1. THE NITROGEN CYCLE

2. TOPICS FOR TODAY 1.The Nitrogen Cycle 2.Fixed Nitrogen in the Atmosphere 3.Sources of NOx 4.What about N 2 O? 5.Nitrogen Cycle: on the particle side 6.How might the nitrogen cycle be affected by climate change?

3. OXIDATION STATES OF NITROGEN N has 5 electrons in valence shell  9 oxidation states from –3 to +5 -30+1+2+3+4+5 NH 3 Ammonia NH 4 + Ammonium R 1 N(R 2 )R 3 Organic N N2N2 N 2 O Nitrous oxide NO Nitric oxide HONO Nitrous acid NO 2 - Nitrite NO 2 Nitrogen dioxide HNO 3 Nitric acid NO 3 - Nitrate N 2 O 5 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

4. THE NITROGEN CYCLE: MAJOR PROCESSES ATMOSPHERE N2N2 NO HNO 3 NH 3 /NH 4 + NO 3 - orgN BIOSPHERE LITHOSPHERE combustion lightning oxidation deposition assimilation decay nitrification denitri- fication biofixation burial weathering free radical "fixed" or "odd" N is less stable globally=> N 2

5. BOX MODEL OF THE NITROGEN CYCLE Inventories in Tg N Flows in Tg N yr -1 [Jacob, 1999]

6. TOPICS FOR TODAY 1.The Nitrogen Cycle 2.Fixed Nitrogen in the Atmosphere 3.Sources of NOx 4.What about N 2 O? 5.Nitrogen Cycle: on the particle side 6.How might the nitrogen cycle be affected by climate change?

7. NOx: KEY TO MAINTAINING THE OXIDIZING POWER OF THE TROPOSPHERE O3O3 O2O2 h O3O3 OHHO 2 h, H 2 O Deposition NO H2O2H2O2 CO, CH 4 NO 2 h STRATOSPHERE TROPOSPHERE 8-18 km SURFACE ALSO key player in stratospheric O 3 loss

8. NO y CYCLING HO 2 NO NO 2 h O3O3 O3O3 O2O2 Combustion lightning HNO 3 OH, M O3O3 NO 3 N2O5N2O5 M H2OH2O PAN carbonyl oxidation T  ~ 1 day Example of PAN formation from acetaldehyde: CH 3 CHO + OH  CH 3 CO + H 2 O CH 3 CO + O 2 + M  CH 3 C(O)OO + M CH 3 C(O)OO+NO 2 + M  CH 3 C(O)OONO 2 + M

9. PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-RANGE TRANSPORT OF NO x [Jacob, 1999]

10. TOPICS FOR TODAY 1.The Nitrogen Cycle 2.Fixed Nitrogen in the Atmosphere 3.Sources of NOx 4.What about N 2 O? 5.Nitrogen Cycle: on the particle side 6.How might the nitrogen cycle be affected by climate change?

11. NO x EMISSIONS (Tg N yr -1 ) TO TROPOSPHERE Zeldovich Mechanism: combustion and lightning At high T (~2000K) oxygen thermolyzes: O 2  O + O O + N 2  NO + N N + O 2  NO + O [IPCC, 2007]

12. USING SATELLITE OBSERVATIONS OF NO 2 TO MONITOR NO x EMISSIONS SCIAMACHY data. May-Oct 2004 (R.V. Martin, Dalhousie U.) detection limit

13. LIGHTNING FLASHES SEEN FROM SPACE (2000) DJF JJA Bottom-up Emission Estimate: Emission = (# flashes) x (NO x molecules /flash) IC or CG flash? Length of flash? HIGHLY UNCERTAIN

14. TOP-DOWN ESTIMATES OF GLOBAL LIGHTNING NOx EMISSIONS [Martin et al., 2007] Using SCIAMACHY (NO 2 ), OMI (O 3 ), ACE-FTS (HNO 3 ): Target locations/times where NO 2 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 (no lightning)

15. USING SATELLITE OBSERVATIONS TO ESTIMATE SOIL NOx EMISSIONS Use GOME observations over Africa: Soils: 3.3 TgN/year Biomass Burning: 3.8 TgN/year  40% of surface NOx emissions! Extrapolating to all the tropics: 7.3 TgN/year biogenic soil (twice the IPCC value) Biomass Burning Soils Fossil + biofuels [Jaeglé et al., 2004]

16. GROWING CONTRIBUTION OF AGRICULTURE TO N CYCLE [IPCC, 2007]

17. TOPICS FOR TODAY 1.The Nitrogen Cycle 2.Fixed Nitrogen in the Atmosphere 3.Sources of NOx 4.What about N 2 O? 5.Nitrogen Cycle: on the particle side 6.How might the nitrogen cycle be affected by climate change?

18. N 2 O: LOW-YIELD PRODUCT OF BACTERIAL NITRIFICATION AND DENITRIFICATION Important as source of NO x radicals in stratosphere greenhouse gas [IPCC, 2007]

19. N 2 O EMISSIONS (Tg N yr -1 ) TO TROPOSPHERE [IPCC, 2007] Source is MOSTLY (~75%) natural

20. Inventories in Tg N Flows in Tg N yr -1 ADDING N 2 O TO THE NITROGEN BOX MODEL 48 4 1.53 x10 3 N 2 O Although a closed budget can be constructed, uncertainties in sources are large! (N 2 O atm mass = 5.13 10 18 kg x 3.1 10 -7 x28/29 = 1535 Tg )

21. TOPICS FOR TODAY 1.The Nitrogen Cycle 2.Fixed Nitrogen in the Atmosphere 3.Sources of NOx 4.What about N 2 O? 5.Nitrogen Cycle: on the particle side 6.How might the nitrogen cycle be affected by climate change?

22. ANNUAL MEAN PM 2.5 CONCENTRATIONS AT U.S. SITES Air quality standard Dry mass concentrations

23. FORMATION OF SULFATE-NITRATE-AMMONIUM AEROSOLS 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 NH 3 is available after sulfate titration HNO 3 and excess NH 3 can also form a solid aerosol if RH is low Thermodynamic rules: [Park et al., 2006] HNO 3 NO 3 - NH 3 NH 4 + H+H+ OH - SO 4 2-

24. GLOBAL SOURCES OF AMMONIA [Park et al., 2004] VERY UNCERTAIN! Measurements are tough, so hard to verify regional estimates.

25. Efficient scavenging of both HNO 3 (g) and nitrate aerosol Efficient scavenging of both NH 3 (g) and ammonium aerosol

26. TOPICS FOR TODAY 1.The Nitrogen Cycle 2.Fixed Nitrogen in the Atmosphere 3.Sources of NOx 4.What about N 2 O? 5.Nitrogen Cycle: on the particle side 6.How might the nitrogen cycle be affected by climate change?

27. PREDICTED CHANGES IN ANTHROPOGENIC NO X 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)

28. CHANGING LNO X ? Warmer climate = more thunderclouds = more lightning Impact: (1)increasing UT ozone formation (positive forcing) (2)Increasing OH leads to small reductions in CH 4 (negative forcing) Models predict + 4-60 % LNO x per °K

29. THE NITROGEN CYCLE: MAJOR PROCESSES ATMOSPHERE N2N2 NO HNO 3 NH 3 /NH 4 + NO 3 - orgN BIOSPHERE LITHOSPHERE combustion lightning oxidation deposition assimilation decay nitrification denitri- fication biofixation burial weathering "fixed" or "odd" N is less stable globally=> N 2

30. NO y CYCLING HO 2 NO NO 2 h O3O3 O3O3 O2O2 Combustion lightning HNO 3 OH, M O3O3 NO 3 N2O5N2O5 M H2OH2O PAN carbonyl oxidation T  ~ 1 day Example of PAN formation from acetaldehyde: CH 3 CHO + OH  CH 3 CO + H 2 O CH 3 CO + O 2 + M  CH 3 C(O)OO + M CH 3 C(O)OO+NO 2 + M  CH 3 C(O)OONO 2 + M