Widespread Halogen Activation by N2O5 Heterogeneous Chemistry

Joel ThorntonDepartment of Atmospheric Sciences

University of Washington, Seattlethornton@atmos.washington.edu

J.P. Kercher, T.P. Riedel, N.L. Wagner, J. Cozic, J. Holloway, W.P. Dubé,

G.M. Wolfe, P.K. Quinn, A.M. Middlebrook, B. Alexander, and S.S. Brown

UW – NOAA ESRL and PMEL Collaboration

Tropospheric Chlorine Cycling

ClCl-X

activationactivation CCxxHHyy

acid acid displacementdisplacementCl- HCl

sea spraysea spray~10,000 Tg~10,000 Tg

Anthro. +Anthro. +3 – 5 Tg3 – 5 Tg

Graedel and Keene, GBC,1995

25-35 Tg* *From methane isotopes measured in remote SH MBL

Platt, ACP 2004Allan, JGR 2007

Chlorine Cycling: New Addition

NO3

NO2 ClNO2

N2O5acid acid

displacementdisplacementpCl-

Cl

HCl

activationactivation CCxxHHyy

8 – 22 Tg Cl yr-1

Reference: Thornton, et al Nature 2010

ClNO2 Production

HX

(s)

HX(g)

XNO 2(s) + HNO3(s)

References: Finlayson-Pitts et al. 1989; Behnke et al, 1989, 1992; Thornton and Abbatt, 2005; Bertram et al 2009; Raff et al 2009

Instantaneous ClNO2 Yield

References: Benkhe, et al JGR 1997; Roberts, et al GRL 2009; Bertram and Thornton, ACP 2009

0.0

0.2

0.4

0.6

0.8

1.0

ClN

O 2 Yie

ld

Fine Mode Chloride Mass Fraction

80% RH

30% RH

10-6 10-5 10-4 10-3 10-2 10-10.0

0.2

0.4

0.6

0.8

1.0

50% RH

N2O5(aq)

ClNO2 + NO3-

2HNO3

Cl-

H2O

2 2

1

1 H O

Cl

k H O

k Cl

Population Average Instantaneous ClNO2 Yield

References: Benkhe, et al JGR 1997; Roberts, et al GRL 2009; Bertram and Thornton, ACP 2009

10 100 1000Dp (nm)

dS

/dlo

g(D

p)

(rp) ~ 0.1

=1 =0

Surface Area Distribution

Total Chlorine = pCl- + HCl(g)

Cl- HCl(g)Equilibrium Equilibrium

repartitioningrepartitioning

0 1 2 3 4 5 610

-1

100

101

102

103

104

105

pH

HC

l(g

)/p

Cl

(mo

l/m

ol)

ClNO2 as a Cl Atom Source

Erickson et al 1996 0.06 Tg Cl yr-1 (MBL only)

Osthoff et al 2008 3.2 Tg Cl yr-1 (Coastal and MBL only)

“Bottom up” global Cl atom source from ClNO2

“Top-down” global Cl atom source

Allan, et al 2004 22 - 35 Tg Cl yr-1

Platt, et al 2004 ~ 35 Tg Cl yr-1

“Bottom up” local Cl atom source from ClNO2

Pechtl and von Glasow: ClNO2 < 50 ppt in Long Island Sound (during June)

UW-Chemical Ionization Mass SpectrometerCDC

Octupole

Quadrupole

electronmultiplier

CH3I/ N2

IMR

I- + ClNO2 I-ClNO2-

I- + N2O5 I-N2O5-

McNeill, et al Atmos. Chem. Phys. 2006Kercher, et al Atmos. Meas. Tech. 2009

~ 1-5 pptv in 1 second

V. Faye McNeill (now at Columbia University)

James P. Kercher (now at Hiram College)

Theran P. Riedel (UW Graduate Student)

ClNO2 in the Long Island Sound and Beyondlog([ClNO2])

78 79 80 81 82 83 84 850

250

500

750 N

2O

5

ClNO2

N2O

5 &

ClN

O2

Mix

ing

Rat

ion

/ppt

Fractional DOY /UTC

53W

57W63W71W

1500ppt

Observed ClNO2 is 2 – 20x greater than previous model predictions for Long Island

Sound (e.g. Pechtl and von Glasow, GRL 2007)

ClNO2 production still evident in outflow 1 – 2 days downwind

N2O5

HNO3

ClNO2

Cl- Cl

NO2

N2O5

HNO3

ClNO2

Cl- Cl

NO2

ClNO2 ~0.5

Psuedo-Lagrangian Model Predictionsp

pb

vN

O2 p

pb

v

ClN

O2 o

r N

2O

5 p

ptv

Fraction of NOx Reacting via N2O5

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

A B

C D

W Sp

Su Au

~ 38% of NOx removed by N2O5 over U.S.

GEOS-Chem output from B. Alexander

25.5 26.0 26.50

200

400

600

800

1000

N2O

5

ClNO2

Mix

ing

Ra

tio (

pp

tv)

February 2008 (local time)

(*Parking Lot behind ESRL’s David H. Skaags Building)

ClNO2 and N2O5 in Boulder, CO*

37Cl (cps)

35 C

l (cp

s)

Detailed Behavior of N2O5 and ClNO2

1 1.2 1.40

100

200

300

400

500

600

700

Hour of Day (local)

Mix

ing

Ra

tio

(p

ptv

)

6 7 8 9 10 110

200

400

600

800

1000

1200

1400

Hour of Day (local)

N2O

5

ClNO2

NO /10

BA

ACCRONIM February 11 - 25 2009

N2O5 and ClNO2

CO, O3

NO, NO2

Particle surface area

Water-soluble particle composition

Meteorology (RH, T, Winds)

Kohler Mesa, Boulder, CO

Reference: Thornton, et al Nature 2010

ACCRONIM Overview

12 14 16 18 20 22 240

50

100

0

500

1000

1500

0

100

200

300

400

500

February 2009

pC

l- (p

ptv

)

N2O

5 (p

ptv

)

ClN

O2 (

pp

tv)

Reactant and Product Relationships

12 14 16 18 20 22 240

50

100

0

500

1000

1500

0

100

200

300

400

500

February 2009

pC

l- (p

ptv

)

N2O

5 (p

ptv

)

ClN

O2 (

pp

tv)

47.5 47.55 47.6

250

500

750

300

600

900

1200N2O

5

ClNO2

0 200 400 600 800 1000 1200 14000

100

200

300

400

500

Feb. 13 - 14th

Feb. 15 - 16th

Feb. 21 - 22nd

ClN

O2 (

pp

tv)

N2O

5 (pptv)

ClNO2 and N2O5 broadly correlated

But relationship changes night-to-night and within a night

Total Chloride

0 3 6 9 12 15 18 21 240

50

100

150

200

0 4 8 12

0

100

200

300

400

500

600

ClNO2

4X pCl-

Mix

ing

Rat

io (

pptv

)

Hour of Day (local)

A

ClNO2

pCl-

B

Mix

ing

Rat

io (

pptv

)

Hours Since Sunset

Feb. 15 - 16 Observations and Modeling

0 3 6 9 12 15 18 21 240

50

100

150

200

0 4 8 12

0

100

200

300

400

500

600

ClNO2

4X pCl-

Mix

ing

Rat

io (

pptv

)

Hour of Day (local)

A

ClNO2

pCl-

B

Mix

ing

Rat

io (

pptv

)

Hours Since Sunset

Feb. 15 - 16 Observations and Modeling

ClNO2 routinely 4 – 10x greater than particulate Cl-, suggesting important role for HCl(g)

Consistent with observationally constrained thermodynamic aerosol model

Chemical Box Modeling – 2 Examples

12 14 16 18 20 22 240

50

100

0

500

1000

1500

0

100

200

300

400

500

February 2009

pC

l- (p

ptv

)

N2O

5 (p

ptv

)

ClN

O2 (

pp

tv)

Chemical Modeling Example -2

0

10

20

30

40

O3

pp

bv

0

10

20

30

40

NO2

0 2 4 6 8 10 120

500

1000

1500

2000

2500

N2O

5

pp

tv

Hours Since Sunset

0 2 4 6 8 10 120

50

100

150

200

250

300

350

ClNO2

pCl-

Hours Since Sunset

ClNO2 over campaign ranged from ~ 7 – 36%

February 22nd-23rd

N2O5

HNO3

ClNO2

Cl- Cl

NO2

N2O5

HNO3

ClNO2

Cl- Cl

NO2

ClNO2 ~0.18

135oW 120oW 105oW 90oW 75oW 24oN

30oN

36oN

42oN

48oN

54oN

135oW 120oW 105oW 90oW 75oW 24oN

30oN

36oN

42oN

48oN

54oN

IMPROVE Network NADP Network

Is Boulder Special?

0.0

0.2

0.4

0.6

0.8

1.0

ClN

O 2 Yie

ld

Fine Mode Chloride Mass Fraction

80% RH

30% RH

10-6 10-5 10-4 10-3 10-2 10-10.0

0.2

0.4

0.6

0.8

1.0

50% RH

fine mode mCl/mtotal

Aerosol Inorganics Model

nCl-/nNO3-

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

A B

C D

W Sp

Su Au

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

A B

C D

W Sp

Su Au

W Sp

Su Au

nCl-/(fN2O5nNO3-)

135oW 120oW 105oW 90oW 75oW 24oN

30oN

36oN

42oN

48oN

54oN

135oW 120oW 105oW 90oW 75oW 24oN

30oN

36oN

42oN

48oN

54oN

IMPROVE Network NADP Network

Is Boulder Special?

Aerosol Inorganics Model

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

A B

C D

W Sp

Su Au

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

120 W 110

W 100

W 90

W 80

W 70

W

30 N

35 N

40 N

45 N

0.1 0.2 0.3 0.4 0.5 0.6 0.7

A B

C D

W Sp

Su Au

W Sp

Su Au

Aerosol Chloride Based Yield Chloride moles per N2O5 moles reacted

Estimating ClNO2 Production over U.S.

N2O5

HNO3

ClNO2

Cl- Cl

NO2

N2O5

HNO3

ClNO2

Cl- Cl

NO2

fN2O5

ClNO2

PClNO2 =ClNO2 fN2O5ENOx

Constrain withObservations

GEOS-Chem EDGAR Database

HNO3

ENOx = LNOx

NOx

ENOx

LNOx

Estimating ClNO2 Production over U.S.

Log(ENOx)

ClNO2

fN2O5

Log(PClNO2)

U.S. PClNO2 = 1.4 - 3.5 Tg Cl yr-1

ClNO2 and the Global Cl Atom Source

Erickson et al 0.06 Tg Cl yr-1

Osthoff et al 3.2 Tg Cl yr-1

“Bottom up” global Cl atom source from ClNO2

“Top-down” total global Cl atom source

Allan, et al 2004 22 - 35 Tg Cl yr-1

Platt, et al 2004 ~ 35 Tg Cl yr-1

Our estimates 8 – 22 Tg Cl yr-1

MAP OF NO2

Chlorine Cycling: New Addition

Anthropogenic NOx represents a large perturbation of Cl-atom budget

Cl-atom source tied to our understanding of N2O5 reactive uptake

Nighttime chemistry not just a sink of Ox – but a potential source

NO3

NO2 ClNO2

N2O5acid acid

displacementdisplacementCl-

Cl

HCl

activationactivation CCxxHHyy

8 – 22 Tg Cl yr-1

Implications: e.g. Wintertime Oxidants

0

1

2

3

4 x 104

Cl

Mo

lec

cm

-3

0 5 10 15 200

5

10 x 104

ClO

Mo

lec

cm

-3

Hours Since Midnight

0

2

4x 10

6

OH

0

1

2

3x 10

7

HO2

Mo

lec

cm-3

0 5 10 15 200

5

10

15x 10

6

RO2

Hours Since Midnight

ClNO2 = 600 pptvClNO2 = 350 pptvClNO2 = 0 pptv

For 600 pptv ClNO2 in FebruaryCl + RH dominates HOx production (by >10x) from sunrise to 10AM

Cl + RH leads to >30% more daytime HOx production

Some Outstanding Issues

1. Studies of wintertime nocturnal reactive nitrogen and morning HOx chemistry

2. HCl measurements are likely necessary to demonstrate “closure” between integrated LN2O5 and PClNO2

3. ClNO2 yields inferred from [N2O5] and [ClNO2] are often lower than predictions based on [pCl-] Chloride distribution? Phase? Losses of N2O5 and/or ClNO2?

4. Can we better validate/constrain fN2O5?

Where does the chloride in come from?

Sea SprayCoal BurningBiomass/crop burningBiofuelWaste incineration (e.g. PVC)Playa dustRoad salt (?)Cooling towersSwimming pools (?)…

References: Graedel and Keene, 1995; Reff, et al, 2009

Kholer Mesa Often Above Nocturnal Surface Layer

Predicting Annual Average U.S. PClNO2

Log(ENOx)

ClNO2

fN2O5

Log(PClNO2)

U.S. PClNO2 = 1.4 - 3.5 Tg Cl yr-1

Measured Chloride Deposition

Log(mCl) kg ha-1 yr-1

From the National Atmospheric Deposition Program (NADP)

Aerosol Chloride is Ubiquitous

1E-4

1E-3

0.01

0.1

Ch

lori

de

Mas

s F

ract

ion ClNO2 >90%

ClNO2 >50%

Q. Zhang, et al GRL 2007

NOx, Air Quality, and Climate Forcings

Catalyze ozone production

Regulate oxidant abundance

Shindell, et al Science 2009

NOx

NOx emissions couple air quality and climate concerns

Chlorine Activation by N2O5: Model Predictions

1996 Erickson, et al JGR•Global ClNO2 Production From Sea Spray 0.06 Tg Cl/yr

2007 Pechtl and von Glasow, GRL Chlorine Activation in Long Island Sound

Maximum ClNO2 mixing ratio ~ 50 pptv (only on “first night”)

1-2 days downwind negligible

Always less than 5% of Cl atom source

Atomic Chlorine: powerful oxidant

CH4 + OH Products

CH4 + Cl Products

CH4oxidant

0.05 ppt ~10 years

0.05 ppt 0.5 years

Tropospheric Cl atoms

We know they exist, but their sources, distribution, and abundance are poorly constrained

Baring Head, New Zealand

Jobson, et al JGR 1994

Platt, et al ACP 2004

Where there’s chloride for ClNO2 production

U.S. IMPROVE Network fine-mode particle chloride

ClNO2 Yield

From U.S. NADP precipitation Cl- and NO3

-

Chlorine Availability:[Cl-] / f[NO3

-]

Current Constraints from ClNO2 Observations

1. TexAQS – GoMACCS[ClNO2] ~ 50 - > 1000 ppt Osthoff, et al, Nature Geo. 2008

1

2. ICEALOT-LILAQS[ClNO2] ~ 50 - > 1000 pptKercher, et al, AMT 2009

2 3. ACCRONIM-Boulder, CO[ClNO2] ~ 50 – 450Thornton, et al submitted 2009

3

Current Constraints from ClNO2 Observations

1. TexAQS – GoMACCS[ClNO2] ~ 50 - > 1000 ppt Osthoff, et al, Nature Geo. 2008

1

2. ICEALOT-LILAQS[ClNO2] ~ 50 - > 1000 pptKercher, et al, AMT 2009

2 3. ACCRONIM-Boulder, CO[ClNO2] ~ 50 – 450 pptvThornton, et al submitted 2009

3

Where there’s NOx

Courtesy of NASA GSFC

Cl

NO2

Chlorine Activation by N2O5

N2O5

2HNO3

HNO3 + ClNO2

Cl-

H2O

Finlayson-Pitts, Nature 1989Benkhe, et al JGR 1997

0 1 2 3 4 5

x 104

0

10

20

30

40

50

60

NO2 (pptv)

Ma

x C

lNO

pro

du

ce

d (

pp

tv)

Tropospheric Chlorine Cycling

ClCl-X

activationactivation CCxxHHyy

acid acid displacementdisplacementCl- HCl

sea spraysea spray~10,000 Tg~10,000 Tg

Anthro. +Anthro. +3 – 5 Tg3 – 5 Tg

Graedel and Keene, GBC,1995

22-35 Tg* *From methane isotopes measured in remote SH MBL

Platt, ACP 2004Allan, JGR 2007

Chemical Modeling Example - 10 3 6 9 12 15 18 21 24

0

50

100

150

200

0 4 8 12 160

100

200

300

400

500

600

ClNO2

4X pCl-

Mix

ing

Rat

io (

pptv

)Hour of Day (local)

a

ClNO2

pCl-b

Mix

ing

Rat

io (

pptv

)

Hours Since Sunset

Feb. 15 - 16 Observations and Modeling

N2O5

HNO3

ClNO2

Cl- Cl

NO2

N2O5

HNO3

ClNO2

Cl- Cl

NO2

ClNO2 ~0.14

Feb 15 – 16th -highest ClNO2

-low winds-constant yield captures ClNO2 growth