Assessing exposure to air pollution among workers in Bangkok

Thailand’s particulate pollution reached 23.8 μg/m3 in 2020, according to the Air Quality Life Index (Energy Policy Institute 2022) – four times higher than the global standard and annual 5 μg/m3 recommendation put forth by the World Health Organization in 2021. With air pollution highest in the Bangkok Metropolis, Nakhon Ratchasima and Chiang Mai, the average gain in life expectancy from clean air in these areas would be between 1.5 and 2.4 years. Therefore, research to better understand who is exposed to air pollution and to what extent, is important to target measures to limit exposure.

The study had three prongs, focusing respectively on indoor air pollution in Chulalongkorn University (CU) buildings, outdoor air pollution in the district and policy recommendations relating to air pollution management. It was expected that the burden of exposure would be higher amongst outdoor workers who cannot use methods, such as air purifiers or shutting windows to keep out pollutants, however, the results suggest that exposure remains high indoors too.

Colleagues at CU first assessed outdoor air quality by identifying potential PM2.5 hotspots in Patumwan district using computational modelling (AERMOD), which included meteorological data, surface data, overall land uses and traffic data along the road intersections within the area of study. The highest average 24-hour PM2.5 concentration was found along Rama IV Road due to its high volume of traffic throughout the day. The university campus had lower concentrations of PM2.5, as it has less traffic and higher vegetation cover.

Indoor air quality data within the university was then collected over the year from seven real-time monitoring stations (data collection includes PM10, PM2.5, PM1.0, temperature and relative humidity) installed in faculty offices, laboratories and meeting rooms around the campus. As staff and students spend up to eight hours a day working indoors, the indoor air quality, as well as indoor climate is important for their health and comfort. The data shows that the levels of PM10, PM2.5 and PM1.0 was relatively high compared with the outdoor level whether the doors and/or windows were opened or not. In terms of PM2.5, most of the offices experienced air quality exceeding the WHO 24-hour standard for six months of the year, from October/November through to April/May. The collected data has been made publicly accessible online and through a mobile application, which provides up-to-date information to increase the awareness and self-preparedness of people on campus.

The arrangement of the furniture inside the room also plays an important role on the air ventilation and pollutant accumulation within the room. The study employed computer simulations to visualize airflow behaviour and investigate indoor air ventilation, according to the furniture configuration in each room. The results suggest that the particulate matter accumulation hotspots tend to form in the air pockets behind large furniture, such as cupboards and cabinets. These PM accumulation hotspots can be avoided by making sure large pieces of furniture do no obstruct air ducts or aircon units. In terms of thermal comfort, the automatic air conditioning deflectors helped to distribute the air evenly and ensure that indoor comfort is maximized.

During this time, SEI carried out an assessment of outdoor air quality using mobile PM2.5 monitoring to supplement questionnaires of workers in the area. Responses from 198 people were gathered, the majority of whom were women (102) with an average age of 39 years. Most workers were employees (100), followed by street sweepers (32), security guards (23) and motorbike taxi drivers (20).

When it came to working conditions, the majority work at least a full working week outdoors: 81 respondents work outside six days a week, 71 work outside seven days a week and 25 work outside five days a week. The majority – 128 respondents – work between 8-10 hours a day, of which 93 spent that length of time working outdoors daily. Therefore, ambient air quality is going to be an important determinant of their health.

With regards to face masks, 179 respondents (90%) always wear them outdoors – at the time of the data collection, there was near universal mask wearing due to Covid-19 regulations. The types of facemasks include surgical or other disposable masks, including KF94 (84 respondents), cloth masks (65 respondents) and disposable N95 masks (35 respondents). KF94 and N95 masks are the most suitable to protect against PM2.5 particles.

As the respondents’ livelihoods are very much tied to their outdoor place of work and the daily income they can generate, not going to work on days where air pollution is high was not an option they could consider. One security guard said that having to work in poor air quality is normal for them. A motorbike driver explained how his home in the city outskirts has comparatively better air than the city centre where he works, and so he mentally prepares himself for air pollution, as he travels in to work.

The survey was followed by some mobile PM2.5 monitoring, in an experiment where participants were asked to carry a portable sensor alongside a GPS sensor during their working day. As both PM2.5 data and GPS data were collected, it was possible to geolocate every PM2.5 measurement at two minute intervals. This was then amalgamated into hourly PM2.5 data, which could then be overlaid onto the local map, which had been divided up into a 100m x 100m grid. Vegetation cover versus built-up cover were also analysed, with Lumpini Park and the Royal Bangkok Sports Club having the higher percentage of green cover, while Chulalongkorn University has balanced green and built-up cover.

As shown below, average levels of PM2.5 tended to be higher during the morning period, compared to the evening rush hour, while average PM2.5 levels tended to be slightly lower in the university campus areas, which have more vegetation, compared to areas west of the campus, which have more built-up cover.

Based on the findings of this study, air quality both indoors and outdoors must be improved to ensure workers in Thailand are not exposed to air pollution. The results of this study were shared at a policy event with attendees from Chulalongkorn University management and representatives of the Bangkok Metropolitan Authority and Pollution Control Department of Thailand.

This piece is co-authored with Dr Ratchanon Piemjaiswang, a researcher at Environmental Research Institute, Chulalongkorn University. SEI Asia, in collaboration with Chulalongkorn University (CU) in Bangkok, studied particulate matter pollution in Bangkok, focusing on the Pathumwan district where the University and SEI offices are located, as part of a Joint Research Cluster on transdisciplinary research to support the implementation of the United Nation Sustainable Development Goals (SDGs).