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A new mechanism for regional atmospheric chemistry modeling

27 Nov 1997-Journal of Geophysical Research (John Wiley & Sons, Ltd)-Vol. 102, pp 25847-25879
TL;DR: The Regional Atmospheric Chemistry Mechanism (RACM) as discussed by the authors is a gas-phase chemical mechanism for the modeling of regional atmospheric chemistry, the mechanism is intended to be valid for remote to polluted conditions and from the Earth's surface through the upper troposphere.
Abstract: A new gas-phase chemical mechanism for the modeling of regional atmospheric chemistry, the “Regional Atmospheric Chemistry Mechanism” (RACM) is presented. The mechanism is intended to be valid for remote to polluted conditions and from the Earth's surface through the upper troposphere. The RACM mechanism is based upon the earlier Regional Acid Deposition Model, version 2 (RADM2) mechanism [Stockwell et al., 1990] and the more detailed Euro-RADM mechanism [Stockwell and Kley, 1994]. The RACM mechanism includes rate constants and product yields from the most recent laboratory measurements, and it has been tested against environmental chamber data. A new condensed reaction mechanism is included for biogenic compounds: isoprene, α-pinene, and d-limonene. The branching ratios for alkane decay were reevaluated, and in the revised mechanism the aldehyde to ketone ratios were significantly reduced. The relatively large amounts of nitrates resulting from the reactions of unbranched alkenes with NO3 are now included, and the production of HO from the ozonolysis of alkenes has a much greater yield. The aromatic chemistry has been revised through the use of new laboratory data. The yield of cresol production from aromatics was reduced, while the reactions of HO, NO3, and O3 with unsaturated dicarbonyl species and unsaturated peroxynitrate are now included in the RACM mechanism. The peroxyacetyl nitrate chemistry and the organic peroxy radical-peroxy radical reactions were revised, and organic peroxy radical +NO3 reactions were added.

Summary (3 min read)

3. Organic Chemistry

  • The recent mechanisms of Andersson-Skold [1995] and Jenkin et al. [1996] include highly detailed descriptions of atmospheric organic oxidation mechanisms.
  • The mechanism of Jenkin et al. is even larger with 120 emitted organic compounds reacting in 2500 chemical species and 7000 chemical reactions.
  • Emissions inventories include hundreds of emitted volatile organic compounds (VOC) [Middleton et al., 1990] .
  • Given the need to conserve computational resources for a transport/transformation model and the complexity of explicit detailed mechanisms, it is necessary to group organic compounds together to form a manageable set of model classes.
  • For the same reason, many multiple pathways are formulated as one reaction in the RACM mechanism, and not all organic intermediates (i.e., alkyl radicals) are explicitly described.

3.1. Aggregation of Organic Compounds

  • For cases where this rate constant is not known the authors calculated aggregation factors for categories, Aggcat.
  • Because species in a category react similarly, the aggregation factors of categories, Aggm, can be used as an approximation for the aggregation factors of chemical species, Aggi belonging to a category.
  • The rate constants used to calculate kca,,HO were taken from the recommendations of Atkinson [1994] or calculated according to the procedure of Kwok and Atkinson [1995] by using a structure-reactivity relationship.
  • As an example of the aggregation process, Table 4 shows the complete set of rate constants and aggregation factors for chemical species, classes, and model species for alkanes.
  • Any anthropogenic emissions of isoprene and terpenes should be aggregated together into the primarily biogenic model species.'.

P

  • Here BQHQX was calculated using product yield of the reactions R-+ HO, RO2-+ X and R0-decomposition.
  • If no product yields were available from laboratory studies, they were calculated following the procedure proposed by Kwok and Atkinson [1995] .

3.4. Carbonyls

  • To simplify the mechanism, the model species TCO3 was also used to represent the unsaturated acyl products.
  • It is probable that the acyl radicals produced from unsaturated dicarbonyls react with NO2 to produce peroxynitrates; however, these products have_ not been observed.
  • The comparable product, produced in methacrolein degradation, methacrylic peroxynitrate, has been reasonably well investigated.
  • These reactions are further discussed by Kirchner and Stockwell [1996b] .
  • For the reaction of HO with cresol (CSL) it was assumed that an unsaturated dicarbonyl enol was formed which can isomerize via keto-enol-tautomerie into a saturated tricarbonyl compound which is treated as MGLY.

Q on

  • The rate constant for (82) is not known; therefore the rate constant for the analogous CH3O-+ N02 addition reaction was used.
  • For the PHO + HO2 reaction the rate constant for Ph-CH2OO-+ HO2 was used.
  • There is also experimental evidence for the formation of quinones from cresols [Wiesen et al., 1995] through the reactions of phenoxy radicals, but not enough is known about the quinone chemistry to include it in the RACM mechanism.

3.7. Biogenic Organic Species

  • The RACM mechanism also includes a mechanism for the oxidation of at-pinene and d-limonene.
  • The new oxidation mechanism for a-pinene and d-limonene is based upon the limited available experimental data for terpene reactions [Atkinson, 1994] .
  • To include the large number of different monoterpenes in the mechanism, it was necessary to group the individual monoterpenes into a few groups.
  • This grouping was done according to similarities in rate constants and structure.
  • The mechanism was successfully tested against environmental chamber runs [ Kirchner and Stockwell, 1996b] .

3.8. Parameters for Organic Peroxy Radical-Peroxy Radical Reactions and the Reactions of Nitrate Radical With Organic Peroxy Radicals

  • The reactions of organic peroxy radical with NO, NO3, HO2, and with other organic peroxy radicals were revised as described by Kirchner and Stockwell [1996a] .
  • The revised rate constants were significantly different from those used by Stockwell et al. [1990] in several cases.
  • Simulations made using the original mechanism and a version with the updated rate con-stants for the peroxy radical reactions were compared.
  • The calculated concentrations (especially the nighttime concentrations) of PAN, higher organic hydroperoxides, peroxyacetic acid organic peroxy radicals, HO2, HO, and N03 were strongly affected by the revisions to peroxy radical chemistry.
  • On the basis of that study it appears that RO2-+ N03 reactions are more important in the nighttime atmosphere than RO2-+ R05 reactions.

4. Comparison With Environmental Chamber Data

  • Both mechanisms predict peak NO3 concentrations very well .
  • The mean normalized deviations of N02 peak concentrations from the EC chamber experimental measurements for RACM and RADM2 are 10 and 9%, respectively.
  • The timing of the NO2 peak concentration predicted by RACM and RADM2 are very similar .
  • The timing of the simulated N02 maxima is later in most cases, but the overall performance of RACM is only slightly improved .
  • The ability of the mechanism to correctly simulate the NO and N02 profiles suggests that not only the HO concentrations but also the underlying acyl peroxy radical concentrations and their effect on the chemistry NO2 are well simulated because under these conditions, significant amounts of PAN and PAN analogs are produced.

6. Conclusions

  • More environmental chamber and field data are required to test the mechanisms.
  • Cleaner environmental experiments with a wider number of measured species are required.
  • Field measurements suffer from uncertainties in meteorological conditions, photolysis rates, emissions, initial concentrations and air mass age, effects of heterogeneous and aqueous phase reactions, deposition rates, etc.
  • These tests and similar ones should be repeated for the new mechanism.
  • Finally, simultaneous field measurements of NOX, PAN, organic nitrates, and HNO3 would be a useful test of the mechanism because the secondary peroxy radical chemistry strongly affects the partitioning between nitrogen species [Stockwell et al., 1990 [Stockwell et al., , 1995;; Kirchner and Stockwell, 1996a] .

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JOURNAL
OF
GEOPHYSICAL
RESEARCH,
VOL.
102,
NO.
D22,
PAGES
25,847—25,879,
NOVEMBER
27,
1997
A
new
mechanism
for
regional
atmospheric
chemistry
modeling
William
R.
Stockwell,
Frank
Kirchner,
and
Michael
Kuhn
Fraunhofer
Institute
for
Atmospheric
Environmental
Research
(IFU),
Garmisch-Partenkirchen,
Germany
Stephan
Seefeld
Swiss
Federal
Institute
for
Environmental
Science
and
Technology
(EAWAG),
ETH
Zurich,
Switzerland
Abstract.
A
new
gas-phase
chemical
mechanism
for
the
modeling
of
regional
atmospheric
chemistry,
the
“Regional
Atmospheric
Chemistry
Mechanism”
(RACM)
is
presented.
The
mechanism
is
intended
to
be
valid
for
remote
to
polluted
conditions
and
from
the
Earth’s
surface
through
the
upper
troposphere.
The
RACM
mechanism
is
based
upon
the
earlier
Regional
Acid
Deposition
Model,
version
2
(RADM2)
mechanism
[Stockwell
et
al.,
1990]
and
the
more
detailed
Euro-RADM
mechanism
[Stockwell
and
Kley,
1994].
The
RACM
mechanism
includes
rate
constants
and
product
yields
from
the
most
recent
laboratory
measurements,
and
it
has
been
tested
against
environmental
chamber
data.
A
new
condensed
reaction
mechanism
is
included
for
biogenic
compounds:
isoprene,
oz-pinene,
and
d-limonene.
The
branching
ratios
for
alkane
decay
were
reevaluated,
and
in
the
revised
mechanism
the
aldehyde
to
ketone
ratios
were
significantly
reduced.-The
relatively
large
amounts
of
nitrates
resulting
from
the
reactions
of
unbranched
alkenes
with
NO3
are
now
included,
and
the
production
of
HO
from
the
ozonolysis
of
alkenes
has
a
much
greater
yield.
The
aromatic
chemistry
has
been
revised
through
the
use
of
new
laboratory
data.
The
yield
of
cresol
production
from
aromatics
was
reduced,
while
the
reactions
of
HO,
N03,
and
O3
with
unsaturated
dicarbonyl
species
and
unsaturated
peroxynitrate
are
now
included
in
the
RACM
mechanism.
The
peroxyacetyl
nitrate
chemistry
and
the
organic
peroxy
radical—peroxy
radical
reactions
were
revised,
and
organic
peroxy
radical
+
NO3
reactions
were
added.
1.
Introduction
The
gas-phase
chemical
mechanism
is
one
of
the
most
im-
portant
components
of
an
atmospheric
chemistry
model.
These
models
require
high-quality
gas-phase
chemical
mecha-
nisms
to
calculate
the
concentrations
of
atmospheric
chemical
species.
The
concentrations
of
ozone
and
other
air
pollutants
are
determined
by
the
emissions
of
nitrogen
oxides
and
reac-
tive
organic
species,
gas-
and
aqueous-phase
chemical
reaction
rates,
deposition,
and
meteorological
conditions.
There
are
several
important
mechanisms
which
are
widely
used
for
modeling
the
chemistry
of
the
troposphere
including
the
mechanism
of
Lurmann
et
al.
[1986],
the
carbon
bond
IV
mechanism
of
Gery
et
al.
[1989],
and
the
mechanism
for
the
Regional
Acid
Deposition
Model
(RADM2)
[Stockwell
et
al.,
1990].
For
example,
the
RADM2
mechanism
is
used
in
many
photochemical
transport/transformation
atmospheric
chemis-
try
models
to
predict
concentrations
of
oxidants
and
other
air
pollutants
[Chang
et
al.,
1991;
Hass
et
al.,
1995;
Vogel
et
al.,
1995].
Since
these
mechanisms
have
been
published,
much
new
laboratory
work
has
become
available
[Le
Bras,
1997;
DeM0re
et
al.,
1994;Atkins0n
et
al.,
1992b;Atkins0n,
1994].
The
purpose
of
this
paper
is
to
present
a
completely
revised
version
of
the
mechanism
of
Stockwell
et
al.
[1990]
and
to
show
the
effect
of
the
revisions
on
calculated
chemical
concentrations.
Since
the
purpose
of
the
new
mechanism
is
to
describe
atmospheric
Copyright
1997
by
the
American
Geophysical
Union.
Paper
number
97JD00849.
0148-0227/97/97JD-00849$09.00
chemistry
on
a
regional
scale,
we
have
named
it
the
“Regional
Atmospheric
Chemistry
Mechanism”
(RACM).
The
RACM
mechanism
was
created
to
be
capable
of
simulating
the
tropo-
sphere
from
the
Earth’s
surface
through
the
upper
troposphere
and
to
be
valid
for
Simulating
remote
to
polluted
urban
con-
ditions.
The
mechanism
includes
17
stable
inorganic
species,
4
inor-
ganic
intermediates,
32
stable
organic
species
(4
of
these
are
primarily
of
biogenic
origin),
and
24
organic
intermediates
(Table
1).
The
RACM
mechanism
includes
237
reactions
(Table
2).
The
mechanism
and
its
use
are
described
in
the
subsequent
text.
The
text
is
divided
into
section
2
on
the
inorganic
chemistry
and
section
3
on
the
organic
chemistry.
The
organic
chemistry
section
includes
a
description
of
the
aggregation
procedures
for
emissions
and
the
development
of
the
chemistry
for
alkanes,
carbonyls,
alkenes,
aromatics;
the
decomposition
products
of
aromatics;
and
the
primarily
bio-
genic
species,
isoprene,
oz-pinene,
and
d-limonene.
The
oxida-
tion
mechanism
for
isoprene,
oz-pinene,
and
d-limonene
is
much
more
detailed
and
realistic
than
that
in
the
RADM2
mechanism
[Stockwell
et
al.,
1990].
The
aggregation
factors
for
the
organic
emissions
are
given
in
Table
3.
Sections
4
and
5
present
comparisons
of
the
mechanism
with
environmental
chamber
data
and
with
the
RADM2
mechanism,
respectively.
The
treatment
of
peroxy
radical
reactions
were
described
by
Kirchner
and
Stockwell
[1996a].
2.
Inorganic
Chemistry
Tropospheric
inorganic
chemistry
is
relatively
well
known.
During
the
day
the
chemistry
is
driven
by
the
photolysis
of
25,847

25,848
STOCKWELL
ET
AL.:
REGIONAL
ATMOSPHERIC
CHEMISTRY
MECHANISM
Table
1.
RACM
Mechanism
Species
List
No.
Species
Carbon
Molecular
Definition
Number
Weight
1
2
\0O0\IO\Ln-I>Ln
10
11
12
13
>—\r—\\—\>—\
\lO\U\-P
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
Oxidants
03
H202
Nitrogenous
compounds
N0
N02
N03
N205
HONO
HN03
HN04
Sulfur
compounds
S02
SULF
Carbon
oxides
CO
co,
N
2
01
H20
H2
03P
01D
Odd
hydrogen
HO
HO2
Alkanes
CH4
ETH
HC3
HC5
HC8
Alkenes
ETE
OLT
OLI
DIEN
Stable
biogenic
alkenes
ISO
API
LIM
Aromatics
TOL
XYL
CSL
Carbonyls
HCHO
ALD
KET
GLY
MGLY
DCB
MACR
UDD
HKET
Stable
Inorganic
Compounds
ozone
hydrogen
peroxide
nitric
oxide
nitrogen
dioxide
nitrogen
trioxide
dinitrogen
pentoxide
nitrous
acid
nitric
acid
pernitric
acid
sulfur
dioxide
sulfuric
acid
carbon
monoxide
1
carbon
dioxide
1
Abundant
Stable
Species
nitrogen
oxygen
water
hydrogen
Inorganic
Short-Lived
Intermediates
ground
state
oxygen
atom,
0(3P)
excited
state
oxygen
atom,
0(1D)
hydroxy
radical
hydroperoxy
radical
Stable
Organic
Compounds
methane
1.0
ethane
2.0
alkanes,
alcohols,
esters,
and
alkynes
with
H0
rate
2.9
constant
(298
K,
1
atm)
less
than
3.4
><
10'”
cm3
s_1
alkanes,
alcohols,
esters,
and
alkynes
with
HO
rate
4.8
constant
(298
K,
1
atm)
between
3.4
><
10_12
and
6.8
><
10712
cm3
s'1
alkanes,
alcohols,
esters,
and
alkynes
with
H0
rate
7.9
constant
(298
K,
1
atm)
greater
than
6.8
><
10'”
cm3
s_1
ethene
2.0
terminal
alkenes
3.8
internal
alkenes
5.0
butadiene
and
other
anthropogenic
dienes
4.0
isoprene
5.0
oz-pinene
and
other
cyclic
terpenes
with
one
double
10.0
bond
d-limonene
and
other
cyclic
diene-terpenes
10.0
toluene
and
less
reactive
aromatics
7.1
xylene
and
more
reactive
aromatics
8.9
cresol
and
other
hydroxy
substituted
aromatics
6.6
formaldehyde
1.0
acetaldehyde
and
higher
aldehydes
2.4
ketones
3.5
glyoxal
_
2.0
methylglyoxal
and
other
a-carbonyl
aldehydes
3.0
unsaturated
dicarbonyls
4.2
methacrolein
and
other
unsaturated
monoaldehydes
4.0
unsaturated
dihydroxy
dicarbonyl
4.2
hydroxy
ketone
3.0

STOCKWELL
ET
AL.:
REGIONAL
ATMOSPHERIC
CHEMISTRY
MECHANISM
25,849
Table
1.
(continued)
No.
Species
Carbon
Molecular
Definition
Number
Weight
Organic
nitrogen
46
ON
IT
47
PAN
48
TPAN
Organic
peroxides
49
0P1
50
OP2
51
PAA
Organic
acids
52
ORA1
53
ORA2
organic
nitrate
unsaturated
PAN
s
formic
acid
peroxyacetyl
nitrate
and
higher
saturated
PANs
4.0
119
2.0
121
4.0
147
methyl
hydrogen
peroxide
1.0
48
higher
organic
peroxides
peroxyacetic
acid
and
higher
analogs
2.0
76
2.0 62
1.0
46
acetic
acid
and
higher
acids
2.0 60
Organic
Short-Lived
Intermediates
Peroxy
radicals
from
alkanes
54
MO2
methyl
peroxy
radical
55
ETHP
56
HC3P
57
HCSP
58
HC8P
Peroxy
radicals
from
alkenes
59
ETEP
60
OLTP
61
OLIP
Peroxy
radicals
from
biogenic
alkenes
62
ISOP
63
APIP
64
LIMP
Radicals
produced
from
aromatics
65
PHO
66
ADDT
67
ADDX
68
ADDC
69
TOLP
70
XYLP
7
1
CSLP
Peroxy
radicals
with
carbonyl
groups
72
AC03
radicals
73
TC03
74
KETP
Other
peroxy
radicals
75
OLNN
76
OLND
77
X02
1.0
47
peroxy
radical
formed
from
ETH
2.0
61
peroxy
radical
formed
from
HC3
2.9
75
peroxy
radical
formed
from
HC5
4.8
103
peroxy
radical
formed
from
HC8
7.9
145
peroxy
radicals
formed
from
ETE
2.0 77
peroxy
radicals
formed
from
0LT
3.8
91
peroxy
radicals
formed
from
OLI
4.8
117
peroxy
radicals
formed
from
ISO
and
DIEN
5.0
117
peroxy
radicals
formed
from
API
peroxy
radicals
formed
from
LIM
10.0
185
10.0
185
phenoxy
radical
and
similar
radicals
6.6
107
aromatic-HO
adduct
from
TOL
7.1
109
aromatic-H0
adduct
from
XYL
8.9
123
aromatic-HO
adduct
from
CSL
6.6
125
peroxy
radicals
formed
from
TOL
7.1
141
peroxy
radicals
formed
from
XYL
8.9
155
peroxy
radicals
formed
from
CSL
6.6
157
acetyl
peroxy
and
higher
saturated
acyl
peroxy
2.0
75
unsatured
acyl
peroxy
radicals
4.0
115
peroxy
radicals
formed
from
KET
3.9
103
N03-alkene
adduct
reacting
to
form
carbonitrates
+
HO2
3.0
136
NO3-akene
adduct
reacting
via
decomposition
3.0
136
accounts
for
additional
NO
to
N02
conversions
-
--
- - -
ozone
and
nitrogen
dioxide
[Warneck,
1988].
The
photolysis
of
ozone
produces
excited
oxygen
atoms,
0(1D),
and
a
fraction
of
these
react
with
H20
to
produce
the
hydroxy]
radical
(H0).
H0
reacts
with
inorganic
and
organic
species
to
oxidize
them.
Many
of
these
reactions
produce
H02
or
organic
peroxy
rad-
icals
which
either
react
with
N0
to
convert
it
to
N02
or
(under
low
N0,
conditions)
react
to
produce
hydroperoxides.
The
conversion
of
NO
to
N02
and
the
subsequent
photolysis
of
N02
produces
more
ozone.
Ozone
and
N02
react
to
form
nitrate
radical
(NO3)
which
is
a
very
important
reactive
species
during
the
nighttime
[Morris
and
Niki,
1974;
Japar
and
Niki,
1975;
Platt
et
al.,
1980].
The
RACM
mechanism
has
a
reason-
ably
complete
set
of
inorganic
reactions.
The
inorganic
rate
constants
were
set
to
the
values
recommended
by
DeMore
et
al.
[1994],
and
most
of
these
changes
from
RADM2
were
rela-
tively
small.
.
The
cross
sections
and
quantum
yields
for
the
photolysis
of
the
inorganic
species
are
taken
from
DeMore
et
al.
[1994].
For
N03,
DeMore
et
al.
[1994]
recommended
the
data
from
the
review
of
Wayne
et
al.
[1991].
Comparing
the
revised
photolysis
frequencies
to
the
previous
RADM2
values,
there
is
an
in-
crease
of
15-20%
in
the
photolysis
frequencies
for
HONO
and
a
similar
percent
increase
for
both
N03
photolysis
channels.
Larger
relative
changes
occur
for
the
relatively
low
photolysis
frequencies
of
HNO3
and
H02N02.
The
photolysis
frequen-
cies
for
N02
and
O3
remained
nearly
unchanged
after
the
updates.
Several
inorganic
reactions
were
added
to
the
RACM
mech-

25,850
STOCKWELL
ET
AL.:
REGIONAL
ATMOSPHERIC
CHEMISTRY
MECHANISM
Table
2a.
The
RACM
Mechanism:
Photolysis
Reactions
Reaction
No.
Reaction
Photolysis
Frequency,“
s01
Cross
Section
Quantum
Yield
(R1)
(R2)
(R3)
N02
~>
03P
+
NO
O3
—>
O1D
+
O2
03
—>
03P
+
O2
HONO
~>
HO
+
N0
HNO3
—>
H0
+
N02
HNO4
->
0.65
H02
+
0.65
N02
+
0.35
HO
+
0.35
N03
N03 ->
NO
+
02
N03
->
N02
+
03P
.
H202
->
H0
+
HO
HCHO
->
H2
+
co
(R4)
(R5)
(R6)
(R7)
(R8)
(R9)
(R10)
(R11)
(R12)
(R13)
(R14)
(R15)
HCHO
->
2
HO2
+
CO
ALD
—>MO2
+
HO2
+
co
OP1
->
HCHO
+
HO2
+
HO
OP2
+ALD
+
HO2
+
HO
PAA
—>
M02
+
HO
(R16)
(R17)
KET
32
ETHP
+
AC03
GLY
->
0.13
HCHO
+
1.87
co
+
0.87
H2
(R18)
GLY
-—>
0.45
HCHO
+
1.55
CO
+
0.80
HO2
+
0.15
H2
(R19)
MGLY
->
co
+
no,
+
ACO3
DCB
->
TC03
+
H02
5
1
ONIT
»>
0.20
ALD
+
0.80
KET
+
H02
+
N02
(R20)
(R21)
(R22)
MACR
—>
CO
+
HCHO
+
HO2
+
ACO3
(R23)
HKET
->
HCHO
+
HO2
+
AC03
7.50
><
10-3
1.62
><
1075
4.17
><
10-4
DeMore
et
al.
[1994]
DeMore
et
al.
[1994]
DeMore
et
al.
[1994]
1.63
><
10-3
4.50
><
10-’
3.17
><
107“
2.33
><
10-2
1.87
><
10-1
6.00
><
10'°
3.50
><
10-5
DeMore
et
al.
[1994]
DeMore
et
al.
[1994]
DeMore
et
al.
[1994]
Wayne
et
al.
[1991]
Wayne
et
al.
[1991]
DeMore
et
al.
[1994]
wavelengths
<300
nm:
Moortgat
et
al.
[1980]
wavelengths
>300
nm:
Cantrell
et
al.
[1990]
same
references
as
(R10)
Martinez
et
al.
[1992]
DeMore
et
al.
[1994]
same
as
(R13)
H202
cross
sections
2.17
><
10-5
3.67
X
10-6
4.17
><
10*“
4.17
><
10"‘
1.57
><
107°
DeMore
er
al.
[1994]
DeMore
et
al.
[1994]
total
yield
of
01D
and
O3P
asstuned
to
be
unity
DeMore
et
al.
[1994]
assumed
to
be
unity
assumed
to
be
unity
Wayne
et
al.
[1991]
Wayne
et
al.
[1991]
assumed
to
be
unity
wavelengths
<300
nm:
Atkinson
et
al.
[1994]‘°
wavelengths
>300
nm:
DeMore
et
al.
[1994]b
same
references
as
(R10)b
Atkinson
[1994]b
DeMore
et
al.
[1994]
same
as
(R13)
assumed
to
be
unity
scaled
by
0.28;
Giguere
and
Olmos
[1956]
Martinez
et
al.
[1992]
Atkinson
et
al.
[1992b]
6.67
><
10‘7
5.83
X
10_5
Atkinson
[1994]
wavelengths
<340:
0.0
wavelengths
>340:
0.029
Atkinson
et
al.
[1992b]
Wavelengths
<340:
0.4
wavelengths
>340:
0.0
Atkinson
et
al.
[1992b]
estimated
from
Koch
and
Moortgat
[1996]
Stockwell
et
al.
[1990]
Atkinson
[1994]
2.00
><
1005
Atkinson
et
al.
[1992b]
9.33
><
1075
Atkinson
[1994] and
Stajfelbach
et
al.
[1995]
Stockwell
et
al.
[1990]
assumed
to
be
mixture
of
20%
n-propyl
nitrate
and
80%
i-propyl
nitrate;
Atkinson
[1994]
Gardner
et
al.
[1987]
assumed
equal
to
acrolein
same
as
(R16)
4.33
><
10“
2.17
><
10*"
1.33
><
1076
Gardner
et
al.
[1987]
6.67
><
10-7
same
as
(R16)
“Typical
photolysis
frequencies
are
given
for
solar
zenith
angle
40°,
June
21,
summer
surface
40°
northern
latitude.
“Pressure
dependences
given
by
<p()\,
P)
=
<p()t,
1
atm)/{<p(/\,
1
atm)
+
[1
<p()t,
1
atm)]
><
P},
where
P
is
in
atmospheres.
anism.
The
reaction
of
0(3P)
with
nitrogen
oxides,
especially
the
reaction
of
O(3P)
with
N02,
can
be
important
in
the
upper
atmosphere
[Warneck,
1988]:
0(3P)
+
N02
->
NO
+
o,
(1)
O(3P)
+
NO2(+M)
_>
N03(+M)
(2)
0(3P)
+
N0(+M)
->
NO2(+M)
(3)
In
the
original
RADM2
mechanism
the
reaction
of
O(3P)
with
N02
produced
only
NO;
however,
O(3P)
can
also
add
to
N02
to
produce
N03
[DeMore
et
al.,
1994].
Both
reactions
are
now
included
although
rapid
photolysis
of
N03
would
be
expected
to
limit
the
importance
of
(2).
The
reaction
of
0(3P)
with
ozone
was
added
because
it
is
important
in
the
upper
atmosphere
[War-neck,
1988]:
0(3P)
+
03
—>
202
(4)
The
reaction
of
H0
with
H2
is
a
significant
loss
reaction
for
HO
in
the
remote
atmosphere:
no
+
H2
+
(0,)
H02
+
H20
(5)
The rate
constant
for
(5)
at
298
K
is
6.7
><
10'“
cm”
s7‘
[DeMore
et
al.,
1994]
which
is
about
equal
to
the
rate
constant
for
the
HO
+
CH4
reaction,
6.9
><
10_15
cm_3
s_1
[Atkins0n,
1994].
If
the
surface
concentrations
for
H2
and
CH4
are
as-
sumed
to
be
500
and
1700
ppbv,
respectively,
then
the
rate
of
the
reaction
of
HO
with
H2
is
about
30%
that
of
the
H0
+
CH4
reaction.
,
For
completeness,
the
reaction
of
H0
with
nitrous
acid
(6)
was
added.
The
rate
constant
for
this
reaction
is
4.86
><
10712
cm_3
s_1
at
298
K.
The
rate
of
the
HONO
+
HO
is
about
2.4%
of
the
HON
0
photolysis
reaction
if
an
H0
concentration
of
1
><
107
cm_3
and
a
HONO
photolysis
frequency
of
2
><
10-3
s
are
assumed:
I
no
+
HONO
-3
N02
+
H20
(6)
The
reactions
of
N03
are
very
important
for
nighttime
atmo-
spheric
chemistry.
The
N03
self-reaction
(7)
was
added
for
atmospheric
conditions
with
very
high
N0,‘
and
O3
concentra-
tions
during
the
nighttime.
For
example,
for
N03
concentra-
tion
of
300
parts
per
trillion
(ppt)
[Platt
et
al.,
1980]
and
a
NO

STOCKWELL
ET
AL.:
REGIONAL
ATMOSPHERIC
CHEMISTRY
MECHANISM
25,851
Table
2b.
The
RACM
Mechanism
Reaction
No.
Reaction
Au
crn3
s-1
E/R.
K
kfl
Note
(R24)
(R25)
(R26)
(R27)
(R28)
(R29)
(R30)
(R31)
(R32)
(R33)
(R34)
(R35)
(R36)
(R37)
(R33)
(R39)
(R40)
(R41)
(R42)
(R43)
(R44)
(R45)
(R46)
(R47)
(R48)
(R49)
(R50)
(R5.
1)
(R52)
(R53)
(R54)
(R55)
(R56)
(R57)
(R58)
(R59)
(R60)
(R61)
(R62)
(R63)
(R64)
(R65)
(R66)
(R67)
(R68)
(R69)
(R70)
(R71)
(R72)
(R73)
(R74)
(R75)
(R76)
(R77)
(R78)
(R79)
(R80)
(R81)
(R82)
(R83)
(R84)
(R85)
1
Inorganic
Reactions
O3P
+
o2
->
0,
_O3P
+
03
-—>
2
02
010
+
N2
——>O2P
+
N2
Q11)
+
02
->O2P
+
02
010
+
H20
—>HO
+
HO
03+H0-—>HO2+
O2
O3+HO2—>HO
+
202
H0
+
HO2
-.—>
H20
+
02
H202
+
HO
-+
HO2
+
H20
H02
+
H02
-,>
H202
+
02
H02
+
H02
+
H20
—>
H202
+
02
+
H20
03P
+
NO
->
N02
03P
+
N02
—>NO
+
o2
031*
+
N02
->
N03
Ho
+
N0
->
HONO
H0
+
N02
->
HNO3
H0
+
N03
——>
N02
+
H02
H02
+
NO
—>NO2
+
Ho
H02
+
N02
—>
HN04
HNO4
—>
H02
+
N02
H02
+
N03 ->
0.3
HNO3‘+
0.7
N02
+
0.7
HO
+
o2
HO
+
HONO
->
N02
+
H20
HO
+
HNO3
->
N03
+
H20
Ho
+
HN04
->
N02
+
02
+
H20
O3+NO—>NO2+O2
0,
+
N02
—->NO3
+
02
NO
+
N0
+
02->No2
+
N02
N03
+
N0
->
N02
+
N02
N03
+
N02
->NO
+
N02
+
02
NO3
+
N02
->
N205
N20,
->
N02
+
N03
N03
+
N03
->
N02
+
N02
+
02
Ho
+
H2
—>H2O
+
H02
Ho
+
so2
->
SULF
+
H02
co
+
Ho
-—>I-I02
+
co2
O31’
+
Organic
Compounds
ISO
+
O21’
—>
0.86
OLT
+
0.05
HCHO
+
0.02
I-IO
+0.01
CO
+
0.13
DCB
+
0.28
HO2
+
0.15
xo2
MACR
+
0212
-—>
ALD
HO
+
Organic
Compounds
CH4
+
H0
-—>
M02
+
H20
ETH
+
H0
—>
ETHP
+
H20
.
HC3
+
HO
—>
0.583
HC3P
+~
0.381
HO2
+
0.335
ALD
+
0.036
ORA1
+
0.036
C0
+
0.0361GLY
+
0.036
HO
+
0.010
HCHO
+
H20
HC5
+
HO
->
0.75
HC5P
+
0.25
KET
+
0.25
H02
+
I-I20
HC8
+
HO
—_>
0.951
HC8P
+
0.025
+
0.024
HKET
+
0.049
HO2
+
H20
'
ETE
+
Ho
->
ETEP
OLT
+
HO
—>
OLTP
OLI
+
H0
—>
OLIP
DIEN
+
I-IO
->
ISOP
ISO
+
H0
—>
ISOP
API
+
H0
—>
APIP
LIM
+
HO
-—>
LIMP
TOL
+
HO
-—>
0.90
ADDT
+
0.10
X02
+
0.10
HO2
XYL
+
H0
~>
0.90
ADDX
+
0.10
X02
+
0.10
HO2
csr.
+
Ho
->
0.85
ADDC
+
0.10
PHO
+
0.05
H02
+
0.05
xo2
HCHO
+
H0
——>
H02
+
C0
+
H20
ALD
+
H0
—>
ACO3
+
H20
KET
+
H0
—>
KETP
+
H20
HKET
+
HO
-> H02
+
MGLY
+
H20
GLY
+
H0——>H02
+
2C0
+
H20
MGLY
+
Ho
->
AC03
+
co
+
H20
MACR
+
HO
—>
0.51
TCO3
+
0.41
HKET
+
0.08
MGLY
+
0.41
C0
+
0.08
HCHO
+
0.49
Ho,
+
0.49
xo2
DCB
+
H0
—~—>0.50
TC03
+
0.50
H02
+
0.50
X02
+
0.35
UDD
+
0.15
GLY
+
0.15
MGLY
1
UDD
+
I-I0
——>
0.88
ALD
+
0.12
+
HO2
OP1
+
HO
->
0.65
M02
+
0.35
HCHO
+
0.35
H0
Table
2f
8.00
X‘
10'“
1.80
X
10'“
3.20
X
10'“
2.20
><
10-1°
1.60
X
10'12
1.10
><
10-“
4.80
X
10'“
2.90
><
10'”
Table
2f
Table
2f
Table
2d
6.50
X
10'“
'
Table
2d
Table
2d
Table
2d
2.20
X
10'“
3.70
X
10'”
Table
2d
Table
2e
3.50
X
10'12
1.80
><
10'“
Table
2f
1.30
X
10'”
2.00
X
10'“
1.20
><
10'“
3.30
X
10'”
1.50
X
10'“
4.50
X
10'“
Table
2d
Table
2e
8.50
X
10'”
5.50
><
10'12
Table
2d
Table
2f
6.00
X
10-11
1.59
X
10'“
Table
2c
Table
2c
5.26
X
10'12
8.02
X
10-12
1.64
X
10-“
1.96
X
10-12
5.72
X
10-12
1.33
X
10-“
1.48
X
10'-11
2.54
X
10-11
1.21
X
10-“
1.70
X
10-1°
1.81
><
10-12
7.30
X
10-12
6.00
X
10-11
1.00
X
10'“
5.55
><
10-12
Table
2c
3.00
><
10-"
1,14
X
10-“
1.72
X
10-11
1.86
X
10-11
2.80
><
10-"
2.70
><
10-1°
2.93
><
10-12
2060
-
110
_7Q
940
500
_25O
160
-120
-250
390
-380
1400
2450
-530
-170
1260
2450
2000
-13
260
155
125
-438
~500
-500
-448
-410
-444
-355
-355
-331
-175
-
175
-190
1.50
X
10-14
7,96
><
10-15
2.60
X
10-11
4.05
X
10-“
2.20
X
10-1°
6.83
X
10-14
2.05
X
10-15
1.11
X
10-1°
1.70
><
10-"
2.92
X
10-12
6.58
X
10-2°
1.66
X
10-12
9.72
><
10"’
1.58
x
10-12
4.87
><
10'”
1.15
X
10-11
2.20
X
10-11
8.56
><
10'“
1.39
X
10-12
8.62
X
10-2
3.50
X
10-12
4.86
><
10-12
1.47
X
10-12
4.65
X
10-12
1.82
x
10'“
3.23
X
10-17
1.95
><
10-38
2.65
X
10-“
6.56
x
10'“
1.27
><
10'“
4.36
X
10-2
2.29
X
10-16
6.69
><
10'“
8.89
X
10-13
2.40
X
10-12
6.00
X
10-“
1.66
X
10-11
6.86
X
10-15
2.57
X
10-12
2.20
X
10"?
4.77
X
10-12
1.08
X
10-“
8.52
><
10-"
3.06
><
10-“
7.12
><
10-"
6.65
><
10-"
1.01
><
10-1°
5.37
><
10'“
1.71
x
10-1°
5.96
><
10-12
2.40
><
10-“
6.00
><
10-“
1.00
><
10-“
1.69
><
10-"
6.87
><
10-“
3.00
><
1,0-12
1.14
><
10-“
1.72
><
10-"
3.35
><
10'“
5.04
X
10-“
2.70
X
10-1°
5.54
><
10-"
ti.
,4
o—l>—\>—\t-I>-\|-\1-rd-At-rt-ILard!-+l\)-r—\>—\t~t-4tied)-\>~>-mar-1»-\>—\>-Aland»-1»-¢1—t—\
5
6
7
7
8
8
8
>1
>1.“
-)—l
F-11
i—\0@
r.»\n\>\1\:\1t->-o~4\|\z\-|\1oooo\|
14
15
7

Citations
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Journal ArticleDOI
TL;DR: Air pollutants consist of a complex combination of gases and particulate matter, which is emitted directly into the atmosphere or formed in the atmosphere through gas-to-particle conversion (secondary) (Figure 1).
Abstract: Urban air pollution represents one of the greatest environmental challenges facing mankind in the 21st century. Noticeably, many developing countries, such as China and India, have experienced severe air pollution because of their fast-developing economy and urbanization. Globally, the urbanization trend is projected to continue: 70% of the world population will reside in urban centers by 2050, and there will exist 41 megacities (with more than 10 million inhabitants) by 2030. Air pollutants consist of a complex combination of gases and particulate matter (PM). In particular, fine PM (particles with the aerodynamic diameter smaller than 2.5 μm or PM_(2.5)) profoundly impacts human health, visibility, the ecosystem, the weather, and the climate, and these PM effects are largely dependent on the aerosol properties, including the number concentration, size, and chemical composition. PM is emitted directly into the atmosphere (primary) or formed in the atmosphere through gas-to-particle conversion (secondary) (Figure 1). Also, primary and secondary PM undergoes chemical and physical transformations and is subjected to transport, cloud processing, and removal from the atmosphere.

931 citations

Journal ArticleDOI
TL;DR: Current knowledge about the phloem transport mechanisms is summarized and the effects of several abiotic (water and salt stress, mineral deficiency, CO2, light, temperature, air, and soil pollutants) and biotic andmutualistic and pathogenic microbes, viruses, aphids, and parasitic plants are reviewed.
Abstract: Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose (and some other sugars such as raffinose and polyols) across plant organs through the phloem. However, sugar transport through the phloem can be affected by many environmental factors that alter source/sink relationships. In this paper, we summarize current knowledge about the phloem transport mechanisms and review the effects of several abiotic (water and salt stress, mineral deficiency, CO2, light, temperature, air, and soil pollutants) and biotic (mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants) factors. Concerning abiotic constraints, alteration of the distribution of sugar among sinks is often reported, with some sinks as roots favored in case of mineral deficiency. Many of these constraints impair the transport function of the phloem but the exact mechanisms are far from being completely known. Phloem integrity can be disrupted (e.g., by callose deposition) and under certain conditions, phloem transport is affected, earlier than photosynthesis. Photosynthesis inhibition could result from the increase in sugar concentration due to phloem transport decrease. Biotic interactions (aphids, fungi, viruses…) also affect crop plant productivity. Recent breakthroughs have identified some of the sugar transporters involved in these interactions on the host and pathogen sides. The different data are discussed in relation to the phloem transport pathways. When possible, the link with current knowledge on the pathways at the molecular level will be highlighted.

852 citations


Cites background from "A new mechanism for regional atmosp..."

  • ...Ozone mainly originates from photochemical reactions of volatile organic compounds with nitrogen oxides (NOx) released from anthropogenic and natural sources (Stockwell et al., 1997)....

    [...]

Journal ArticleDOI
TL;DR: The Secondary Organic Aerosol Model (SORGAM) as mentioned in this paper has been developed for use in comprehensive air quality model systems and is capable of simulating secondary organic aerosol (SOA) formation including the production of lowvolatility products and their subsequent gas/particle partitioning.
Abstract: The Secondary Organic Aerosol Model (SORGAM) has been developed for use in comprehensive air quality model systems. Coupled to a chemistry-transport model, SORGAM is capable of simulating secondary organic aerosol (SOA) formation including the production of low-volatility products and their subsequent gas/particle partitioning. The current model formulation assumes that all SOA compounds interact and form a quasi-ideal solution. This has significant impact on the gas/particle partitioning, since in this case the saturation concentrations of the SOA compounds depend on the composition of the SOA and the amount of absorbing material present. Box model simulations have been performed to investigate the sensitivity of the model against several parameters. Results clearly show the importance of the temperature dependence of saturation concentrations on the partitioning process. Furthermore, SORGAM has been coupled to the comprehensive European Air Pollution and Dispersion/Modal Aerosol Dynamics Model for Europe air quality model system, and results of a three-dimensional model application are presented. The model results indicate that assuming interacting SOA compounds, biogenic and anthropogenic contributions significantly influence each other and cannot be treated independently.

811 citations

Journal ArticleDOI
TL;DR: In this paper, a new lumped-structure mechanism called CBM-Z was proposed, which extends the original framework to function properly at larger spatial and longer time scales.
Abstract: The lumped-structure approach for condensing organic chemical mechanisms is attractive, since it yields fewer species and reactions, and reduces computational costs. This paper leads through the development of a new lumped-structure mechanism, largely based on the widely used Carbon Bond Mechanism (CBM-IV) developed by Gery et al.[1989]. The new mechanism called CBM-Z, extends the original framework to function properly at larger spatial and longer time scales. The major modifications in the mechanism include: revised inorganic chemistry; explicit treatment of the lesser reactive paraffins - methane and ethane; revised parameterizations of the reactive paraffin, olefin and aromatic reactions; inclusion of alkyl and acyl peroxy radical interactions and their reactions with NO3; inclusion of organic nitrates and hydroperoxides; and refined isoprene chemistry based on the condensed one-product mechanism of Carter[1996a,b]. CBM-Z was successfully evaluated along with the CBM-IV, a partially revised CBM-IV and a revised RADM2 mechanism[Stockwell et al., 1990; Kirchner and Stockwell, 1996] using the low VOC and NOx concentration smog chamber experiments of Simonaitis et al.[1997]. Box-model versions of the four mechanisms were also evaluated under a variety of hypothetical urban and rural scenarios for a period of 30 days. Results from CBM-Z and revised RADM2 were found to bemore » within (+/-) 20% of each other, while CBM-IV and revised CBM-IV results deviated significantly by up to 50-95%. Sensitivity tests were performed to elucidate the effects of some of the new features added in CBM-Z. Relative computational memory and time requirements of these mechanisms are also discussed.« less

739 citations

References
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15 Aug 1992
TL;DR: As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided in this article, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena.
Abstract: As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided. The primary application of the data is in the modeling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. Copies of this evaluation are available from the Jet Propulsion Laboratory.

3,218 citations

01 Aug 1992
TL;DR: As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided in this paper, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena.
Abstract: As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided. The primary application of the data is in the modeling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. Copies of this evaluation are available from the Jet Propulsion Laboratory.

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TL;DR: The Gaussian Plume Equation and Air Quality Models Atmospheric Removal Processes and Residence Times Air Pollution Statistics Acid Rain Index (AIRI) as mentioned in this paper, which measures the amount of acid rain in the air.
Abstract: Air Pollutants Effects of Air Pollution Sources of Pollutants in Combustion Processes Gas-Phase Atmospheric Chemistry Aqueous-Phase Atmospheric Chemistry Mass Transfer Aspects of Atmospheric Chemistry Properties of Aerosols Dynamics of Single Aerosol Particles Thermodynamics of Aerosols and Nucleation Theory Dynamics of Aerosol Population Air Pollution Meteorology Micrometeorology Atmospheric Diffusion Theories The Gaussian Plume Equation The Atmospheric Diffusion Equation and Air Quality Models Atmospheric Removal Processes and Residence Times Air Pollution Statistics Acid Rain Index.

2,708 citations

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29 Oct 1999
TL;DR: In this paper, the authors present the bulk composition, structure, and dynamics of the atmosphere and discuss the chemistry of the Troposphere: the Methane Oxidation Cycle, ozone, and sulfur compounds.
Abstract: Bulk Composition, Structure, and Dynamics of the Atmosphere. Photochemical Processes and Elementary Reactions. Chemistry of the Stratosphere. Chemistry of the Troposphere: The Methane Oxidation Cycle. Ozone in the Troposphere. Hydrocarbons, Halocarbons, and Other Volatile Organic Compounds. The Atmospheric Aerosol. Chemistry of Clouds and Precipitation. Nitrogen Compounds in the Troposphere. Sulfur Compounds in the Atmosphere. Geochemistry of Carbon Dioxide. The Evolution of the Atmosphere. References. Appendix: Supplementary Tables.

1,528 citations

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01 Jan 1986
TL;DR: In this article, the authors provide a comprehensive coverage of the discipline of atmospheric chemistry, starting with the fundamentals of kinetics and photochemistry, and show how the experimental techniques in these areas are applied to the study and control of chemical reactions in the troposphere.
Abstract: This book provides coverage of the discipline of atmospheric chemistry. Starting with the fundamentals of kinetics and photochemistry, it shows how the experimental techniques in these areas are applied to the study and control of chemical reactions in the troposphere. It gives detailed analysis of such major societal issues as smog, acid rain and volatile toxic organics. It also treats the seven criteria pollutants considered by the U.S. Environmental Protection Agency to be hazardous, as well as a variety of trace noncriteria pollutants, such as those cited in the Clean Air Act of 1977.

1,298 citations

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Q1. What contributions have the authors mentioned in the paper "A new mechanism for regional atmospheric chemistry modeling" ?

A new gas-phase chemical mechanism for the modeling of regional atmospheric chemistry, the “ Regional Atmospheric Chemistry Mechanism ” ( RACM ) is presented.