Overhead Slides for Chapter 12, Part 2
of Fundamentals of Atmospheric Modeling
by Mark Z. Jacobson Department of Civil & Environmental Engineering Stanford University Stanford, CA 94305-4020 January 30, 2002 Alkene Reaction With Ozone
Ethene
H H O 37% C O + C O H H H H O C C + O Formaldehyde Criegee biradical 3 O O H H H H O* H2C CH2 63% C O + C O Ethene Ethene molozonide H H Formaldehyde Excited Criegee biradical (12.89) Criegee biradical reaction
+ NO H O H C O C O H H NO2 Criegee biradical Formaldehyde (12.90)
Excited criegee biradical decomposition
60% CO + H2O
H O* H C O C O 21% CO2 + H2 H H O * + O2 Excited Criegee Excited formic 19% CO + OH + HO2 biradical acid (12.91) Alkene Reaction With Ozone
Propene
H H3C O 7.5% C O + C O H H Formaldehyde Methyl criegee biradical
H H3C O* C O + C O 42.5% H H O H O O Formaldehyde Excited methyl criegee C CH + O biradical 2 3 H3C CH CH2 H3C H O H3C C O + C O 18.5% H H Propene Propene molozonide Acetaldehyde Criegee biradical H3C H O* 33.5% C O + C O H H Acetaldehyde Excited criegee biradical
(12.92) Alkene Reaction With Ozone
Methylcriegee biradical reaction
+ NO H3C O H3C C O C O H H NO2 Methyl criegee Acetaldehyde biradical (12.93)
Excited methylcriegee biradical decomposition
16% CH4 + CO2 H3C O* H3C C O C O 64% CH3 + CO + OH H H O * 20% CH3O + HO2 + CO Excited methyl criegee Excited acetic biradical acid (12.94) Alkene Reaction With Nitrate
Ethene --> nitrated organic radicals
O O O + NO O H H + NO3 O N + O2 O O N O O N C C H H H O O O H H C CH2 C CH2 C CH2 H H NO2 H Ethene Ethyl nitrate radical Ethylperoxy nitrate Ethoxy nitrate radical radical (12.95)
Propene --> nitrated organic radicals
O O O O + NO H H O O N O O N + NO3 H O N + O2 H H C C O C CH O C CH O C CH2 2 2 H3C H H C H3C H3C 3 NO2 Propene Propyl nitrate radical Propylperoxy nitrate Propoxy nitrate radical radical (12.96) Aromatic Reaction With Hydroxyl Radical
Toluene oxidation
CH2 H2C O O + OH + O2 Benzylperoxy 8% radical
H2O Benzyl O CH3 radical O CH3 H OH
CH3 + O Toluene-hydroxyl- + OH H 2 radical adduct Toluene 92% OH CH3 OH o-Hydroxytoluene + HO2
o-Cresol
(12.97) Aromatic Reaction With Hydroxyl Radical
Benzylperoxy radical reaction with NO
H2C O O CH
+ NO + O2
H C O O NO2 HO2 2 Benzoxy Benzaldehyde radical O H C O N + NO 2 O Benzylperoxy radical
Benzyl nitrate
(12.98)
Toluene-hydroxyl radical adduct reaction
O CH3 CH3 O O + NO H H OH OH NO2 Toluene-hydroxyl radical adduct (12.99) Fate of Cresol
Cresol --> methylphenylperoxy radical and nitrocresol
CH3 + OH, 2O 2 O O
CH 3 2HO2 OH Methylphenylperoxy radical CH3 CH3 + OH OH o-Cresol O + NO2 O N H2O O Methylphenoxy m-Nitrocresol radical (12.100) Terpene Reaction With OH
HO HO CH3 CH3 H CH C C C (1) O (4) O O C H2C C O 16.4% CH2 23.6% H2 H2 O O O H CH3 + OH, O O CH 2 (2) CH3 (5) H 3 C C 21.2% C C 12.3% CH C OH H C CH HO 2 2 C H2C C CH2 H2 H2 Isoprene
CH3 CH (3) H (6) H 3 HO C C 14.1% O C C 12.3% O O O OH C C C C H2 H H2 2 H2
Isoprene peroxy radicals (12.101)
All six products convert NO to NO2 Terpene Reaction With OH
Methacrolein production via second product (12.102)
O O + NO + O2 CH CH3 H 3 H C C + C O HO CH C C CH O CH2 H H 2 2 NO2 HO2 Isoprene peroxy radical Methacrolein Formaldehyde
Methylvinylketone production via fifth product (12.103)
O + NO + O O 2 CH3 H H CH3 H C C C C + C O OH H C H H2C C 2 O H2 NO2 HO2 Isoprene peroxy radical Methylvinylketone Formaldehyde Terpene Reaction With Ozone
H CH3 H C C O + C O H2C O H Methylvinylketone Criegee biradical CH H 3 H O C C + C O O CH H CH 2 H 3 + O3 C C Methacrolein Criegee biradical H C CH 2 CH2 H 3 H C C C O Isoprene + H2C O O H Ozonide product Formaldehyde CH H 3 H C C C O O O + CH2 H Ozonide product Formaldehyde
(12.104) Alcohol Reactions
Hydroxyl radical scavenges methanol (36-hour lifetime)
H + O2 O 85% H C O H C + OH H H H HO H 2 Formaldehyde H C O H
H H2O 15% H C O Methanol H Methoxy radical
(12.105)
Hydroxyl radical scavenges ethanol (10-hour lifetime)
H H 5% H C C O H H
H + O H O H H + OH H 2 H 90% H C C O H C C H C C O H H H H H H H O HO2 2 H H Acetaldehyde Ethanol 5% H C C O H H Ethoxy radical
(12.106) Carbon Bond Lumping
Organic gases lumped into surrogate groups.
PAR (paraffins) -- Single carbon atoms with a single-bond between them
OLE (olefins) -- Terminal carbon atom pair with a double-bond between the two atoms
ALD2 -- Non-terminal carbon atom pairs with a double bond attached to one of the carbons and terminal two-carbon carbonyl groups [C-C(=O)H]
KET -- Single carbon ketone groups (C=O)
TOL (toluene) -- 7-carbon aromatics
XYL (m-xylene) -- 8-carbon aromatics
ISOP (isoprene) -- Terpenes
UNR -- Unreactive Carbon Bond Lumping (Table 12.7)
Chemical Name Chemical Name Chemical Name Chemical Name Carbon Bond Group Carbon Bond Group Carbon Bond Group Carbon Bond Group Chemical Structure Chemical Structure Chemical Structure Chemical Structure Ethane n-Butane 2,2,4-Trimethylpentane Cyclopentane 0.4 PAR +1.6 4 PAR 8 PAR 5 PAR UNR H2 H H H H CH3 CH3 H C C H H 2 H C C C C H H C C C C CH CH2 3 3 H C H C C H H H2 2 C H H H H CH3 H2 H H Ethene Trans 2-butene Propene Ethyne 1 ETH 2 ALD2 1 PAR + 1 OLE 1 PAR + 1 UNR H H H H H H C C C CH H C C C C H 2 H C C H H H H3C H H H Formaldehyde Acetaldehyde Propionaldehyde Benzaldehyde 1 FORM 1 ALD2 1 PAR + 1 ALD2 1 ALD2 + 5 UNR O CH O H O H C CH2 H C H C C O CH3 H H H
Toluene Ethylbenzene m-Xylene 1,2,3- 1 TOL 1 PAR + 1 TOL 1 XYL Trimethylbenzene 1 PAR + 1 XYL H3C CH CH CH 3 2 3 CH3
CH3
CH 3 CH3 Stratospheric Chemistry
Ozone mixing ratios stratosphere » 10 ppmv free troposphere » 40 ppbv urban air » 0.1 - 0.3 ppmv
Ozone production in the stratosphere
Oxygen photolysis
1 O2 + hn O( D) + O l < 175 nm (12.107)
O2 + hn O + O 175 < l < 245 nm (12.108)
Ozone formation
M 1 O( D) O (12.109)
O + O2 + M O3 + M (12.110)
Ozone photodissociation
O + hn 1 l < 310 nm 3 O2 + O( D) (12.111)
O3 + hn O2 + O l > 310 nm (12.112) Ozone Destruction by NOx
Nitrous oxide reaction: 10% of N2O destruction
64% 2NO 1 N2O + O( D) 36% N2 + O2 (12.113)
Nitrous oxide photolysis: 90% of N2O destruction (12.114)
1 N2O + hn N2 + O( D) l < 240 nm
NO catalytically destroys ozone in the upper stratosphere
NO + O3 NO2 + O2 (12.115)
NO2 + O NO + O2 (12.116) ------
O + O3 2O2 (12.117) Ozone Destruction by HOx
Hydroxyl radical formation in stratosphere
H2O 2OH
1 O( D) + CH4 CH3 + OH
H2 H + OH (12.118)
OH catalytically destroys ozone in the lower stratosphere
OH + O3 HO2 + O2 (12.119)
HO2 + O3 OH + 2O2 (12.120) ------2O3 3O2 (12.121) Removal of HOx and NOx
Removal reactions
HO2 + OH H2O + O2 (12.122)
M NO2 + OH HNO3 (12.123)
M HO2 + NO2 HO2NO2 (12.124)
Nitric acid and peroxynitric acid photodissociation is slow
Source of Water Vapor
CH4 + OH CH3 + H2O (12.125)
Methane and carbon monoxide reactions in the stratosphere are similar to those in the free troposphere Chlorine Emissions to Stratosphere
Table 12.8. WMO (1994)
Chemical Trade Name Chemical Name Percent Formula Contribution to Stratospheric Emissions Anthropogenic Sources
CF2Cl2 CFC-12 Dichlorodifluoromethane 28
CFCl3 CFC-11 Trichlorofluoromethane 23
CCl4 Carbon tetrachloride 12
CH3CCl3 Methyl chloroform 10
CFCl2CF2Cl CFC-113 1-Fluorodichloro,2- 6 difluorochloroethane
CF2ClH HCFC-22 Chlorodifluoromethane 3
Natural Sources
CH3Cl --- Methyl chloride 15
HCl --- Hydrochloric acid 3
Total 100% Ozone Destruction by Chlorine
Photolysis of chlorinated compounds above 20 km
Cl Cl F C Cl + hn F C + Cl l < 250 nm Cl Cl (12.126)
Cl Cl F C Cl + hn F C + Cl l < 230 nm F F (12.127)
Cl Cl Cl C Cl + hn Cl C + Cl l < 250 nm Cl Cl (12.129)
H H H C Cl + hn H C + Cl l < 220 nm H H (12.130)
Methyl chloride scavenging by hydroxyl radical
H + OH H C Cl H C Cl H H H2O (12.128) Ozone Destruction by Chlorine
Catalytic ozone destruction by chlorine
Cl + O3 ClO + O2 (12.131)
ClO + O Cl + O2 (12.132) ------
O + O3 2O2 (12.133)
Only 1% of chlorine is typically active as Cl or ClO. Removal of Active Chlorine
Removal of Cl and ClO
CH4 HCl + CH3
HO2 HCl + O2 Cl + H2 HCl + H
H2O2 HCl + HO2 (12.134)
O M N Cl O + NO2 Cl O O Chlorine Chlorine monoxide nitrate (12.135)
+ HO2 H Cl O Cl O
Chlorine O2 Hypochlorous monoxide acid (12.136) Removal of Active Chlorine
HCl reservoir leaks
hn H + Cl l < 220 nm
HCl + OH Cl + H2O O Cl + OH (12.137)
ClONO2 reservoir leaks
O O N + hn Cl + O N l < 400 nm Cl O O O Chlorine Nitrate radical nitrate (12.138) HOCl reservoir leaks
H + hn Cl + OH l < 375 nm Cl O (12.139) Ozone Destruction by Bromine
CH3Br = methyl bromide (produced biogenically in the oceans and anthropogenically as soil fumigant)
Photolysis of methyl above 20 km
H H H C Br + hn H C + Br l < 260 nm H H (12.140)
Catalytic ozone destruction by bromine
Br + O3 BrO + O2 (12.141)
BrO + O Br + O2 (12.142) ------
O + O3 2O2 (12.143) Removal of Active Bromine
Removal of Br and BrO
HO2 HBr + O2 Br + H2O2 HBr + HO2 (12.144)
O M N Br O + NO2 Br O O Bromine Bromine monoxide nitrate (12.145)
HBr and BrONO2 reservoir leaks
HBr + OH Br + H2O (12.146)
O O N + hn Br + O N l < 390 nm Br O O O
Bromine Nitrate radical nitrate (12.147) Ozone Regeneration
Figs. 12.4 a, b. Time-evolution of modeled profile of ozone (a) mixing ratio and (b) number concentration at 34oN latitude, starting with zero ozone.
Hour 1 Hour 6 Hour 24 Day 5 40 40 Day 50 Day 464 30 30
20 20 Altitude (km) Altitude (km) 10 10
0 0 0 2 4 6 8 10 0 10 20 30 40 50 60 Ozone volume mixing ratio (ppmv) Ozone (1011 molecules cm-3) Regeneration Rate of the Global Ozone Layer
Fig. 12.2. Change in ozone column abundance, averaged over the globe, during two global model simulations in which chlorine was present and absent, respectively. In both cases, ozone was initially removed from the model atmosphere.
350 300 No chlorine
250 With chlorine 200 150 100 (Dobson units) 50 0
Avgerage global ozone column 0 100 200 300 400 10/1 1/7 4/17 7/26 11/4 Day and date of simulation Ozone Hole Growth
Table 12.9. Minimum measured values of ozone column abundances and areal extent of the ozone hole over Antarctic region from 1979 - 1994. Data from NASA Goddard Space Flight Center. The area of the Antarctic is about 13 million km2 and the area of North America is about 24 million km2. Ozone Minima Size (DU) (million km2) 1979 210 0 1980 195 0.5 1981 206 0 1982 182 3 1983 170 7 1984 154 9 1985 143 13 1986 159 9.5 1987 121 19 1988 179 8 1989 124 18.5 1990 126 17.5 1991 110 18 1992 121 21 1993 86 22 1994 90 23 Polar Stratospheric Cloud Reactions
Type I Polar Stratospheric Clouds (PSCs) nitric acid and water temperature of formation < 195 K diameter » 0.01 - 3 mm number concentration » 1 partic. cm-3
Type II Polar Stratospheric Clouds Water ice temperature of formation < 187 K diameter » 1 - 100 mm number concentration » 0.1 partic. cm-3
Reactions on Polar Stratospheric Cloud Surfaces
ClONO2(g) + H2O(a) HOCl(g) + HNO3(a) (12.148)
ClONO2(g) + HCl(a) Cl2(g) + HNO3(a) (12.149)
N2O5(g) + H2O(a) 2HNO3(a) (12.150)
N2O5(g) + HCl(a) ClNO2(g) + HNO3(a) (12.151)
HOCl(g) + HCl(a) Cl2(g) + H2O(a) (12.152) Surface Reaction Rates
First-order rate coefficient (s-1)
1 k = v g a (12.153) s,q 4 q q
Thermal velocity of impinging gas (cm s-1)
æ ö1 2 8kBT v q = ç ÷ (12.154) è pMq ø
Table 12.10. Estimated reaction probabilities for the gases in reactions (12.147) - (12.151) on Type I and II PSC surfaces. Data from DeMore et al. (1997) and references therein.
Reaction Type I PSCs Type II PSCs ClONO2(g) + H2O(a) 0.001 0.3
ClONO2(g) + HCl(a) 0.1 0.3
N2O5(g) + H2O(a) 0.0003 0.01
N2O5(g) + HCl(a) 0.003 0.03
HOCl(g) + HCl(a) 0.1 0.3 Polar Ozone Destruction
Cl2 and HOCl photolysis in early spring
Cl2 + hn 2Cl l < 450 nm (12.164)
HOCl + hn Cl + OH l < 375 nm (12.165)
Chlorine nitrite photolysis in early spring
ClNO2 + hn Cl + NO2 l < 370 nm (12.166)
Catalytic ozone destruction by dimer mechanism
2 x ( ClO + O ) Cl + O3 2 (12.167)
M ClO + ClO Cl2O2 (12.168)
Cl2O2 + hn ClOO + Cl l < 360 nm
M ClOO Cl + O2 (12.170) ------2O3 3O2 (12.171) Polar Ozone Destruction
A second catalytic cycle that involves bromine
Cl + O3 ClO + O2 (12.172)
Br + O3 BrO + O2 (12.173)
BrO + ClO Br + Cl + O2 (12.174) ------2O3 3O2 (12.175) Conversion of Chlorine Reservoirs to Active Chlorine
Fig. 12.5.
1% Cl, ClO
37% ClONO 2 62% HCl
Before PSC and photolysis reactions ClONO 2
HCl
Cl, ClO
After PSC and photolysis reactions