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

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.

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

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

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

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

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

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

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

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

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)

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

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)

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

• 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

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

Acknowledgement

Caltech

California Air Resources Board