Aerosols Flashcards by Rebecca Davies

Why is studying aerosols important for air quality and health?

-Exposure to particulate matter decreases life expectancy of every person by almost 1 year
-Life expectancy could be increased by ~2 years in most polluted cities if long term PM2.5 was decreased to EU WHO guideline level

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Why is studying aerosols important for visibility?

High aerosol concentrations can lead to visibility issues e.g. planes not being able to fly

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Why is studying aerosols important for climate?

Aerosols can have both a positive and negative radiative effect, but usually negative

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Why is studying aerosols important for fertilisation?

Aerosols fertilise land and oceans (leading to eutrophication)

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What questions should we be asking about climate change?

-how is the radiative balance of the Earth changing?
-how much of this is human caused?
-what are the impacts of this change?

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Where do the measurements for probability density function come from? (PDF vs radiative forcing graph)

From climate models

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How can the impact of aerosols be seen in history?

Red skies in paintings

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What is an aerosol?

A dispersion of solid and liquid particles suspended in gas

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What is the main characteristic of aerosols?

They are disperse

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What are monodisperse aerosols?

All the suspended particles have the same size

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Where do monodisperse aerosols come from?

Usually the lab

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What are polydisperse particles?

A wide range of particle sizes

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Where do polydisperse aerosols come from?

Usually natural, generated by several different mechanisms

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How is aerosol particle size defined?

Either by diameter D_p or radius R_p

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What measurements are aerosol diameters given in?

Microns or nm

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What is a micron in nm

1 micron = 1000nm

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What is 1nm in microns?

1 nm = 0.001 micron

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What is the range of sizes for aerosol diameter?

A few nm to tens of microns

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Why is there a very large range of particle masses

Mass of 1 micron particle equal to mass of 100nm particles

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Why do assume particles to be spherical?

To more easily measure particle diameter

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What are some natural aerosol sources?

Snow, salt spray, pollen, sand, dust

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What are some anthropogenic aerosol sources?

Smoke from burning fire, burning of fossil fuels, burning fuel/petrol

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What are externally mixed aerosol particles?

Where each particle is physically separated from the other components

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What are internally mixed aerosol particles?

A homogeneous material reflecting the chemical and physical average of the contributing components

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What are primary aerosols?

Aerosols emitted directly into the atmosphere

What are some natural sources of primary aerosols?

Volcanoes, forest fires, sea spray, wind borne dust

What is an anthropogenic source of primary aerosols

Fossil fuel burning

What is a secondary aerosol?

Aerosols produced from precursor gases

How are secondary aerosols formed?

Formed in the atmosphere through gas-to-particle conversion of both natural and anthropogenic gaseous precursors such as dimethyl sulphide

What are the four aerosol modes?

Nucleation, Aitkin, accumulation, coarse

Do aerosols have a short or long lifespan?

Short lifespan

What is the distribution of aerosols like?

Highly variable both temporally and spatially

What is the lifetime of aerosols in different parts of the atmosphere?

Few days to few weeks in boundary layer, up to 1 year in stratosphere

Why does dust have a longer lifespan than sea salt?

Because sea salt has a higher affinity for water so is more likely to become part of a cloud

What does AOT stand for?

Aerosol optical thickness

What does AOD stand for?

Aerosol optical depth

What are the peaks on aerosol size distribution graphs called?

Modes of aerosol size distribution

What is AOD related to?

Related to the amount of light that has been scattered or absorbed in a column through the atmosphere and depends on wavelength

What is the distribution of fine AOT like globally?

N. America and Europe: pollution S. America and Southern Africa: vegetation fires South and East Asia: pollution

What is the distribution of coarse AOT globally

Africa: coarse dust Southern Hemisphere: salt particles Middle east/ East Africa/ South Asia: desert dust

Why is it difficult to determine surface aerosol conc from current satellite instruments (4 points)

-they are sensitive to total column rather than surface conditions -most satellite instruments cant distinguish particles close to the ground from those high in the atmosphere -clouds tend to obscure the view of aerosols below -bright land surfaces e.g. snow, desert sand cane impair satellite retrievals

What suggested % of people breathe polluted air that exceeds WHO reccomended level of 10mg/cm³

Over 80%

What does N represent in aerosol data?

Aerosol particle concentration -defined as no. Particles per unit volume

What does PM₁₀ mean?

Mass of particles with D_p > 10 microns

What is the diameter of nucleation mode aerosols?

1-10nm

What is the diameter of Aitken mode aerosols?

10-100nm

What is the diameter of accumulation mode aerosols?

100-1000nm

What is the diameter of coarse mode aerosols?

1000-10000nm

Where are Aitken mode concentrations highest?

Over land regions with strong SO₂ emissions

What is the spatial distribution of accumulation mode related to?

Closely related to the anthropogenic emissions in the climate model

Where does coarse mode have the highest conc?

In regions of dust and sea salt particles

How do aerosol distributions vary?

Seasonally and regionally

What are aerosol modes tightly coupled with?

Aerosol formation pathways

What are aerosol size distributions controlled by?

Prevailing aerosol sources and sinks during transport

Why are physical properties of aerosols important to understand?

Important if we wish to describe in climate models how particles interact with clouds and radiation

What does cloud droplet number depend on? (3 things)

-particle numbers and sizes -cloud dynamics -particle chemical composition

What is DMPS and what is it used for?

DMPS=differential mobility particle sizer Used for measuring the aerosol size distribution

How can we compare models with different channel resolutions?

We can normalise by bin size

What is the number per cm3 of aerosols for urban environment?

10⁵ -10⁶ cm^-3

What is the number per cm3 of aerosols for rural continental environment?

2000-10000 cm^-3

What is the number per cm3 of aerosols for remote continental environment?

1000-10000 cm^-3

What is the number per cm3 of aerosols for marine environment?

100-400 cm^-3

What is the dominant source of aerosols for an urban environment?

Dominated by emissions Includes primary particulate emissions from industries, transport, power generation

What size aerosol particle dominates the urban environment

Dominated by ultra fine particle Dp <0.10 micron, but this varies depending on the proximity to sources and prevailing meteorology

What are the two main modes for mass distribution in urban environment?

Accumulation and coarse

What is the main source of rural continental aerosols?

Mainly natural with moderate anthropogenic influence

What are the dominating mass mode of aerosols for rural continental environment?

Coarse mode

What is the main source of aerosols in the remote continental environment?

Natural primary particles e.g. dust, pollens, secondary oxidation products

What are the two dominating modes for aerosol number?

Nucleation and accumulation

In rural continental environment, what do particles smaller than 2.5 microns consist of?

Sulfate, ammonium and organics

What is the main source of aerosols for marine environments?

Primary production or sea-salt aerosol particles from bubble-bursting from breaking waves

What is the main mode for Aerosol mass distribution for a marine environment?

Coarse mode

What causes the seasonal cycle in aerosols in marine environments?

Meteorology/biology (e.g. algae)

What is the main source of aerosol emissions in a desert environment?

Desert dust but strongly dependent on wind velocity

How do dust storms affect aerosol particles cross-continentally?

Individual dust storms can transfer smaller desert particles <10 microns from Africa over oceans to Amazon rainforest

Why is the accumulation mode of aerosols typically higher in free troposphere rather than lower troposphere?

No precipitation scavenging by clouds

What mode is often present in free troposphere environment and why?

Nucleation mode often present as conditions suitable for second age aerosol formation

What are the poles like in regards to aerosol conc

-Very low no. Conc -strong seasonal cycle in aerosol size distribution