University of California, Los Angeles
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University of California, Los Angeles
Nocturnal Vertical Gradients of O3, NO2, NO3, HONO, HCHO, and SO2
during CalNex 2010
Tsai Catalina, Kam Weng Wong, Olga Pikelnaya, Steven C. Hurlock, Ross Cheung, Christine Haman, Barry Lefer, and Jochen Stutz
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Motivation
• To better understand the chemical and mixing processes that influence atmospheric composition at night.
• To determine the removal of NOx from the nocturnal boundary layer by NO3 chemistry.
• To study the formation of HONO and its impact on OH.
• To examine how nocturnal chemistry affects the initial condition for ozone formation during the day.
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Nocturnal Chemistry
NO3O3
N2O5
HONO
HC
NO2
NO
O3
NO3
O3
N2O5
NO2
Stable Nocturnal Boundary Layer
Residual Layer
Capping Inversion
NO2 NO
O3
OH + NO
Nocturnal Chemistry in the Polluted BL
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O3 [ppb]
NO2 [ppb]
HONO [ppb]
HCHO [ppb]
SO2 [ppb]
NO3 [ppt]
1.83
0.12 0.04 0.32 0.05
2.20
0.4750.023 0.009 0.093 0.019
0.544
Detection Limits
Average Best
CalNex LP-DOAS Set Up
(Google map)
(LP-DOAS)• May 15 2010 – June 16 2010• Los Angeles Supersite: Caltech
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Trace Gas Profile Retrieval
33m 78m
556m
(255-556m) 301m
(121-255m) 134m
(78-121m) 43m
(33-78m) 45m
5.4 km5.6 km6.3 km7.0 km
Highest Interval
Upper Interval
Middle Interval
Lowest Interval
Measured Path Averaged ConcentrationsRetrieved Height Interval Concentrations (subtracting scale from the ground upwards)
255m121m
10m 78m
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Trace Gases Vertical Profiles
0
20
0.00.5
0
5
0
50
5/23 5/24 5/25 5/26 5/27 5/28 5/29 5/30012
0
100
NO3
[ppt]
HONO[ppb]
SO2
[ppb]
O3
[ppb]
HCHO[ppb]
NO2
[ppb]
lower (33-78m) middle (78-121m) upper (121-255m) highest (255-556m)
PDT
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Trace Gases Vertical ProfilesMay 29– 30, 2010
2000
1500
1000
500
0
20:00 02:00 08:00
2
2.5
3
3.5
4
Los Angeles log10 of backscatter in 10-9 m-1 sr-1
Heig
ht in
m, 2
40 m
mea
n til
ted
by 2
0
Time 1200 s mean20
40
60
18:00 20:00 22:00 00:00 02:00 04:00 06:00 08:000
10
20
30
30
45
60
75
Ox (NO2+O3)
[ppb]
lower (33-78m) upper (121-255m) middle (78-121m) highest (255-556m)
O3
[ppb]
NO2
[ppb]
PDT
•Stable Nocturnal Boundary Layer.•Profiles are driven by titration of O3 by NO.
O3 + NO → NO2 + O2
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0
20
0.00.5
0
3
10
50
18:00 20:00 22:00 00:00 02:00 04:00 06:00 08:000.0
0.5
0
100
NO3
[ppt]
HONO[ppb]
SO2
[ppb]
O3
[ppb]
HCHO[ppb]
NO2
[ppb]
lower (33-78m) middle (78-121m) upper (121-255m) highest (255-556m)
PDT
Nocturnal Vertical GradientMay 29 – 30, 2010
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010002000
0
50
0
50
18:00 20:00 22:00 00:00 02:00 04:00 06:00 08:000
20
10100
100010000
NO3[s]
N2O5
[ppt]
NO2
[ppb]
O3
[ppb]
NO3
[ppt]
lower (33-78m) upper (121-255m) middle (78-121m) highest (255-556m)
PDT
NO3 ChemistryMay 26 – 27, 2010
NO3 production rate:
τNO3(PSS) = (K1(T) •[NO2] •[O3]) [NO3]
P(NO3) = K1(T) •[NO2] •[O3]
K1 = 1.43x10-13*e-2470/T
Mixing ratio of N2O5
NO3 + NO2 + M ↔ N2O5 + M
K = 5.58x10-27*e10724/T
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NO3 Chemistry
010002000
0
100
0
50
5/23 5/24 5/25 5/26 5/27 5/28 5/29 5/300
20
10100
100010000
lower (33-78m) middle (78-121m) upper (121-255m) highest (255-556m)
NO3[s]
N2O5
[ppt]
NO2
[ppb]
O3
[ppb]
NO3
[ppt]
PDT
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NOx loss in the NBL
(Stutz et al., 2010)
Reactions of NO3 radical:
a) NO3 + NO → 2 NO2 zero NOx loss
b) NO3 + HC → organic nitrates → → SOA 1 NOx loss
c) NO3 → → aerosol uptake 1 NOx loss
d) NO3 + NO2 ↔ N2O5 →aerosol uptake 2 NOx loss
Overall loss frequency of NO3 radical :
fNO3(tot) = fNO3(NO) + fNO3(HC) + fNO3(aer) + fNO3(N2O5)
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RCAT8.2 1-D radical chemistry and transport model
• Gas-phase Regional Atmospheric Chemistry Mechanism (RACM) : - 84 reactive species - 249 gas-phase chemical reactions
• 27 boxes from 0-3 km (log scale below 1 m).
• Biogenic and anthropogenic emissions .
• Deposition and chemistry on ground and aerosol.
May 27 – 28, 2010
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Preliminary NO3 Loss Rate
(HC data provided by NOAA)
fNO3(tot) = fNO3(NO) + fNO3(HC) + fNO3(aer) + fNO3(N2O5)
5/30 6/1 6/3 6/5 6/7 6/9 6/110.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
fNO3
[s-1]
PDT
fNO3(PSS) altitude 33-78m fNO3(HC) altitude 33-50m
(Observations scaled with vertical profiles)
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5/21 5/22 5/23 5/24 5/25 5/26 5/27 5/28 5/29 5/300
1
2
3
4
NOx lo
ss [p
pb/h
r]
PDT
Lower (33-78m)Middle (78-121m)Upper (121-255m)Highest (255-556m)All intervals (33-556m)Mean All intervals(33-556m) Mean lowest 3 intervals (33-255m)
Preliminary NOx Loss
NOx Loss Rate
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• Nocturnal vertical gradients of trace gases were observed during CalNex.
• Ozone and NO2 showed typical diurnal variation found in polluted areas: small ozone and large NO2 mixing ratios at night and the opposite during the day.
• Nocturnal NO3 and N2O5 mixing ratios were elevated during the experiment, indicating an active radical chemistry in the nocturnal boundary layer during CalNex -Los Angeles
• Assuming that NO3 is predominantly lost through N2O5 uptake we found ~ 1ppb/hr nocturnal NOx loss averaged over the lowest 500 m of the atmosphere (Houston ~1ppb/hr).
Conclusion
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OUTLOOK• Vertical profiles of HCHO and HONO will be investigated.
• Further analysis using the 1D model will be performed to analyze NO3 ,HCHO, HONO and ClNO2.
20:00 00:00 04:00 08:00 12:00 16:00 20:000.0
0.1
0.2
0.3
0.40.00
0.01
0.02
0.03
0.04
0.05
[HON
O]/[N
O 2]
HONO[ppb]
PDT
O3
HC
HO
12:00 16:00 20:00 24:00 04:00 08:00 12:000
1
2
3
4
PDT
HCHO[ppb]
Lower Middle Upper Highest
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Acknowledgement
Caltech
California Air Resources Board