Air Pollution during the Hungry Ghost Festival

Background: The Hungry Ghost Festival is celebrated annually in Chinese communities in August/September and involves the open air burning of large amounts of joss paper, incense and papier-mâché objects as offerings to appease the spirits of dead ancestors. In this study, we examined the levels of ambient pollution in the form of increases in the elemental composition of PM_2.5(particulate matter less than 2.5 micron) and increases in the elemental and ionic composition of rainwater caused by the burning. The data from the air samples were compared with elemental data collected from authentic samples of burnt and unburnt joss paper, incense and papier-mâché. Methods: Samples of PM_2.5 were collected on borosilicate glass microfibers reinforced with woven glass cloth and bonded with PTFE (sized 8 × 10 inch) using a high volume air sampler located on the roof of the School of Physical and Mathematical Sciences at Nanyang Technological University in Singapore over a five year period. Rain water samples were collected at the same location using an automatic sampler. PM_2.5samples underwent microwave assisted acid digestion with a mixture of ultra-pure concentrated nitric and hydrochloric acids and were subsequently analysed using inductively coupled plasma – mass spectrometry (ICP-MS) to quantify 58 elements. Rain water samples were analysed for pH, conductivity, ICP-MS (for elemental composition) as well as via ion chromatography. Results: In total, 551 PM_2.5 and 574 rainwater samples were collected over a 5 year period. During August and September each year, there was a notable increase in the elemental chemical composition of PM_2.5. Nine metals (Cr, Mn, Ni, Co, As, Cd, Sn, Sb and Pb) that are listed among the 188 hazardous air pollutant substances defined under the Clean Air Act Amendments of 1990 showed increases between 20 – 50% above the yearly monthly mean values. Other less toxic elements (such as Zn, Ca, K, Mg, Fe and Al) also showed relatively large % increases compared to their monthly averages. Similar results were obtained for the rainwater samples that showed spikes in the elemental and ionic concentrations during the 3 festival dates where extensive burning occurred. The increases in elemental concentrations could be directly correlated with the elemental composition of the joss paper, incense and papier-mâché materials. Conclusions: Singapore has relatively high average PM₁₀ values (40 – 50 microgram m^–3) due to local industrial activity and haze pollution caused by slash and burn practices in neighbouring countries. Therefore, the annual increase in air pollution caused by the Hungry Ghost Festival is potentially a cause for concern since it contributes to the already relatively high levels of PM. Recommendations to alleviate this problem while still maintaining the culturally important religious festivities are to introduce closed furnaces with filtering systems, and possibly use less environmentally toxic materials in the manufacture of the materials that are burnt.