Aerosol and trace gas processingby CRPAQS fogs

J. Collett, P. Herckes, H. Chang and T. LeeAtmospheric Science Department

Colorado State UniversityFort Collins, Colorado USA

Outline• Particle and gas scavenging by fogs• SJV fogs

– Past lessons– CRPAQS observations

• Aerosol and gas processing by CRPAQS fogs– Importance of organics– Deposition– New particle production - HMS

• Summary concepts and future research needs

Particle and gas scavenging

• Particlesscavenged bynucleation,diffusion,impaction,interception

• Soluble gasespartition todrop

Gas-liquid equilibrium• Models and field

observationssuggest commonlack of gas-liquidequilibrium– Highly soluble

gases haveinsufficient time toequilibrate withlarge drops

– Species derivedfrom aerosolparticles may besupersaturated indrops (e.g., Ricciet al., 1998)

Equilibrium time for pH 7 drops with r = 10 µmCourtesy of B. Ervens, NOAA

SJV fogs • Dense, widespread radiationfogs occur during winter– Moist air trapped in valley by

thermal inversion– Radiative cooling produces

fogs• Fogs affect particles by

– Production of non-volatilesolute mass

– scavenging and deposition

Particles

Fog Dropsreactions

Fog Drops

Deposition

Evaporation Gases

Past Studies of SJV fogs - I

• Nitrate andammonium typicallymajor species– pH high– Important organic

carbon contributions– Nitrite and sulfate

also present– Composition variable

in time and space

Ammonium1087

Nitrate567

Acetate151

Sulfate100

Formate83

Other Anions44

Other Cations31

Major Ion Concentrations (µN)Fresno Fog (December 10, 1995, 03:00-04:00)

2.0

3.0

4.0

5.0

6.0

7.0

8.0

SJV

Cal

.

Sac

Val

Cal

.

So.

Cal

.

Ore

gon

Coa

st

Col

orad

oR

ocki

es

Mt.

Mitc

hell

Whi

tefa

ceM

t.

pH

Past Studies of SJV fogs - II

• Deposition ofinorganic ionsimportant– What about OC?

• Sulfate production ~balances sulfatedeposition– Secondary organic

aerosol production? Pre-fog

After Fog

Gas Prod.

Aq. Prod.

Wet D

ep.

Dry D

ep.

Emissions

Net C

hange

-10

0

10

20

30

Thou

sand

sSp

ecie

s 1

km C

olum

n Bu

rden

(µg/

m2) Total Sulfate

Total NitrateTotal Ammonia

CRPAQS Fog Measurements

• Angiola– Bulk and

size-resolved fogcomposition

– Vertical fogprofilesfrom tower

– Fogdepositionfluxes

• Other sites– Helm– McKittrick– Bakersfield

CRPAQS Fog Measurements - II

• Fog deposition

Vd = Flux/C

• Lab Analyses– Major ions and metals– Total/Dissolved Organic

Carbon (TOC/DOC)– Organic composition

• Organic acids• Carbonyls• Other trace species by

GC/MSFlux

C

Vd

CRPAQS FogFindings

• Several fog episodes atAngiola and Helm– No fog at McKittrick– 1 event at Bakersfield

• Composition similar to pastSJV fog studies

Angiola

[H+][Na+][NH4+] [K+][Mg++][Ca++][Cl-][NO2-][NO3-][SO4=]

Bakersfield (1 sample) Helm

0

200

400

600

800

1000

12/13 12/23 1/2 1/12 1/22 2/1

Liqu

id w

ater

con

tent

(mg/

m3)

Angiola fogcharacteristics

• Fog layer veryshallow– Rarely reached top

level of tower

• Fog drops very large– Drizzle formation

from shallow fog• Strong radiative

cooling of largedrops

– Fast deposition

0:00-1:00

010203040506070

5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 38 41 43 47Diameter (um)

num

ber c

once

ntra

tion

(cm

-3)

Effective diameters during 12/18/00 event

24.0

26.0

28.0

30.0

32.0

34.0

36.0

38.0

40.0

0:00

1:00

2:00

3:00

4:00

5:00

effe

ctiv

e di

amet

er (u

m)

CRPAQS FogOrganics

• Organic carbon iskey component ofCRPAQS fogs

• ~75% of OC isdissolved

• Fogs process solubleand insoluble OC

0

5

10

15

20

0 5 10 15 20

TOC (ppmC)

Dis

solv

ed O

C (p

pmC

)

n-alkanoic acids - Angiola, 12/17/00

0

5

10

15

20

25

C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26

ng/m

L

insolublessolubles

CRPAQS typical fog mass composition

NO3-39%

NO2-3%SO42-

6%

NH4+23%

Organic matter29%

CRPAQS FogOrganics - II

• Many organiccompoundspresent– PM source

tracers• Lots of high

molecularweightmaterial

Organic Carbon Molecular Weight Distribution

0%

20%

40%

60%

80%

100%

12/17 1/10 1/15 1/17 1/21 1/31

MW < 500

500 < MW < 1000

MW > 1000

OOH

benzoic acidCO2Hpimaric acid

vanillin

OOOH

syringol OOH

Opyrene

21.0%

22 .2%4 .8%

8 .3%

21.7%

2 .2%

0 .1%

1.9%

0 .2%

17.6%

56 .8%

MW > 1000

1000> MW >500

Fo rmaldehyde

Fo rmate

Aceta te

diac ids (C2-C5)

n-a lkanes (C11-C40)

n-a lkano ic ac ids (C9-C33)

P AH + o xy-P AH

o ther MW < 500

Fog Dissolved Organic Carbon Composition

Importance ofhigher MWcarbonyls

• HPLC analysis ofCRPAQS samplesshowed fewcarbonyls– Tests show rapid

loss in fog• Not in H2O

• Preserved Fresno1/04 fog samplesreveal largecontributions fromseveral carbonylsand dicarbonyls

Carbonyl stability test

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

9/15

9/18

9/22

9/29

10/7

10/1

5

Date

Con

cent

ratio

n (u

g/m

l)

Acetone

Benzaldehyde

Glyoxal

Methyl Glyoxal

Figure 5.x Typical composition of carbonaceous material comprising the total dissolved organic carbon (DOC) content observed for several California Fresno

radiation fog samples.

Carbonyls9%

o-Tolualdehyde0.01%

Isovaleraldehyde1%

Butyraldehyde0.03%

Acetone&Acrolein0.4%

HCHO3%

Organic Acid29%

m-Tolualdehyde0.06%

Acetaldehyde1%

p-Tolualdehyde0.1%

Hexaldehyde0.2%

Glyoxal2%

Methyl Glyoxal 2%

Unknown

Organic Acid

HCHO

Acetaldehyde

Acetone&Acrolein

Butyraldehyde

Isovaleraldehyde

o-Tolualdehyde

m-Tolualdehyde

p-Tolualdehyde

Hexaldehyde

Methyl Glyoxal

Jan. 2004 Fresno Fog DOC

Composition size-dependence

• Drop composition varieswith size– Pattern varies between

species– Most enriched in small drops

5-stage collector - Jan 17

0

500

1000

1500

2000

2500

NO3- SO42- NH4+

Con

cent

ratio

n (u

N)

V1V2V3V4V5

0

20

40

60

80

100

120

0 20 40 60 80 100 120

small drop nitrite (µN)

larg

e dr

op n

itrite

(µN

)

05

10152025303540

0 5 10 15 20 25 30 35 40

small drop TOC (ppmC)

larg

e dr

op T

OC

(ppm

C)

CRPAQS FogDeposition

• Depositionvelocities inCRPAQS fogshigh– ~ 1-2 cm/s– >> PM2.5

• Depositionvelocity dependson solutedistribution withdrop size

0

1

2

3

4

5

6

7

NO3- SO42- TOC NH4+ Water NO2-

Dep

ositi

on v

eloc

ity (c

m/s

)

0

1

2

3

4

5

6

0 1 2 3 4 5 6

small/large drop concentration ratio

Dep

ositi

on v

eloc

ity (c

m/s

)

CRPAQS FogDeposition

• Fog event fluxes rangefrom 10s to 1000s ofµg/m2

• Assuming a 100 m deepfog, concentrations woulddecrease typically~ 0.5 µg/m3/hr sulfate~ 1 µg/m3/hr nitrate~ 1 µg/m3/hr ammonium~ 0.7 µgC/m3/hr TOC

• Remember, fog solutescan be volatile or non-volatile

Fog deposition

Aqueous reactions andnew particle production

• S(IV) reactions– Oxidation

• by H2O2, O3 andO2/Fe(III)+Mn(II)

• S(IV)-aldehydecomplex formation

• e.g., HCHO + HSO3-

CH2(OH)SO3-

0 2 4 6 8pH

1E-15

1E-13

1E-11

1E-9

1E-7

1E-5

1E-3

1E-2

-d [S

(IV)]

/ dt

(M/s

)

H2O2O3O2/Fe(III) +Mn(II)

Typical Fog Conditions

S(IV)simulations

• Fate of dissolvedSO2 simulated forall sample periodswith single dropmodel– Oxidation by O3

and H2O2

– Rxn with HCHO• Most SO2

expected to formHMS at high fogpH

Large Drops

O3

80%

H2O2

20%HMS97%

S(VI)3%

S(IV) Sinks S(IV) Oxidation

CMUModeling

(Fahey and Pandis)

• Fog modelreasonablypredicts– Bulk fog

composition

– Size-dependence

– Deposition fluxes

00.20.40.60.8

11.21.41.6

0 5 10 15 20

time (hr)

Sulfa

te ( µ

g/m

3 )

Predicted

Observed

01234567

0 5 10 15 20

time (hr)

Nitr

ate

( µg/

m3 )

PredictedObserved

(a) (b)

0

10

20

30

40

50

60

0 20 40 60

Diameter (mm)

Sulfa

te ( µ

M)

0100200300400500600700800900

0 20 40 60

Diameter (mm)

Am

mon

ium

( µM

)

PredictedPredicted

(a) (b)

0

50

100

150

200

250

0 5 10 15 20

time (hr)

Am

mon

ium

Dep

ositi

onal

Flu

x (n

eq/m

2 /min

)

02468

101214161820

0 5 10 15 20

time (hr)C

hlor

ide D

epos

ition

al F

lux

(neq

/m2 /m

in)

Predicted

Observed

(a)

Predicted

Observed

(b)

Acknowledgements

• CSU– S. Kreidenweis, G. Kang. J. Reilly, E. Sherman

• Carnegie Mellon– S. Pandis and K. Fahey

• National Science Foundation

Summary concepts and future needs

• Nitrogen species dominate fogcomposition

• Fogs are effective cleansers of theSJV atmosphere

– Removal rates depend on speciesdistributions across fog drop sizespectrum

– Sulfate removal balanced byproduction

• Organic matter comprises a largeportion of fog solutes

– Combination of volatiles and non-volatiles

– Large amount of high MWmaterial

– Large OC deposition fluxes

• High time resolution aerosol andfog measurements

– PILS + OC/EC in Fresno• Better characterization of organic

matter scavenged by fogs– Improved speciation– Source marker tracking

• Role of fogs in secondary organicaerosol formation

CRPAQS fog papers• Herckes et al. (2002) Organic

Matter in central Californiaradiation fogs, ES&T 36, 4777-4782.

• Ervens et al. (2003) On thedrop-size dependence oforganic acid and formaldehydeconcentrations in fog, J. Atmos.Chem. 46, 239-269.

• Fahey et al. (2004) Theinfluence of size-dependentdroplet composition onpollutant processing by SanJoaquin Valley fogs, submitted.

• Overview paper for specialissue (tbd)