# Effects of aerosol dynamics and gas–particle conversion on dry deposition of inorganic reactive nitrogen in a temperate forest

Dry deposition has an impact on nitrogen status in forest environments. However, the mechanism for the high dry-deposition rates of fine nitrate particles (inline-formula $M1inlinescrollmathmlchem{\mathrm{normal NO}}_{normal 3}^{-}$ 25pt16ptsvg-formulamathimg57a4663cbf0d11bf294d99bb32c9ae29 acp-20-4933-2020-ie00001.svg25pt16ptacp-20-4933-2020-ie00001.png ) observed in forests remains unknown and is thus a potential source of error in chemical transport models (CTMs). Here, we modified and applied a multilayer land surface model coupled with dry-deposition and aerosol dynamic processes for a temperate mixed forest in Japan. This represents the first application of such a model to ammonium nitrate (inline-formulaNH4NO3) gas–particle conversion (gpc) and the aerosol water uptake of reactive nitrogen compounds. Thermodynamics, kinetics, and dry deposition for mixed inorganic particles are modeled by a triple-moment modal method. Data for inorganic mass and size-resolved total number concentrations measured by a filter pack and electrical low-pressure impactor in autumn were used for model inputs and subsequent numerical analysis. The model successfully reproduces turbulent fluxes observed above the canopy and vertical micrometeorological profiles noted in our previous studies. The sensitivity tests with and without gpc demonstrated clear changes in the inorganic mass and size-resolved total number concentrations within the canopy. The results also revealed that within-canopy evaporation of inline-formulaNH4NO3 under dry conditions significantly enhances the deposition flux of fine-inline-formula $M4inlinescrollmathmlchem{\mathrm{normal NO}}_{normal 3}^{-}$ 25pt16ptsvg-formulamathimge16cba38499a6a16cb1a10e488ec56da acp-20-4933-2020-ie00002.svg25pt16ptacp-20-4933-2020-ie00002.png and fine-inline-formula $M5inlinescrollmathmlchem{\mathrm{normal NH}}_{normal 4}^{+}$ 24pt15ptsvg-formulamathimg68d940fa21d9c6691de36bd82f3e56d8 acp-20-4933-2020-ie00003.svg24pt15ptacp-20-4933-2020-ie00003.png particles, while reducing the deposition flux of nitric acid gas (inline-formulaHNO3). As a result of the evaporation of particulate inline-formulaNH4NO3, the calculated daytime mass flux of fine inline-formula $M8inlinescrollmathmlchem{\mathrm{normal NO}}_{normal 3}^{-}$ 25pt16ptsvg-formulamathimg8a872e45f44a0fc3c08e466e371cfb3a acp-20-4933-2020-ie00004.svg25pt16ptacp-20-4933-2020-ie00004.png over the canopy was 15 times higher in the scenario of “gpc” than in the scenario of “no gpc”. This increase caused high contributions from particle deposition flux (inline-formula $M9inlinescrollmathmlchem{\mathrm{normal NO}}_{normal 3}^{-}$ 25pt16ptsvg-formulamathimgb3512ed4eb493ff037a5c39221523c47 acp-20-4933-2020-ie00005.svg25pt16ptacp-20-4933-2020-ie00005.png and inline-formula $M10inlinescrollmathmlchem{\mathrm{normal NH}}_{normal 4}^{+}$ 24pt15ptsvg-formulamathimg1828c3f6b34695d5ee1ef7c7b60e0fa3 acp-20-4933-2020-ie00006.svg24pt15ptacp-20-4933-2020-ie00006.png ) to total nitrogen flux over the forest ecosystem (inline-formula∼39 %), although the contribution of inline-formulaNH3 was still considerable. A dry-deposition scheme coupled with aerosol dynamics may be required to improve the predictive accuracy of chemical transport models for the surface concentration of inorganic reactive nitrogen.

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Katata, Genki / Matsuda, Kazuhide / Sorimachi, Atsuyuki / et al: Effects of aerosol dynamics and gas–particle conversion on dry deposition of inorganic reactive nitrogen in a temperate forest. 2020. Copernicus Publications.

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