Nocturnal Vertical Gradients of O

3

, NO

2

, NO

3

, HONO, HCHO, and SO

2

during CalNex 2010

Tsai Catalina, Kam Weng Wong, Olga Pikelnaya, Steven C. Hurlock, Ross Cheung, Christine Haman, Barry Lefer, and Jochen Stutz University of California, Los Angeles

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 NO 3 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 in the Polluted BL

O 3 NO 3 NO 2

Residual Layer

O 3 NO N 2 O 5

Stable Nocturnal Boundary Layer

O 3

HC

NO 3 NO 2 N 2 HONO O 5 NO 2 OH + NO O 3 NO

CalNex LP-DOAS Set Up

• •

May 15 2010 – June 16 2010 Los Angeles Supersite: Caltech Detection Limits

2,20 1,8 Average Best 0,48 0,12 0,023 0,04 0,009 0,32 0,093 0,05 0,019 O3 [ppb] NO2 [ppb] HONO [ppb] HCHO [ppb] SO2 [ppb] 0,54 NO3 [ppt] (LP-DOAS) (Google map)

Trace Gas Profile Retrieval

Measured Path Averaged Concentrations Retrieved Height Interval Concentrations (subtracting scale from the ground upwards)

Highest Interval (255-556m) 301m (121-255m) 134m (78-121m) 43m (33-78m) 45m 10m 33m Upper Interval Middle Interval Lowest Interval 5.4 km 5.6 km 6.3 km 7.0 km

Trace Gases Vertical Profiles

NO 3 [ppt] 100 0 NO 2 [ppb] 20 0 HONO [ppb] 0.5

0.0

HCHO [ppb] 5 0 O 3 [ppb] 50 SO 2 [ppb] 0 2 1 0 5/23 5/24 5/25 5/26 PDT 5/27 5/28 5/29 5/30 lower (33-78m) middle (78-121m) upper (121-255m) highest (255-556m)

Trace Gases Vertical Profiles

75 Ox (NO 2 +O 3 ) [ppb] 60 45 30 May 29– 30, 2010 lower (33-78m) middle (78-121m) upper (121-255m) highest (255-556m) O 3 [ppb] 60 40 20 30 NO 2 [ppb] 20 10 0 18:00 20:00 22:00 00:00 PDT 02:00 04:00 06:00 08:00 2000 Los Angeles log 10 of backscatter in 10 -9 m -1 sr -1 1500 1000 4 3.5

500 0 3 2.5

2 20:00 02:00 Time 1200 s mean 08:00 • Stable Nocturnal Boundary Layer.

• Profiles are driven by titration of O 3 by NO.

O

3

+ NO → NO

2

+ O

2

Nocturnal Vertical Gradient

NO 3 [ppt] 100 0 NO 2 [ppb] 20 0 HONO [ppb] 0.5

0.0

HCHO [ppb] 3 0 O 3 [ppb] 50 10 SO 2 [ppb] 0.5

0.0

18:00 20:00 22:00 00:00 PDT 02:00 04:00 06:00 08:00 lower (33-78m) middle (78-121m) upper (121-255m) highest (255-556m)

NO

3

Chemistry

 NO3 10000 1000 100 [s] 10 N 2 O 5 [ppt] 2000 1000 0 NO 3 [ppt] 50 0 O 3 [ppb] 50 0 NO 2 [ppb] 20 0 18:00 May 26 – 27, 2010 lower (33-78m) middle (78-121m) upper (121-255m) highest (255-556m) 20:00 22:00 00:00 PDT 02:00 04:00 06:00 08:00

NO 3 production rate:

τ NO3 (PSS) = (K 1 (T) •[NO 2 ] •[O 3 ]) [NO 3 ] P(NO 3 ) = K 1 (T) •[NO 2 ] •[O 3 ] K 1 = 1.43x10

-13 *e -2470/T

Mixing ratio of N

NO 3 + NO 2 + M ↔ N 2 O 5 + M K = 5.58x10

-27 *e 10724/T

2 O 5

NO

3

Chemistry

 NO3 10000 1000 100 [s] 10 N 2 O 5 [ppt] 2000 1000 0 NO 3 [ppt] 100 0 O 3 [ppb] 50 NO 2 [ppb] 0 20 0 5/23 5/24 5/25 5/26 PDT 5/27 5/28 5/29 5/30 lower (33-78m) middle (78-121m) upper (121-255m) highest (255-556m)

NOx loss in the NBL

Reactions of NO 3 radical: a) NO 3 + NO → 2 NO 2

zero NOx loss

b) NO 3 + HC → organic nitrates → → SOA c) NO 3 → → aerosol uptake

1 NOx loss 1 NOx loss

d) NO 3 + NO 2 ↔ N 2 O 5 →aerosol uptake

2 NOx loss

Overall loss frequency of NO 3 radical : f NO3 (tot) = f NO3 (NO) + f NO3 (HC) + f NO3 (aer) + f NO3 (N 2 O 5 )

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 NO

3

Loss Rate

f NO3 (tot) = f NO3 (NO) + f NO3 (HC) + f NO3 (aer) + f NO3 (N 2 O 5 )

(Observations scaled with vertical profiles)

0.35

0.30

f NO3 (PSS) altitude 33-78m f NO3 (HC) altitude 33-50m 0.25

f NO3 [s -1 ] 0.20

0.15

0.10

0.05

0.00

5/30 6/1 6/3 6/5 6/7 6/9 6/11 PDT

(HC data provided by NOAA)

Preliminary NOx Loss

NOx Loss Rate 4 3 2 1 0 5/21 5/22 5/23 5/24 5/25 5/26 5/27 5/28 5/29 5/30 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)

Conclusion

•

Nocturnal vertical gradients

of trace gases were observed during CalNex. •

Ozone and NO 2

showed typical

diurnal variation

polluted areas: small ozone and large NO 2 found in mixing ratios at night and the opposite during the day.

•

Nocturnal NO 3 and N 2 O 5

mixing ratios were elevated during the experiment, indicating an

active radical chemistry

in the nocturnal boundary layer during CalNex -Los Angeles • Assuming that NO 3 is predominantly lost through N 2 O 5 uptake we found

~ 1ppb/hr nocturnal NOx loss

averaged over the lowest 500 m of the atmosphere (Houston ~1ppb/hr).

OUTLOOK

• Vertical profiles of HCHO and HONO will be investigated.

4 3 HCHO [ppb] 2 1 Lower Middle Upper Highest 0 12:00 16:00 20:00 24:00 PDT 04:00 08:00 12:00 0.05

0.04

0.03

0.02

0.01

0.00

0.4

HONO [ppb] 0.3

0.2

0.1

0.0

20:00 00:00 04:00 08:00 PDT 12:00 16:00 20:00 • Further analysis using the 1D model will be performed to analyze NO 3 ,HCHO, HONO and ClNO 2 .

Acknowledgement

California Air Resources Board Caltech