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<p>Chemical ionization mass spectrometry with the nitrate reagent ion (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="57a4663cbf0d11bf294d99bb32c9ae29"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-9017-2022-ie00001.svg" width="25pt" height="16pt" src="acp-22-9017-2022-ie00001.png"/></svg:svg></span></span> CIMS) was used to investigate the products of the nitrate radical (<span class="inline-formula">NO₃</span>) initiated oxidation of four monoterpenes in laboratory chamber experiments. <span class="inline-formula"><i>α</i></span>-Pinene, <span class="inline-formula"><i>β</i></span>-pinene, <span class="inline-formula">Δ</span>-3-carene, and <span class="inline-formula"><i>α</i></span>-thujene were studied. The major gas-phase species produced in each system were distinctly different, showing the effect of monoterpene structure on the oxidation mechanism and further elucidating the contributions of these species to particle formation and growth. By comparing groupings of products based on the ratios of elements in the general formula <span class="inline-formula">C_<i>w</i>H_<i>x</i>N_<i>y</i>O_<i>z</i></span>, the relative importance of specific mechanistic pathways (fragmentation, termination, and radical rearrangement) can be assessed for each system. Additionally, the measured time series of the highly oxidized reaction products provide insights into the ratio of relative production and loss rates of the high-molecular-weight products of the <span class="inline-formula">Δ</span>-3-carene system. The measured effective <span class="inline-formula">O:C</span> ratios of reaction products were anticorrelated with new particle formation intensity and number concentration for each system; however, the monomer : dimer ratios of products had a small positive trend. Gas-phase yields of oxidation products measured by <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="dd23f13eb24280cbe650be4567ce8571"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-9017-2022-ie00002.svg" width="25pt" height="16pt" src="acp-22-9017-2022-ie00002.png"/></svg:svg></span></span> CIMS correlated with particle number concentrations for each monoterpene system, with the exception of <span class="inline-formula"><i>α</i></span>-thujene, which produced a considerable amount of low-volatility products but no particles. Species-resolved wall loss was measured with <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="737339a8d3517116341490f01d8cfecf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-9017-2022-ie00003.svg" width="25pt" height="16pt" src="acp-22-9017-2022-ie00003.png"/></svg:svg></span></span> CIMS and found to be highly variable among oxidized reaction products in our stainless steel chamber.</p>