Ozone, Theory and Mechanisms Behind its Formation

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Ozone, Theory and Mechanisms Behind its Formation
O2
O
O3

• Marcus Walter
• Dr. William Brune
• Penn State University
• SROP 2006

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Introduction

• What is Ozone
• Reactive gas, a part of the Earth atmosphere
• Two Classifications
• Good Ozone
• Forms in the stratosphere and blocks UV rays from
  the sun
• Bad Ozone
• Forms in the lowest part of the atmosphere,
  Troposphere and blocks UV rays from the sun
• Harmful to Humans, Crops, and other vegetation

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• Scientist have a basic theory for how bad ozone
  forms
• Nitric Oxide (NO) from combustion volatile
  organic compounds (VOCs) sunlight lead to the
  production of ozone
• There is a Problem
• Using this theory, the predicted and actual
  amounts of atmospheric ozone dont agree
• If scientists are able to learn all the
  mechanisms that produce ozone in the troposphere,
  possibly regulations can be put in place that
  will most effectively control the formation of
  ozone and other secondary pollutants

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Research

• Study the theory of Ozone formation in the
  troposphere
• Want to answer two main questions
• Is the theory on Ozone formation correct?
• Are there other mechanisms that form ozone?
• Will involve building an atmospheric chamber to
  perform controlled experiments
• Chamber will be used to verify the basic theory
  of ozone formation
• The chamber will simulate real atmospheric
  conditions
• Once the theory is verified, more complex systems
  with more reactants will be studied to search for
  unknown mechanisms that form ozone

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Theory of Ozone Balance

• Formed by the combo of atomic Oxygen and
  Molecular Oxygen
• (1) O O2 M? O3 M
• M is a third body that absorbs energy from the
  reaction
• Only Significant source of O in the troposphere
  is created from the photodissociation of NO2
• (2) NO2 hv ? NO O
• hv is the ultraviolet energy from the sun
• This NO formed reacts with O3
• (3) NO O3 ? O2 NO2

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Photostationary Steady State (PSS)

• With only reactions 1, 2, and 3, PSS occurs
• No change in concentration of O3, NO2, NO
• Reactions cause N and O to cycle between the
  gases but concentrations stay the same.
• In remote regions, PSS is valid in general
• In industrial areas, PSS gets a little out of
  balance

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Ozone Formation

• Reaction path that convert NO to NO2 without
  consuming O3 allows for O3 formation
• Path is created by hydrocarbons, specifically
  peroxy radicals
• Peroxy radicals are organic molecules chemically
  bonded to O2 (ex. CH3O2)
• Here are the reactions
• (4) RO2 NO ? NO2 RO
• (5) NO2 hv ? NO O
• (6) O O2 M ? O3 M
• _________________________
• (7) RO2 O2 hv ? RO O3
• (R CH3, C2H5, C3H7, )
• Other set of reactions the lead to ozone
  formation
• (8) OH RH ? RO2 HO2
• (9) OH CO O2 ? HO2 CO2
• (10) HO2 NO ? OH NO2
• NO2 then reacts and eventually forms ozone

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Environmental Chamber

• Used to simulate atmospheric conditions
• Made of various materials
• Black light surround the chamber
• Simple reaction will occur within the chamber to
  form ozone
• More complex reactions will be included to find
  unknown chemical reactions that form ozone

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PSS Experiment

• Chamber was filled with NO2 mixed with purified
  air (zero air)
• Allowed to come to a constant concentration in
  parts per billion
• UV lights were turned on, start of the breakdown
  of NO2 which eventually forms ozone, through
  reaction 1, 2, and 3
• Chamber is allowed to reach PSS

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Results

• Was not able to verify basic theory
• Caused by limited supplies
• Only able to do one run
• With the one run
• Data did not match theory
• Probably due to a number of things
• Impurities in zero air which entered the chamber
• O3 reacts with impurity thus lower O3
  concentration
• Gas escaping out the chamber
• O3 reacting with impurities on the walls of
  chamber

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Conclusion

• Results didnt match theory
• Next time do more runs
• Make sure the zero air is definitely purified air
• Increase thickness of the PFA to make sure no gas
  escapes out of the chamber

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References

• Seinfeld, John H. Urban Air Pollution State of
  the Science. Science, Volume 243, Issue 4892, pp.
  745-752, 1989
• Wallace, John M., Peter Hobbs. Atmospheric
  Science, an Introductory Survey, Second Edition,
  Academic Press 2006
• J. Timmerman, private communication, 2006
• A. R. Metcalf, A chamber study of photochemical
  oxidation processes in the atmosphere, M.S.
  Thesis, Pennsylvania State University, 2005
• www.epa.gov
• Dr. William Brune, Meteorology Professor, Penn
  State University
• Dr. Verlinde, Meteorology Professor, Penn State
  University
• William Ryan, Meteorology Professor, Penn State
  University

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Thanks

• Dr. William Brune, Meteorology Professor, Penn
  State University
• Amber Ortega, Undergraduate Meteorology Student,
  Penn State University
• Xingron Ren, Postdoctoral Student, Penn State
  University