06-620 / 09-532 Global Atmospheric Chemistry:
Fundamentals and Data Analysis Methods

9 Units

Short Description

Prerequisites

Objectives

The objective of this course is to expose graduate students or well prepared undergraduates with a strong background in mathematics and chemistry to a range of real world issues associated with atmospheric chemistry. The field cuts across several disciplines, including chemistry, meteorology, and radiative physics, all of which must be understood at a theoretical level, but all of which must also be integrated into an approach that allows one to pose answerable questions and test them with field observations. Thus, rather than going into great depth in a particular area, we will use rigorous but relatively simple examples that span these disciplines, first establishing the theoretical underpinnings of a each issue, then turning to archival data to directly examine them. A particular emphasis of the course will be to consider how to combine theoretical models, laboratory kinetics, and in-situ field observations into a manner that permits the direct testing of well-posed hypotheses about atmospheric chemistry.

In the process, students will acquire a collection of tools, each of which is extensible and potentially useful during the remainder of the students' research careers. These will include a perl-based chemical parser designed to facilitate the incorporation of arbitrary mechanisms into chemical solvers that uses standard chemical reaction notation as input, a series of simple models, including a 0-dimensional chemical box model, a 1-dimensional radiative transfer model, a small 2-dimensional global inverse model, and various data analysis packages providing access to archival atmospheric data.

The course will be organized as a series of 3 case studies, each of which will serve as a focus for a relatively broad-ranging discussion of associated issues. These cases will build on each other. The cases are: stratospheric ozone depletion, global tropospheric hydroxyl, and urban and regional ozone control. The unifying question of the course is this: We have learned a great deal from studying stratospheric chemistry about how to pose questions and convincingly demonstrate what chemical processes actually dominate a given situation -- how can we apply this knowledge to the far more complex problems of regional ozone and the coupling between aerosols and climate. I do not know the answer to this question.

Evaluation

Grades will be assigned based on 2 factors: adequate completion of a series of exercises connecting each lecture to the subsequent lecture (ie, homework exercise) and preparation of two projects. The final grade will be weighted, with 1/3 of the grade based on the homework exercises and 1/3 each based on the projects.

The exercises will involve integrating aspects of each lecture in preparation for a subsequent lecture -- thus they will be assigned at the end of each lecture when the following lecture is substantially related to the following one (approximately 2/3 or the time). Students must complete 2/3 or these assignments to receive a passing grade for the homework portion of the course. These assignments will be handed in at the beginning of each class, after which they will be discussed. Students may collaborate on completion of the assignments, and the material to be handed in will in general be quite brief. Collaborators should be identified on the submitted assignments.

The mid term project will involve applying some of the tools introduced in the first part of the course to a known problem, in essence reproducing the analysis behind a published paper. Several papers will be distributed as possible sources -- students may work with one of these or with a paper of their own choosing, provided it has been read and approved by the instructor.

The final project will consist of application of the tools and methods taught in the course to a real-world problem in atmospheric chemistry. The work need not be unique, but it should be new -- in other words, a review of existing work is necessary but not sufficient, but a re-analysis of data or a re-evaluation of a modeling problem in the context of this course would be acceptable. Again, collaborative work is permissible, but those intending to do so should consult with me before hand in order to arrange for individual evaluation. As a rule, collaborative projects should be divided into subsets controlled by individual students. A preliminary proposal for the final project should be submitted one week following the end of the second case study. Projects building on the mid-term project are allowed. 2 weeks before the due date a very rough description of initial results and the overall scope of the project will be handed in as a homework assignment.

There will be no text for the course. However, at least 2 lectures before each topic is presented, several journal articles or book chapters will be handed out as background reading. Lecture notes will in general be posted on the web in advance of each lecture.

Cases

1. Stratospheric Ozone Depletion

1. Chappman Cycle
   1. Basic Description of Odd-Oxygen Reactions
      1. Js provided as pure numbers at this point
      2. Pseudo-first order eigenvalue problem
      3. Discussion of timescales, steady-state, and chemical families
   2. Radiative transfer -- how do we get the photodissociation rates?
      1. Basic radiative transfer w/o scattering, 2-stream
      2. Overlap integrals, resolution, etc
      3. J vs altitude for O2, O3
   3. 1 Dimensional Steady state model, no mixing
      1. Find ozone profile
      2. Compare w/ observed profiles -- 5x too much
2. Catalysis
   1. Why was the simple model so far off?
   2. Concept of catalysis
   3. Introduce single catalytic cycle, ClOx
   4. Box model in upper stratosphere
      1. Perl based chemical parser
      2. Still steady-state iterator
      3. Key reactions, includes Cl + methane
   5. Chemical kinetics
      1. Arrhenius plots
      2. Non-linear least squares fitting
   6. Coupling of radical cycles, reservoirs, etc
3. Vertical transport in the atmosphere
   1. Continuity Equation
   2. Reynolds averaging and eddy diffusion
   3. 1-Dimensional diffusive model
4. Testing knowledge of chemistry
   1. Observing rates of rate limiting steps in catalytic cycles
   2. Taking partial derivatives with large datasets
5. The ozone hole and heterogeneous chemistry

2. Global OH and Methylchloroform

1. Chemistry in the global troposphere -- why do we care??
   1. Global methane cycle, greenhouse effect, and oxidative capacity
   2. Global tropospheric ozone
   3. Other RITS (radiatively important trace species)
2. Central role of OH -- what is global average distribution??
   1. HOx - NOx hydrocarbon oxidation cycle
   2. Factors controlling global distribution
3. Kalman Filter and Inverse theory -- extension of NLL Least Squares
   1. Formal presentation of inverse problem
   2. In context with 9 box atmospheric model
4. Real data -- AGAGE MeCl record and ways to estimate global OH
   1. Different ways to invert
      1. Global burden method
      2. Global trend method
5. Testing HOx control
   1. HOx data from ER2 in the troposphere
   2. Upper tropospheric HOx and the acetone? source
   3. GTE data from Bill Brune
6. What can influence global OH, and how?
   1. What goes up must come down -- sink = source

3. Urban and Regional Ozone

1. Basic ozone production chemistry extended from global picture
2. Isopleth idea, HC limited vs NOx limited conditions
3. How to control?
4. Local vs regional issues