Atmospheric 2 Flashcards
trace gas transport depends on
on
advection and
turbulent mixing
how can atmospheric movement be defined as ?
▪ Time-integrated transport
can be approximated by a
set of convection “cells”
▪ Prevailing winds are
easterly in the tropics and
westerly in the
extratropics
– Meteorologists describe
wind direction in terms of
the origin of the air mass
(i.e., westerly = from the
west)
how are green house gases lost?
: reaction
with hydroxyl
radical
“Inverse modelling” or “topdown”
▪ Requires:
– Atmospheric measurements
– Atmospheric chemical
transport model
what does AGAGE network detect
– High-frequency
observations of nonCO2 GHGs
types of emission inference
– Global mass balance
– Point source emissions evaluation
➢ “Integrated mass enhancement”, satellite-based methods
➢ Gaussian dispersion models
Trend
= sources – sinks
Short-wave infrared (SWIR) satellites used
to detect …
solar backscatter More uniform sensitivity across atmospheric column
Thermal infrared (TIR) sensitive to
emission from higher in the atmosphere
characteristics of point emissions
Estimated that 60% of oil and gas
methane emissions from 10% of
the point sources
* A “heavy-tailed” distribution
* Do not emit continuously, i.e.
“episodic Short Duration, High Impact: , unpredictable
Mass balance
▪ Can infer flux by
considering mass of
GHG entering and
leaving airmass
Gaussian dispersion modelling
▪ Gases and particles are
dispersed by the wind
(advection) and turbulent, eddy-driven diffusion
▪ When averaged over time,
concentration downwind
resembles a Gaussian
distribution
Gaussian dispersion modelling
▪ Assumptions:
– Time averaged concentration (not instantaneous)
– Constant source strength and meteorological conditions
– Constant advection along x-axis (along mean direction of travel)
– Wind speed is much larger than diffusion along the x-axis
– No significant variations in topography
– The pollutant cannot penetrate the ground (total “reflection”)
black body
A black body is a theoretical
object that absorbs all
incoming electromagnetic
radiation
Stefan Boltzman law:
o Relationship between
temperature and total
energy radiated per unit
area per unit time:
Albedo
the fraction of
sunlight that is diffusively
reflected by a body
– 0 = black body (absorbs
everything)
– 1 = white body (reflects
everything)
earth as black body
At equilibrium, incoming and outgoing flux balance, T0 ~ 255K temperature will be lower
black body assumption
No Reflectivity: Earth would be darker, absorbing all visible and non-visible light. - albedo
No Atmospheric Effects: No scattering or greenhouse effects, making it colder than the real Earth.
Simplified Energy Balance: The model would not account for climate systems, cloud cover, or feedback mechanisms
slab problem
In the real atmosphere, GHGs aren’t arranged in a slab. They are distributed
throughout the atmosphere.
– Recall that pressure and density drop with altitude
▪ Infrared radiation is continually absorbed and reemitted, until density drops
sufficiently that photons can escape to space
global warming
As concentration increases, absorption
increases (α): broadening seen at
edges
▪ More wavelengths emit at lower
temperature: more heat “trapped”
▪ So, CO2 greenhouse effect not caused
by centre of absorption peak getting
stronger, but by broadening of the
peak
▪ Logarithmic dependence of radiative
forcing with concentration
Radiative properties:
– Must be able to absorb IR
– Is the absorption peak saturated?
-stability
Radiative forcing
▪ Radiative forcing is the net
change in energy balance
due to some imposed
perturbation
– Expressed in W m-2
Potential (GWP)
▪ GWP is the radiative
forcing due to a
pulse emission of a
GHG, integrated over
some time horizon,
compared to a pulse
of the same mass of
CO2
limiting to the GWP model
WP ▪ A pulse of CO2
leads to
a relatively constant
radiative forcing
▪ However, for short
-lived
GHGs (e.g., methane,
~10 year lifetime), the
pulse decays away
▪ Potentially misleading
response of
temperatures to
cumulative CO
2
