Study on Coagulation and Deposition of Nanoparticles Generated by Gas and Electric Stoves or Cooking Activities

In HK and many countries of the world the control of aerosol emission has a very high priority as scientific evidence has shown aerosol concentration correlates with adverse health effects. Smoking is banned in public places. However there is another combustible source which cannot be ignored. We can avoid the second hand smoke but we cannot stay away from exposure to cooking. One feature of cooking-generated particles is their extremely small sizes (2-10 nm). Common residential hoods cannot remove this size range of ultrafine particles effectively. Cooking-generated ultrafine particles are highly diffusive and they can escape from kitchens and be transported to other places within the residences. Coagulation and deposition are extremely important and dominant for this size range. To assess and control such exposure, we need to gain more fundamental understanding of the physical and chemical properties of the particles generated by stoves (gas flame, electric heating elements) and food.Numerical and experimental approaches will be applied. Computational fluid dynamics (CFD) will be adopted to resolve this complex issue. Current commercial CFD cannot model the growth and loss dynamics for this size range accurately. New numerical kernels will be incorporated to account for coagulation and deposition. Prior to applying the developed CFD tool to model cooking scenarios, the code will be validated. Experiments will be conducted in a research house at the National Institute of Standards and Technology and a small-scale chamber and a full size environmentally controlled chamber in CityU. A modified particle scanning instrument will be used to measure the size distribution from 2 to 100 nm. Gas stoves and electric appliances will be used to generate particles with and without food. The results obtained will gain invaluable information to better model the particles. The particles generated will also be sampled and the composition analyzed. The results will be fed back to optimize the modeling parameters.It is anticipated that the current design of the hoods cannot remove effectively the nanoparticles. Cooking experiments will be conducted to measure the removal effectiveness.With the completion of proposed project, a more accurate numerical model, particularly for coagulation and deposition, will be developed. More chemical and physical characteristics of nanoparticles will be revealed. All these will become very important tools to develop engineering strategies to reduce exposure in residential settling. This will be very important in helping policymakers to review or amend current ambient air standards or policies.