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<p>Secondary organic aerosol (SOA) represents a significant fraction of the tropospheric aerosol and its precursors are volatile organic compounds (VOCs). Anthropogenic VOCs (AVOC) dominate the VOC budget in many urban areas with 1,3,5-trimethylbenzene (TMB) being among the most reactive aromatic AVOCs. TMB formed highly oxygenated organic molecules (HOMs) in an <span class="inline-formula">NO_<i>x</i></span>-free environment, which could contribute to new particle formation (NPF) depending on oxidation conditions where elevated OH oxidation enhanced particle formation. The experiments were performed in an oxidation flow reactor, the Go:PAM unit, under controlled OH oxidation conditions. By addition of <span class="inline-formula">NO_<i>x</i></span> to the system we investigated the effect of <span class="inline-formula">NO_<i>x</i></span> on particle formation and on the product distribution. We show that the formation of HOMs, and especially HOM accretion products, strongly varies with <span class="inline-formula">NO_<i>x</i></span> conditions. We observe a suppression of HOM and particle formation with increasing <span class="inline-formula">NO_<i>x</i></span>/<span class="inline-formula">Δ</span>TMB ratio and an increase in the formation of organonitrates (ONs) mostly at the expense of HOM accretion products. We propose reaction mechanisms and pathways that explain the formation and observed product distributions with respect to oxidation conditions. We hypothesise that, based on our findings from TMB oxidation studies, aromatic AVOCs may not contribute significantly to NPF under typical <span class="inline-formula">NO_<i>x</i></span>/AVOC conditions found in urban atmospheres.</p>