Indoor air quality (IAQ) evaluation in a naturally ventilated church: Key pollutants concentrations determined by incense burning practice over liturgical celebrations

Among indoor sources linked to combustion processes, relatively less attention has been paid to incense burning over liturgical celebrations in the churches. Therefore, a real-time monitoring campaign was carried out in 2023 from February 2nd to April 10th inside a naturally ventilated Italian church where the size distribution of airborne particles and the concentrations of total volatile organic compounds (TVOCs), benzene, toluene and carbon dioxide (CO2) were continuously monitored. Moreover, tailored experimental sessions burning four different typologies of incense were carried out inside a large-scale test chamber under controlled micro-environmental conditions (temperature, relative humidity and air exchange rate) miming priest actions during the liturgical celebrations. Investigations inside the church highlighted a significant increment of PM10 (max value: 203 μg/m3), PM2.5 (max value: 171 μg/m3), PM1 (max value: 108 μg/m3),TVOCs (max value: 3.9 ppm) and Benzene (maxvalue: 5.86 μg/m3) concentrations during liturgical celebrations and in correspondence of incense use. These peak concentrations were significantly higher than the limit values established by recent WHO air quality guidelines (AQGs) for outdoor. Moreover, the combustion tests highlighted that the qualitative and quantitative differences in pollutants concentrations emitted by incense combustion were linked to the intrinsic variability of combustions performance rather than to the typologies of incense and charcoal used.