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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)