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<p>An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed along with other online instruments to study the highly time resolved chemistry and sources of submicron aerosols (PM<span class="inline-formula">₁</span>) at Waliguan (WLG) Baseline Observatory, a high-altitude (3816&thinsp;m&thinsp;a.s.l.) background station located at the northeast edge of the Qinghai–Tibet Plateau (QTP), during 1–31 July 2017. The average PM<span class="inline-formula">₁</span> mass concentration during this study was 9.1&thinsp;<span class="inline-formula">µ</span>g&thinsp;m<span class="inline-formula">⁻³</span> (ranging from 0.3 to 28.1&thinsp;<span class="inline-formula">µ</span>g&thinsp;m<span class="inline-formula">⁻³</span>), which was distinctly higher than those (2.0–5.7&thinsp;<span class="inline-formula">µ</span>g&thinsp;m<span class="inline-formula">⁻³</span>) measured with the Aerodyne AMS at other high-elevation sites in the southern or central QTP. Sulfate showed a dominant contribution (38.1&thinsp;%) to PM<span class="inline-formula">₁</span> at WLG followed by organics (34.5&thinsp;%), ammonium (15.2&thinsp;%), nitrate (8.1&thinsp;%), BC (3.0&thinsp;%) and chloride (1.1&thinsp;%). Accordingly, bulk aerosols appeared to be slightly acidic throughout this study, mainly related to the enhanced sulfate contribution. All chemical species peaked at the accumulation mode, indicating the well-mixed and highly aged aerosol particles at WLG from long-range transport. Positive matrix factorization (PMF) on the high-resolution organic mass spectra resolved four distinct organic aerosol (OA) components, including a traffic-related hydrocarbon-like OA (HOA), a relatively fresh biomass burning OA (BBOA), an aged biomass burning OA (agBBOA) and a more-oxidized oxygenated OA (OOA). On average, the two relatively oxidized OAs, OOA and agBBOA, contributed 34.4&thinsp;% and 40.4&thinsp;% of organics, respectively, while the rest were 18.4&thinsp;% for BBOA and 6.8&thinsp;% for HOA. Source analysis for air masses showed that higher mass concentrations of PM<span class="inline-formula">₁</span> and enhanced contributions of sulfate and biomass-burning-related OA components (agBBOA <span class="inline-formula">+</span> BBOA) were from the northeast of the WLG with shorter transport distance, whereas lower PM<span class="inline-formula">₁</span> mass concentrations with enhanced OOA contribution were from the west after long-range transport, suggesting their distinct aerosol sources and significant impacts of regional transport on aerosol mass loadings and chemistry at WLG.</p>