Ironing as a Source of Indoor Aerosol Particles: Effects of Ventilation and Ironing Conditions

This study investigates particle number concentrations (PNCs), particle number size distributions (PNSDs), and equivalent black carbon (eBC) concentrations during ironing with a typical steam iron and a steam iron with a portable boiler under different ventilation conditions. Measurements were conducted in a residential environment under low- and higher-ventilation conditions. Ironing caused a rapid and substantial increase in PNC, with concentrations increasing by up to approximately two orders of magnitude during the activity, particularly for particles between 20 and 80 nm. The maximum PNC reached 7.12 × 105 particles cm−3 for the typical steam iron under low-ventilation conditions. Particle concentrations decreased after ironing, although the decay was slower for particles larger than approximately 80 nm. Estimated particle number emission rates ranged from 8.1 × 1011 to 1.5 × 1012 particles min−1, with the highest emission rate obtained for the steam iron with a portable boiler under low-ventilation conditions. PNSDs were fitted using one or two lognormal distributions, depending on the shape of the measured distributions. Ironing produced a shift in the modal particle diameters towards larger sizes, particularly during the post-ironing period. Higher ventilation reduced particle concentrations and accelerated particle removal from the indoor environment. eBC concentrations showed only modest changes during ironing, with a slight increase under low-ventilation conditions. These results demonstrate that ironing can be an important indoor source of ultrafine and fine particles and that ventilation plays an important role in controlling their indoor concentration and persistence.