Characterization of Indoor Air Emissions from the Burning of Candles, Mosquito Coils and Incenses  

Project Title: Characterization of Indoor Air Emissions from the Burning of Candles, Mosquito Coils and Incenses

Applicant: The Hong Kong Polytechnic University

Total Approved Grant: $434,369.25 (jointly funded by ECF and WWGF on a 50/50 basis)

Duration: December 2002 - April 2004

Project Status/Remarks: Completed

Scope:

The project aims to characterize emissions of air pollutants from the burning of candles, mosquito coils and incense using a large environmental chamber; to investigate air pollutant emissions of different types of candles; mosquito coils and incense that are popular in Hong Kong; to qualify and quantify emissions of air pollutants from burning of candles and incense with respect to particulate matters; and to develop and validate a model for air pollutant emissions from the burning of incenses, candles and mosquito coils. This information will be useful to assess the human exposure from the burning of candles, mosquito coils and incenses, and understand the potential impacts of these sources on indoor air quality in Hong Kong.

Summary of Findings/Outcomes:

Ten incense samples, five mosquito coils and five candles were tested in a large environmental chamber. The CO peak levels of seven incense types greatly exceeded the IAQO Good Class level. The formaldehyde concentrations of six types of incense were higher than the IAQO. In addition, the benzene concentrations of all tested incense samples were significantly higher than the IAQO standard. Generally, the traditional incense has the highest gas emission factors of the three incense types. The average OC and EC concentrations in PM2.5 of three incense categories were in the order of church incense > traditional incense > aromatic incense. The concentrations of Cl-, SO42-, Na+ and K+ were highly variable. Although Incense 2 and 6 were claimed to be environmental-friendly, the quantity of the pollutants emitted was not observed to be lower than the others. The average PM10 concentrations of all tested mosquito coils significantly exceeded the Good Class of IAQO level. CO was one of the most abundant gas pollutant species resulting from the smoldering effect of mosquito coils. The concentrations of formaldehyde and acetaldehyde were the highest among all the identified carbonyl compounds in the coil smoke. The average formaldehyde concentrations of all tested mosquito coils exceeded the IAQO Good Class level. Benzene, methylene chloride, and toluene were the most abundant VOC species from mosquito coil burning. The benzene concentrations of all tested mosquito coils significantly exceeded the IAQO Good Glass level. Generally, PM2.5 and PM10 concentrations of tested candles were relatively lower than the tested incense and mosquito coils. NOx was the most abundant gas pollutants relating to candles burning. Based on the raw materials of these three candle types, it was concluded that beeswax candles were cleaner.

Two of the most famous temples in Hong Kong were selected to investigate the characteristics of air pollutant emissions associated with incense burning. The non-peak/peak CO ratios were around 0.5 for both temples. The peak NOx level at Temple 2 was about three times that of the non-peak, and the peak NOx concentration at temple 1 was almost twice that during the non-peak period. The highest average CO level and particulate levels were obtained from Temple 1 during the peak period. The PM2.5/PM10 ratios at both temples were approximately 70%, which reveals that fine particulates (PM2.5) constitute the majority of suspended particulates during both peak and non-peak periods. The results show that the formaldehyde levels at both temples exceeded the IAQO Good Class level except that of the one obtained at the outdoor sampling site at Temple 2 during non-peak periods. Benzene and methyl chloride was the most abundant species in temple air. It is concluded that incense burning in temples is a significant source of air pollution. It is suggested that visitors may decrease the amount of incense burnt and better with the period short in the temple, especially during peak periods in order to reduce the health impact.

Five types of mosquito coils, five types of incense sticks and three types of Chinese candles were tested in a residential house. The average concentrations of PM10 from mosquito coils, incense and Chinese candle ranged from 526 µg/m3 to 3921 µg/m3, 860 µg/m3 to 4466 µg/m3 and 152 µg/m3 to 8609 µg/m3, respectively. It was concluded that the PM10 emissions from the burning mosquito coils, incense and Chinese candles far exceeded the IAQO Good Class level. The HCHO emission from the mosquito coils ranged from 48.06 µg/m3 to 83.84 µg/m3 whereas the emissions from the incense and Chinese candles were from 71.06 µg/m3 to 105.32 µg/m3 and 58.9 µg/m3 to 125.15 µg/m3, respectively.