Transcript aerosols
CE 401
Climate Change Science and Engineering
aerosols, carbon cycle
31 January 2012
31 January 2012
HW 4 is due today
HW 5 is posted on the web – due Tuesday 2/7/2012
on Thursday, class will be held in Sloan 242b – bring flash drive
and be sure you can log in via a CEE login
team assignments for CE 401
approved choice of paper due 21 February
for Thursday
any questions from last time?
radiative forcing, aerosols (will finish today)
aerosols:
• physical properties
• interactions with the atmosphere – direct/indirect
• shapes and the models
• optical depth
• aerosol distributions
• types of aerosols and lifetimes
aerosols:
• solid particles or liquid particles suspended in the air
• size: few nanometers to microns in size: x100 - 1000 variation in size
• have major impacts on climate
• physical properties: shape, size, chemical composition
• particles at the small end play a large role in cloud physics
• condensation nuclei for clouds
• EPA regulates particles in the US PM10 and PM2.5 – CEE 341, 415
• key aerosol groups:
• sulfates
• organic carbon
• black carbon
• nitrates
• mineral dust
• sea salt
• aerosols of clump together to form complex mixtures
• 90% of aerosols (by mass) are natural in origin
• about 10% of global aerosols are generated by human activity
• problems in dealing with aerosol effect: diversity in size, composition and origin;
spatial and temporal variability; source; injection height
• aerosols removed primarily through cloud processing and wet and dry deposition
aerosol RF effects are categorized into direct and indirect effects:
• direct: mechanism by which aerosols directly scatter and absorb radiation change in the
radiative balance of the Earth system
• organic carbon, sulphate, nitrate, black carbon, dust, biomass burning
• indirect: mechanism by which aerosols modify the microphysical and hence the
radiative properties, amount, and lifetimes of clouds
• size, shape, chemical composition, etc.
volcanic
pollen
sea salt
soot
fossil fuel combustion SO2 which reacts with H2O and gases to sulfate aerosols
biomass burning organic carbon and black carbon
transportation sector prolific producer of aerosols
aerosols are usually modeled as spherical in shape – do they look spherical??????
properties: shape, size, composition, chemistry, polarization, index of refraction, mass,
- aerosol optical depth is the fundamental measure of quantity and distribution of aerosols
- absorbance is proportional to
exp{-t}
where t is the optical depth. AOD is a measure of incident light scattered or absorbed.
2003-2006
average AOD
t
is prop to path length
and extinction cross section
global aerosol distribution. Yellow = coarse particles like dust, red = fine particles like smoke
or air pollution.
How do you compute light attenuation at a location from this picture???
MODIS data
MODIS 9 Oct 2010
average tropospheric aerosol lifetime at a week or less can travel 1000’s of km
indirect effects of aerosols: cloud formation and cooling
• aerosols play a critical role in cloud formation
• natural aerosols are most important
• but human produced aerosols have a significant impact
ship tracks – white
clouds and map of
cloud droplet size
where ship exhaust
is mixed with cloud
layer, droplets are
smaller
measurements of aerosols
from satellites and networks
of instruments
AERONET
NASA Global Hawk at Edwards AFB, CA
you guys ought to get involved in atmospheric studies – it is one heck of a lot of fun!
outstanding issues in aerosol effects on climate change:
• composition
• optical absorption
• impacts on surface radiation and heating
• long term trends
• total RF
global carbon cycle
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importance
carbon dioxide and methane
how much remains in the atmosphere
carbon exchange – the cycle – reservoirs and fluxes
emissions
• over millions of years, CO2 is removed from the atmosphere through weathering of rocks
and through burial in marine sediments of carbon fixed by marine plants
• burning fossil fuels returns carbon captured by plants in geologic history to the atmosphere
• current levels of CO2 are nearly 50% higher than in the past 700k yrs
• during glacial periods, CO2 removed from the atmosphere was stored in the oceans
• CO2 prior to 1750 was about 280 ppm and had been stable for ~ 10k yrs
• since 1750 the amount of CO2 in the atmosphere has increased ~ 40% from human activities
• fossil fuel combustion
• deforestation
• land use change
• biomass burning
• crop production
• conversion of grasslands to croplands
CO2 and CH4
• CO2 and CH4 play major roles in the natural cycle of carbon
• large flows of carbon among the ocean, terrestrial biosphere and atmosphere
• stable for past 10k yrs
• terrestrial plants capture CO2 from the atmosphere
• photosynthesis
• plant, soil, and animal respiration carbon to atmosphere
• CO2 is continuously exchanged between atmosphere and ocean
• CO2 entering ocean waters bicarbonate (HCO3-) and carbonate (CO32-) ions
• residence time of dissolved inorganic carbon in surface ~ 10 yrs
• intermediate depths circulate on decades to centuries time scale
• abyssal depths mix on millennial time scales
what are the fluxes of carbon between the atmosphere, biosphere, hydrosphere
HW 2 – change in annual CO2 in the atmosphere
source: IPCC 2007
The Climate System - very complicated
www.globalcarbonproject.org
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