PM2.5 from cooking is one of the most underestimated indoor air problems in UK homes. People often assume that once the visible steam or smell fades, the event is over. In reality, fine particles can remain suspended, drift into nearby rooms and decay much more slowly than expected when the home lacks strong extraction or central air movement.

What PM2.5 actually is

PM2.5 means airborne particles with an aerodynamic diameter of 2.5 micrometres or smaller. These particles are tiny enough to remain airborne for long periods and small enough to reach deep into the respiratory system. Indoors, the biggest short-term source is often cooking rather than outdoor pollution.

Frying, grilling, searing, toasting and even some oven use can generate large numbers of fine particles. Gas hobs can worsen the picture because they add combustion products as well as heat.

Why cooking creates such strong spikes

Cooking releases aerosols made from oil droplets, combustion particles, food fragments and condensed vapours. A kitchen can jump from single-digit PM2.5 levels to tens or hundreds of micrograms per cubic metre in minutes.

That matters when compared with health guidance. The WHO 2021 guideline for PM2.5 is 15 μg/m³ as a 24-hour mean and 5 μg/m³ annual mean. A cooking event does not mean your daily mean will automatically exceed those values, but it does show how quickly indoor air can move into a poor range if extraction is weak.

Why kitchens without HVAC behave badly

In homes with no central HVAC, there is little active removal or dilution once particles are released:

  • the kitchen fills first
  • some particles deposit on surfaces
  • some stay suspended in the room
  • some drift into adjoining spaces through doors and air leakage paths

Because the particles are small, they do not simply fall straight to the floor. Many remain suspended long enough to travel. This is why the smell of cooking often appears in the hall, living room or upstairs landing even if the source was downstairs.

The cooker hood question

Cooker hoods help, but their real-world performance varies enormously. A hood works best when it:

  • is switched on before cooking starts
  • vents outdoors rather than recirculating through a tired filter
  • is run at a meaningful airflow setting
  • continues running after cooking to clear the residual plume

A hood works badly when it is turned on late, set too low or relies on dirty recirculation filters. In many homes, people only switch extraction on once they notice smell or steam, which means the particle peak has already happened.

Why PM2.5 hangs around after the meal

Even after the visible cooking activity ends, the kitchen can stay elevated because:

  • particles are still suspended
  • warm air keeps them mixed
  • there may be no fresh-air supply to flush the room
  • doors and corridors let the plume spread rather than exit

In winter, this effect becomes stronger because windows stay shut longer.

Why multi-room monitoring helps

Multi-room monitoring answers two questions a single kitchen timer cannot:

  1. How bad was the source event?
  2. Did it stay local or contaminate the rest of the home?

With separate room sensors, you can see whether the cooker hood contained the event, whether the living room was affected and how long recovery actually took.

Practical advice

If kitchen PM2.5 is regularly high:

  • Start extraction before heat and oil go on
  • Keep the hood running after cooking finishes
  • Open a window strategically if outdoor conditions permit
  • Keep kitchen doors closed during heavy cooking where that helps contain spread
  • Use room-level alerts so spikes are visible immediately