CE 401Climate Change Science and Engineering

aerosols, carbon cycle31 January 2012

31 January 2012

on Thursday, class will be held in Sloan 242b – bring flash driveand be sure you can log in via a CEE login

HW 4 is due today

HW 5 is posted on the web – due Tuesday 2/7/2012

team assignments for CE 401

for Thursdayapproved choice of paper due 21 February

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 theradiative balance of the Earth system

• organic carbon, sulphate, nitrate, black carbon, dust, biomass burning

• indirect: mechanism by which aerosols modify the microphysical and hence theradiative 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{-}

where is the optical depth. AOD is a measure of incident light scattered or absorbed.

is prop to path lengthand extinction cross section

2003-2006average AOD

global aerosol distribution. Yellow = coarse particles like dust, red = fine particles like smokeor 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 – whiteclouds and map ofcloud droplet size where ship exhaustis mixed with cloudlayer, droplets are smaller

measurements of aerosolsfrom satellites and networksof 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

• 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 rocksand 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

compare these two figures some idea of the errors involved in the fluxes