CE 401 Climate Change Science and Engineering aerosols, carbon cycle 31 January 2012

1. CE 401 Climate Change Science and Engineering aerosols, carbon cycle 31 January 2012

2. 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

3. team assignments for CE 401 approved choice of paper due 21 February for Thursday

4. any questions from last time? radiative forcing, aerosols (will finish today)

5. aerosols: • physical properties • interactions with the atmosphere – direct/indirect • shapes and the models • optical depth • aerosol distributions • types of aerosols and lifetimes

6. 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

7. 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.

8. 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,

9. - 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

10. 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

13. MODIS 9 Oct 2010

14. average tropospheric aerosol lifetime at a week or less  can travel 1000’s of km

15. 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

16. measurements of aerosols from satellites and networks of instruments AERONET

17. 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!

18. outstanding issues in aerosol effects on climate change: • composition • optical absorption • impacts on surface radiation and heating • long term trends • total RF

19. global carbon cycle • importance • carbon dioxide and methane • how much remains in the atmosphere • carbon exchange – the cycle – reservoirs and fluxes • emissions

20. 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

21. CO2 and CH4

22. 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

23. HW 2 – change in annual CO2 in the atmosphere

26. source: IPCC 2007 The Climate System - very complicated

27. www.globalcarbonproject.org

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