Incense powder and particle emission characteristics during and after burning incense in an unventilated room setting

Despite being a recognized health hazard, burning incense remains in widespread use. A number of studies have investigated the emissions of air pollulants from incense burning, but less attention has been given to particle decay following incense burning. We have studied the elemental composition and indoor emission characteristics of incense sticks in terms of the size distribution and concentrations of fine particles. The results of chemical analysis and energy dispersive X-ray spectroscopy showed that the primary constituents of the emissions were CaCO3 and SiO2, together with lesser amounts of Mg, K, Al, Fe, and Cl. Analysis using a scanning mobility particle sizer revealed that the maximum total particle concentration at the end of the burning period was up to 30-fold higher than that of the initial background levels and that it remained elevated even 100 min after the incense sticks had been completely burned up. Emitted incense particles decayed in a biexponential manner, with particles of up to 100 nm in size decaying with lifetimes of several tens of minutes, while nanoparticles with diameters of 100–700 nm having lifetimes of > 100 min, as their removal mechanisms are slower. The peak particle size immediately following the end of incense burning was 85 nm, and this increased to 110 nm at 100 min after completion of burning. This result indicates that a high proportion of emitted particles can be inhaled into the alveolar region of the lung, where the potential for adverse health effects is the greatest. These findings provide a more detailed insight into particle decay mechanisms under conditions of low ventilation, with implications for human health.