the nitrogen cycle. topics for today 1.the nitrogen cycle 2.fixed nitrogen in the atmosphere...
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THE NITROGEN CYCLETHE NITROGEN CYCLE
TOPICS FOR TODAYTOPICS FOR TODAY
1. The Nitrogen Cycle
2. Fixed Nitrogen in the Atmosphere
3. Sources of NOx
4. What about N2O?
5. Nitrogen Cycle: on the particle side
6. How might the nitrogen cycle be affected by climate
change?
OXIDATION STATES OF NITROGENOXIDATION STATES OF NITROGENN has 5 electrons in valence shell N has 5 electrons in valence shell 9 oxidation states from –3 to +59 oxidation states from –3 to +5
-3 0 +1 +2 +3 +4 +5
NH3
Ammonia
NH4+
Ammonium
R1N(R2)R3
Organic N
N2 N2O
Nitrous
oxide
NO
Nitric oxide
HONO
Nitrous acid
NO2-
Nitrite
NO2
Nitrogen dioxide
HNO3
Nitric acid
NO3-
Nitrate
N2O5
Nitrogen pentoxide
Decreasing oxidation number (reduction reactions)
Increasing oxidation number (oxidation reactions)
Nitrogen: Nitrogen is a major component of the atmosphere, but an essential nutrient in short
supply to living organisms.
free radical free radical
THE THE NITROGEN CYCLENITROGEN CYCLE: MAJOR PROCESSES: MAJOR PROCESSES
ATMOSPHEREN2 NO
HNO3
NH3/NH4+ NO3
-
orgN
BIOSPHERE
LITHOSPHERE
combustionlightning
oxidation
deposition
assimilation
decay
nitrification
denitri-fication
biofixation
burial weathering
free radical
"fixed" or "odd" N is less stable globally=> N2
BOX MODEL OF THE NITROGEN CYCLEBOX MODEL OF THE NITROGEN CYCLE
Inventories in Tg NFlows in Tg N yr-1
[Jacob, 1999]
TOPICS FOR TODAYTOPICS FOR TODAY
1. The Nitrogen Cycle
2. Fixed Nitrogen in the Atmosphere
3. Sources of NOx
4. What about N2O?
5. Nitrogen Cycle: on the particle side
6. How might the nitrogen cycle be affected by climate
change?
NOx: KEY TO MAINTAINING THE OXIDIZING POWER OF THE NOx: KEY TO MAINTAINING THE OXIDIZING POWER OF THE TROPOSPHERETROPOSPHERE
O3
O2 h
O3
OH HO2
h, H2O
Deposition
NO
H2O2
CO, CH4
NO2
h
STRATOSPHERE
TROPOSPHERE
8-18 km
SURFACE
•ALSO key player in stratospheric O3 loss
NONOyy CYCLING CYCLING
HO2
NONO2
h
O3
O3
O2
Combustionlightning
HNO3
OH, M
O3
NO3
N2O5
M
H2O
PANcarbonyloxidation
T
~ 1 day
Example of PAN formation from acetaldehyde:CH3CHO + OH CH3CO + H2OCH3CO + O2 + M CH3C(O)OO + MCH3C(O)OO+NO2 + M CH3C(O)OONO2 + M
PEROXYACETYLNITRATE (PAN) AS RESERVOIR PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-RANGE TRANSPORT OF NOFOR LONG-RANGE TRANSPORT OF NOxx
[Jacob, 1999]
TOPICS FOR TODAYTOPICS FOR TODAY
1. The Nitrogen Cycle
2. Fixed Nitrogen in the Atmosphere
3. Sources of NOx
4. What about N2O?
5. Nitrogen Cycle: on the particle side
6. How might the nitrogen cycle be affected by climate
change?
NONOxx EMISSIONS (Tg N yr EMISSIONS (Tg N yr-1-1) TO TROPOSPHERE) TO TROPOSPHERE
Zeldovich Mechanism: combustion and lightningAt high T (~2000K) oxygen thermolyzes:
O2 O + OO + N2 NO + NN + O2 NO + O
[IPCC, 2007]
USING SATELLITE OBSERVATIONS OF NOUSING SATELLITE OBSERVATIONS OF NO22 TO MONITOR NO TO MONITOR NOxx EMISSIONS EMISSIONS
SCIAMACHY data. May-Oct 2004
(R.V. Martin, Dalhousie U.)
detectionlimit
LIGHTNING FLASHES SEEN FROM SPACE (2000)LIGHTNING FLASHES SEEN FROM SPACE (2000)
DJF
JJA
Bottom-up Emission Estimate:Emission = (# flashes) x (NOx molecules /flash)
IC or CG flash?Length of flash?
HIGHLYUNCERTAIN
TOP-DOWN ESTIMATES OF GLOBAL LIGHTNING TOP-DOWN ESTIMATES OF GLOBAL LIGHTNING NOx EMISSIONSNOx EMISSIONS
[Martin et al., 2007]
Using SCIAMACHY (NO2), OMI (O3), ACE-FTS (HNO3): Target locations/times where NO2 column is dominated by
lightning source
Global source of 6 ± 2 TgN/yr from lightning
Obs (satellite)Model (6 TgN/yr)Model (4-8 TgN/yr)Model (4-8 TgN/yr)Model (no lightning)
USING SATELLITE OBSERVATIONS TO ESTIMATE USING SATELLITE OBSERVATIONS TO ESTIMATE SOIL NOx EMISSIONSSOIL NOx EMISSIONS
Use GOME observations over Africa:Soils: 3.3 TgN/yearBiomass Burning: 3.8 TgN/year40% of surface NOx emissions!
Extrapolating to all the tropics:7.3 TgN/year biogenic soil(twice the IPCC value)
Biomass BurningSoilsFossil + biofuels
[Jaeglé et al., 2004]
GROWING CONTRIBUTION OF AGRICULTURE TO GROWING CONTRIBUTION OF AGRICULTURE TO N CYCLEN CYCLE
[IPCC, 2007]
TOPICS FOR TODAYTOPICS FOR TODAY
1. The Nitrogen Cycle
2. Fixed Nitrogen in the Atmosphere
3. Sources of NOx
4. What about N2O?
5. Nitrogen Cycle: on the particle side
6. How might the nitrogen cycle be affected by climate
change?
NN22O: LOW-YIELD PRODUCT OF BACTERIAL O: LOW-YIELD PRODUCT OF BACTERIAL
NITRIFICATION AND DENITRIFICATIONNITRIFICATION AND DENITRIFICATIONImportant as
• source of NOx radicals in stratosphere• greenhouse gas
[IPCC, 2007]
NN22O EMISSIONS (Tg N yrO EMISSIONS (Tg N yr-1-1) TO TROPOSPHERE) TO TROPOSPHERE
[IPCC, 2007]Source is MOSTLY (~75%) natural
Inventories in Tg NFlows in Tg N yr-1
ADDING NADDING N22O TO THE NITROGEN BOX MODELO TO THE NITROGEN BOX MODEL
48 4
1.53 x103 N2O
Although a closed budget can be constructed, uncertainties in sources are large! (N2O atm mass = 5.13 1018 kg x 3.1 10-7 x28/29 = 1535 Tg )
TOPICS FOR TODAYTOPICS FOR TODAY
1. The Nitrogen Cycle
2. Fixed Nitrogen in the Atmosphere
3. Sources of NOx
4. What about N2O?
5. Nitrogen Cycle: on the particle side
6. How might the nitrogen cycle be affected by climate
change?
ANNUAL MEAN PMANNUAL MEAN PM2.52.5 CONCENTRATIONS AT U.S. SITES CONCENTRATIONS AT U.S. SITES
Air qualitystandard
Dry mass concentrations
FORMATION OF SULFATE-NITRATE-AMMONIUM AEROSOLSFORMATION OF SULFATE-NITRATE-AMMONIUM AEROSOLS
2
2
2
22 4 4
3 4
3 3
3 3 4 3
( ) 2
( )
( )
( ) ( ) ( )
H O
H O
H O
H SO g SO H
NH g NH OH
HNO g NO H
NH g HNO g NH NO aerosol
Sulfate always forms an aqueous aerosol
Ammonia dissolves in the sulfate aerosol totally or until titration of acidity, whichever happens first
Nitrate is taken up by aerosol if (and only if)excess NH3 is available after sulfate titration
HNO3 and excess NH3 can also form a solid aerosol if RH is low
Thermodynamic rules:
[Park et al., 2006]
HNO3 NO3-
NH3 NH4+
H+
OH-
SO42-
GLOBAL SOURCES OF AMMONIAGLOBAL SOURCES OF AMMONIA
[Park et al., 2004]
VERY UNCERTAIN!Measurements are tough, so hard to verify regional estimates.
Efficient scavengingof both HNO3(g) and nitrate aerosol
Efficient scavengingof both NH3(g) and ammonium aerosol
TOPICS FOR TODAYTOPICS FOR TODAY
1. The Nitrogen Cycle
2. Fixed Nitrogen in the Atmosphere
3. Sources of NOx
4. What about N2O?
5. Nitrogen Cycle: on the particle side
6. How might the nitrogen cycle be affected by climate
change?
PREDICTED CHANGES IN ANTHROPOGENIC NOPREDICTED CHANGES IN ANTHROPOGENIC NOXX EMISSIONS EMISSIONS
[IPCC 2007 (WG3)]
Emissions declining in NA, EU, growing in AS (transportation), but predicted to level off (may peak as early as 2015). What about natural sources?
Note: this include aviation NOx sources which are small but in UT and have grown from 0.55 to 0.7 Tg/yr from 1992-2002 (may double in next 20 years)
CHANGING LNOCHANGING LNOXX??
Warmer climate = more thunderclouds = more lightning
Impact:(1)increasing UT ozone formation (positive forcing)(2)Increasing OH leads to small reductions in CH4 (negative forcing)
Models predict + 4-60 % LNOx per °K
THE THE NITROGEN CYCLENITROGEN CYCLE: MAJOR PROCESSES: MAJOR PROCESSES
ATMOSPHEREN2 NO
HNO3
NH3/NH4+ NO3
-
orgN
BIOSPHERE
LITHOSPHERE
combustionlightning
oxidation
deposition
assimilation
decay
nitrification
denitri-fication
biofixation
burial weathering
"fixed" or "odd" N is less stable globally=> N2
NONOyy CYCLING CYCLING
HO2
NONO2
h
O3
O3
O2
Combustionlightning
HNO3
OH, M
O3
NO3
N2O5
M
H2O
PANcarbonyloxidation
T
~ 1 day
Example of PAN formation from acetaldehyde:CH3CHO + OH CH3CO + H2OCH3CO + O2 + M CH3C(O)OO + MCH3C(O)OO+NO2 + M CH3C(O)OONO2 + M
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