Characterizing PM2.5 Emissions and Organic Composition from Incense Use in a California Residence

Ambient fine particulate matter (PM2.5) pollution is the leading environmental risk factor for morbidity and premature mortality. Since people spend about two-thirds of their time at home, indoor conditions can strongly influence personal exposure. Therefore, efforts to understand sources of indoor pollution such as incense burning are well-founded. Incense burning is an important source of PM2.5 and other toxic pollutants, receiving sparse attention in Western literature despite its importance in many cultures. The goal of the current work is to extensively characterize and quantify the chemical composition of PM2.5 associated with the burning of incense in a normally occupied, single-family residence in Oakland, California. Measurements were made during a vacant period of the H3 campaign conducted in autumn 2021. This work focuses on major compounds detected as direct emissions and the amounts and identities of semivolatile organic compounds (SVOCs) present indoors that partition onto particles generated by incense use. Indoor and outdoor PM2.5 samples were collected with 6-hour time resolution after the combustion of eight incense sticks during a 60-minute combustion period. The particulate organic composition is characterized using a system of thermal desorption two-dimensional gas chromatography electron ionization high resolution time of flight mass spectrometry (TD-GCxGC-EI-HR-ToF-MS). Supporting data were provided from additional instruments measuring hourly chemical composition for targeted species. Over 1000 unique compounds were separated and detected indoors and over 500 outdoors. Known incense tracer compounds (e.g., levoglucosan and the resin acids, isopimaric and dehydroabietic acid) observed across sample replicates show consistency in relative amounts emitted. Indoor SVOCs such as phthalates were observed to partition from the gas phase into incense-generated particles. Initial results indicate that incense emissions can be a significant source of indoor organic chemicals that are persistent, particularly in an indoor environment with poor ventilation.