Estimation of particulate organic nitrates from thermodenuder–aerosol mass spectrometer measurements in the North China Plain

Xu, Weiqi; Takeuchi, Masayuki; Chen, Chun; Qiu, Yanmei; Xie, Conghui; Xu, Wanyun; Ma, Nan; Worsnop, Douglas R.; Ng, Nga Lee; Sun, Yele

Particulate organic nitrates (pON) are an important component of secondary organic aerosol in biogenic-emission-dominant environments and play a critical role in NOinline-formulax cycles. However, estimation of pON has been a challenge in polluted environments, e.g., North China Plain, with high concentrations of inorganic nitrate and NOinline-formulax. Here we developed a method for estimation of pON from the measurements of high-resolution aerosol mass spectrometer coupled with a thermodenuder based on the volatility differences between inorganic nitrate and pON. The results generally correlated well with those estimated from positive matrix factorization of combined organic and inorganic mass spectra and from the ratio of NOinline-formula+ to NOinline-formula M4inlinescrollmathml normal 2 + 8pt15ptsvg-formulamathimgd7f2ee209205b974ae323652b1975b71 amt-14-3693-2021-ie00001.svg8pt15ptamt-14-3693-2021-ie00001.png (NOinline-formula M5inlinescrollmathml x + 8pt14ptsvg-formulamathimgafae45a7e2cf6dcf9e0c2a47bbf9be82 amt-14-3693-2021-ie00002.svg8pt14ptamt-14-3693-2021-ie00002.png ratio), yet they had improvements in reducing negative values due to the influences of high concentration of inorganic nitrate and constant NOinline-formula M6inlinescrollmathml x + 8pt14ptsvg-formulamathimg75c22ae4d75c7009d9c821fc7e697768 amt-14-3693-2021-ie00003.svg8pt14ptamt-14-3693-2021-ie00003.png ratio of organic nitrates (inline-formulaRON). By applying this approach to the measurements at an urban (Beijing) and a rural site (Gucheng) in summer and winter in the North China Plain, we estimated that the average mass concentrations of NOinline-formula3,org (1.8 inline-formulaµg minline-formula−3 vs. 1.0 inline-formulaµg minline-formula−3) and pON to OA (27.5 % vs. 14.8 %) were higher in summer than in winter in Beijing, indicating more pON formation in biogenically and anthropogenically mixed environments. In addition, the average NOinline-formula3,org loading in Gucheng was 1.9 inline-formulaµg minline-formula−3, and the pON at the rural site also showed higher contribution to OA than that in Beijing during wintertime due to higher primary emissions and gaseous precursors in Gucheng. In addition, inline-formulaRON was determined and showed considerable differences between day–night and clean–polluted periods, highlighting the complexity of pON compounds from different chemical pathways (e.g., OH and NOinline-formula3 oxidation) and sources.

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Xu, Weiqi / Takeuchi, Masayuki / Chen, Chun / et al: Estimation of particulate organic nitrates from thermodenuder–aerosol mass spectrometer measurements in the North China Plain. 2021. Copernicus Publications.

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