When organics and inorganics share the same aerosol
SOAS thermodynamics match MARGA ammonium–sulfate data if models mix phases carefully and nonvolatile-cation emissions are revised.
Source
Coupling of organic and inorganic aerosol systems and the effect on gas-particle partitioning in the southeastern US
Study at a glance
- Design
- Computational / modelling — CMAQ 5.2 and thermodynamic box models evaluated against SOAS inorganic/organic observations
- N
- Model–observation comparison for June–July 2013 SOAS; not a primary sample N
- Population
- Southeastern US aerosol thermodynamics during SOAS at Centreville and domain monitors
- Outcome
- Ammonium–sulfate partitioning and organic gas–particle bias under phase-mixing assumptions
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
When organics and inorganics share the same aerosol
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
CMAQ predicted a mean RN/2S of 0.73 versus observed 0.67.
CMAQ predicted a mean R N/2S of 0.73 over the US compared to the observed mean of 0.67.
CMAQ was run at 12 km by 12 km for 1 June–15 July 2013.
CMAQ version 5.2-gamma was run over the continental US at 12 km by 12 km horizontal resolution for 1 June–15 July 2013, coinciding with the Southern Oxidant and Aerosol Study (SOAS) field campaign and the Centreville, Alabama, US, field site.
What they did
Authors ran CMAQ 5.2 at 12 km for June–July 2013 and ISORROPIA/AIOMFAC box models against SEARCH, CSN, AMS, MARGA, and SV-TAG during SOAS at Centreville.
What they found
CMAQ mean ammonium/2×sulfate is 0.73 versus CSN 0.67. MARGA ratios ~0.8–0.9 agree with equilibrium models; AMS/CSN look too ammonium-poor. Mixing organics with inorganics can raise pH but is not the main model-evaluation problem. Organic Fp bias falls if vapor pressures drop by 4.2.
The limits
What it doesn't show
AMS nitrate includes organonitrates so inorganic nitrate was zeroed; 50% of 2-methyltetrols may be dimers; cation emissions remain uncertain by about a factor of three.
Key terms
- ISORROPIA
- Inorganic aerosol thermodynamic model used in CMAQ.
- AIOMFAC
- Activity-coefficient model for organic–inorganic liquid mixtures.
- Phase separation
- Organic and aqueous inorganic liquids occupying distinct particle phases.
- RN/2S
- Molar ammonium divided by twice total sulfate.
- MARGA
- Monitor for Aerosols and Gases in Ambient air measuring PM2.5 ions.
Flashcards
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Quiz yourself
CMAQ mean RN/2S vs CSN:
Common questions
Which observations match thermodynamics?
MARGA, not AMS or CSN ammonium/sulfate.
CMAQ domain RN/2S?
0.73 versus CSN 0.67.
Do organics mixing fix inorganic bias?
They can change pH but are likely not the main issue.
Organic vapor-pressure tweak?
EVAPORATION Psat cut by 4.2 reduces bias.
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