Atmospheric composition

What are primary aerosols?

- Natural

- 90% of aerosols

- Natural fires, volcanoes, salt crystals, etc

What are secondary aerosols?

- Transformation (bonding to form new substance)

- Coagulation (mix and combine/stick together)

- 10% of aerosols

- Sulfates, organic carbon, etc

What are the four effects of aerosols and why?

1. Cloud formation (condensation nuclei)

2. Visibility (more stuff to look through)

3. Precipitation (can allow water drops to get bigger)

4. Radiation (absorbs/reflects which changes temperatures)

How do aerosol concentrations vary with latitude?

- Northern hemisphere, more land

- Southern hemisphere more ocean

- Changes stuff found

- Higher concentrations in northern latitudes due to geography

How do aerosol concentrations vary with altitude?

- Decrease with increasing altitude

- Gravity, aerosols are heavy

- Condensation process, get captured as clouds form, generally low level

How do aerosol concentrations vary with seasons?

- Temperature variation

- Summer air is warmer, less dense, more space for other stuff, more mixing

- Salt water evaporates from oceans causing greater instability

- More moving air picking up more stuff from the ground

What are the differences in aerosol concentrations over land vs ocean surfaces?

Land = carbon-based, pollen, plant-based matter

Ocean = salt, some sand and land-based aerosols from wind, etc

Why is the ozone important in meteorology?

- Ozone effective at absorbing UV from solar radiation

- Heats the atmosphere

- Creates inversion layer (stratosphere)

- Inversion traps atmospheric mass in troposphere

How is ozone concentration measured?

- Dobson Units (DU)

- 1 DU = ozone molecules required to form layer of ozone 0.01mm thick at 0°C at sea-level pressure

How do ozone concentrations vary with altitude?

- Average thickness is 300 DU (approx 15ppm)

- Below 220 DU indicates weak/failing layer

- Winter is weaker

- Stronger in summer

- Ozone hole, not enough ozone but still some

How is ozone created and destroyed?

- Oxygen is split by sunlight into single oxygen atoms, these rejoin or form O3

- Near surface, forms if nitrogen oxide react with organic compounds

- It's destroyed when reacting to molecules with nitrogen, hydrogen, chlorine or bromine

Why is carbon dioxide important?

- Greenhouse gas

- Traps and absorbs terrestrial radiation

- Increases temperatures

- Stays in the atmosphere for a long time before it's circulated out

What is the current CO2 level and the trend?

430ppm

Gradually increasing by varying amounts over the years, some years more than others

Where does water vapour come from?

- Hydrologic cycle

- Evaporation

- Transpiration (photosynthesis)

- Condenses, forms clouds, moves over land and precipitates

- Residence time 7-10 days

- 0.25% of atmosphere

- State changes give off latent heat

How do water vapour concentrations vary with latitude?

- Increasing latitude decreases water vapour content

- Tropics has 1-5%

- Poles have 10ppm

How do water vapour concentrations vary with altitude?

- 50% concentration below 1.5km

- Less than 5% above 5km

- Less than 1% above 12km

- 3ppm in stratosphere

- Most in troposphere, it condenses before it can reach higher altitudes

How do water vapour concentrations vary with temperature?

- RH decreases in the day

- Temperatures naturally increase

- Warmer air has more space

How does water vapour content affect atmospheric density?

- Increasing water vapour content reduces atmospheric density

- Lighter molecular weight than oxygen and nitrogen

- Not super significant

Define diabatic process

- Open system

- Takes/gives energy to/from environment

- Substance changes state (phase) but not temperature

Define endothermic reaction

- Energy enters system

- Fuels change

- Prevents temperature decrease

Define exothermic reaction

- Energy released into environment

- Less needed in new state

- Prevents temperature increase

Why are phase changes endothermic? (6)

- Energy is required for phase change

- So temperature doesn't reduce

- Energy taken from environment

- Surroundings are cooled down

- Particles have enough energy to break bonds

- Enough energy to exist in the next state

Why are phase changes exothermic? (6)

- Energy given to environment

- Particles have too much energy

- Expelled so particles slow down

- Bonds are formed

- Temperature doesn't increase

- Surrounding temperature does increase

Which water phase changes are endothermic?

Melting (solid to liquid)

Evaporation (liquid to gas)

Sublimation (solid to gas)

Which water phase changes are exothermic?

Condensation (gas to liquid)

Freezing (liquid to solid)

Deposition (gas to solid)

Why are there different specific energy requirements for the phase changes?

Differences in energy requirements in regards to strength and number of molecular bonds to be broken or formed during the phase change

What is the specific energy requirement of melting/freezing?

334kj/kg

What is the specific energy requirement of evaporation/condensation?

2260kj/kg

What is the specific energy requirement of sublimation/deposition?

2834kj/kg

What is latent heat?

Energy released or absorbed during diabatic phase changes (hidden energy)

How do latent heat transfers affect the atmosphere?

- Changes temperature, therefore behaviour and weather

- When released into environment, warms it up, extra energy moves molecules more

- Removing latent heat, cools environment, molecules have less energy

What is conduction?

Transfer of heat due to touch

How does conduction affect the troposphere?

- Ground warms/cools air directly above it

- Small effect

- Moved throughout atmosphere from wind

- Brings cooler air in contact with hot surface

What is convection?

Vertical movement of air through the atmosphere

How does convection affect the troposphere?

- Air must be heated by conduction

- Air rises when heated

- Positively buoyant

- Heat transferred into upper troposphere

- Leads to thunderstorms developing

- Updrafts and downdrafts can form (creates convective current)

What is advection?

Horizontal movement of air (from changes in pressure - wind)

How does advection affect the troposphere?

- Conduction first

- Wind from sub-tropics as warm advection, high dew point, low clouds, poor vis, drizzle

- Worsened with frontal/orographic lifting

- Cold advection with southern oceans dry air, works with convection creating thunderstorms and showers

How do carbon dioxide concentrations change in the atmosphere?