1. ATS 621 Fall 2012
Lecture 13

2. Methane

3. Fate of peroxy radicals (HO2., RO2.)

5. The importance of NOx

7. Where are the net ozone production and destruction occurring
Where are the net ozone production and destruction occurring? (remote troposphere)
Model simulations of present day NOx and O3 distributions (Jacob, chapter 11)
From Jacob text: Ozone concentrations generally increase with altitude, mainly because of the lack of chemical loss in the upper troposphere (water vapor and hence HOx concentrations are low). Higher O3 concentrations are found in the northern than in the southern hemisphere, reflecting the abundance of NOx.

9. Oxidizing capacity of the troposphere
The anthropogenic influence on OH is complicated.
Increasing NOx and O3 act to increase OH, while increasing CO
and hydrocarbons act to deplete OH (section 11.3). Because CO
and CH4 have longer lifetimes than NOx and O3, their
anthropogenic enhancements are more evenly distributed in the
troposphere. It is thus found in the model that the net effect of
human activity is to increase OH in most of the lower troposphere
and to decrease OH in the upper troposphere and in the remote
southern hemisphere (Figure 11-6). There is compensation on the
global scale so that the global mean OH concentration as defined by
(11.5) decreases by only 7% since preindustrial times (other models
find decreases in the range 5-20%). The relative constancy of OH
since preindustrial times is remarkable in view of the several-fold
increases of NOx, CO, and CH4. There remain large uncertainties
in these model analyses. From the CH3CCl3 observational record,
which started in 1978, we do know that there has been no
significant global change in OH concentrations for the past 20
years.
[Jacob text]

10. Does NOx in remote ocean regions represent “clean, unperturbed background”?
Jacob text: NO, “Recycling of NOx through PAN maintains NOx concentrations in the range of pptv throughout the remote troposphere.”
PEROXYACETYLNITRATE (PAN)

12. DECOMPOSITION OF PAN LEADING TO OZONE PRODUCTION
Chemistry: Changing NOy speciation
Origin: Warm Conveyor Belt over Asia
ECMWF
Evolution: Split by blocking high pressure O3 H CO
Slide courtesy C. Heald
[Heald et al., 2004]

13. Formation of PAN
In smog: PAN is eye, lung irritant; damaging to plants

14. Alkane reaction mechanisms

15. Alkane reaction mechanisms, continued

17. Alkoxy radicals
Notice formation of carbonyls, which can photolyze

18. Alkene mechanisms

20. Aromatic mechanisms
Glyoxal & methylglyoxal common in aged, urban plumes

21. Building atmospheric chemical mechanisms

22. EXTRAS (slides courtesy Prof. Colette Heald)

24. CARBON MONOXIDE IN ATMOSPHERE
Source: incomplete combustion
Sink: oxidation by OH (lifetime of 2 months)

25. SATELLITE OBSERVATION OF CARBON MONOXIDE
MOPITT CO
(2000)

26. SATELLITE OBSERVATIONS OF BIOMASS FIRES (1997)

27. GLOBAL DISTRIBUTION OF CO NOAA/GMD surface air measurements

28. SPACE-BASED METHANE COLUMN OBSERVATIONS
by solar backscatter at nm

29. GLOBAL DISTRIBUTION OF METHANE NOAA/CMDL surface air measurements
Sink: oxidation by OH (lifetime of 10 years)

30. HISTORICAL TRENDS IN METHANE
The last 30 years
The last 1000 years

31. NOx EMISSIONS (Tg N yr-1) TO TROPOSPHERE
Zeldovich Mechanism: combustion and lightning
At high T (~2000K) oxygen thermolyzes:
O2  O + O
O + N2  NO + N
N + O2  NO + O
FOSSIL FUEL
23.1
AIRCRAFT
0.5
BIOFUEL
2.2
BIOMASS
BURNING
5.2
SOILS
5.1
LIGHTNING
5.8
STRATOSPHERE
0.2

32. LIGHTNING FLASHES SEEN FROM SPACE (2000)
DJF
JJA

33. USING SATELLITE OBSERVATIONS OF NO2 TO MONITOR NOx EMISSIONS
SCIAMACHY data. May-Oct 2004
(R.V. Martin, Dalhousie U.)
detection
limit

34. PAN NO3 N2O5 NO2 NO HNO3 NOX CYCLING hn Combustion lightning ~ 1 day
Example of PAN formation from acetaldehyde:
CH3CHO + OH  CH3CO + H2O
CH3CO + O2 + M  CH3C(O)OO + M
CH3C(O)OO+NO2 + M  CH3C(O)OONO2 + M
PAN
carbonyl
oxidation T
NO3 O3 O3 M O2 hn
N2O5
NO2 NO
Combustion
lightning
H2O
OH, M
HO2
HNO3 O3
~ 1 day

35. GLOBAL BUDGET OF TROPOSPHERIC OZONE
Chem prod in troposphere,
Tg y-1
4300
1600
Chem loss in troposphere,
4000
Transport from stratosphere,
400
Deposition,
700
Burden, Tg
360
230
Lifetime, days 28 42
Present-day
Preindustrial O2 hn O3
STRATOSPHERE
8-18 km
TROPOSPHERE hn
NO2 NO O3
hn, H2O OH
HO2
H2O2
Deposition
CO, VOC
NO+peroxy radicals is rate-limiting, so:

36. GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE
Climatology of observed ozone at 400 hPa in July from ozonesondes and MOZAIC aircraft (circles) and corresponding GEOS-Chem model results for 1997 (contours).
GEOS-Chem tropospheric
ozone columns for July 1997.
[Li et al., 2001]

37. 1996-2005 NOx EMISSION TREND SEEN FROM SPACE
[Van der A et al., 2008]

38. POWER PLANT EMISSION REDUCTIONS IN THE EASTERN US
Effects of NOx controls on large point sources in the Eastern US beginning in the late 1990s
Acid Rain Program, NOx SIP Call, NOx Budget Trading Program
Focus on coal-burning power plants
Improved burner technology, post-burner ammonia scrubbers
Northeast Urban Corridor
E(NOx) < 20% power plant
Ohio River Valley 1997
E(NOx) ~ 50% power plant
Ohio River Valley 2005
E(NOx) ~ 20% power plant
Courtesy: Greg Frost (NOAA)
[Kim et al., 2006]

39. POWER PLANT POINT SOURCES IN WESTERN US SEEN FROM SPACE
North Valmy
Intermountain
Hunter /
Huntington
Mohave
Navajo
Four Corners/
San Juan
Cholla/Coronado/ Springerville
Bonanza
Craig/Hayden
Jim Bridger/
Naughton
Dave Johnston/
Laramie River
Colstrip
Reid Gardener
Courtesy: Greg Frost (NOAA)
[Kim et al., 2009]