The impact of short-term exposure to black carbon air pollution on asthma exacerbations in Thai children: a time-stratified case-crossover nationwide study from 2015 to 2022.

backgroundBlack carbon is a critical component of ambient particulate matter and a recognized trigger of respiratory morbidity. Although existing studies have explored the link between black carbon exposure and pediatric asthma, evidence specific to rapidly industrializing middle-income regions remains scarce. In Thailand, increasing industrial activities, agricultural burning, and vehicle emissions have resulted in higher black carbon concentrations; however, comprehensive epidemiological data on the impact of this on children with asthma exacerbations remain limited.

methodsWe performed a nationwide retrospective study with time-stratified case-crossover analysis of children (< 18 years) hospitalized for asthma exacerbations under Thailand's Universal Coverage Scheme from 2015 to 2022. Asthma exacerbation admissions were identified using ICD-10 codes (J45.9, J46). Ambient black carbon levels were obtained from NASA's Modern-Era Retrospective Analysis for Research and Application (MERRA-2). Conditional Poisson regression was used to calculate incidence rate ratios (IRRs) for pediatric asthma hospitalizations per 1 µg/m³ increase in black carbon, controlling for intra-week variations.

resultsAmong 163,825 asthma exacerbation-related hospital admissions (37.3% male, 62.7% female), children aged < 5 years accounted for 49.6% of cases, 5-<10 years for 33.1%, 10-<15 years for 14.1%, and 15-<18 years for 3.2%. The mean black carbon concentration was 1.00 ± 0.46 µg/m³, peaking during summer. On the day of hospitalization (Lag 0), a 1 µg/m³ increase in black carbon was associated with elevated IRR in children aged < 5 (IRR: 1.14; 95%CI: 1.05-1.25; p = 0.002), 5-<10 (IRR: 1.31; 95%CI: 1.18-1.45; p < 0.001), and 10-<15 (IRR: 1.35; 95%CI: 1.16-1.59; p < 0.001). Delayed effects (Lag 1) remained significant for children 5-<10 (IRR: 1.18; 95%CI: 1.06-1.31; p = 0.002) and 10-<15 (IRR: 1.26; 95%CI: 1.07-1.47; p = 0.004) but not for those 15-<18 years.

conclusionsShort-term exposure to black carbon significantly increases the risk of hospitalizations from pediatric asthma exacerbation in Thailand, especially among children under 15 years of age and particularly on the day of exposure. These findings underscore the urgent need for effective air quality interventions, such as cleaner fuel technologies, stricter policies on industrial and agricultural emissions, and enhanced public health measures to mitigate black carbon pollution. Future investigations should integrate personal-level exposures, assess interactions with other pollutants, and evaluate the outcomes of interventions to reduce the respiratory health burden in this vulnerable population.