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<p>Oxygenated organic molecules (OOMs) are dominated by the N-containing species in polluted urban environments. As N-containing OOMs, especially those with more than one nitrogen atom, prevail in the high <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>m</mi><mo>/</mo><mi>z</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="91270dba487782af7360c80516416e4b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-3233-2023-ie00001.svg" width="23pt" height="14pt" src="acp-23-3233-2023-ie00001.png"/></svg:svg></span></span> (mass-to-charge) range (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>m</mi><mo>/</mo><mi>z</mi><mi mathvariant="italic">&gt;</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="31pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="de68db45df1feb3c43f70b6cf2165c80"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-3233-2023-ie00002.svg" width="31pt" height="14pt" src="acp-23-3233-2023-ie00002.png"/></svg:svg></span></span> 350 Th), unambiguous identification of N-containing OOMs is highly desirable for understanding of their formation processes, precursors and influencing factors. To achieve this, we applied an ultra-high-resolution chemical-ionization Orbitrap (CI-Orbitrap) in a field campaign and found that OOMs contain one (1N-OOMs), two (2N-OOMs) and three (3N-OOMs) nitrogen atoms comprised 50 %, 26 % and 4 %, respectively, of total OOMs. More interestingly, the fraction of 2N-OOMs increased with the increase in carbon number (nC) and was dominated by the ones derived from aliphatic precursors (2N-OOM<span class="inline-formula">_Ali</span>, 64.2 %), indicating the importance of multistep oxidation. Plausible precursors of 2N-OOMs were aliphatics (2N-OOM<span class="inline-formula">_Ali</span>, 64.2 %), aromatics (2N-OOM<span class="inline-formula">_Aro</span>, 16 %) and monoterpenes (2N-OOM<span class="inline-formula">_MT</span>, 15.4 %). The absolute concentrations of 2N-OOMs were greatly affected by the pollution level for most cases. The 2N-OOM<span class="inline-formula">_Ali</span> was the most abundant 2N-OOM, and its fraction even increased on the polluted day with an enhanced proportion of the ones with nC <span class="inline-formula"><i>&gt;</i>10</span>. While 2N-OOM<span class="inline-formula">_Ali</span> and 2N-OOM<span class="inline-formula">_Aro</span> were dominated by daytime photochemical production, nighttime NO<span class="inline-formula">₃</span>-initiated oxidation played a comparable role to the daytime photochemistry in the formation of 2N-OOM<span class="inline-formula">_MT</span>. The 2N-OOM<span class="inline-formula">_Aro</span> species were of the highest oxygenation level, followed by 2N-OOM<span class="inline-formula">_MT</span> and 2N-OOM<span class="inline-formula">_Ali</span>, which were affected by photochemistry and NO<span class="inline-formula">_<i>x</i></span> concentrations. These results highlight the significant formation of 2N-OOMs and the influencing factors on their formation in polluted urban environments, where various volatile organic compound (VOC) precursors and atmospheric oxidants are present.</p>