Emission characteristics and assessment of potential health risks on PM_2.5-bound organics from incense burning

Incense burning is a nonnegligible indoor air pollution source in many Asian countries, particularly in China. There is a lack of regulation on the formations of incense and its emissions. Herein, the emission factors (EFs) of important particulate phase toxic compounds, parent polycyclic aromatic hydrocarbons (pPAHs), alkylated PAHs (APAHs), oxygenated PAHs (OPAHs), nitro PAHs (NPAHs), and cyclohexanes were determined from the burning of the most representative types of Chinese incenses (i.e., five Nimu Tibetan incenses [NTI], one ordinary smoke incense [SI], and one smoke-free incense [SFI]). The total EFs of the quantified organic species (EF_Σorganics) for NTI was 7.44 ± 2.72 μg g⁻¹ on average, within the levels of SI to SFI. The pPAHs showed the largest proportion (41.5%–63.7%) of the total quantified organics. The total cancer risks for all examined incenses severely exceeded the health risk threshold value of 1 × 10⁻⁴, verifying that incense burning poses certain extent damage to human health. Notably, the organic compositions of NTI and SFI burnings were similar, with lower EFs and inhalation lifetime cancer risks than SI. The present results suggest that the advanced types of incenses of NTI or SFI should be better choices than SI while the incense burning is necessary. This acts as a guide for the residents, visitors, and workers in the selections of incenses that offer lower toxic substances emissions in dwellings or temples. In addition, the high health risks for incense emissions alert the establishment of more restrictive regulations on incense production and emission are compulsory.