How is PM2.5 reduced? Here’s a list of interventions and problems:

• Switching to cleaner-burning fuels such as LPG. Smoke can be made by other stoves when switching is only partial.
• Improved heat transfer decreases the fuel used to cook resulting in fewer emissions. This summer the new forced draft Rocket with 6mm skirt consumed an average of 256 grams of wood to boil 5 liters of water and to simmer the remaining water for 35 minutes using retained heat. Since no biomass was burned during the simmering phase the emissions of PM2.5 were below detectable levels.
• Improved combustion efficiency with TLUDs and forced draft stoves. Other stoves, like the open fire, are used in the same kitchen and the imperfect fuel and rate of feeding still cause smoke.
• Use of a chimney. The chimney gets clogged or the stove lets smoke into the room (fugitive emissions).
• Increasing ventilation or cooking outside. Can decrease PM2.5 90% compared to a closed room but the remaining 10% does not meet WHO indoor air standards.
• Capturing PM2.5 in a filter as used in industry. Still experimental.
• Avoiding smoke production by simmering using retained heat. The heat absorbed by the stove and the heat from the charcoal made during high power can often simmer food to completion when thermal efficiency is above 45%. Lots of stoves have lower heat transfer efficiency.