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Looking at Ammonia in ACE-1 Data. Sara Lance. Aerosol Characterization Experiments (ACE). Goal of ACE is “to provide the necessary data to incorporate aerosol particles into global climate models and to reduce the overall uncertainty in calculating the climatic effect of aerosols” ACE-1

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aerosol characterization experiments ace
Aerosol Characterization Experiments (ACE)
  • Goal of ACE is “to provide the necessary data to incorporate aerosol particles into global climate models and to reduce the overall uncertainty in calculating the climatic effect of aerosols”
  • ACE-1
    • Remote Marine Environment, Nov/Dec 1995
  • ACE –2
    • Northeastern Atlantic, June/July 1997
  • ACE-ASIA
    • March-May 2001
so what did we see at ace 1 that s worth talking about
So – what did we see at ACE-1 that’s worth talking about?
  • Persistent peak in NH3 concentration
  • How many of the flights showed this phenomena?
    • Flights 16-23, 25, 27-32 (out of 33 Flights)
    • Allflights with NH3/NH4+ measurements show a peak in NH3 concentration between ~100-600m
  • My Focus:Flight-18 (December 1st, 1995)
    • NH3 peak at ~600m
possible remote marine sources of nh 3 g nh 4
Possible Remote Marine Sources of NH3(g)/NH4+
  • Sea salt spray – NH4+
  • Marine biogenic emissions – NH3(g)
  • Advection of continental sources– NH3(g)/NH4+
thermodynamic modeling

NH3(g)

NH4+

SO4=

Thermodynamic Modeling

The higher aerosol SO4= concentration, the more NH3(g) is absorbed by a cloud droplet (in order to regulate the pH), thereby causing a sink of gas phase ammonia.

NH3(aq) + H2O(aq)  NH4+(aq) + OH-(aq)

NH3(g)  NH3(aq)

HSO4-(aq)  H+(aq) + SO42=

isorropia
ISORROPIA
  • Thermodynamic equilibrium model for multiphase multi-component inorganic aerosols

Assumption: Chemical Equilibrium

Valid when ambient conditions change slowly compared to chemical changes within the aerosol droplet.

SOLID

LIQUID

GAS PHASE

isorropia speciation
ISORROPIA - speciation
  • Gas: HNO3, HCl, NH3, H2O
  • Liquid: Na+, NH4+, H+, OH-, HSO4-, SO42-,
  • NO3-, Cl-, H2O
  • Solid: NaHSO4 , NH4HSO4 , Na2SO4 ,
  • (NH4)2SO4 , (NH4)3H(SO4)2, NH4NO3,
  • NH4Cl, NaNO3 , NaCl
isorropia inputs
ISORROPIA - inputs
  • If the system is in thermodynamic equilibrium, then the model should give a good estimate of the gas phase ammonia concentration given the total concentrations (gas+aerosol) of:
    • Na+
    • HCl/Cl-
    • NH3/NH4+
    • H2SO4/SO4=
    • HNO3/NO3-
  • The model also needs the corresponding relative humidity and temperatures
conclusion
Conclusion
  • The NH3 (g) concentration measured during ACE-1 is consistent with a thermodynamic equilibrium model (ISORROPIA) for points above, within and below a cloud.
  • Because the concentration of SO42= in the ACE-1 measurements was so low, nearly all of the NH3 was partitioned to the gas phase.
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