Chem. 253

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Chem. 253 1/28 Lecture
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Introduction- Instructors Roy Dixon

• Educational Background in Environmental
  Analytical Chemistry
• My research in environmental chemistry has been
  in the following areas
• Cloud and Precipitation Chemistry
• Measurement of constituents of cloud droplets,
  rain and snow
• Effects of snow formation type on chemical
  composition
• Aerosol Composition and Tracer Measurement
• Bio- and Synthetic Fuel Testing

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Introduction

• Undergrad at UC-San Diego (B.S., Environmental
  Chemistry)
• Ph.D. in Analytical Chemistry at University of
  Washington
• Thesis Quantification of low level organic
  tracer of diesel exhaust in atmospheric
  particulate by HPLC-MS/MS
• Postdoc 1 University of Wisconsin
• Projects Source apportionment of atmospheric
  particulate in Asia, Europe, HPLC-ICP-MS for
  chlorinated Pt species
• Postdoc 2 UW-Tacoma/Center for Urban Waters
• Projects HPLC-MS/MS for pharmaceuticalspersonal
  care products in water as tracers of water
  quality, also PAHs in air
• At Sac State, continue quantifying water quality
  tracers, moving into agricultural runoff and
  stormwater tracers

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Introduction- Students

• Introduce yourself (name/degree plan)
• Is there anything specific you expect to get out
  of the class?

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Syllabus Instructors

• I will be teaching the first third (atmospheric
  chemistry) and last third (various topics) and
  Dr. Miller-Schulze will be covering the middle
  third (water chemistry and various compound
  classes)
• I will maintain a website through my individual
  website/Dr. Miller-Schulze will use Blackboard

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Syllabus Meeting/Exams

• In graduate classes, I will typically have a 10
  minute break in the middle of the lecture (with
  class ending at 810 instead)
• This may be skipped due to class assignment in
  middle of class period
• Exams 3 exams (one on each third no cumulative
  exam exam 3 is on day of final but will be as
  long as exams 1 and 2)
• Exams will involve qualitative and quantitative
  knowledge

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Syllabus Text/Exams/Reading

• Because of the single 2.5 block of time, we will
  try to have group activities in the middle of the
  lecture
• Exams 3 exams (one 1 hour on each third no
  cumulative exam exam 3 is on day of final)
• Exams will involve qualitative and quantitative
  knowledge
• Most of the information will come from the Baird
  and Cann text (with some supplementary readings
  made available)

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Syllabus- Course Overview

• The course is partially broken up by spheres
• Atmosphere
• Hydrosphere
• Lithosphere
• Others Biosphere
• We study chemistry in each regime
• Environmental Chemists can also study
• Natural (unperturbed) Systems
• Cause and Effect of Perturbations (e.g.
  pollution)
• Ways to Mitigate or Adapt to Perturbation

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Syllabus- Notes on Grading I

• Exams 84 of total (28 each)
• Homework (8 of total)
• Mostly assigned from book
• Some problems (e.g. review questions) are not
  graded
• Will randomly select one or two problems for
  grading must show work, not just answer

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Syllabus- Notes on Grading II

• In Class Group Assignments (8 of grade)
• - Goal is to increase in-class participation,
  break up a long lecture, and encourage learning
  by doing
• - Expect to have groups of 3 (could depend on
  class size), assigned by instructor, with
  different tasks assigned to each participant
• - Will work on problems, and then turn in
  results
• - New activity for me
• - Will start with an ungraded activity today

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Syllabus- Notes on Grading III

• Group Assignments (cont.)
• This is how the active learning exercises will
  work logistically
• There will be a class list available that gives
  the groups and roles for each worksheet
• Youll sit with your group (by number) and work
  on an Activity
• Groups will be of 3 (and some 2s or 4s
  depending on attendance, of students in class)
• One person in the group will be the calculator,
  one person will be the recorder, one person
  will be the manager

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Syllabus- Notes on Grading IV

• Group Assignments (cont.)
• Role Descriptions
• Calculator (C) This is the person who operates
  the calculator and performs all calculations
• Recorder (R) This is the only person who can
  write answers on the worksheet to be turned in at
  the end
• Manager (M) This is the person who manages the
  group. This is the only person who can ask me
  questions during the active learning time

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Typical Lectures(My part)

• Mostly by powerpoint (with some example
  calculations)
• Announcements in beginning
• Powerpoint slides will be made available on
  website
• Group activities will be in the middle (30 min)
• No break planned, but I could have a break before
  or following the group activity

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Homework Set 1

• To do before 1st Exam.
• Working on entire set, but
• Set 1.1 Ch. 1
• Problems 2, 4, 5
• Review Questions 1, 3-10
• Additional Problems 1, 5
• bold problems to be turned in next lecture
• Problems to be turned in should be worked on
  independently.

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Todays Topics

• Biogeochemical Cycles
• Introduction to Atmospheric Chemistry
• The Stratosphere
• Stratospheric Chemistry

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Biogeochemical Cycles

• Mostly not covered in text
• What is a Biogeochemical Cycle?
• If we can define different regions as spheres,
  we can define biogeochemical cycles as the set of
  spheres and the flow paths in and between
  different spheres
• Why am I covering them?
• They are very useful for putting problems in
  perspective
• Examples
• anthropogenic vs. natural sources
• reservoir vs. flux species

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Biogeochemical Cycles

• Familiar Example (that is in text)

Water Cycle a largely non-chemical
transformation cycle
Green Numbers are Amounts (Reservoirs)
Black Numbers are Fluxes (transport from one to
another reservoir)
Baird and Cann, p. 410
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Biogeochemical Cycles

• Can also use box and arrow approach
• Box models are among the simplest models
  describing cycling

atmosphere
Ice
oceans
Note atmosphere is nearly insignificant as
reservoir, but very important for fluxes
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Biogeochemical Cycles

• Another Example Sulfur Cycle

Pollution (e.g. burning S-containing coal)
significantly affects continental atmosphere
Although Sulfate is a major constituent of sea
water, marine biota emissions ((CH3)2S) is a
significant source of atmospheric S
Butcher et al., Global Biogeochemical Cycles
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Biogeochemical Cycles

• Carbon Cycle small fluxes (Fossil Fuel C) can
  put reservoirs out of balance due to quick
  cycling (in surface ocean and biota)

Butcher et al., Global Biogeochemical Cycles
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Biogeochemical Cycles

• Cycles covered are very general and dont cover a
  variety of pathways within boxes
• Additionally most spheres or boxes need to be
  subdivided due to differences in pathways

Butcher et al., Global Biogeochemical Cycles
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Biogeochemical Cycles

• Simple Modeling Math
• For a reservoir (mass M) with one source (Q) and
  one sink (S), at steady state
• dM/dt Q - S
• turnover time t M/S (how long it would take
  the reservoir to empty if the Q 0)
• A common sink is proportional to concentration
  (or reservoir mass, M) S kM and t M/S 1/k
• With S proportional to M, exponential decay is
  expected and t is also the e-folding time

Reservoir
S (flux out)
Q (source)
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Introduction to Atmospheric Chemistry

• Atmospheric Composition
• 78 nitrogen (N2) pretty inert
• 21 oxygen (O2) fairly inert in lower
  atmosphere
• 1 Ar
• Concentration units (for non-major species)
• parts per million by volume (ppmv)
• (nX/nair)106 (where n moles)
• partial pressures (atm, e.g. for Henrys law
  calculations)
• concentrations (molecules/cm3 for kinetic
  calculations)
• A well mixed gas (e.g. Ar) will have constant
  mixing ratio with altitude but a decreasing
  concentration

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Introduction to Atmospheric Chemistry

• Source of Oxygen
• Not a stable gas (metals, carbon like to be
  oxidized)
• Produced by biota (and then changed the
  atmosphere)
• Structure of Atmosphere
• Pressure decreases with height (as with other
  fluids)
• If the atmosphere is considered isothermal (it
  isnt), P Poe-Z/H (where P pressure, Po 1
  atm, Z height, and H 8 km)

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Introduction to Atmospheric Chemistry

• Structure of Atmosphere cont.
• The main gases are invisible to the light
  reaching the lower atmosphere
• Little direct solar heating occurs in the lower
  atmosphere
• Surface heating from sunlight creates less dense
  air (n/V P/RT), which rises and cools
  adiabatically
• This results in a general decrease in T with
  increase in Z (height above sea level).

Z (km)
T (C)
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Introduction to Atmospheric Chemistry

• Structure of Atmosphere cont.
• Exceptions to profile
• near ground at night (radiation cools surface
  faster than surrounding air why we can have
  frost at T gt 0C)
• In stratosphere (to be explained in more detail)

Z (km)
T (C)
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Introduction to Atmospheric Chemistry

• Atmospheric Layers
• highest layers (not covered here)
• stratosphere (12 to 48 km)
• troposphere (0 to 12 km)
• Stratosphere occurs due to change in lapse rate
  due to atmospheric heating from absorption of
  solar light
• Warmer stratosphere makes mixing with lower
  atmosphere very slow (hard to get cold
  tropospheric air to rise into warmer stratosphere)

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Stratospheric Chemistry
Z (km)
short UV

• The sun emits a full range of light
• Short UV light is absorbed by nearly all gases
• O2 absorbs light under 220 nm
• This generates heat (and the reversing of the
  lapse rate)
• some absorption results in photolysis
• O2 hn ? 2O

visible light
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Stratospheric Chemistry

• Prediction of efficacy of light for photolyzing
  bonds
• can compare Ephoton with Ebond
• when Ephoton gt Ebond, photolysis is possible
• Ephoton hc/l (note calculated per molecule
  while E is given per mole)

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Stratospheric Chemistry

• Ozone Formation Reaction
• O O2 M ? O3 M
• M is needed to remove excess energy (can write in
  more detail as
• O O2 ? O3
• and O3 M ? O3 M heat, where O3 refers to
  an excited state of O3)
• Ozone is generated where O can form (also is
  generated through separate tropospheric chemistry
  reactions)

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Stratospheric Chemistry

• Value of Ozone in the Stratosphere
• Ozone has weaker bonds than O2 and absorbs longer
  wavelength UV light
• Absorbs light effectively in the 220 to 290 nm
  range
• This protects life in the lower atmosphere
• Full Set of O only reactions
• O3 hn ? O2 O
• and O3 O ? 2O2 (odd O ending rxn)