How routine fragrance product use elevates indoor PM2.5 exposure in London households.

Fragrance products are ubiquitous in UK homes, yet the associated indoorPM2.5 exposure remains poorly quantified under real residential conditions. Using high time-resolution measurements from 112 London homes between 2022 and 2024, together with a source-resolved framework, our study found that fragrance use markedly elevated indoor PM2.5 exposure, with hourly peaks up to 1293 μg/m3 for incense, 858 μg/m3 for oil diffusers, and 622 μg/m3 for candles. Across homes using those fragrance products, incense and oil diffusers each accounted for nearly 50 % of bedroom PM2.5 exposure, whereas candles contributed 14 %.Exceedance of the WHO 24-hguideline (15 μg/m3) was frequent, with a median exceedance rate of 40 %in candle-using homes, and in some incense-using households, exceedances occurring on the majority of monitored days. Exposures were highest in compact dwellings and under inadequate room ventilation. As UK housing moves toward greater airtightness, these findings identify fragrance products as a dominant indoor PM2.5 source and provide empirical evidence relevant to source-aware ventilation design and Net Zero housing assessments.