Goal of Atmospheric Chemistry

Home , Atmospheric chemistry

Understand the chemical and physical processes which control the amounts and distributions of atmospheric constituents.

1 Course Goals

This class will provide an introduction to fundamental aspects of atmospheric chemistry and so that you can:

•!Describe the workings of the atmosphere as a chemical reactor

•!Explain several important atmospheric phenomena from the molecular to the global scale

•!Critically evaluate and participate in public discussions of air pollution

Information about Course Level

•!this is a required course for ATMS majors

•!university-level chemistry helpful, not required

•!equivalent of 1 year university-level math and physics strongly recommended

•!high proficiency in algebra needed.

•!most important: curiosity and interest in quantitative problem solving

2 Course Related Activities

Lectures/Discussion Questions: For your benefit!

Problem Sets w/in-class discussion: 25% Graded as CR/NCR. Participation during discussion is included.

3 In-class Exams: 45%

Final exam: 30%

Extra Credit: Seminar attendance/write-up up to 5%

How to do well

•! Take the problem sets seriously, they are very similar to exam questions

•! Take notes: anything on the board is testable, lecture slides reinforce board

•! Read the textbook for broader perspective: Introduction to Atmospheric Chemistry, by D.J. Jacob, Princeton University Press, 1999. Can download pdf. Or available in bookstore. http://acmg.seas.harvard.edu/people/faculty/djj/book/index.html •! Study your notes and problem sets

3 Course Web Site

•! Link to website available via canvas: https://canvas.uw.edu/courses/813205

•! Most info available on class website: –! Announcements (changes in schedule, seminars of interest, etc) –! Problem set questions/solutions –! Electronic submission of problem sets –! Exam keys –! Weekly lecture visuals

Goal of Atmospheric Chemistry

Understand the chemical and physical processes which control the amounts and distributions of atmospheric constituents.

4 The Atmosphere Moves

NASA Visible Earth NASA Visible Earth http://visibleearth.nasa.gov/view_rec.php?id=6198 http://visibleearth.nasa.gov/view_rec.php?id=18564

NASA http://svs.gsfc.nasa.gov/vis/a000000/a002100/a002149/index.html

http://photojournal.jpl.nasa.gov/animation/PIA09936

Spatial and Temporal Scales of Change

Gases trapped in ice show changes over millenial and annual timescales.

Chemical change occurs on time scales ranging from <1 second to >millennia

5 StratosphericStratospheric Ozone Depletion Depletion

Air pollution

1948 – noontime (PA) 160 million people •! Complex regulatory issues •! Global chemistry and climate http://www.epa.gov/oar/oaqps/greenbk implications

Mexico City Beijing Los Angeles

6 Air Pollution Among Top Global Health Risks

How Do We Begin?

Describe the general physical characteristics mass, temperature, vertical extent, motions

Determine the major and minor components describe absolute and relative amounts

Develop a physical-chemical framework to: predict how a species evolves in time and space

Apply this framework to important problems

7 This Week/Today

READING: Chapter 1 of text

DUE Friday April 12: PROBLEM SET 1, will be posted on class web site on Friday

Note: No class on Friday this week (April 5)

•!Measures of Composition: •! Mixing Ratio •! Number Density •! Column Concentration •! Partial Pressure

Periodic Table of Elements

8 Average Composition of Atmosphere

Trace! gases!

Table 1.1 Textbook

Examples

•! How many molecules of “air” are there in 1 cm3 of this room?

Simple application of the Ideal gas law PV=NRT Number of molecules of air in 1 cm3= nair=Av!N=Av!PV/(RT) P = 1013.25 hPa = 101325 Pa V = 1 cm3 = 10-6 m3 T = 20C=273.15+20=293.15K R = 8.314 J/mol K Av=6.022 1023 molecules/mol 23 -6 nair= 6.022 10 !101325! 10 /(8.314!293.15) =2.5!1019 molecules

9 Examples

•! How many molecules of CO2 are there in 1 cm3 of this room given a mixing ratio of 390 ppm for CO2?

-6 nco2=nair!390!10 =9.75!1015 molecules

Column Concentration (molecules cm-2)

Proper measure for absorption or scattering of radiation by atmosphere

Io z = zt

2 A=1cm # of x in slab = nx(z)Adz dz

z = 0 I

Total # of molecules in column = nx

Divide both sides by unit area A to get…

2 Column concentration (units of molecules/cm ) = nx

10 Sunday’s Stratospheric Ozone Layer http://macuv.gsfc.nasa.gov/

1 “Dobson Unit (DU)” = 0.01 mm ozone at STP! standard temperature and pressure (STP): 1.013x105 Pa, 273.15K"

Examples

•! 1. How many molecules of “air” are there in 1 cm3 of this room?

•! 2. The ozone column over Seattle in March was about 400 DU. What is the corresponding column concentration?

11 Annual Mean Particulate Matter (PM)

EPA “Our Nation’s Air” Concentrations at U.S. Sites, 2008 document, 2008 PM2.5 (aerosol particles < 2.5 µm diameter) !

U.S. air quality standard:! PM2.5 = 15 µg m-3 ! (annual mean)!

Red and yellow circles indicate sites in violation of the standard! http://www.epa.gov/airtrends/2010/index.html

STANDARD IS EXPRESSED AS A MASS CONCENTRATION ! Total Mass of Particles PER UNIT VOLUME AIR!

Chemical Composition of PM2.5

EPA “Our Nation’s Air” document, 2008

12 Related Measures of Composition

Mixing Ratio" •!Constant w.r.t. changes in air density"

Number Density is proper measure for" nx •! calculation of reaction rates" •! optical properties of atmosphere" nX and CX are related by the ideal gas law:!

Av nx nair

Also deﬁne the mass concentration (g cm-3 of air):!

Not to be confused with the density of a substance (g cm-3 of substance)!

H2O Phase Diagram

PH2O,SAT(T)

From text Relative humidity (%) = 100(PH2O/PH2O,SAT)!

Dew point: Temperature Td such that PH2O = PH2O,SAT(Td)!