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Abstract. Cooking is an important but understudied source of urban anthropogenic fine particulate matter (PM2.5). Using a mobile laboratory, we measured PM size and composition in urban restaurant plumes. Size distribution measurements indicate that restaurants are a source of urban ultrafine particles (UFPs, particles <100 nm mobility diameter), with a mode diameter <50 nm across sampled restaurants and particle number concentrations (PNCs, a proxy for UFPs) that were substantially elevated relative to the urban background. In our observations, PM mass emitted from restaurants was almost entirely organic aerosol (OA). Aerosol mass spectra show that while emissions from most restaurants were similar, there were key mass spectral differences. All restaurants emit OA at m/z 41, 43, and 55, though the composition (e.g., the ratio of oxygenated to reduced ions at specific m/z) varied across locations. All restaurant emissions included reduced-nitrogen species detected as CxHyN+ fragments, making up ∼15 % of OA mass measured in plumes, with reduced molecular functionalities (e.g., amines, imides) that were often accompanied by oxygen-containing functional groups. The largest reduced-nitrogen emissions were observed from a commercial bread bakery (i.e., 30 %–50 % of OA mass), highlighting the marked differences between restaurants and their importance for emissions of both urban UFPs and reduced nitrogen.