The population-weighted daily average concentration of PM10 from vegetation fires across UNT during 2014–2018 was 106.5 µg/m3 (range: 58.7-171.9 µg/m3). In general, fire-originated PM10 concentrations was lower after burning ban enforcement in 2016.
Despite the growing concern about air pollution caused by vegetation fire events, its far-reaching health effects are often ignored. The present study showed that exposure to particles emitted from vegetation fire events throughout UNT poses health risks, such as increased respiratory morbidity, with 132,923 hospital visits (1.3% of total) being attributed to fire-originated PM10 for all ages. Moreover, approximately one-third of these visits occurred in vulnerable groups. The number of hospital visits for respiratory diseases attributable to PM10 decreased after burning ban enforcement.
Only a few studies have estimated the health burden of exposure to air pollution from vegetation fire events, particularly in terms of morbidity. Previously studies mainly addressed mortality on a global scale or in the equatorial Southeast Asian region 26–29,31,32,35−37. Some studies used morbidity as a health outcome, such as a study in Australia which examined hospitalization for cardiovascular disease and asthma 38, and another that targeted respiratory diseases in the United States 39. While the impact of long-term exposure to particles from all sources in Thailand has been reported 40, no study has estimated morbidity impacts of short-term exposure to particles emitted from vegetation fire events in MSEA. The study estimated the number of health burden attributable to fire-originated PM10 is needed because air pollution from this events has continuously affected people in UNT and it may be useful for further policy making.
Quantifying the health burden of air pollution exposure due to vegetation burning may be useful from a policy-making perspective. We observed decreases in fire-originated PM10 concentration, number of burning days, and number of hospital visits for respiratory diseases attributable to PM10 after burning ban enforcement. These findings are consistent with previous reports that PM10 concentrations in the area have decreased since the enforcement of the burning ban policy 9. While the policy may have helped reduce toxic components of particles emitted from burning activities, such as carbonaceous aerosols (black and organic carbon), Polycyclic Aromatic Hydrocarbons (PAHs), and levoglucosan 41, it does not appear to offer sustainable measures against smoke haze events. In fact, we observed increases in fire-originated PM10 concentration as well as the number of hospital visits attributable to PM10 in 2018 (i.e., after ban enforcement).
In addition to the policy, global climate factors may have influenced PM10 emission from vegetation fires. The strong El Nino phenomenon was observed during 2015–2016, resulting in dry conditions, followed by La Nina events (i.e., wet climate) in 2017 42. During the study period, we estimated the highest number of hospital visits for respiratory diseases attributable to fire-originated PM10 to be approximately 40,000 during the time of strong El Nino (2015–2016). A previous study also estimated a high global health burden attributable to particles released from burning sources due to the influence of El Nino 43.
There are some limitations to this study. In exposure assessment, we estimated the health burden of PM10 exposure using PM10 concentrations derived from ambient air pollution monitoring data, which may not have accurately reflected actual individual exposure. The inaccurate number of hospital visits for respiratory diseases attributable to fire-originated PM10 may be caused from several stages of health burden estimation (i.e., exposure assessment and applying of concentration response function). To identify burning days, we used a cut-point reported in a previous study for the occurrence of intensive fires. PM10 concentrations on the remaining days (i.e., non-burning days) were averaged as the background concentration, but small burning events might have occurred during non-burning days, contributing to the estimated background concentration. However, the background PM10 concentration did not differ from PM10 concentrations reported for non-burning months (May-December) in a previous study 20.
According to the WHO guideline, the concentration of daily PM10 should not exceeded 50 µg/m3. We thus performed a sensitivity analysis by changing the cut-point from 100 µg/m3 to 50 µg/m3 in order to capture more burning events, and to lower the average fire-originated PM10 concentration as compared to the principal analysis. The proportions of estimated hospital visits during the 5-year period did not significantly differ between principal and sensitivity analyses, but the proportion during burning days was smaller when using the WHO guideline concentration. These results suggest that using the guideline concentration, which has been set based on ambient air particles, may lead to underestimation.
Despite these limitations, the present study has the following strengths. We used effect coefficients obtained from epidemiological studies that conducted with the same health outcomes in UNT. This might have helped reduce the uncertainty of health burden estimation attributable to fire-originated PM10 because the same factors were considered such as health care system, vegetation fire particle compositions, and behavioral responses to the smoke haze of people in this area. Another strength is that we estimated the number of hospital visits for respiratory diseases attributable to fire-originated PM10 in vulnerable groups. We found a larger impact of short-term exposure to fire-originated PM10 among older adults. With the increasing aging population, this study highlights the need to address the effect of burning events on the health of older people. Our findings may help prepare for and implement preventive measures against smoke haze risk in vulnerable populations.