atmospheric formation of ultrafine particles...220 fixed size sections ranging in size from 0.8 nm...

1

Atmospheric Formation of Ultrafine Particles

Charles Stanier, Assistant ProfessorUniversity of IowaDepartment of Chemical and

Biochemical [email protected]

2

Outline

What is atmospheric new particle formationSome examples

Physical measurementsChemical measurementsModeling

What fraction of particles are from new particle formation vs. combustion?

3

What is Nucleation?

Molecules

Neutral or ion clusters

Ternary or Ion-Induced Nucleation

Detectable Aerosol Particles0.01-10 cm-3s-1 regional eventsup to 105 cm-3s-1 in plumes

Initial Growth

Further Growth (1-20 nm/hr)

CCNAmmoniumSulfateOrganics~ 1 nm 3 nm

LossBy

CondensationTo Pre-existingSurface Area

4

Nucleation Overview

SO2(g) + OH· + H2O →HO2· + H2SO4·nH2O

SO2

NH3

5

Nucleation Observations

Kulmala, McMurry, et al. (2004) J. Aerosol Sci. 35 pp. 143-176

6

Particle Size

nmµm

10.001

100.01

1000.1

1,0001 10 100

Ultrafine

Fine Particles (< 2.5 µm)

Con

cent

ratio

n Number Distribution

Mass Distribution

7

Diurnal Pattern

0

20,000

40,000

60,000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour

3-50

0 nm

Par

ticle

Cou

nt (c

m-3

)

Non-nucleation w orkdays Non-nucleation w eekends

Regional nucleation days

(b)

0

20,000

40,000

60,000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour

3-50

0 nm

Par

ticle

Cou

nt (c

m-3

)



(b)



(b)

8

0 25 50 75 100

Number vs. Mass Distribution

Pittsburgh, PA2001-2002

Aerosol Mass (µg/m3)

Num

ber

(#/c

m3 )

10x104

20x104

Negative correlationRelated to nucleation activityOccurring over wide area

9

New Particle Formation vs. Visibility

USX Tower

USX Tower

10

Other Aerosol Impacts: Visibility & Climate

EPA (2001) National Air Quality: Status and Trends

Yosemite, CA

CloudFormation

CloudParticles

ScatteredRadiation

ScatteredRadiation

Earth

Sun

CloudFormation

CloudParticles

ScatteredRadiation

ScatteredRadiation

Earth

Sun

11

Physical Measurements

12

Dry-Ambient Aerosol Size Spectrometer

Reconfigured commercial instrumentsRH control systemInlet particle losses characterizationCustom control, data acquisition, and data reduction software

13

Nucleation Frequency by Month

0%

50%

100%

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun

> 1-hr Duration < 1-hr Duration None

2001 2002

Frac

tion

of

Day

s W

ith

Nu

clea

tion

Significant fraction of days (30%+)Most prevalent in spring, fall

Pittsburgh 2001-2002

14

Example: No NucleationP

arti

cle

Size

(n

m)

10

100

500

00:00Time of Day

06:00 12:00 18:00 24:00

105

104

103

102

Res

pon

sedN

/dlo

gDp

(cm

-3)

Nu

mbe

r (#

/cm

3)

12x104

6x104

Pittsburgh, August 10, 2001

15

Example: Weak Nucleation

105

104

103

102

Res

pon

sedN

/dlo

gDp

(cm

-3)

Par

ticl

e Si

ze (

nm

)

10

100

500

Nu

mbe

r (#

/cm

3)

12x104

6x104

00:00Time of Day

06:00 12:00 18:00 24:00

Pittsburgh, July 2, 2001

16

Sunlight and New Particle Formation

SUNRISE

Cloudy Morning

00:00Time of Day

06:00 12:00 18:00 24:00

Cloud Free Morning

Par

ticl

e Si

ze (

nm

)

10

100

500

10

100

500Pittsburgh

Nov 10, 2001

PittsburghNov 11, 2001

17

Nucleation’s Spatial Coverage

Method: simultaneous sampling

WindPittsburgh Philadelphia

RuralSampler

Main (Urban)Sampler

PhiladelphiaSampler

38 km 400 km

18

Spatial Coverage ResultP

arti

cle

Size

(n

m)

10

100

200

10

100200

38 km apartFebruary 25, 2002

Pittsburgh

38 km Upwind Rural Location

400 km apartJuly 2, 2001

Pittsburgh

Philadelphia

19

Diurnal Pattern

0

20,000

40,000

60,000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour

3-50

0 nm

Par

ticle

Cou

nt (c

m-3

)



(b)

0

20,000

40,000

60,000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour

3-50

0 nm

Par

ticle

Cou

nt (c

m-3

)



(b)



(b)

20

Chemical Measurements

21

Aerosol Mass Spectrometer

Zhang, Q.; Jimenez, J.L.; Caragaratna, M.; Worsnop, D.

22

Aerosol Mass Spectrometer

Particle Inlet (1 atm)

Jayne et al., Aerosol Science and Technology 33:1-2(49-70), 2000.Jimenez et al., Journal of Geophysical Research, in press, 2002.

QuadrupoleMass Spectrometer

Thermal Vaporization

&Electron Impact

Ionization

Aerodynamic Lens

(2 Torr)

Chopper

Turbo Pump

Turbo Pump

Turbo Pump

Time of Flight Region

Particle BeamGeneration

Aerodynamic Sizing Particle Composition

23

September 12, 2002 Nucleation EventP

arti

cle

Size

(n

m)

10

100

500

00:00 06:00 12:00 18:00 24:00

24

September 12, 2002 Nucleation EventP

arti

cle

Size

(n

m)

10

100

500

00:00 06:00 12:00 18:00 24:00

50%

0%

100%

Mas

s Fr

acti

on1

0-6

0 n

m

Nitrate

Ammonium

SulfateOrganics

Mass Fraction (10-60 nm Particles) Aerosol Mass Spectrometer*

*Zhang & Jimenez (Univ. Colorado-Boulder)

25

Chemistry of Growth: Particle Mass Spectra at 20-33 nm

Detection of Nucleationby Particle Sizer

Zhang, et. al. Insights into the Chemistry of Nucleation Bursts and New Particle Growth Events in Pittsburgh based on Aerosol Mass Spectrometry. Environ. Sci. Technol., in press.

26

Modeling

27

Chemistry of Nucleation: Simulation1

SO2(g) + OH· + H2O →HO2· + H2SO4·nH2O

SO2

Inputs Processes Modeled OutputPreexisting Aerosol Distribution

SO2 ConcentrationNH3 ConcentrationUV Light IntensityTemperature & RH

NH3

SO2 Oxidation to H2SO4H2SO4-H2O-NH3 Nucleation

H2SO4 CondensationParticle Coagulation

Predicted Aerosol Distribution

1Model adapted from Capaldo, Kasibhatla, Pandis. J. Geophys. Res., 1999.

28

Modeling H2SO4 Nucleation

Photochemical box model

Modeled gas-phase species:SO2, H2SO4, OH, NH3SO2 measured, OH and NH3 calculated from measurements

220 fixed size sections ranging in size from 0.8 nm to 10 µm

T, RH, SO2 and UV radiation from measurements

Initial distribution available from dry size distributions

Maximum OH concentration assumed for each month, scaled based onUV

5 x 106 molecules/cm3 in summer11 x 106 molecules/cm3 in winter2

1Ren et al. (2003)2Heard et al. (2001)

29

Comparison on July 27, 2001

Model predicted presence or lack of nucleation on all 19 daysTiming of onset of nucleation within one hour of observations for all 13 eventsSize and shape of growth curve consistent with observationsHigh number concentrations predicted

30

Comparison on January 28, 2002

25 out of 29 days predicted correctlyTiming of onset of nucleation not as good (6 of 12 within one hour)Growth generally underpredictedwith two exceptionsHigh number concentrations predicted

31

Sensitivities

NPF is thought to be sensitive to:PM2.5 ↓ NPF ↑Ammonia ↑ NPF ↑ (but not sure how strong this effect)SO2 ↓ NPF ↓ (if NH3 in excess … that covers

most locations)SO2 ↓ NPF ↑ (if NH3 limited, e.g. northeast U.S.

in summer)Reactive VOCs ↓NPF ? – but growth of particles will be

limited – so they will not last aslong in the atmosphere

0102030405060708090100

-100-80 -60 -40 -20 0 20 40 60 80 1000

2

4

6

8

10

12

14

16

18

Day

s w

ith n

ucle

atio

n

Change in SO2 Concentration (%)

July

% o

f mod

eled

day

s

32

What fraction of ultrafines are from NPF?

To a large extent, we do not knowWill vary by locationNPF most important at midday and afternoons

Traffic

Smog

and

Reg

iona

l Haz

e NPF LessImportant

NPF MoreImportant

Threshold chemistrystill Unclear (SO2 + ???)and will vary from place to pla

33

Traffic

Smog

and

Reg

iona

l Haz

e NPF LessImportant

NPF MoreImportant

Heavy TrafficUrban

AfternoonDownwindSuburbs

Rura

l U.S

.

34

0

10000

20000

30000

40000

50000

0:00 6:00 12:00 18:00 0:00

#/cc

C C a t c e Cou t (b ue) s S S a t c e Cou t ( ed)Pa

rtic

le S

ize

(nm

)

Res

pons

edN

/dlo

gDp

(cm

-3)

Bondville Illinois, 2005

Traffic

Smog

and

Reg

iona

l Haz

e NPF LessImportant

NPF MoreImportant

35

Mexico City Mar 17, 2006

Traffic

Smog

and

Reg

iona

l Haz

e NPF LessImportant

NPF MoreImportant

36

Pittsburgh PA

NOV 1

NOV 2

NOV 3

37

Pittsburgh PA

NOV 1

NOV 2

NOV 3

Traffic

Smog

and

Reg

iona

l Haz

e NPF LessImportant

NPF MoreImportant

38

DOWNY DEC 2000 RIVERSIDE MAY 2001

39

DOWNY DEC 2000 RIVERSIDE MAY 2001

Traffic

Smog

and

Reg

iona

l Haz

e NPF LessImportant

NPF MoreImportant

40

Future Work

In the process of summarizing comparisons between Pittsburgh, Rochester, New York City, Atlanta, LA, and St. Louis.Unify measurements, detailed modeling, and a “screening” model that attributes ultrafines to traffic vs. new particle formationSort out some details of chemistry and meteorologyMonitor how implementation of further sulfur reductions from power plants, and advanced diesel influence new particle formation

41

Acknowledgements

Students:Alicia Kalafut – Ultrafine Particle SamplingKazeem Olanrewaju – Ultrafine Particle Modeling

University of Iowa Callaborators:Greg Carmichael, Jerry Schnoor, Bill Eichinger

Carnegie Mellon Collaborators:Spyros Pandis, Tim Gaydos, Andrey Khlystov,

Outside Collaborators:Allen Williams

Illinois Soil and Water SurveyPeter McMurry

University of MinnesotaJimenez Group, University of Colorado-Boulder

Jose-Luis Jimenez & Qi Zhang

42

Additional Material

Modeling FrameworkFuture WorkMeasurement TechniqueTraffic and ModelingBondvilleMexicoBackground on PM

43

Modeling framework

44

Modeling H2SO4 Nucleation

Photochemical box modelModeled gas-phase species:

SO2, H2SO4, OH, NH3SO2 measured, OH and NH3 calculated from measurements

220 fixed size sectoins ranging in size from 0.8 nm to 10 µm

( ) ( )( ) ( )

4242

42

42

42

,

,,,,,, 3*

2

SOHdepSOHSOH

cond

SOHnucgasSOH

CRRHCR

RHTNHCRnPTOHSORt

C

−+

+=∂

∂

( )( ) ( ) ( )idepSOHNcondjcoag

SOHnuci

NRRHCRRHNR

RHTNHCRt

N

i −++

=∂∂

,,

,,,

42

42 3

45

Sulfuric Acid Nucleation Formation

SO2 + OH· + M → HOSO2· + MHOSO2· + O2 → HO2· + SO3(g)

SO3(g) + H2O + M → H2SO4(g) + MH2SO4(g) + nH2O(g) → H2SO4·nH2O(aq)

________________________________________________________________________________________

SO2(g) + OH· + O2 + (n+1)H2O → HO2· + H2SO4·nH2O(aq)

46

Chemistry and deposition

Sulfuric acid is produced from the reaction of SO2 and OH1

Deposition:

vdep for aerosol dependent on particle size2, 1.0 cm/s used for H2SO4 3

]][[ 22 OHSOkR SOgas =

1kSO2 from DeMore et al. (1994)

Hcv

R iidrydep,=

3Brook et al. (1999)2Hummelshoj et al. (1992)

47

Condensation

Condensation rate:

Change in number concentration:

Flux between fixed sections:

)()(2 0ppAKnFDDNJ pi −= π

42421 SOHiiSOHiiNcond CNFCNFR i −= −

( ) ( )[ ]33142

6ip

ip

pimtSOH

iDDRT

DKMF

−=

+ρπ

48

Coagulation

Coagulation rate:

Generalized coagulation coefficient*

Linear interpolation to preserve mass, number:

2,21

1,

1, ≥−= ∑∑

∞

=−

=− kNKNNNKfR

jjjkkjkj

k

jjkjkcoag

( )( )βπ 212112 2 DDDDK pp ++=

kk

pkk VV

VVf

−

−=

+

+

1

1

kk

kpk VV

VVf

−

−=

++

11

*β calculated using method of Fuchs, (1964)

49

Ternary nucleation correlation

Parameterization from Napari et al. (2002)Calculates nucleation rate using parameters of T, RH, NH3, H2SO4

Approximation for initial nuclei size dependent on nucleation rate and T1 nm under typical July conditions0.8 nm under typical January conditions

Approximation for composition of initial nuclei, also dependent on nucleation rate and T

Approximately 4 molecules of sulfuric acid, 4 of ammonium in July2 molecules of sulfuric acid, 2 of ammonium in January

50

Nucleation rates

Presence of gas-phase ammonia necessary for nucleation in July

10 ppt generally enough

Both ammonia and sulfuric acid play important role in January

Cloud cover, weaker UV radiation limit production of sulfuric acid

1 2 3 40.1

1

10

100

Sulfuric acid concentration (ppt)

Am

mon

ia (p

pt)

0.01 0.1 10.1

1

10

100

Sulfuric acid concentration (ppt)

Am

mon

ia (p

pt)

July

January

10-5 10-3 10

-1

101 103

105 106

10-5 10-3

10-1

101 103

105 106

51

Sensitivity to SO2 Emissions

0102030405060708090100

-100-80 -60 -40 -20 0 20 40 60 80 1000

2

4

6

8

10

12

14

16

18

Day

s w

ith n

ucle

atio

n

Change in SO2 Concentration (%)

July

% o

f mod

eled

day

s

0102030405060708090100

-100-80 -60 -40 -20 0 20 40 60 80 10002468

10121416182022242628

Day

s w

ith n

ucle

atio

nChange in SO2 Concentration (%)

January

% o

f mod

eled

day

s

52

Sensitivity to NH3 Emissions

0102030405060708090100

-100-80 -60 -40 -20 0 20 40 60 80 1000

2

4

6

8

10

12

14

16

18

Day

s w

ith n

ucle

atio

n

Change in NH3 Concentration (%)

July

% o

f mod

eled

day

s

0102030405060708090100

-100-80 -60 -40 -20 0 20 40 60 80 10002468

10121416182022242628

Day

s w

ith n

ucle

atio

n

Change in NH3 Concentration (%)

January

% o

f mod

eled

day

s

53

Future Work

54

Observational Analysis

Determine spatial extent of nucleation from “Supersite” 2001 observations and compare to SO2and NH3 maps.

55

Observation-Model Hybrid

Prepare model-based predictions of seasonal nucleation frequency, timing, and growth rateCompare to previous (or new) measurements

56

Vertical Profile Sampling

57

Vertical Mixing Models

58

Perturbed Real Air Samples

59

Measurement technique

60R

H

APSAPS

Dry sheath airfor Nafion dryers

Vent excessdry air1 LPM

RH

RH

LL -- DM

AD

MA

NN-- D

MA

DM

A

RH

HEPA MFHEPA

HEPA

RH

HEPAMFHEPA

HEPA

AmbientAir In

Dry AirExhaust

CPCCPC

CPCCPC

AmbientAir In

AerosolInlets

MF

Clean, Dry &Regulated Air

3-Way Plug Valvew/ Solenoid Actuator∆P Flowmeter

Ball Valve, Air Actuated

Mass Flow Meter

Bipolar Charger

Nafion DryerRotameter

DryDry--Ambient Aerosol Size SpectrometerAmbient Aerosol Size Spectrometer

Add RH controlled inlets (aerosol water measurement)Control & data acquisition hardware and software Data processing software to make 6 instruments behave like 1Extensive calibrationSynthesis with other instruments and web-based data visualization

61

Scanning Mobility Particle Sizer

Condensation Particle

Counter (CPC)

Sheath Flow

AerosolIn Charger

-

-

62



Counter (CPC)

Sheath Flow

AerosolIn Charger

-

-

63



Counter (CPC)

Sheath Flow

AerosolIn Charger

-

-

64



Counter (CPC)

Sheath Flow

AerosolIn Charger

-

-

65

Traffic and modeling

66

Traffic Emission Sampling

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0.001 0.01 0.1 1

Mobility Diameter (µm)

dN/d

log(

Dp)

, Dilu

tion

Cor

rect

ed (

cm-3

)

0.E+00

1.E+06

2.E+06

3.E+06

4.E+06

0.001 0.01 0.1 1

Log Scale Linear Scale

90thPercentile

10thPercentile

Note: 10th and 90th percentiles on 30-min average size distributions

67

Total # Emission Factors for Vehicles

0

1E+16

2E+16

3E+16

> 95% CarsLow Speed

> 95% CarsHigh Speed

< 90% CarsHigh Speed

# / k

g fu

el

68

“Spin-Off” of Modeling Techniques

69

Calculation of gas-phase ammonia

Estimated from comparison of measured total NH3with PM2.5 SO4, NO3

When sufficient ammonia is available to neutralize these species, excess ammonia assumed to be in gas-phaseOtherwise, lower limit for parameterization used

Compared to equilibrium calculations using GFEMN for total NH3, NO3, and SO4

70

Bondville

71

0

10000

20000

30000

40000

50000

0:00 6:00 12:00 18:00 0:00

#/cc

-1

1

3

0:00 6:00 12:00 18:00 0:00

SO2 Concentration (ppb)

September 18, 2005CPC Particle Count (blue) vs. SMPS Particle Count (red)

Part

icle

Siz

e (n

m)

Res

pons

edN

/dlo

gDp

(cm

-3)

72

Nucleation Box Model with May 2003 SWS Data

Constant NH3 of 1.5 µg m-3 (2200 ppt)Constant SO2 of 4 µg m-3 (1.54 ppb)Actual median RH and T from May datasetBright sun used for UV / OH calculation

73

0 3 6 9 12 15 18 21 24

10

100

500

May Base Case

2.5

3

3.5

4

4.5

Part

icle

Siz

e (n

m)

Res

pons

edN

/dlo

gDp

(cm

-3)

74

Mexico

75

PM Background Info

76

Typical Chemical Makeup

InorganicSaltsSO42-NO3-NH4+Na+Cl-

OrganicCompounds

Black Carbon

Metals

atmospheric formation of ultrafine particles...220 fixed size sections ranging in size from 0.8 nm...

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