Introduction to Environmental Biophysics

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Introduction to Environmental Biophysics
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Introduction to Environmental Biophysics

• Study movement of mass and energy between living
  organisms and their environment

Environment
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Environmental Biophysics

• Combination of disciplines
• Engineering and physics
• Principles to calculate movement of energy and
  mass
• Science
• Principles to understand fundamentals of what is
  happening in systems

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Env. Biophys. As a Discipline

• My desk on which I now write, and the lock of my
  desk, are both exposed to the same temperature of
  the air, and have therefore the same degree of
  heat or cold yet if I lay my hand successively
  on the wood and on the metal, the latter feels
  much the coldest, not that it is really so, but
  being a better conductor, it more readily than
  the wood takes away and draws into itself the
  fire that was in my skin
• Benjamin Franklin, 1757

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More from Benjamin Franklin

• Damp winds, though not colder by the
  thermometer, give a more uneasy sensation of cold
  than dry ones. Because, to speak like an
  electrician, they conduct better that is, are
  better fitted to convey the heat away from our
  bodies.
• Benjamin Franklin, 1753
• Source Editors. Science Milestones. Windsor
  Press NY 1954.

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Environmental Biophysicists, All

• Fundamental understanding of environmental
  biophysics is basic to all of us
• Required at most for our survival
• Needed at least for our comfort
• Although we did not know it, we make decisions
  with this knowledge all the time
• Clothes
• Environment

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Heat and Mass Transport

• Heat and mass transport all around
• Virtually every interaction that we have
• Sight
• Reflect and emitted photons
• Photochemical reactions in the eyes
• Smell
• Fluxes of gases sensed by our olfactory sensors
• Also widely misinterpreted
• Benjamin Franklin and his desk
• Assume a temperature when things feel cold
• However, we only sense fluxes, not amounts

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Fluxes

• Flux Quantity per unit time
• Flux density Quantity per unit time per unit
  area
• Fluxes consist of two parts
• Concentration difference
• Conductance
• Ability of a substance to transport heat or mass
• Our opinion of concentration (i.e. temperature)
  is almost always influence by conductance

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Our Approach
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Principles of Energy Exchange

• Four modes of energy exchange
• Conduction
• Heat transfer by direct contact between two
  bodies
• Bare feet on a concrete floor
• Convection
• Heat or mass transport by fluid flow
• Wind blowing across warm soil surface
• Radiation
• Transfer of energy by photons (electromagnetic
  energy)
• Sun shining on plant leaf
• Latent Heat Flux
• Movement of heat by water changing states (liquid
  to vapor) (2450 kJ/kg-1)
• Person sweating while exercising

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Conservation of Energy and Mass

• Basic What goes in must go out or be stored in
  the system
• Ein Eout- EStored
• Neither energy or mass can be created or
  destroyed by any ordinary means

Energy Input
Energy Stored
Energy Output
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Ecosystem Energy Balance
Rn - Radiation
lE - Latent Heat Flux
H Sensible heat flux
M Energy Used by System (photosynthesis, ground
storage)
Energy Balance Rn M - lE H 0
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Continuity in Mass and Energy

• Movement of energy and mass are closely tied
• Solar radiation (energy) into a system will cause
  the movement of water (transpiration) and CO2
  (photosynthesis)
• For this class
• First consider the movement of each individually
• Then, combine together to describe the biosphere
• Mass and Energy can move from one part or scale
  to another

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Things to Consider

• Models
• Simple representations of complex phenomena
• Necessary to allow interpretation of data
• Creative application of models art of
  environmental biophysics
• Heterogeneity
• Systems are heterogeneous
• Much of what we will learn is where we can apply
  simplifications
• Albert Einstein Make everything as simple as
  possible, but not simpler

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Units

• Always use SI (Systeme International)
• Meter, kilogram, second
• Rules and exceptions
• Always remove prefixes from denominator
• 1.45 Mg/m3 not 1.45 g/cm3
• Use scientific notation
• 5.67 x 10-8 T-4 not 0.0000000567 T-4

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Units

• Rules and exceptions (continued)
• Watch significant digits
• If question has 3 significant digits, answer
  should too
• Early in semester, use oC (273.15o K)
• In radiation section, switch to Kelvin temp
• Notes
• Homework and quiz questions sometimes require
  assumptions
• Pay attention to learn where they can be used
• Carry units through problems
• Often will help to solve problem