Cooking can make indoors as polluted as London streets
Frying food and burning wood may trap high levels of air pollution inside homes.
24-hour tests took place in houses in London, Pontypridd, Liverpool and Lancaster.
In Lancaster, number of particles inside was seven times the outdoor average.
Peak indoor pollution resulted from frying sausages and steaks.
Global Action Plan (GAP) is organising Clean Air Day on 20 June.
Advice: open a window when cooking at home.