Ammonia / ammonium interactions:

Effects on surface/atmosphere exchange fluxes and the atmospheric aerosol loading

Eiko Nemitz, Gavin Phillips, Rick Thomas, Mark Sutton, MarsailidhTwigg, Daniela Famulari, Sim Tang, Ron Smith, David Fowler:

Centre for Ecology and Hydrology (CEH) Edinburgh, U.K.

Ammonia Chemistry1. Ammonia as an aerosol precursor

• Contributing to PM with impacts on human health

• Radiative cooling

• Promoting nucleation

2. Processes controlling gas-to-particle conversion

3. Effects of chemistry on the measurement of surface / atmosphere exchange fluxes (NH3, aerosols, acids)

Ammonia as an Aerosol Precursor

NH3

HNO3

NH4NO3

NH4HSO4,

(NH4)2SO4H2SO4

SO2

OH

NH4Cl

Cloud processingHCl

NaCl

N2O5

NO2

SO2 and HNO3 compete for the NH3

H2O OH

NO3 NO

O3

hν

Concentrations of Ammonium Aerosols

Jungfraujoch

Mace Head

Bush (S. Scotland)

Payerne

Vancouver

Manchester Winter

Manchester Summer

Mexico CityHarwell

CabauwHarwell

Cabauw

Aer

osol

con

cent

ratio

n [μ

g m

-3]

0

2

4

6

8

10

12

14

16

18

20

AmmoniumNitrateSulphateNSS Chloride

PM1 PM2.5 PM10

Contribution of Regional Ammonium Aerosols to Exceedances of PM10 Air Quality Standards in Urban Areas

70

60

50

40

30

20

10

0

Aer

osol

Mas

s [μ

g m

-3]

9-Jun 11-Jun 13-Jun 15-Jun 17-Jun 19-Jun 21-Jun 23-Jun 25-Jun 27-Jun 29-Jun 1-Jul 3-Jul 5-Jul

24-hour Air Quality Standard (PM10)

Annual Mean Air Quality Standard (PM10)

Ammonium Chloride (NR) Nitrate Sulphate Organics PM10 Edinburgh

Other urban PM10:Organic carbon,elemental carbon,resuspended material,urban AN, AS

Regional SO42-

Regional NO3-

Regional NH4+

Climate Forcing of Ammonium Aerosols

0.00

0.25

0.50

0.75

1.00

1.25

1.50

0 0.1 0.2 0.3 0.4 0.5 0.6

Anthropogenic SO42- (Tg S)

-For

cing

(W /

m2 )

SO42-/NO3

-

SO42- only

SO42- - f(RH)

Koch, 99Charlson, 91NCAR

Feichter, 97

Boucher, 95Kiehl, 93

0

0.5

1

1.5

2

2.5

3

3.5

4

1800 2000 2100

Year

-For

cing

(W/m

2 )

NO3-

SO42-

SO42- : -0.95 W/m2

NO3- : -0.19 W/m2

NO3- : -1.28 W/m2

SO42- : -0.85 W/m2

Adams, Seinfeld et al., J. Geophys. Res., 106, 1097-1111, 2001

The mean global radiative forcing of the climate system for the year 2000, relative to 1750 (IPCC, 2001)

Level of scientific understanding

High Med Med Low V Low V Low V Low V Low V Low V Low V Low V Low

Rad

iativ

e Fo

rcin

g (W

m-2

)

-2

-1

0

1

2

3

HalocarbonsN2O

CH4

CO2

stratosphericozone

troposphericozone

sulphate

fossil fuelBC

fossil fuelOC

mineraldust

biomassburning

aerosolindirecteffect

contrailscirrus

landuse (albedo only)

solar

European vs. US Aerosol

y = 0.9341x - 0.0396R2 = 0.9846

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0.0 0.5 1.0 1.5 2.0

predicted NH4+ = (2 SO4 / 96 + NO3 / 62) * 18

mea

sure

d N

H4+

3

2

1

0

Mea

sure

d N

H4 (μg

/m3 )

3.02.01.00.0Predicted NH4 (μg/m3)

Europe (CEH Bush):

USA (Prophet, Michigan):

UK network:

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025

Ann

ual e

mis

sion

(Teq

/yr)

NH3 EuropeNOx EuropeSO2 EuropeNH3 USANOx USASO2 USA

Emissions

Shift from (NH4)2SO4 to NH4NO3 Chemistry

Modelling the Response of Ammonium Concentration to Emission Reduction of Precursor Gases

• S. German study (S. Drechsler et al., 2006):– In the rural environment AN formation is NH3 limited and

responds to changes of NH3 only.– In the urban environment AN formation is NOx limited and

responds to changes of NOx only.

• Swiss study (Spirig and Neftel, 2006): – 10% reduction of NH3 emissions 0.5% decrease in PM10– 50% reduction of NH3 emissions 3-10% decrease in PM10

• Easter US winter study (Vayenas et al., JGR, 2005):– Sulphur reduction by 50% inorg. PM2.5 reduction of 8-23%– Ammonia reduction by 50% inorg. PM2.5 reduction of 29%– Nitric acid reduction by 50% inorg. PM2.5 reduction of 17%

Time-scales of NH4NO3 Formation

CO Concentration 29/09/05 (ppb)

200

180

160

140

120

100

80

7:40

8:30

9:00

9:30

10:00

10:30

12:30

13:00

13:30

14:00

14:30

15:0015:3016:00

16:30

NO2-NO3- oxidation rate (B111-14/07/05)

10:15 – Central Scotland plume11:35 – Newcastle plume12:00 – Midlands plume12:30 – London plume

Average wind speed = 4.48m/sAverage wind direction = 208deg 10:15 11:35 12:00 12:30

Distance aircraft from source (km) 90 50 70 100Air parcel travel time (hours) 5.6 3.1 4.3 6.2% N oxidised to HNO3 (%) 22.8 20.3 32.5 35.5% N oxidised to NO3

- (%) 9.4 7.5 2.1 16.6Oxidation rate to HNO3 (%N hr-1) 4.1 6.6 7.5 5.7Oxidation rate to NO3

- (%N hr-1) 1.7 2.4 (0.48) 2.7Total oxidation rate (%N hr-1) 5.8 9.0 8.0 8.4

25

20

15

10

5

0

-5

NO

2 [μg

m-3

]

09:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00

16

14

12

10

8

6

4

2

0

HN

O3 [μg m

-3]5

4

3

2

1

0

-1

NO

3 - aerosol [μg m-3]

Nitrogen dioxide (180 s mean) Nitric acid (180 s mean) Nitrate aerosol (180 s mean)

Highly resolved Ammonium measurements across Europe (1st EMEP Intensive Measurement Period, June 2006; unratified)

15

10

5

0

1/6 5/6 9/6 13/6 17/6 21/6 25/6 29/6 3/7

15

10

5

0

Amm

oniu

m A

eros

ol M

ass

[μg

m-3

]

15

10

5

0

Aerosol Mass [μg m

-3]15

10

5

015

10

5

0

Mace Head, Ireland

Auchencorth, Scotland

Harwell, England

Cabauw, The Netherlands

Payerne, Switzerland

Results:

• Aerosol nitrate emissions from urban areas appear to be ubiquitous, indicating that NOxoxidation is very fast.

• Nitrate formed in urban areas is in the Aitken mode (observed worldwide).

• They occur during both summer and winter, but vary between days.

• In winter emissions appear to be larger on inversion days (build-up of HNO3 & NH3?)

-100

-50

0

50

100

Par

ticle

Flu

x [ n

g m

-2 s

-1]

Feb 13 Feb 14 Feb 15 Feb 16 Feb 17 Feb 18 Feb 19 Feb 20 Feb 21 Feb 22 Feb 23 Feb 24 Feb 25 Feb 26 Feb 27 Feb 28 Mar 1

80x103

6040200

CN

Flux [ # cm-2 s

-1]

40

20

0

CO

2 Fl

ux [

µmol

m-2

s-1

]

12840

Temp [ oC

]

HOA SOA (m/z44)

CN CO2

Temp at 3m oC

SO42-

NO3- (m/z 30)

NO3- (m/z 46)

3

2

1

0

Aero

sol c

once

ntra

tion

[μg

m-3

]

Feb 14 Feb 15 Feb 16 Feb 17 Feb 18 Feb 19 Feb 20 Feb 21 Feb 22 Feb 23 Feb 24 Feb 25 Feb 26 Feb 27 Feb 28 Mar 1

360270180900

Win

d di

rect

ion

1612840

Win

d sp

eed

[m/s

]

-4-202

T(3

m) -

T(8

5 m

) [°C

]

SO42-

Org Cl-

NO3-

NH4+

Inversions

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

dM/d

logD

va (µ

g m

-3)

5 6 7 8100

2 3 4 5 6 7 81000

Vacuum Aerodynamic Diameter (nm)

2.0

1.5

1.0

0.5

0.0

dM/d

logD

va (µ

g m

-3)

5 6 7 8100

2 3 4 5 6 7 81000

Vacuum Aerodynamic Diameter (nm)

4

3

2

1

0

dM/d

logD

va (µ

g m

-3)

5 6 7 8 9100

2 3 4 5 6 7 8 91000

Vacuum Aerodynamic Diameter (nm)

Ammonium Nitrate Sulphate Chloride Organics

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

dM/d

logD

va (µ

g m

-3)

5 6 7 8100

2 3 4 5 6 7 81000

Vacuum Aerodynamic Diameter (nm)

1.0

0.8

0.6

0.4

0.2

0.0dM

/dlo

gDva

(µg

m-3

)

5 6 7 8100

2 3 4 5 6 7 81000

Vacuum Aerodynamic Diameter (nm)

Urban Aerosol Fluxes by Aerosol

Mass Spectrometry(Gothenburg)

Observations of Aerosol NitrateFluxes above Urban Areas

Mexico City (20,000,000)

Boulder, CO(80,000)

Gothenburg(480,000)

Edinburgh(435,000)

10

8

6

4

2

0

Nitr

ate

Flux

[ng

m-2

s-1

]

24181260

15

10

5

0

25

20

15

10

5

0

20

15

10

5

0

Edinburgh

Gothenburg

Boulder, CO

Mexico City

?

Effects of Chemistry on Flux Measurements

Ke{RH(z1), T(z1)}

Ke{RH(z2), T(z2)}

NH3HNO3NH4NO3

height z2:

height z1:

Effects of vertical gradients.

τd

τc

χ [μeq m-3]0.0 0.1 0.2 0.3

z-d

[m]

0

1

2

3

Fχ [neq m-2s-1]-3 -2 -1 0

Km / Ke

0.0 0.5 1.0

HNO3

NH3

NH4NO3

Example 1:NH4NO3 evaporation above heathland

15

10

5

0NH

4+ con

cent

ratio

n [μg

m-3

]

6/3/1996 6/5/1996 6/7/1996 6/9/1996

0.8

0.6

0.4

0.2

0.0

Ion concentration [μeq m

-3]

30

20

10

0

-10

Vd(

NH

4+ ) [m

m s

-1]

SJAC Cl-

SJAC NO3-

SJAC SO42-

SJAC NH4+

Filter Pack NH4+

15:00 18:00 21:00 00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00

F χ [n

g m

-2 s

-1]

-40

-30

-20

-10

0

10

15:00 18:00 21:00 00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00

Rc [

s m

-1]

0

100

200

300

400

500

15:00 18:00 21:00 00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00

u * [m

s-1

]

0.0

0.1

0.2

0.3

0.4

0.5

RH

(z0')

[%]

0

20

40

60

80

100

120

RH u*

15:00 18:00 21:00 00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00

Vd [

mm

s-1

]

0

5

10

15

20

25

30

Vmax(HNO3)Vmax(HCl)Vd(HNO3)Vd(HCl)

HNO3

HCl

HNO3 HCl

Example 2:Aerosol growth above a NH4NO3-fertilised grassland

FNH3 [ng m-2 s-1]

0 500 1000 1500 2000 2500 3000

F N [c

m-2

s-1

]

0

1000

2000

3000

4000

-200

-150

-100

-50

0

50

HNO

3 flu

x [ng

m-2

s-1]

09/06/2000 11/06/2000 13/06/2000

Fmea su red

Fma x

NH4NO3 pellets

soil solution high in NH4+ & NO3

-

stomatalemission

ATMOSPHEREATMOSPHERE

CANOPYNH3

NH4NO3

HNO3

NH4NO3 pellets

soil solution high in NH4+ & NO3

-

stomatalemission

ATMOSPHEREATMOSPHERE

CANOPYNH3

NH4NO3

HNO3

1) At about 400 to 450 nm hr-1, growth rates of 11 nm particles are fast. In this NH3-rich environment 200 nm particles grow at 40 to 45 nm hr-1, an order of magnitude faster than after nucleation bursts in semi-natural environments.

2) Average NH4NO3 production rates are 52 and 78 μg m-3 hr-1 during the day and at night, respectively.

6000

4000

2000

0

-2000

Parti

cle

flux

[cm

-2 s

-1]

5 /29/2000 6/2/2000 6/6/2000 6/10/2000 6/14/2000

2500

2000

1500

1000

500

0Am

mon

ia fl

ux [μg

m-2

s-1

]

cut fertilizationturning & lifting

NH3

G R A M I N A E

Example 3:Aerosol

formation following slurry

application

0.60.40.20.0

(μg

m-3

)

00:0029/04/2005

00:0001/05/2005

00:0003/05/2005

-15-10-505

(ng m-2 s

-1)4020

0(mm

s-1

)

12840

-200

20

20100

-10-20

Vd N

O3 - (m

m s

-1)

6040200

(µg m-2 s

-1)

Fertilised fieldControl fieldFertilised field

χ 1m

HN

O3

Flux HNO

3

Vd H

NO

3

Flux NH

3

Flux

NO

3-

(ng

m-2

s-1

)

χ1m

NO3 -

(μg m-3)

Concentration HNO3

Vd HNO3

Flux NH3

HNO3 Vmax HNO3 Vd

Concentration NO3-

Flux HNO3

Flux NO3-

Vd NO3-

Summary I: Ammonium Concentrations

• Ammonium aerosols (AN, AS) are ubiquitous in the atmosphere; contribution from AC is usually negligible

• Regional AN & AS make an important contribution to exceedances of Air Quality Standards in urban areas

• The cooling of ammonium aerosols is thought to be - 0.5 (- 0.25 to – 1.2) W m-2

• European aerosol is generally neutralised; US aerosol is often acidic.

Summary II: Changes in Ammonium

• There is an ongoing shift from sulphates to nitrates, complicating the description of the chemistry.

• Responses to reduction in precursor gases are poorly understood and verified.

• The urban environment appears to be an important (under-studied) area of AN production

• Aircraft measurements and EMEP Intensive Measurement Periods provide powerful datasets for model development / validation

Summary III: Effect of Ammonia Chemistry on Fluxes

• Chemistry leads to errors when using standard micrometeorological approaches

• Non-conservation needs to be considered for the interpretation of flux measurements (not just ammonia, but also aerosol)

• The conversion between gas and aerosol phase changes net exchange of NHx (and also NOx)

• These processes are confined to the lowest metres of the atmosphere. Larger scale models are not able to reproduce this aerosol formation need for sub-grid parameterisations.

Acknowledgements

• European funding: EXAMINE, GRAMINAE and NitroEurope IP

• National funding from the UK Department for Environment, Food and Rural Affairs.

• Data sources: – Michigan data: Alice Delia, Univ. Colorado– EMEP Intensive Campaign:

• Jan Willem Erisman & Rene Otjes, ECN, NL• Univ. Kopio, FI• Urs Baltensperger & Rami Alfarra, Paul Scherer Institute, CH

Observations of significant aerosol nitrate formation in urban areasEiko Nemitz, Rick Thomas, Gavin Phillips, David FowlerAtmospheric Sciences, Centre for Ecology and Hydrology (CEH), Bush Estate, Penicuik, Midlothian, EH26 0QB, U.K.

Composition resolved flux measurements using eddy-covariance with an aerosol mass spectrometer reveal urban areas are source of aerosol nitrate.

20

15

10

5

0

-5Org

anic

Flu

x [ n

g m

-2 s

-1]

12

8

4

0CO

2 Flu

x [µ

mol

m-2 s

-1]

30x103

20

10

0

Particle Flux [ #cm-2 s

-1]

16

12

8

4

0

NO

3 - Flux [ ng m-2 s

-1]

SOA (m/z 44) Average HOA m/z 43 m/z 55 m/z 57

CO2

Small particles

Nitrate

CO

2 flu

x [μ

mol

m-2

s-1

]

0

20

40

60

80

CN

flux

[# c

m-2

s-1

]

0

10000

20000

30000

40000CO2

CN

Time of day0 6 12 18 24

Aer

osol

flux

[ng

m-2

s-1

]0

5

10

15

20 SO42-

NO3-

organics

Hea

t flu

x [W

m-2

]

-50

0

50

100

150

200

250

sensible heatlatent heat

Gothenburg, Sweden (winter) Boulder, Colorado (summer)

Results:

• Aerosol nitrate emissions from urban areas appear to be ubiquitous, indicating that NOxoxidation is very fast.

• Nitrate formed in urban areas is in the Aitken mode (observed worldwide).

• They occur during both summer and winter, but vary between days.

• In winter emissions appear to be larger on inversion days (build-up of HNO3 & NH3?)

Implications:

• Urban areas are important for NOx oxidation.

• Urban areas may be more important for NH4NO3 formation than agricultural areas.

-100

-50

0

50

100

Parti

cle

Flux

[ ng

m-2

s-1

]

Feb 13 Feb 14 Feb 15 Feb 16 Feb 17 Feb 18 Feb 19 Feb 20 Feb 21 Feb 22 Feb 23 Feb 24 Feb 25 Feb 26 Feb 27 Feb 28 Mar 1

80x103

6040200

CN

Flux [ # cm-2 s

-1]

40

20

0

CO

2 Fl

ux [

µmol

m-2

s-1

]

12840

Temp [ oC

]

HOA SOA (m/z44)

CN CO2

Temp at 3m oC

SO42-

NO3- (m/z 30)

NO3- (m/z 46)

3

2

1

0

Aero

sol c

once

ntra

tion

[μg

m-3

]

Feb 14 Feb 15 Feb 16 Feb 17 Feb 18 Feb 19 Feb 20 Feb 21 Feb 22 Feb 23 Feb 24 Feb 25 Feb 26 Feb 27 Feb 28 Mar 1

360270180900

Win

d di

rect

ion

1612840

Win

d sp

eed

[m/s

]

-4-202

T(3

m) -

T(8

5 m

) [°C

]

SO42-

Org Cl-

NO3-

NH4+

Inversions

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

dM/d

logD

va (µ

g m

-3)

5 6 7 8100

2 3 4 5 6 7 81000

Vacuum Aerodynamic Diameter (nm)

2.0

1.5

1.0

0.5

0.0

dM/d

logD

va (µ

g m

-3)

5 6 7 8100

2 3 4 5 6 7 81000

Vacuum Aerodynamic Diameter (nm)

4

3

2

1

0

dM/d

logD

va (µ

g m

-3)

5 6 7 8 9100

2 3 4 5 6 7 8 91000

Vacuum Aerodynamic Diameter (nm)

Ammonium Nitrate Sulphate Chloride Organics

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

dM/d

logD

va (µ

g m

-3)

5 6 7 8100

2 3 4 5 6 7 81000

Vacuum Aerodynamic Diameter (nm)

1.0

0.8

0.6

0.4

0.2

0.0dM

/dlo

gDva

(µg

m-3

)

5 6 7 8100

2 3 4 5 6 7 81000

Vacuum Aerodynamic Diameter (nm)