1. Envr 890 Organic Aerosols: Lecture 2
Envr 890 Organic Aerosols: Lecture 2. What questions do we have to start asking if we are to build a kinetics model to predict aerosol formation from isoprene reactions?

2. Objective
To describe a predictive technique for the formation of aerosols from biogenic hydrocarbons based on fundamental principals and apply it to isoprene
Have the ability to embrace a range of different atmospheric chemical and physical conditions which bring about aerosol formation.

3. Chemical System
+ NOx+ sunlight + ozone----> aerosols
a-pinene

4. Overview
This reaction system produces low vapor pressure reaction products that distribute between gas and particle phases.

5. Gas Particle Partitioning
gas phase products
COOH O
cis-pinonic
acid
particle

6. Equilibrium partitioning between the gas and particle phases is assumed for all products.
Kinetically this is represented as forward and backward reactions.
Kp = kon/koff

7. The equilibrium constant Kp can be calculated from
[gas] + [surface] [particle]

8. Overview
Gas and particle phase reactions were linked in one mechanism and a chemical kinetics solver was used to simulate the reaction over time
Model simulations were compared with aerosol concentrations obtained by reacting -pinene with either O3 or NOx in sunlight in an outdoor chamber.

10. -pinene-O3 experiments in the UNC 190m3 outdoor chamber
1. added O3 O3
-pine O3
2. added -pinene O3 O3
-pine O3 O3
-pine

11. -pinene-O3 experiments in the UNC 190m3 outdoor chamber
1. added O3 O3
-pine O3
2. added -pinene O3 O3
-pine
3. immediate burst of particles O3 O3
-pine

12. Products pinald - pinacid - diacid - oxy-pinald - oxy-acid-
pinonaldehyde
CHO O
nor-pinonaldehyde
Pinic acid
HOOC
COOH
COO
C8 diacid OH
Pinonic acid
Norpinonic acid

13. Mechanism OH Criegee2 Criegee1 + other products + CO, HO a -pinene
pinonic acid
CHO
COOH
+ CO, HO 2, OH
norpinonaldehyde
norpinonic
acid
Mechanism
CHO O CH 3
Criegee2
Criegee1 O a
-pinene 3
COOH
pinic acid
+ other
products

14. Now you need to know about the reactions of alkenes with O3
C=C +O3
See pages Pitts and Pitts, 2000, pages

15. How do we chemically represent his reaction scheme?
1st the reaction of O3 with an alkene generates an aldehyde +a high energy bi-radical called a Criegee bi-radical
2nd a certain fraction of these “hot” Criegee’s stabilize and the rest decomposes. (see page 198 of Pitts and Pitts, Table 6.10)
3rd “Hot” Criegee’s R-(H)C.-00. decompose to OH, CO and an R. group

16. For the propylene +O3 reaction (page 198 Pitts and Pitts)
propylene +O3  two Criegee’s
C-C=C +O3  H2C.OO.* + CH3C.HOO.*
+ what two aldehydes?
CH3C.HOO.* 0.15 Stabilized Criegee
 0.54 (CH3. + CO +OH.)
 CH3. + CO2+ H.
 HCO +CH3O 0.17
 0.14 (CH4 + CO2)

17. How do we chemically represent this for the a-pinene system?
apine + O3  0.4*crieg *crieg min-1 or ppm-1min-1
1.492 e-732/T
More highly substituted Criegee’s are more stable
crieg1 = 0.47*pinacid *stabcrieg1 1x106
+ 0.8*OH + 0.3*HO *pinald
+ 0.01*oxypinald *O *CO

18. What would we do for isoprene (see Kamens et al, IJKS, 1982?

20. OH attack on a-pinene
CHO O OH
HOO
+ OH 2 OO
a-pinene
pinonaldehyde

21. Each Reaction can be represented as a differential equation
a-pinene + ozone --> pinald
d[a-pinene]/dt = -krate1 [a-pinene][O3]
d[pinald]/dt = -krate2[pinal][OH]

22. Particle formation-self nucleation

23. Particle formation-self nucleation
Criegee’s can react with aldehydes and carboxylic groups to form secondary ozonides and anhydrides.
O=C
C=O CH 3 + C .
oo. C
C=O CH 3 O oo

24. Estimating rates that gas phase products enter and leave the particle
The equilibrium between the gas and particle phases is:
Kp = kon/koff

25. Kp = kon/koff The equilibrium constant Kp can be calculated from
[gas] + [surface] [particle]
Kp = kon/koff

26. A general Flux expression for evaporation from a liquid surface is
 is the energy barrier for single molecule to evaporate from the surface (Joules)
koff = k evap  in koff =  e -Ea/RT is: kbT/h
From koff and Kp the rate coefficient kon can now be calculated

27. Overall Mechanism
linked gas and particle phase rate expressions

29. Where do the rate coefficients come from??
Diacid is generated in the gas phase. How do we get it on and off the particle phase??
diacidgas + pinacidpart --> pinacidpart + diacidpart 68
diacidpart  diacidgas x1014 e-10285/T
Where do the rate coefficients come from??

30. Kp = kon/koff koff =  e -Ea/RT
We need vapor pressure (poL ) to calculate Kp
for koff , we need kbT/h for , and an activation energy, Ea
To calculate vapor pressures see Chapter 4 of (Schwarzenbach et al, Environmental Organic Chemistry, 2003)

31. if we substitute DSvap Tb= 88J mol-1 K-1 and R =8.31 Jmol-1 K-1
This means we need Tb or boiling point

32. Boiling points can be estimated based on chemical structure (Joback, 1984) Tb= 198 + S DTb  
DT (oK)
-CH3 = K
-Cl = 38.13
-NH2 = 73.23
C=O = 76.75
CbenzH- = 26.73
C-OH = 93
  Joback obs
(K) (K)
acetonitrile
acetone
benzene
amino benzene
benzoic acid
toluene
pentane
methyl amine
trichlorethylene
phenanthrene

33. Stein, S.E., Brown, R.L. Estimating Normal boiling Points from Group Contributions, J.Chem. Inf Comput. Sci, 34, , 1994

35. Chamber Data
First look at experiments with different temperatures and gas phase concentrations of -pinene and ozone

36. A high concentration warm experiment
0.82 ppmV -pinene ppm O3
Temp = ~295K
%RH = ~61%

37. Gas Phase -pinene and O3 data and model

39. Particle concentration. Warm high concentration experiment
Reacted -pinene
mg/m3
Observed
model

40. Other Conditons 0.88 ppmv a-pinene + 0.47 ppm O3(269K)

41. Lower concentration experiments

42. 0.20 ppm a-pinene ppm O3
model
data

43. How do we start to build an Isoprene + O3 mechanism??

44. The initail attack of O3 on an olefin (alkene) generates two possible Criegee high energy bi-radicals and two possible aldehydes.

45. A general rule is that the more highly substituted carbon will form a higher fraction of Criegee’s

46. C=C-C=C + O3  MACR + H2C.OO.  CI1.OO. + HCHO  MVK + H2C.OO.

47. What would we do for isoprene (see Kamens et al, IJKS, 1982?

49. There are 4 general product channels by which high energy Criegee’s (Criegee intermediates) decompose:
Stabilized Criegee biradicals
an Ester Channel
O-atom elimination
Hydroperoxide channel

51. The hydroperoxide channel is a
source of dark OH
Homework 3: For MVK write a set of
Chemical equations to show it’s
decomposition

52. MVK + O3 H2C=C - C-CH3 H O (MVK) MVK + O3 MGLY+ H2C.OO.*
.OOC.C(H)-C(=O)-CH3 +HCHO
let’s assign splitting ratios
2. MVK + O3 0.4 MGLY+ 0.4 H2C.OO.*
0.6 CI2*+0.6 HCHO

53. MVK + O3 MVK + O3 0.4 MGLY+ 0.4 H2C.OO.* 0.6 CI2 * +0.6 HCHO
how does H2C.OO. decompose??
(look at page 197 of Pitts and Pitts,2000)
H2C.OO.*  0.37 Stabcrieg HCO OH CO H2O

54. Stabilized Criegee’s usually react with water
Stabcrieg + H2O  Aldehyde +H2O2
H2C.OO.* + H2O H2C=O + H2O2
Stabcrieg + Aldehyde  secondary ozonide
How do we add rate constants??

55. Adding Rate constants MVK + O3 MGLY+ H2C.OO.
.OOC.C(H)-C(=O)-CH3 +HCHO
6X10-3 ppm-1 min-1
H2C H2O H2C=O + H2O2
5.4x10-2 ppm-1 min-1
look in Pitts and Pitts to convert
ppm-1 min-1 to cm3molecule-1sec-1

56. Does OH attack Isoprene, MACR,MVK,MGLY and HCHO???
isoprene + OH  products
MACR+ OH  products
MVK + OH  products
MGLY +OH  products
H2C=O +OH  products
NO3+alkenes  products
radical +radicals  stable products
aldehydes photolyze

58. Light model for a-pinene + NOx
a-pinene + OH Noizoire et al.
a-pinene + NO3 Martinez et al., Wangberg et al.
a-pinene(OH)-OO + NOx--> products Aschmann et al.
pinonaldehyde +OH or NO3 Calogirou et al.
pinonaldehyde photolysis Hallquist et al
acyl peroxy + NO2 --> PAN analogues Noizoire et al.
partition nitrate products

59. pinonaldehyde

60. Pinonaldehyde chemistry
Pinald +hn = 0.65pinO CO + HO *C8O2 `
# hnpinald
pinO2 + NO= .765pinald HO2 +
0.1*acetone +0.2C2O3 +
.865NO2
# 6056
exp 180/T
C8O2 + NO = NO2 {+ C8-dicarb }
# 6056
exp 180/T
pinald + OH = . 8 pinald-oo + 0.1C3O2
+ 0.1C8O
acetone +0.3XO2
# ,
pinald + NO3 = 0.95*pinald-oo +0.03*pinO2
+0.02*C8O *CO +NO
# 79 2
pinald-
oo + NO = pinO2 +CO2 +NO
# 7915 exp250/T 2
pinald-
oo + NO
= pinald-PAN
#3885exp380/T 2
pinald-PAN = pinald-
oo + NO2
# 1.067e11 exp-8864/T
pinald-
oo + pinald-
oo = 2*pinO2
# 2551
pinald-
oo + HO2 =
Pinacid #

61. Pinonaldehyde quantum yields in natural sunlight
kphototyis = S ( al fl Il )
By adding pinonaldehyde to the chamber in clear sunlight in the presence of an OH scavenger and measuring its rate of decay
fl can be fit to the decay data assuming a shape with wave length similar to other aldehydes

62. Pinonaldehyde quantum yields in sunlight
Normalized to one
pinonaldehyde
CH3CH2CH2=O
CH2=O O
pinonaldehyde
CH3CH2=O

63. 0.97 ppm a-pinene + 0. 48ppm NOx; October Sunlight

64. a-pinene data vs. model
model
data

65. Gas phase pinonaldehye
model
pinonaldehyde O
data
norpinonaldehyde

66. Particle phase pinonic acid
model
pinonic acid data
norpinonic acid

67. Measured particle mass vs. model
Particle phase
model
mg/m3
S products
filter data

68. 0.95 ppm a-pinene ppm NOx
model
data NO O3
NO2
NO2

69. Measured particle mass vs. model
reacted a-pinene
data
model

70. Gas phase pinonaldehye

71. particle phase pinonaldehye
data
model

72. d-limonene + O3
(Sirakarn Leungsakul, ES&T 2004)

73. Major particle phase products
keto-limononaldehyde
limononaldehyde
7OH-limononic acid
7OH-limononaldehyde
7OH-keto-limononaldehyde
7OH-keto-limononic acid
keto-limononic acid

74. d-limonene keto-limald limononaldehyde limonalic acid
0.68
+ CH
-OO 2
0.15
OOO
0.32 + O 3 O
keto-limonene
0.85 OO
0.30 O O O + H O
0.35 O
0.50 2 OH
0.63 O OO OO
limononic acid
0.65
Stab-Crieg1
Crieg1*
0.37 + H O O 2 O
+ OH OO O
0.25 OO
0.20 + H O 2 O O O
0.20 O
keto-limald + H O
Stab-Crieg2
limononaldehyde 2
Crieg2* OH
0.10 HO O CH
-OH + 3 O O
limonalic acid O
7OH-limononaldehyde

75. d-limonene + O3 (Sirakarn Leungsakul, 2004) aerosol (mg/m3)v
ppmV
aerosol (mg/m3)v
Filter data and Model O3

76. d-limonene + O3 (Sirakarn Leungsakul, 2004) Filter Model O3 .00 .02
.04
.06
.08
.10 18 19 20 21 22 23 24
1:00
LDT (hour)
(ppm)
0.00 30 60 90
120
150
aerosol (mg/m3) O3
Filter
d-limonene + O3
(Sirakarn Leungsakul, 2004)
Model

77. b-pinene + O3
(Mohammed Jaoui, 2003)

78. b-pinene + O3

79. * toluene O2 . . OH oxygen bridge rearrangement butenedial
O=CH CH 3 OH
+ HO 2
+ H O
o-cresol
benzaldehyde CH 3 OH 2 . NO +O H * O2 +
toluene CH 3 H OH O . NO 2 +O
rearrangement
oxygen bridge OH H O . +O 2 CH 3 +
methylglyoxal
butenedial
+ HO
ring cleavage
radical

81. Experiments that explore heterogeneous carbonyl reactions (Myoseon Jang et al., Science, 2002)
Nebulizes NH4(SO4)2 acid coated aerosols into Teflon bags
Reacts aldehydes on the surface of the acid coated particles (~2% H2SO4 by weight)
Diesel exhaust is 1-5% sulfuric acid
Aldehyde products such as pinonaldehyde, norpinonaldehyde, hydroxy pinonaldehyde, and oxo-pinonaldehyde are products from the a-pinene/ozone reaction and
Methacrolein and formaldehyde are common products of the ozonation of isoprene
In addition, the indigenous acid in many aerosol systems would be able to catalyze these reactions
BE CLEAR: These heterogeneous reactions take place in the particle phase and use the acid present in the particle phase as a catalyst
Thus we wanted to test how an aldehyde would interact on acidic particles compared to non acidic particles and what we found was that when particle phase acids are present, more SOA mass is observed than in a non acid environment

82. 500 liter Teflon bag nebulizer (NH4)2SO4 (NH4)2SO4+H2SO4 Solution
aldehydes
alcohols
glyoxal

83. The aldehyde phenomenon can be explained as follows:
Aldehyde functional groups can further react in the aerosol phase through heterogeneous reactions via hydration, polymerization, and hemiacetal/acetal formation with alcohols.
Aldehyde reactions can be radically accelerated by acid catalysts such as particle sulfuric acid

84. Acid catalyzing step Hydration Polyimerization OH O H + H O OH + -H 2

85. Hemiacetal and acetal formationOH + OH OH -H H H +
ROH R H O H OR H H H
hemiacetal + OH + -H O OR OH H 2 2 H H H OR H H H OR + H O OR R
ROH -H
acetal

86. Aerosol yields from aldehydes
Notice greater yields for all aldehydes when an acid catalyst is present.
Now that we had confirmed that some sort of reaction beyond partitioning was taking place and that the reactions were catalyzed by an acid we can consider a few examples of possible heterogeneous reactions that are taking place
*Yield data and method from Jang et al. 2001

87. Acid seed experiments with O3 + organics
Nebulizer
Ozone
Volatilized organics
Ozone
(NH4)2SO4
Solution
(NH4)2SO4+H2SO4
This is basically the same system as was used in the aldehyde experiments. The only real difference is that ozone is present initially so that when the organics are injected, gas phase oxidation reactions happen immediately.
The time scale of these experiments was on the order of about an hour (much longer compared to the flow reactor) and differ in that the seed aerosol is present from the very beginning of SOA production, not added at a late time.

88. Yields from Teflon bag experiments
Again in each case the yield is much higher in the acidic systems. This increase is especially evident for a-pinene and isoprene. Thus heterogeneous reactions are a role player in biogenic SOA systems in which a SOA precursor must react to form the aldehydes which participate in the heterogeneous reactions. These increases are much greater than those observed in the flow reactor indicating that heterogeneous reactions become more important at longer time scales. It would be interesting to look at even longer time scales and judge the extent of heterogeneous reactions.

89. Aldehyde acid catalyzed heterogeneous reactions
Acid catalyzing step
Hydration
Polymerization H O OH H+ O OH H
+ H 2
The effect is noticed in the presence of an acid catalyst. So the reactions must at least be aided by an acid.
I will demonstrate only a few of the possibilities here.
We have targeted carbonyls as the primary participating group. So the catalytic step would be protonation of the carbonyl group. From there a variety of reactions could happen. I’ll mention a few: hydration to the gem diol and from there it can undergo polymerization with other carbonyls. Such a reaction chain could lead to long chain polymers
Note that the ultimate result of these reactions is to convert the carbonyl group of the aldehyde into hydroxy groups and C-O bonds. H OH O +
Etc...

90. Particle Phase reactions
Gas phase reactions
C=O O
cis-pinonaldhyde
C=O O
polymers
particle

91. Particle Phase reactions
Gas phase reactions
C=O O
cis-pinonaldhyde
C=O O
particle
polymers

92. Particle Phase reactions
Gas phase reactions
C=O O
cis-pinonaldhyde
C=O O
polymers

93. MS Analysis of Filter Samples from the reaction of acid seed particles with a-pinene + O3

94. ESI-QTOF mass spectrum of SOA from reaction of a-pinene + O3 + acid seed aerosol (Tolocka et. al., 2004)

95. Particle phase pinonaldehyde dimers from a-pinene +O3 on acid particles
M Na+ (ESI-QTOF Tolocka et al, 2003)
Similar results were obtain by Hartmut Herrmann’s group (Atmos Envir, 2004)

96. Kalberer and Baltensperger et al
Kalberer and Baltensperger et al. (Science, 2004) identified polymers as the main constituents of SOA formed from the photo-oxidation of 1,3,5-trimethylbezene. These account for about 50% of the aerosol mass after 30 hours of aging.
Without acid seed injection

97. LDI-TOFMS Spectrum of SOA from Photo-oxidation of 1,3,5-Trimethylbezene
This is a LDI-TOFMS spectrum of SOA resulting from photo-oxidation of 650ppbv 1,3,5-TMB. Aerosol sample was collected on steel plates using impactor 5-7.5hrs after start of the photo-oxidation. So far all the compounds identified in the literature are small and just have mass up to aprroximately 200Da. But in this spectrum, a group of peaks are shown in the mass range 400<m/z<900 and they have highly regular mass differences of m/z 14, 16 and 18. Such a regular structure is typical for polymers, suggesting that polymerization reactions are taking place in the aerosol particles.

98. Time Evolution of Polymer in SOA Measured by LDI-MS
2.5hrs
3.5hrs
4.5hrs
6.5hrs
It’s very obvious that with increasing time, the molecular size distribution shifts to higher masses. In spectrum E MGLY shows oligomers up to the 9-mer with m/z=723. One thing we need to keep in mind is that in their experiment, no acidic seed was injected in to the chamber, which means that the organic acids and nitric acid in particle phase have sufficiently high concentrations to catalyze polymerization reactions. Theses measurements proved that polymerization in atmospheric aerosols could take place also without acidic seed particle and in a wide range of atmospheric conditions.
methylglyoxal oligomers
mixture of methylglyoxal, formaldehyde,
2,5-dimethylbenzaldehyde, and pyruvic acid

99. Where do we go from here for isoprene??
Learn what products it makes that go into the particle phase
Begin to describe the chemistry
Start to collect papers on isoprene and SOA