Aerosol water alone cannot fix organic-aerosol bias
Adding aerosol liquid water to SOA partitioning without non-ideality overpredicts nighttime carbon; daytime OA in the southeast US still needs extra sources.
Source
On the implications of aerosol liquid water and phase separation for organic aerosol mass
Inspect source passages
Aerosol water alone cannot fix organic-aerosol bias
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Water-soluble OA accounted for 90% of total OA in the southeast US in summer 2013.
Ambient measurements of WSOC are highly correlated with oxygenated organic aerosol (OOA) (), and water-soluble OA accounted for 90% of total OA on average in the southeast US during summer 2013 ().
The non-ideal simulation had OC biases of −4, −10, and −2% for IMPROVE, CSN, and SEARCH.
A method ( γ ≠ 1 simulation) was developed to take into account deviations from ideality using an activity coefficient calculated based on the species Henry’s law coefficient, pure species saturation concentration ( C 0 , i * ), and the mole fraction of water in the particle that resulted in a normalized mean bias of −4, −10, and −2% for IMPROVE, CSN, and SEARCH SOC.
What they did
Authors updated CMAQ over the eastern United States for June 2013 (SOAS) so semivolatile SOA could interact with aerosol water, including organic-phase water uptake and a non-ideal activity-coefficient case, then compared OC with IMPROVE, CSN, and SEARCH.
What they found
The non-ideal (γ ≠ 1) case cut OC bias to −4, −10, and −2% at IMPROVE, CSN, and SEARCH. Assuming ideality overestimates nighttime aerosol water and carbon. Water-soluble OA was ~90% of total OA in the southeast US summer, but daytime OA remains underpredicted even with water in the partitioning medium.
The limits
What it doesn't show
The work is one summer over the eastern US; it does not identify the missing daytime SOA precursors, and POA is still overestimated by about a factor of two, compensating some SOA underestimate.
Key terms
- SOA
- Secondary organic aerosol formed from oxidation of gas-phase organics.
- Aerosol liquid water
- Water taken up by particles that can change size, chemistry, and partitioning.
- Activity coefficient (γ)
- Factor describing non-ideal mixing; γ ≠ 1 reduces water-driven SOA uptake.
- WSOC
- Water-soluble organic carbon, often used as a SOA/OOA surrogate.
- SOAS
- Southern Oxidant and Aerosol Study (2013) in the southeast United States.
Flashcards
0 of 11 answers reviewed
Research intelligence for this paper
See its role on concept claims, tensions it is part of, placement history, and related discoveries.
Quiz yourself
Adding aerosol water as an ideal solvent tends to:
Common questions
Should models dump all organics into aerosol water?
No—without non-ideality, nighttime water and carbon are overestimated.
Does adding water fix daytime OA?
No; extra daytime precursors or pathways are still needed.
What fraction of southeast US OA was water-soluble in SOAS?
About 90% of total OA on average in summer 2013.
Which biogenic nitrates were least soluble?
Monoterpene nitrates, consistent with similar dry vs humid β-pinene + NO3 yields.
More on Aerosols