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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.
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What is [HONO]*?
Equilibrium gas-phase HONO over aqueous nitrous acid in soil.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
When is the soil–air HONO flux emission versus deposition?
Emission if ambient HONO is below [HONO]*; deposition if above.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
Peak [HONO]* during drying?
About 31 ppb at 0.04 kg kg−1 water (10% WHC).
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
Range of measured chamber HONO fluxes?
−31.1 to 68.6 ng N m−2 s−1.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
What happened at 0 ppb inlet HONO?
Net emission persisted through the whole drying process.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
What happened at 5 and 15 ppb inlet?
Outlet first fell below inlet (net deposition) at higher moisture.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
Why can drying raise [HONO]*?
HNO2(aq) concentrates; Henry’s law raises the equilibrium gas concentration.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
Why is atmospheric HONO important?
Sunlight photolyzes it to OH radicals that drive photo-oxidation.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
How did they derive [HONO]*?
Controlled dynamic-chamber measurements while switching inlet HONO.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
Inlet concentrations used?
0, 5, and 15 ppb switched every 15 minutes.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified
Field HONO levels cited for fertilized North China Plain?
Up to about 10 ppb ambient HONO.
Source: Key Role of Equilibrium HONO Concentration over Soil in Quantifying Soil-Atmosphere HONO Fluxes · DOI · quote verified