Lecture 3 Absorption physics and absorbing materials

Transcription

1 Lecture 3 Absorption physics and absorbing materials Collin Roesler 10 July 2017

2 Lecture Overview Overview of the electromagnetic spectrum What is absorption? What are the major absorbers in the ocean? How do we measure absorption in the ocean?

3 Electromagnetic Radiation Charged particles (dipoles) create electric fields E (oscillation between +,-)

4 Electromagnetic Radiation Charged particles, dipoles, create electric fields E (oscillation between +,-) When a charged particle moves, it creates a magnetic field, B (or H depending on book) The electromagnetic field oscillates as the energy propagates ExB (right hand rule) B B

5 Electromagnetic Radiation Charged particles, dipoles, create electric fields E (oscillation between +,-) When a charged particle moves, it creates a magnetic field, B (or H depending on book) The electromagnetic field oscillates as the energy propagates ExB (right hand rule) the range of oscillation frequencies is described by the EM spectrum

6 What is absorption? Since electromagnetic radiation is energy propagation, when materials absorb radiation, they absorb energy The energy associated with each part of the spectrum is given by E = hc/l What happens to the molecule depends upon the amount of energy, hence the wavelength

7 Interactions between energy and matter Photo-ionization molecular vibration Nuclear configuration Electron transition molecular rotation MICROWAVE

8 Quantized electronic states Amount of energy required to move an electron to another orbital shell (electronic state transition) is quantized A molecule can only absorb radiation of this specific quantized energy or wavelength This determines the absorption peak

9 Quantized vibrational states Each orbital shell is associated with a series of higher excited states, associated with vibrational energy, which are also quantized These determine the wavelengths of the absorption side peaks which are higher (lower) energy but have a lower probability for absorption

10 Quantized rotational states Each vibrational state is associated with a series of higher rotational states, which are also quantized These determine the wavelengths of the absorption that smooth the absorption peaks

11 Chlorophyll a has two electronic states associated with the energy equivalent of blue(443 nm) and red (676 nm) photons

12 Soret band Q-band Chlorophyll a

13 Rückmann et al 1999 Milenković et al. 2012

14 What are the major absorbers in the ocean?

15 Example of absorption spectra for three environments What do they have in common? All have strong red absorption How do they differ? Variable blue absorption

16 Absorption is a conservative property Total absorption = sum of individual absorbing constituents a Total = a water + Sa dissolved compounds + S a particles Absorption is proportional to the concentration (Beer s Law) a chl (m -1 ) = [chl](mg/m 3 ) * a * chl (m 2 /mg)

17 It is impractical to measure absorption spectrum for each absorber a T = a w + a CDOM + a f + a NAP Group components by their common absorption properties (an our inability to separate them operationally)

18 Absorbing Components: Water R. M. Pope and E. S. Fry 1997 Integrating cavity absorption meter Nice (but dated) compendium at

19 Absorbing Components: Water variations are methodological

20 Absorbing Components: Water Temperature 30 o C 5 o C Pegau and Zaneveld 1993 Limnol Oceanogr. natural variations Sullivan et al Appl Opt

21 Absorbing Components: Water Salinity Sullivan et al Appl Opt Pegau etal Appl.Opt. natural variations

22 Absorbing Components: Dissolved inorganic matter Basic for UV detection of nitrate, ISUS Johnson, K. S. and L. J. Coletti

23 Absorbing Components: Colored dissolved organic matter (CDOM) Dierssen et al Kirk

24 Absorbing Components: Colored dissolved organic matter (CDOM) a CDOM (l) = a CDOM (l o ) exp(-s CDOM (l-l o )) Kirk 1983 Carder et al L&O

25 Absorbing Components: Colored dissolved organic matter (CDOM) a CDOM (l) = a CDOM (l o ) exp(-s CDOM (l-l o )) Equatorial Pacific S=0.014 S S=0.011 Carder et al L&O Simeon et al JGR

26 Absorbing Components: Colored dissolved organic matter (CDOM) Roesler et al (global synthesis) Babin et al (European coastal waters)

27 Absorbing Components: Particles Methanol extraction Scan (a nap ) Scan (a p ) difference (a phyt ) Kishino et al. 1985

28 Absorbing Components: Phytoplankton Individual cells, microphotometry 1989 L&O

29 Roesler et al L&O Absorbing Components: Phytoplankton Species

30 Absorbing Components: Phytoplankton Pigment Packaging impact on absorption (1) vary size, maintain constant intracellular pigment concentration or (2) maintain size, vary intracellular pigment concentration Morel and Bricaud 1981 DSR

31 Absorbing Components: Phytoplankton Bricaud et al a* phyt (m 2 /mg chl) Babin et al a phyt (l) a phyt (440) Global Relationships

32 Absorbing Components: other protists ciliates and flagellates heterotrophic bacteria cytochrome 412 Morel and Ahn 1990 JMR

33 Absorbing Components: Non-algal particles a NAP (l) = a NAP (l o ) exp(-s NAP (l-l o )) Babin et al (European coastal waters) Roesler et al (global synthesis)

34 Absorbing Components: Non-algal particles what are they? Iturriaga and Siegel 1989 L&O JMR Photobleaching natural light levels

35 Absorbing Components: inorganic particles Babin and Stramski 2003 Patterson et al JGR

36 Absorbing Components: inorganic particles Measured spectra 2 nd Derivative used to quantify concentration of iron oxide minerals Estapa et al. 2012

37 To model the impacts of absorbing constituents add them up 0.8 absorption (m -1 ) Wavelength (nm) Which component dominates? - blue waters - green waters phytoplankton (V-type) inorganic particles (U-type) Morel and Prieur 1977

38 More on absorption Phytoplankton absorption Lecture tomorrow Measuring absorption Lecture tomorrow CDOM absorption methods Lab tomorrow Particulate absorption methods Lab Wednesday