Copyright © 2010 R. R. Dickerson 1 The Atmospheric Chemistry and Physics of Ammonia and other Reactive N Compounds Examples of applications of physical.

Copyright © 2010 R. R. Dickerson

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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


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Talk Outline

I. Fundamental PropertiesImportanceReactionsAerosol formationThermodynamicsRole as ccn

II. Deposition

III. Local Observations Observed concentrations Impact on visibility Box Model results New Detection Technique


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Atmospheric Ammonia, NH3

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 N2O.


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Fundamental Properties, continued

Thermodynamically unstable wrt oxidation.

NH3 + 1.25O2 → NO + 1.5H2O

H°rxn = −53.93 kcal mole-1

G°rxn = −57.34 kcal mole-1

But the kinetics are slow:NH3 + OH· → NH2 + H2O

k = 1.6 x 10-13 cm3 s-1 (units: (molec cm-3)-1 s-1)Atmospheric lifetime for [OH] = 106 cm-3

τNH3 = (k[OH])-1 ≈ 6x106 s = 72 d. Compare to τH2O ≈ 10 d.


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Gas-phase reactions:

NH3 + OH· → NH2· + H2O

NH2· + O3 → NH, NHO, NO

NH2· + NO2 → N2 or N2O (+ H2O)

Potential source of atmospheric NO and N2O in low-SO2 environments.

Last reaction involved in combustion “deNOx” operations of power plants and large Diesel engines.


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Aqueous phase chemistry:

NH3(g) + H2O ↔ NH3·H2O(aq) ↔ NH4 + + OH−

Henry’s Law Coef. = 62 M atm-1

Would not be rained out without atmospheric acids.

Weak base: Kb = 1.8x10-5

Copyright © 2010 R. R. Dickerson7

Aqueous ammonium concentration as a function of pH for 1 ppb gas-phase NH3. From Seinfeld and Pandis (1998).


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Formation of Aerosols

Nucleation – the transformation from the gaseous to condensed phase; the generation of new particles.

H2SO4/H2O system does not nucleate easily.

NH3/H2SO4/H2O system does (e.g., Coffman & Hegg, 1995).


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Formation of aerosols, continued:

NH3(g) + H2SO4(l) → NH4HSO4(s, l) (ammonium bisulfate) NH3(g) + NH4HSO4(l) → (NH4)2SO4(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 ∽ NH4HSO4).

Efflorescence – the become crystalline through loss of water; literally to flower.

We can calculate the partitioning in the NH4/SO4/NO3/H2O system with a thermodynamic model; see below.


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Cloud⇗


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Formation of aerosols, continued

NH3(g) + HNO3(g) ↔ NH4NO3(s)

G°rxn = −22.17 kcal mole-1

[NH4NO3] Keq = ------------------ = exp (−G/RT) [NH3][HNO3]

Keq = 1.4x1016 at 25°C; = 1.2x1019 at 0°C

Solid ammonium nitrate (NH4NO3) is unstable except at high [NH3] and [HNO3] or at low temperatures. We see more NH4NO3 in the winter in East.


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Ammonium Nitrate Equilibrium in Air = f(T)

NH3(g) + HNO3(g) = NH4NO3(s)

– ln(K) = 118.87 – 24084 – 6.025ln(T) (ppb)2

1/Keq 298K = [NH3][HNO3] (ppb)2 = 41.7 ppb2

(√41.7 ≈ 6.5 ppb each)

1/Keq 273K = 4.3x10-2 ppb2

Water in the system shifts equilibrium to the right.

Copyright © 2010 R. R. Dickerson14

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).


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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 NH3 and HNO3 are fast; deposition of particles is slow.


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Nitrogen DepositionPast and Present

mg N/m2/yr

1860 1993

500020001000 750 500 250 100 50 25 5

Galloway et al., 2003

II. N Deposition CONUS 2012http://nadp.sws.uiuc.edu/committees/tdep/tdepmaps/

The total is composed of: Reduced N (NH3 and NH4

+ mostly

Oxidized N (NO3- mostly)

Both undergo wet and dry deposition.


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Annual mean visibility across the United states

(Data acquired from the IMPROVE network)

Fort Meade, MD


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http://vista.cira.colostate.edu/improve/Data/Graphic_Viewer/seasonal.htm


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III. Local Observations


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Fort Meade, MD


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Summer: Sulfate dominates.

Winter: Nitrate/carbonaceous particles play bigger roles.

Inorganic compounds ~50% (by mass)

Carbonaceous material ~40% (by mass)


34• Seasonal variation of 24-hr average concentration of NOy, NO3-, and NH4

+ at FME.


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ISORROPIA Thermodynamic Model (Nenes, 1998; Chen 2002)

Inputs: Temperature, RH, T-SO42-, T-NO3

-, and T-NH4+

Output: HNO3, NO3-, NH3, NH4

+, HSO4-, H2O, etc.


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ISORROPIA Thermodynamic Model (Nenes, 1998; Chen, 2002)

Inputs: Temperature, RH, T-SO42-, T-NO3

-, and T-NH4+

Output: HNO3, NO3-, NH3, NH4

+, HSO4-, H2O, etc.


37(Data acquired in July 1999)


38(Water amount estimated by ISORROPIA)


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Interferometer for NH3 Detection

Schematic diagram detector based on heating of NH3 with a CO2 laser tuned to 9.22 μm and a HeNe laser interferometer (Owens et al., 1999).


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Linearity over five orders of magnitude.


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Response time (base e) of laser interferometer ∽ 1 s.


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Copyright © 2010 R. R. Dickerson43*Emissions from vehicles can be important in urban areas.


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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.


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Donora, PA Oct. 29, 1948


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Madonna

Harten Castle

Germany: Ruhr area

Portal figure

Sandstone

Sculptured 1702

Photographed 1908


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Madonna

Harten Castle

Germany: Ruhr area

Portal figure

Sandstone

Sculptured 1702

Photographed 1969


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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;333:1586-1587

Published by AAAS

Fig. 1 Coupling of atmospheric HONO with soil nitrite.

H Su et al. Science 2011;333:1616-1618

Published by AAAS

Fig. 2 [HONO]* and Fmax.

H Su et al. Science 2011;333:1616-1618

Published by AAAS

Fig. 4 Diurnal variation of atmospheric [HONO], Pmissing, and Psoil at the Xinken site.

H Su et al. Science 2011;333:1616-1618

Published by AAAS


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The End.


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AcknowledgementsAcknowledgementsContributing Colleagues:

Antony Chen (DRI) Bruce DoddridgeRob Levy (NASA) Jeff StehrCharles Piety Bill Ryan (PSU)Lackson Marufu Melody Avery (NASA)

Funding From:Maryland Department of the Environment & DNRNC Division of Air QualityVA Department of Environmental QualityNASA-GSFCEPRI


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MODIS: August 9, 2001MODIS: August 9, 2001

“Visible” Composite Aerosol Optical Depth at 550 nm

AOT

0.8

0.0

Phila

BaltGSFC GSFC

Balt

Phila

Highest Ozone of the Summer

Robert Levy, NASA

Copyright © 2010 R. R. Dickerson 1 The Atmospheric Chemistry and Physics of Ammonia and other Reactive N Compounds Examples of applications of physical.

Documents

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