Copyright © 2010 R. R. Dickerson 1 The Atmospheric Chemistry and Physics of Ammonia and other Reactive N Compounds Examples of applications of physical chemistry to atmospheric problems. Photo from UMD Aztec, 2002

Copyright © 2010 R. R. Dickerson 2 Talk Outline I. Fundamental Properties Importance Reactions Aerosol formation Thermodynamics Role as ccn II. Deposition III. Local Observations Observed concentrations Impact on visibility Box Model results New Detection Technique

Copyright © 2010 R. R. Dickerson 3 Atmospheric Ammonia, NH 3 I. Fundamental Properties Importance Only gaseous base in the atmosphere. Major role in biogeochemical cycles of N. Produces particles & cloud condensation nuclei. Haze/Visibility Radiative balance; direct & indirect cooling Stability wrt vertical mixing. Precipitation and hydrological cycle. Potential source of NO and N 2 O.

Copyright © 2010 R. R. Dickerson 4 Fundamental Properties, continued Thermodynamically unstable wrt oxidation. NH O 2 → NO + 1.5H 2 O  H° rxn = −53.93 kcal mole -1  G° rxn = −57.34 kcal mole -1 But the kinetics are slow: NH 3 + OH · → NH 2 + H 2 O k = 1.6 x cm 3 s -1 (units: (molec cm -3 ) -1 s -1 ) Atmospheric lifetime for [OH] = 10 6 cm -3 τ NH3 = (k[OH]) -1 ≈ 6x10 6 s = 72 d. Compare to τ H2O ≈ 10 d.

Copyright © 2010 R. R. Dickerson 5 Fundamental Properties, continued Gas-phase reactions: NH 3 + OH· → NH 2 · + H 2 O NH 2 · + O 3 → NH, NHO, NO NH 2 · + NO 2 → N 2 or N 2 O (+ H 2 O) Potential source of atmospheric NO and N 2 O in low-SO 2 environments. Last reaction involved in combustion “ deNOx ” operations of power plants and large Diesel engines.

Copyright © 2010 R. R. Dickerson 6 Fundamental Properties, continued Aqueous phase chemistry: NH 3(g) + H 2 O ↔ NH 3 ·H 2 O (aq) ↔ NH OH − Henry ’ s Law Coef. = 62 M atm -1 Would not be rained out without atmospheric acids. Weak base: K b = 1.8x10 -5

Copyright © 2010 R. R. Dickerson 7 Aqueous ammonium concentration as a function of pH for 1 ppb gas-phase NH 3. From Seinfeld and Pandis (1998).

Copyright © 2010 R. R. Dickerson 8 Formation of Aerosols Nucleation – the transformation from the gaseous to condensed phase; the generation of new particles. H 2 SO 4 /H 2 O system does not nucleate easily. NH 3 /H 2 SO 4 /H 2 O system does (e.g., Coffman & Hegg, 1995).

Copyright © 2010 R. R. Dickerson 9 Formation of aerosols, continued: NH 3(g) + H 2 SO 4(l) → NH 4 HSO 4(s, l) (ammonium bisulfate) NH 3(g) + NH 4 HSO 4(l) → (NH 4 ) 2 SO 4(s, l) (ammonium sulfate) Ammonium sulfates are stable solids, or, at most atmospheric RH, liquids. Deliquescence – to become liquid through the uptake of water at a specific RH ( ∽ 40% RH for NH 4 HSO 4 ). Efflorescence – the become crystalline through loss of water; literally to flower. We can calculate the partitioning in the NH 4 /SO 4 /NO 3 /H 2 O system with a thermodynamic model; see below.

Copyright © 2010 R. R. Dickerson 10 Cloud ⇗

Copyright © 2010 R. R. Dickerson 11

Copyright © 2010 R. R. Dickerson 12 Formation of aerosols, continued NH 3(g) + HNO 3(g) ↔ NH 4 NO 3(s)  G° rxn = −22.17 kcal mole -1 [NH 4 NO 3 ] K eq = = exp (−  G/RT) [NH 3 ][HNO 3 ] K eq = 1.4x10 16 at 25°C; = 1.2x10 19 at 0°C Solid ammonium nitrate (NH 4 NO 3 ) is unstable except at high [NH 3 ] and [HNO 3 ] or at low temperatures. We see more NH 4 NO 3 in the winter in East.

Copyright © 2010 R. R. Dickerson 13 Ammonium Nitrate Equilibrium in Air = f(T) NH 3(g) + HNO 3(g) = NH 4 NO 3(s) – ln(K) = – – 6.025ln(T) (ppb) 2 1/K eq 298K = [NH 3 ][HNO 3 ] (ppb) 2 = 41.7 ppb 2 (√41.7 ≈ 6.5 ppb each) 1/K eq 273K = 4.3x10 -2 ppb 2 Water in the system shifts equilibrium to the right.

Copyright © 2010 R. R. Dickerson 14 Radiative impact on stability: Aerosols reduce heating of the Earth’s surface, and can increase heating aloft. The atmosphere becomes more stable wrt vertical motions and mixing – inversions are intensified, convection (and rain) inhibited (e.g., Park et al., JGR., 2001).

Copyright © 2010 R. R. Dickerson 15 Additional Fundamental Properties Radiative effects of aerosols can accelerate photochemical smog formation. Condensed–phase chemistry tends to inhibit smog production. Too many ccn may decrease the average cloud droplet size and inhibit precipitation. Dry deposition of NH 3 and HNO 3 are fast; deposition of particles is slow.

Copyright © 2010 R. R. Dickerson 16 Nitrogen Deposition Past and Present mg N/m 2 /yr Galloway et al., 2003

II. N Deposition CONUS The total is composed of: Reduced N (NH 3 and NH 4 + mostly Oxidized N (NO 3 - mostly) Both undergo wet and dry deposition. Copyright © 2010 R. R. Dickerson 17

Copyright © 2010 R. R. Dickerson 18

Copyright © 2010 R. R. Dickerson 19

Copyright © 2010 R. R. Dickerson 20

Copyright © 2010 R. R. Dickerson 21

Copyright © 2010 R. R. Dickerson 22

Copyright © 2010 R. R. Dickerson 23

Copyright © 2010 R. R. Dickerson 24

Copyright © 2010 R. R. Dickerson 25

Copyright © 2010 R. R. Dickerson 26

Copyright © 2010 R. R. Dickerson 27 Annual mean visibility across the United states (Data acquired from the IMPROVE network) Fort Meade, MD

Copyright © 2010 R. R. Dickerson 28

Copyright © 2010 R. R. Dickerson 29

Copyright © 2010 R. R. Dickerson 30

Copyright © 2010 R. R. Dickerson 31 III. Local Observations

Copyright © 2010 R. R. Dickerson 32 Fort Meade, MD

Copyright © 2010 R. R. Dickerson 33 Summer: Sulfate dominates. Winter: Nitrate/carbonaceous particles play bigger roles. Inorganic compounds ~50% (by mass) Carbonaceous material ~40% (by mass)

Copyright © 2010 R. R. Dickerson 34 Seasonal variation of 24-hr average concentration of NO y, NO 3 -, and NH 4 + at FME.

Copyright © 2010 R. R. Dickerson 35 ISORROPIA Thermodynamic Model (Nenes, 1998; Chen 2002) Inputs: Temperature, RH, T-SO 4 2-, T-NO 3 -, and T-NH 4 + Output: HNO 3, NO 3 -, NH 3, NH 4 +, HSO 4 -, H 2 O, etc.

Copyright © 2010 R. R. Dickerson 36 ISORROPIA Thermodynamic Model (Nenes, 1998; Chen, 2002) Inputs: Temperature, RH, T-SO 4 2-, T-NO 3 -, and T-NH 4 + Output: HNO 3, NO 3 -, NH 3, NH 4 +, HSO 4 -, H 2 O, etc.

Copyright © 2010 R. R. Dickerson 37 (Data acquired in July 1999)

Copyright © 2010 R. R. Dickerson 38 (Water amount estimated by ISORROPIA)

Copyright © 2010 R. R. Dickerson 39 Interferometer for NH 3 Detection Schematic diagram detector based on heating of NH 3 with a CO 2 laser tuned to 9.22 μm and a HeNe laser interferometer (Owens et al., 1999).

Copyright © 2010 R. R. Dickerson 40 Linearity over five orders of magnitude.

Copyright © 2010 R. R. Dickerson 41 Response time (base e) of laser interferometer ∽ 1 s.

Copyright © 2010 R. R. Dickerson 42

Copyright © 2010 R. R. Dickerson 43 *Emissions from vehicles can be important in urban areas.

Copyright © 2010 R. R. Dickerson 44

Copyright © 2010 R. R. Dickerson 45

Copyright © 2010 R. R. Dickerson 46

Copyright © 2010 R. R. Dickerson 47 Summary: Ammonia plays a major role in the chemistry of the atmosphere. Major sources – agricultural. Major sinks – wet and dry deposition. Positive feedback with pollution – thermal inversions & radiative scattering. Multiphase chemistry Inhibits photochemial smog formation. Major role in new particle formation. Major component of aerosol mass. Thermodynamic models can work. Rapid, reliable measurements will put us over the top.

Copyright © 2010 R. R. Dickerson 48 Donora, PA Oct. 29, 1948

Copyright © 2010 R. R. Dickerson 49 Madonna Harten Castle Germany: Ruhr area Portal figure Sandstone Sculptured 1702 Photographed 1908

Copyright © 2010 R. R. Dickerson 50 Madonna Harten Castle Germany: Ruhr area Portal figure Sandstone Sculptured 1702 Photographed 1969

Copyright © 2010 R. R. Dickerson 51 Soil Nitrite as a Source of Atmospheric HONO and OH Radicals Hang Su,1*† Yafang Cheng,2,3*† Robert Oswald,1 Thomas Behrendt,1 Ivonne Trebs,1 Franz X. Meixner,1,4 Meinrat O. Andreae,1 Peng Cheng,2 Yuanhang Zhang,2 Ulrich Pöschl1† Hydroxyl radicals (OH) are a key species in atmospheric photochemistry. In the lower atmosphere, up to ~30% of the primary OH radical production is attributed to the photolysis of nitrous acid (HONO), and field observations suggest a large missing source of HONO. We show that soil nitrite can release HONO and explain the reported strength and diurnal variation of the missing source. Fertilized soils with low pH appear to be particularly strong sources of HONO and OH. Thus, agricultural activities and land-use changes may strongly influence the oxidizing capacity of the atmosphere. Because of the widespread occurrence of nitrite-producing microbes, the release of HONO from soil may also be important in natural environments, including forests and boreal regions.

Soil-atmosphere connections. M Kulmala, T Petäjä Science 2011;333: Published by AAAS

Fig. 1 Coupling of atmospheric HONO with soil nitrite. H Su et al. Science 2011;333: Published by AAAS

Fig. 2 [HONO]* and Fmax. H Su et al. Science 2011;333: Published by AAAS

Fig. 4 Diurnal variation of atmospheric [HONO], Pmissing, and Psoil at the Xinken site. H Su et al. Science 2011;333: Published by AAAS

Copyright © 2010 R. R. Dickerson 56 The End.

Copyright © 2010 R. R. Dickerson 57 Acknowledgements Contributing Colleagues: Antony Chen (DRI)Bruce Doddridge Rob Levy (NASA)Jeff Stehr Charles PietyBill Ryan (PSU) Lackson Marufu Melody Avery (NASA) Funding From: Maryland Department of the Environment & DNR NC Division of Air Quality VA Department of Environmental Quality NASA-GSFC EPRI

Copyright © 2010 R. R. Dickerson 58 MODIS: August 9, 2001 “Visible” Composite Aerosol Optical Depth at 550 nm AOT Phila Balt GSFC Balt Phila Highest Ozone of the Summer Robert Levy, NASA