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

• Main Authors: W. Xu, M. Takeuchi, C. Chen, Y. Qiu, C. Xie, N. Ma, D. R. Worsnop, N. L. Ng, Y. Sun
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-05-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://amt.copernicus.org/articles/14/3693/2021/amt-14-3693-2021.pdf

<p>Particulate organic nitrates (pON) are an important component of secondary organic aerosol in biogenic-emission-dominant environments and play a critical role in NO<span class="inline-formula">_<i>x</i></span> cycles. However, estimation of pON has been a challenge in polluted environments, e.g., North China Plain, with high concentrations of inorganic nitrate and NO<span class="inline-formula">_<i>x</i></span>. 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 NO<span class="inline-formula">⁺</span> to NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">2</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="d7f2ee209205b974ae323652b1975b71"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-3693-2021-ie00001.svg" width="8pt" height="15pt" src="amt-14-3693-2021-ie00001.png"/></svg:svg></span></span> (NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mi>x</mi><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="afae45a7e2cf6dcf9e0c2a47bbf9be82"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-3693-2021-ie00002.svg" width="8pt" height="14pt" src="amt-14-3693-2021-ie00002.png"/></svg:svg></span></span> ratio), yet they had improvements in reducing negative values due to the influences of high concentration of inorganic nitrate and constant NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mi>x</mi><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="75c22ae4d75c7009d9c821fc7e697768"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-3693-2021-ie00003.svg" width="8pt" height="14pt" src="amt-14-3693-2021-ie00003.png"/></svg:svg></span></span> ratio of organic nitrates (<span class="inline-formula"><i>R</i>_ON</span>). 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 NO<span class="inline-formula">_3,org</span> (1.8 <span class="inline-formula">µ</span>g m<span class="inline-formula">⁻³</span> vs. 1.0 <span class="inline-formula">µ</span>g m<span class="inline-formula">⁻³</span>) 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 NO<span class="inline-formula">_3,org</span> loading in Gucheng was 1.9 <span class="inline-formula">µ</span>g m<span class="inline-formula">⁻³</span>, 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, <span class="inline-formula"><i>R</i>_ON</span> 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 NO<span class="inline-formula">₃</span> oxidation) and sources.</p>