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