Soil HONO flux depends on an equilibrium concentration
Soil–air nitrous acid exchange is set by an equilibrium gas-phase concentration over soil ([HONO]*) versus ambient HONO, so soils can emit or take up HONO as they dry.
Source
Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes
Study at a glance
- Design
- Animal / in-vitro — Dynamic-chamber experiments on drying soil with switched inlet HONO concentrations
- N
- Inlet HONO switched among 0, 5, and 15 ppb across soil water contents
- Population
- Laboratory soil–atmosphere HONO exchange chambers
- Outcome
- Soil–air HONO flux is set by equilibrium [HONO]* versus ambient HONO, so soils can emit or take up HONO as they dry
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
Soil HONO flux depends on an equilibrium concentration
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Range of measured chamber HONO fluxes?
chamber HONO fluxes ranged from −31.1 to 68.6 ng N m –2 s –1
What they did
Authors ran controlled dynamic-chamber experiments on drying soil, switching inlet HONO among 0, 5, and 15 ppb to derive [HONO]* and chamber fluxes across soil water contents.
What they found
[HONO]* peaked near 31 ppb at 0.04 kg kg−1 water (10% WHC). Chamber fluxes ranged from −31.1 to 68.6 ng N m−2 s−1. At 0 ppb inlet, soils always emitted HONO; at 5–15 ppb they first deposited then could emit as they dried.
The limits
What it doesn't show
A chamber study on sampled soil does not map real-world field fluxes across land uses; predicted atmospheric fluxes still depend on assumed transfer velocity and ambient HONO.
Key terms
- HONO
- Gaseous nitrous acid, a major daytime source of hydroxyl radicals in polluted air.
- [HONO]*
- Equilibrium gas-phase HONO concentration over soil nitrous acid in soil water.
- Bidirectional flux
- Net emission when ambient HONO is below [HONO]*; net deposition when ambient HONO is above it.
- Transfer velocity (vt)
- Rate constant linking the [HONO]*–ambient difference to the soil–air flux.
- Soil water content (SWC)
- Mass of water per mass of soil, which changes HNO2(aq) concentration and thus [HONO]* as soil dries.
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Soil HONO exchange is governed by:
Common questions
Can soil take up as well as emit HONO?
Yes—net deposition occurred when inlet HONO was 5 or 15 ppb at higher moisture.
When was [HONO]* highest?
About 31 ppb at 0.04 kg kg−1 soil water (10% WHC).
Why does drying raise [HONO]* at first?
HNO2 concentrates in remaining soil water, raising the Henry’s-law gas concentration.
Why does HONO matter in air?
Photolysis produces OH radicals, a key atmospheric oxidant.
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