# Atmospheric Δ 17O(NO 3−) reveals nocturnal chemistry dominates nitrate production in Beijing haze

The rapid mass increase of atmospheric nitrate is a critical driving force for the occurrence of fine-particle pollution (referred to as haze hereafter) in Beijing. However, the exact mechanisms for this rapid increase of nitrate mass have not been well constrained from field observations. Here we present the first observations of the oxygen-17 excess of atmospheric nitrate inline-formula $M3inlinescrollmathmlchem\left({\mathrm{normal \Delta }}^{normal 17}\mathrm{normal O}\left({\mathrm{normal NO}}_{normal 3}^{-}\right)\right)$ 65pt17ptsvg-formulamathimg43e46d5dbddc058ca3b8b601dae2335d acp-18-14465-2018-ie00004.svg65pt17ptacp-18-14465-2018-ie00004.png collected in Beijing haze to reveal the relative importance of different nitrate formation pathways, and we also present the simultaneously observed inline-formula $M4inlinescrollmathmlchem{\mathrm{italic \delta }}^{normal 15}\mathrm{normal N}\left({\mathrm{normal NO}}_{normal 3}^{-}\right)$ 56pt17ptsvg-formulamathimgaef1d905be85dba77f04e3781a63abae acp-18-14465-2018-ie00005.svg56pt17ptacp-18-14465-2018-ie00005.png . During our sampling period, 12 h averaged mass concentrations of inline-formulaPM2.5 varied from 16 to 323 inline-formulaµg minline-formula−3 with a mean of (inline-formula141±88(1SD)) inline-formulaµg minline-formula−3, with nitrate ranging from 0.3 to 106.7 inline-formulaµg minline-formula−3. The observed inline-formula $M13inlinescrollmathmlchem{\mathrm{normal \Delta }}^{normal 17}\mathrm{normal O}\left({\mathrm{normal NO}}_{normal 3}^{-}\right)$ 58pt17ptsvg-formulamathimgb72a9b7a36f2ab52e8359daf860d0372 acp-18-14465-2018-ie00006.svg58pt17ptacp-18-14465-2018-ie00006.png ranged from 27.5 ‰ to 33.9 ‰ with a mean of (inline-formula30.6±1.8) ‰, while inline-formula $M15inlinescrollmathmlchem{\mathrm{italic \delta }}^{normal 15}\mathrm{normal N}\left({\mathrm{normal NO}}_{normal 3}^{-}\right)$ 56pt17ptsvg-formulamathimgc89e34cb58dfaf93fd28fa0dab11f794 acp-18-14465-2018-ie00007.svg56pt17ptacp-18-14465-2018-ie00007.png ranged from inline-formula−2.5 ‰ to 19.2 ‰ with a mean of (inline-formula7.4±6.8) ‰. inline-formula $M18inlinescrollmathmlchem{\mathrm{normal \Delta }}^{normal 17}\mathrm{normal O}\left({\mathrm{normal NO}}_{normal 3}^{-}\right)$ 58pt17ptsvg-formulamathimg797add8be15c7e34b7c9a04ce9f88577 acp-18-14465-2018-ie00008.svg58pt17ptacp-18-14465-2018-ie00008.png -constrained calculations suggest nocturnal pathways (inline-formula $M19inlinescrollmathmlchem{\mathrm{normal N}}_{normal 2}{\mathrm{normal O}}_{normal 5}+chem{\mathrm{normal H}}_{normal 2}\mathrm{normal O}/{\mathrm{normal Cl}}^{-}$ 84pt15ptsvg-formulamathimgb6d7a648e795b981639feddc0a54ebd1 acp-18-14465-2018-ie00009.svg84pt15ptacp-18-14465-2018-ie00009.png and inline-formulaNO3+HC) dominated nitrate production during polluted days (inline-formulaPM2.5≥75inline-formulaµg minline-formula−3), with a mean possible fraction of 56–97 %. Our results illustrate the potentiality of inline-formulaΔ17O in tracing nitrate formation pathways; future modeling work with the constraint of isotope data reported here may further improve our understanding of the nitrogen cycle during haze.

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He, Pengzhen / Xie, Zhouqing / Chi, Xiyuan / et al: Atmospheric Δ17O(NO3−) reveals nocturnal chemistry dominates nitrate production in Beijing haze. 2018. Copernicus Publications.

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Rechteinhaber: Pengzhen He et al.

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