Characterization of Indoor Ultrafine Particles from Various Cooking Activities and Their Respiratory Deposition Potential

Ultrafine particles (UFP; diameter < 100 nm) in urban environments are emitted from fossil-fuel combustion, particularly vehicular emissions, whereas indoor emissions from cooking activities remain insufficiently characterized. This study examined indoor UFP exposure in 13 restaurants representing diverse cooking methods by measuring particle number concentrations (PNC) and mean particle diameter. On average, indoor PNC were 16.1 and 7.0 times higher than those in background and adjacent outdoor areas, respectively, while mean particle sizes were correspondingly smaller. The indoor-to-outdoor (I/O) ratio of mean PNC was 7.2 (±7.3), whereas that of mean particle size was 0.93 (±0.24), indicating direct emissions of smaller particles from cooking activities. Indoor PNC often approached or exceeded levels observed along major roadways with high heavy-duty diesel traffic. Variations in indoor PNC were governed not only by cooking characteristics but also by ventilation and microenvironmental factors, including room volume, cooking-source location, and the distance between cooking sources and seating areas. Closing windows or doors increased the indoor–outdoor PNC difference by a factor of 2.6 and the I/O ratio by 2.7, highlighting the importance of adequate ventilation.

A simplified respiratory deposition model estimated that 54.8% of inhaled indoor UFPs are deposited in the human respiratory tract, exceeding the factions estimated for background (45.2%) and adjacent outdoor (50.3%) environments. The alveolar deposition fraction averaged 39.4%, comparable to that in major roadways (42.8%). These findings suggest that long-term exposure to cooking-related UFPs in poorly ventilated environments may pose significant health risks and underscore the need for further characterization of their physical and chemical properties.