Chem. 253 - PowerPoint PPT Presentation

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Chem. 253

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Title: Chem. 31 9/15 Lecture Author: RDixon Created Date: 9/14/2005 7:27:31 PM Document presentation format: On-screen Show (4:3) Company: CSUS – PowerPoint PPT presentation

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Title: Chem. 253


1
Chem. 253 1/28 Lecture
2
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

3
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

4
Introduction- Students
  • Introduce yourself (name/degree plan)
  • Is there anything specific you expect to get out
    of the class?

5
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

6
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

7
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)

8
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

9
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

10
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

11
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

12
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

13
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

14
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.

15
Todays Topics
  • Biogeochemical Cycles
  • Introduction to Atmospheric Chemistry
  • The Stratosphere
  • Stratospheric Chemistry

16
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

17
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
18
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
19
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
20
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
21
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
22
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)
23
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

24
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)

25
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)
26
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)
27
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)

28
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
29
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)

30
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)

31
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)
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