amount of NO
However it is a little bit more complicated than this
What happened to ozone levels due the 2020 pandemic
Ozone Conc increased in the pandemic due to lack of NO in the atmosphere
However westerly winds from the Atlantic push ozone away from the UK
Major chemical component composition of PM2.5 were collected during winter campaigns in London, Beijing and Delhi
With PM + nitrate being the biggest in London, PM + nitrate biggest in Beijing and PM+ elemental carbon being the biggest in Delhi
What does this show?
Major chemical compoents are very similar across 3 cities evwn though the overall level is different (but these major constituents do not reveal full information on the sources of PM)
But trace constituents are the detrimental parts of PM
What are the ways sources of PM be inferred
- Assessing local/regional emissions
- Determining air mass trajectories
- Meterorology
- Correlating chemical components
- Measuring close to source
What is one way you could determine the source of Air pollution
Through tagging the fuel
However, this is not always possible
Receptor Modelling for source apportionment uses air quality data to infer the sources responsible for measured air pollution levels
What are the two main approaches
1) Multivariate stastical methods
2) Chemical mass balance methods
Describe the Multivarate stastical method
It involves either PCA - principle component analysis or PMF - positive matrix factorisation
* No assumptions are made about sources
* quantitative identification of constitutents
* chemical profiles of sources
(can work out if compounds are correlated)
Describe the Chemical Mass Balance method
Uses chemical profiles of known sources as an input and fits chemical data with a best linear combination
Within Positive Maxtrix Factorisation
What is the F-Matrix and the G-Matrix
- F-Matrix: How many sources there are and what they look like (fingerprints, factors)
- G-Matrix: How abundant each fingerprint (or source) is in each sample
We can use ……. approaches to determine the sources of pollution
Receptor modelling
What are some important things to note about Postive Matrix Factorisation?
- What was (and what was NOT) measured?
- Careful planning of sampling experiments
- Were all pollutants measured in all samples?
- Are available datasets comparable/Compatible?
