Late last month, Bangkok was ranked as the fourth most polluted city in the world, according to IQAir. The air quality index (AQI) in Bangkok reached 188 and PM2.5 was as high as 108 µg/m³, indicating unhealthy air quality.
To cope with air pollution, Prime Minister Paetongtarn Shinawatra has implemented many measures, such as free rides on public transportation for seven days to reduce the number of vehicles on the roads in the Bangkok metropolitan area.
Before the prime minister began tackling PM2.5 air pollution, Kasetsart University had raised awareness about the issue in a forum titled "PM2.5 and Epidemics – Connected Risk Factors... Two Major Issues Awaiting Resolution".
Although the forum title indicated a discussion on the connection between PM2.5 and epidemics, information about this link was mentioned only briefly. Prof Siwatt Pongpiachan, the director of the NIDA Center for Research & Development of Disaster Prevention & Management, pointed out that his research published in Aerosol Science And Engineering focused on the spread of Covid-19 in the central region.
"During the pandemic, I conducted a study of Covid-19 infection rates in provinces in the Central Region of Thailand. The study aimed to search for correlations leading to Covid-19 infection, including PM2.5, carbon monoxide, nitrogen oxide, ozone, sulfur dioxide and PM10. The results of this study are consistent with research published in China," he said.
Prof Siwatt revealed that the increase in Covid-19 cases was significantly associated with the high level of ozone and not PM2.5.
"My research discovered that ozone causes inflammation in respiratory cells. Areas with high ozone levels pose a high risk of respiratory cell inflammation, which makes cells vulnerable to Covid-19," he said.
Prof Siwatt emphasised that his research focused only in the central region. He explained further that research results differed based on location: "Harvard University's research during the pandemic indicated a correlation between PM2.5 pollution and Covid-19 mortality rates. A university in France which studied correlations between air pollution and Covid-19 infection rates discovered that nitrogen oxide led to high rates of Covid-19 cases."
Some people may wonder why ozone has a negative effect since advertisements promote the benefits of ozone. The American Lung Association has stated that: "Ozone is good up high, bad nearby."
The ozone layer high in the upper atmosphere shields us from the Sun's ultraviolet radiation. However, ozone pollution at ground level where we can breathe causes serious health problems. Ground-level ozone forms from the interaction of pollutants emitted from motor vehicles, industrial facilities, electric utilities and gasoline vapour.
Many experts have pointed out that the main factors causing PM2.5 are transportation and industry, increase of biomass burning and stagnant air caused by temperature inversion due to climate change. Temperature inversion is a layer in the atmosphere where the temperature increases with height, which is the opposite of normal conditions where air cools as it goes higher.
Siwaporn Rangsiyanon, a specialist in air quality and noise management at the Pollution Control Department, said people might wonder why PM2.5 pollution increases during winter even though the number of vehicles in Bangkok remains the same.
"The air pollution is primarily caused by the influence of high-pressure systems. Normally, temperature decreases with altitude. However, during temperature inversion, a layer of warm air traps colder air near the ground which prevents pollutants from rising and dispersing," she said.
In addition to the main factors of PM2.5 as stated above, Prof Siwatt surprised the audience by referring to research by the National Astronomical Research Institute of Thailand which was published in Environmental Pollution. The research indicated that trees release biogenic volatile organic compounds which can interact with nitrogen oxide to develop harmful particles. Nitrogen oxide is released from motor vehicle exhausts, fossil fuel power plants and industrial processes.
"Trees are beneficial, but interaction between their emissions and nitrogen oxide can contribute to harmful particles. When it comes to tree planting, people must select wisely by choosing plants that do not release high levels of compounds," said Prof Siwatt.
"Research also found that rubber trees release high levels of compounds. When rubber trees grow in the South, they do not cause any issue because they are located in well-ventilated areas. However, rubber trees are being planted in the North and Northeast as well, and planting trees in inappropriate places can lead to negative consequences."
Prof Siwatt also revealed research about trees so that people realise how human interference with nature can lead to negative consequences. He emphasised that while particles resulting from the interaction between emissions from trees and nitrogen oxide can contribute to air pollution, they are considered less harmful than particles emitted from vehicle exhaust and biomass burning.
Asst Prof Kitsanaporn Tipkanjanaraykha, a lecturer at the Department of Adult and Gerontological Nursing at the Faculty of Nursing at Kasetsart University, warned that when PM2.5 levels are high, people should avoid outdoor activities.
"Due to their extremely minute size, PM2.5 particles can easily enter the human body, avoid the body's defence mechanisms and enter the bloodstream. Once in the bloodstream, these particles can accumulate in various organs. Prolonged exposure to high levels of PM2.5 pollution can trigger chronic inflammation which can lead to development of a range of diseases including cancer," said Asst Prof Kitsanaporn.
"Exposure to PM2.5 particles can cause health issues even in someone who is healthy. People who have never smoked can have symptoms of chronic obstructive pulmonary disease. PM2.5 is composed of various substances and some substances can increase the risk of cancer. Research conducted by the Chulabhorn Research Institute shows that chemical compounds in particulate matter from incense burning can contribute to the development of lung cancer."
Asst Prof Kitsanaporn warned that people who are most vulnerable to PM2.5 include children, the elderly, pregnant women and people with chronic diseases. Although Asst Prof Kitsanaporn suggested that people should wear N95 masks, she admitted the masks are expensive, suffocating and uncomfortable to wear.
When asked if it is possible to use double surgical masks instead of using N95 masks, Asst Prof Kitsanaporn replied that double surgical masks are only 50% to 60% effective in protecting against PM2.5.
Much scientific evidence links PM2.5 to various diseases such as respiratory diseases, chronic kidney diseases and cardiovascular diseases. Assoc Prof Surat Bualert, the Dean of the Faculty of Environment at Kasetsart University, pointed out that unlike Covid-19 deaths, deaths attributed to PM2.5 are not officially recorded. Instead, these cases are often categorised as other diseases.
"A veterinarian also conducted a study comparing the lung tissues of stray dogs and domestic dogs. The results showed significant differences as stray dogs exhibited chronic inflammation in their lung tissues due to repeated infection. If human doctors could diagnose diseases caused by PM2.5, it would significantly increase public awareness and concern."
Throughout the forum, Prof Siwatt mentioned several times that Thailand should establish specific standards for carcinogenic substances.
"Since Thailand is going to have its own clean air legislation, I always question why we don't set standards for carcinogens found in PM2.5 to provide a practical measure for public health."