Characterization of Ultrafine Particles Generated by Electric Cooking Stoves

Cooking is a process involving high temperature heat sources that can generate high concentrations of air pollutants. Ultrafine particles (UFP), which are defined as particles having an aerodynamic diameter less than 0.1 μm, are a class of air pollutants generated during cooking. UFP are known to cause oxidative stress in cells and exposures to UFP can result in respiratory and cardiovascular diseases. Exposure to cooking-generated ultrafine particles can occur in occupational or residential settings. Occupational exposure may be higher due to more frequent and longer cooking periods. Many factors in cooking affect the characteristics of UFP that are generated, including the style or method of cooking, types of cooking oil used and even the types of stove used. Different types of stoves are used around the world; in the United States gas stoves and electric stoves are most commonly used. Electric stoves use electrical resistance, infrared radiation, or magnetic induction to produce heat. The characteristics of UFP generated from electric stoves are not well characterized and are quite different from gas stoves and even between different types of electric stoves. This dissertation seeks to characterize the morphology and the chemistry of the UFP generated from a coil electric stove, a French style stove, and an infrared stove.;UFP generated from the stoves were collected onto transmission electron microscopy (TEM) grids using a low pressure impactor (LPI). The morphologies of the particles were described from TEM images of the particles. Size distribution measurements were made using a scanning mobility particle sizer (SMPS). Samples were obtained from the stoves operating without and with a load. All three electric stoves generated particles with two types of morphologies. One type was an agglomerated soot particle. Some of the agglomerates had well defined primary particles about 20 to 30 nm in diameter. Semi-volatile particles containing gas bubbles were also observed in the samples. These semi-volatile particles are able to survive the vacuum in the electron microscopes but evaporate under the heat from the electron beam.;The formation mechanisms for these two types of particles are probably different and are temperature dependent. The soot agglomerates are likely formed by the smoldering of contaminants on the heating surface. The semi-volatile particles may have formed from the vaporizing and condensing of some contaminants on the stoves. When the stoves were operated with a load the amount of particle generated by the stoves decreased. In comparing particle counts from the LPI to SMPS data it was found that 78% to 99% of the particles were smaller than 50 nm. This means that the LPI captured only a small percentage of UFP generated from electric stoves. In the 50 nm to 75 nm range, the SMPS measured number concentrations were greater than the LPI measurements by a factor of 10. Therefore the LPI count methodology may not be reliable for quantitative analysis. The amount of particles generated by the stoves is dependent on the temperature of the heating surface. Operating the stoves at lower heat settings or loading the stove will decrease the amount of particles generated.;The particles generated from the electric stoves were also collected on filters and analyzed for iron, aluminum, chromium, and nickel using inductively coupled plasma mass spectrometry (ICP-MS). The mass concentrations were in general very low, in the picogram per cubic centimeter of air range. Nickel and chromium concentrations were not detectable above the field blank concentrations. For the French style stove, the mass concentration of iron (0.28 pg cm –3) was significantly higher than the blank (0.042 pg cm –3). Thus the French style stove may generate iron particles in trace amounts. The concentration of aluminum from the French style stove (0.037 pg cm–3) and the coil electric stove (0.03 pg cm 3) were also higher than the blank (0.015 pg cm–3). However, filter samples of the HEPA chamber also had relatively high concentrations of aluminum (0.044 pg cm–3). A shortcut statistical test for comparing average values to a single value show that the mass concentrations for iron from the French stove and chromium from the coil electric stove are statistically significant p < 0.01. The airborne mass concentrations of these metals were at least 1,000 times lower than current U.S. health standards. Therefore, exposures at these mass concentrations do not present a significant health risk.