The 15th of July in the Chinese lunar calendar is a special day in Taoism. In the old times, people believed that on this day, their ancestors’ spirits would return to the material world and visit their families. Now, this tale has evolved into a festival that focuses on the celebration of good harvest and ancestral respect. Generally, people refer to this day as the “ghost festival” and it is celebrated in regions that were once influenced by Taoism. For example, in Singapore, it is often called the “hungry ghost festival” while the Japanese call it the “bon festival”. Due to the tale behind the festival, people developed traditions that aim to worship their ancestors. While the exact activities differ according to region, these traditions usually include saying Taoist prayers, having big meals, and burning joss paper and incense.
Ghost Festival (photo credit: Tim Riley)
Virtually, there are always some forms of pollution due to the burning of materials. Not only will the combustion release excessive carbon dioxide, but the toxic substances inside the material will also be mobilized. In the case of joss paper, “golden powders”, which consist of heavy metals are used as decoration and would be mobilized after burning. There are multiple studies that revealed the array of pollutants released by burning joss paper and incense, as well as the decrease in air quality that comes after the dispersal of pollutants.
the burning of Joss Paper (photo credit: eazytraveler)
Particulate matters are an important group of pollutants but they are vaguely classified. Nowadays, the classification of PM is done according to their size. However, theoretically, the toxicity of PM would vary greatly according to the substances that comprise them. For example, in the case of joss paper and incense, Khezri et al (2015) examined the increase in heavy metal concentration in Singapore during the ghost festival period and found a proliferation in the heavy metal composition of PM.
Percentage increase in the elemental chemical composition of PM during August and September (Ghost month festival) (photo credit: Khezri et al)
Similarly, another study done in Hong Kong also proved the correlation between joss paper burning and increased heavy metal concentration in PM (Lau and Luk, 2001). In this study, it was found that the amount and type of heavy metal released differ according to the type and color of the “golden powder” attached to joss paper. Overall, the burning of joss paper releases more lead, while the burning of incense releases more iron, copper, and zinc. Moreover, the burning of joss paper and incense usually happens in an uncentralized way meaning there is not one point source of pollutants but many. The tradition is to burn joss paper and incense somewhere outside the residential gate, thus every residence can be seen as a source. The uncentralized burning makes it impossible for the waste gases to go through filtering and treatment, resulting in more severe air pollution.
According to Singapore NEA, the PSI on the 21st of August 2013 (the day of the ghost festival) was 39, in the “good” region, with a PM2.5 concentration of around 24 ug/m3. From my perspective, this result is questionable. The PSI calculation is done according to the PM concentration, regardless of the substances within the PM. PSI would be useful under the assumption that PM constituents are fixed. However, unlike the normal time, the air pollution during the ghost festival has an increased heavy metal composition of over 30%. Heavy metals are widely acknowledged to be extremely toxic to the human body. For example, Cadmium is classified as a Group 1 carcinogen by the WHO, with a suggested daily intake of zero mg (IARC, n.d.). Therefore, the actual PSI should be higher than what we get using the traditional way of calculation. There is a thus need for a more holistic version of PSI to better quantify air quality, taking into consideration the more obscure types of pollutants.
PM is not the only pollutant released from burning joss paper and incense. polychlorinated dibenzo-p-dioxin/dibenzofuran (PCDD/F) was also detected in the burning of joss paper (Hu et al, 2009). PCDDs include a group of toxins that are classified under an extremely toxic pollutant group called dioxins while PCDFs are another group of toxins under the furan group. They are among the deadliest toxins that could greatly damage our reproductive, nervous, and immune systems (Montse and Domingo, 2019). In Hu et al’s research which was conducted in Taiwan, joss paper combustion is proven to be a significant source of PCDD/F emissions as on average, one kilogram of joss paper contains 193 ng of PCDD/F. After combustion, much of the PCDD/F is mobilized into the atmosphere while a small proportion remains in the ash which enters the environment as solid waste. Again, the uncentralized characteristic of joss paper burning makes it very difficult to pollution treatment and control. There is thus a need for regulations on such practices.
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References:
B. Khezri ab, Y. Y. Chan ac, L. Y. D. Tiong a and R. D. Webster (2015). Annual air pollution caused by the Hungry Ghost Festival. Environ. Sci.: Processes Impacts, 2015, 17, 1578-1586, DOI: 10.1039/C5EM00312A, (https://pubs.rsc.org/en/content/articlehtml/2015/em/c5em00312a)
Marquès M, Domingo JL. Concentrations of PCDD/Fs in Human Blood: A Review of Data from the Current Decade. Int J Environ Res Public Health. 2019 Sep 24;16(19):3566. doi: 10.3390/ijerph16193566. PMID: 31554236; PMCID: PMC6801747. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6801747/#B9-ijerph-16-03566)
Ming-Tsan Hu, Shui-Jen Chen, Kuo-Lin Huang, Yuan-Chung Lin, Guo-Ping Chang-Chien, Jen-Hsiung Tsai, Characterization of polychlorinated dibenzo-p-dioxin/dibenzofuran emissions from joss paper burned in a furnace with air pollution control devices, Science of The Total Environment, Volume 407, Issue 10, 2009, Pages 3290-3294, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2009.01.037. (https://www.sciencedirect.com/science/article/pii/S0048969709000771)
National Environmental Agency Singapore (n.d.). Historical PSI readings. (https://www.haze.gov.sg/resources/historical-readings)
O.W Lau, S.F Luk, Leaves of Bauhinia blakeana as indicators of atmospheric pollution in Hong Kong, Atmospheric Environment, Volume 35, Issue 18, 2001, Pages 3113-3120, ISSN 1352-2310, https://doi.org/10.1016/S1352-2310(01)00069-3. (https://www.sciencedirect.com/science/article/pii/S1352231001000693)
World Health Organization, International Agency for Research on Cancer. Agents Classified by the IARC Monographs. (https://monographs.iarc.who.int/agents-classified-by-the-iarc/)