Ammonia (NH₃) is an important agent involved in atmospheric chemistry and nitrogen cycling. Current estimates of NH₃ emissions from biomass burning (BB) differ by more than a factor of 2, impeding a reliable assessment of their environmental consequences. Combining high-resolution satellite observations of NH₃ columns with network measurements of the concentration and stable nitrogen isotope composition (δ¹⁵N) of NH₃, we present coherent estimates of the amount of NH₃ derived from BB in the heartland of Southeast Asia, a tropical monsoon environment. Our results reveal a strong variability in atmospheric NH₃ levels in time and space across different landscapes. All of the evidence on hand suggests that anthropogenic activities are the most important modulating control with respect to the observed patterns of NH₃ distribution in the study area. N-isotope balance considerations revealed that during the intensive fire period, the atmospheric input from BB accounts for no more than 21±5 % (1σ) of the ambient NH₃, even at the rural sites and in the proximity of burning areas. Our N-isotope-based assessment of the variation in the relative contribution of BB-derived NH₃ is further validated independently through the measurements of particulate K⁺, a chemical tracer of BB. Our findings underscore that BB-induced NH₃ emissions in tropical monsoon environments can be much lower than previously anticipated, with important implications for future modeling studies to better constrain the climate and air quality effects of wildfires.

Air pollution exposure has been increasingly linked to adverse pregnancy outcomes. This study aimed to investigate the effects of PM_2.5 exposure throughout pregnancy on preterm birth, low birth weight (LBW), and small for gestational age (SGA). We analyzed a cohort of 16,965 pregnant women living in northern Thailand between 2016 and 2022. PM_2.5 concentration data were collected from two air quality monitoring stations operated by the Pollution Control Department (PCD) of Thailand. Logistic regression models were used to assess the association between daily PM_2.5 exposure and pregnancy outcomes. PM_2.5 exposure at levels exceeding 37.5 μg/m³ throughout pregnancy significantly increased the risk of preterm birth (aOR = 2.19, p < 0.001) and LBW (aOR = 1.99, p < 0.001) compared to the reference group (15.1–37.5 μg/m³). However, exposure at levels ≤15.0 μg/m³ also increased the risk for both outcomes compared to the same reference group. Subgroup analysis of high-risk pregnant women, including women aged > 35 years, with pre-pregnancy BMI (<18.5), pregnancy-induced hypertension, and nulliparous women, showed that the range of the critical PM_2.5 exposure threshold was 32.3–38.4 μg/m³ for preterm birth and 31.2–38.2 μg/m³ for LBW. This study highlights the significant association between PM_2.5 exposure and adverse pregnancy outcomes and suggests the need for targeted interventions to mitigate its effects on maternal and child health.

The concentrations of PM2.5 and metallic elements were measured in Rayong during the dry season (November 2021 to April 2022). The mean PM2.5 concentration was 20.1 ± 10.9 µg/m³ (4.9–52.3 µg/m³). Moreover, the percentages of days when those PM2.5 concentrations exceeded the daily WHO and US-EPA NAAQS limit were 56.8% and 10.2%, respectively. However, the levels did not exceed 50 µg/m³, which is the limit of the 24 h standard defined by the PCD in Thailand. The dominant heavy metals and elements in PM2.5 samples were Cr, Cu, Fe, Mn, Pb, V, and Zn, which constituted 70%. In Rayong, the PCA results showed that industrial emissions (Cd, Cu, Fe, Mn, Pb, and Zn) and traffic emissions (As, Cd, Cr, K, and Ni) were the major sources of PM2.5-bound heavy metals. Exposure to toxic metals in PM2.5 through the inhalation pathway in Rayong obviously entails a high potential risk of cancer (>10⁻⁴) based on the total lung cancer risk (TCR_inh). It was found that the TCR_inh values of Cr for combined age groups were higher than 10⁻⁶, which implies a high cancer risk in Rayong.

We performed a repeated questionnaire study on home environment and health (six medical symptoms) in 1159 junior high school students (age 12.8 ± 0.7 years) in upper northern Thailand in wet and dry seasons. Data on outdoor temperature, relative humidity (RH), and air pollution were collected from nearest monitoring station. Odds ratios (OR) were calculated by multi-level logistic regression. Most common symptoms were rhinitis (62.5%), headache (49.8%), throat (42.8%), and ocular symptoms (42.5%). Ocular symptoms were more common at lower RH and rhinitis more common in dry season. Water leakage (28.2%), indoor mold (7.1%), mold odor (4.1%), and windowpane condensation (13.6%) were associated with all six symptoms (ORs: 1.3–3.5). Other risk factors included cat keeping, environmental tobacco smoke (ETS), other odor than mold odor, gas cooking, and cooking with biomass fire. Biomass burning inside and outside the home for other reasons than cooking was associated with all six symptoms (ORs: 1.5–2.6). Associations between home environment exposure and rhinitis were stronger in wet season. In conclusion, dampness-related exposure, windowpane condensation, cat keeping, ETS, gas cooking, and biomass burning can impair adolescent health in upper northern Thailand. In subtropical areas, environmental health effects should be investigated in wet and dry seasons.

Heavy metals are significant environmental pollutants that are recognized as posing a potential health hazard to human beings. We investigated the concentrations of the heavy metals As, Cd, Cr, Cu, Ni, Pb, and Zn in surface sediments collected from the Mae Chaem River in Chiang Mai, Thailand, during the dry season in 2021. The mean concentrations of heavy metals in sediments were, in decreasing order, Zn > Cr > As > Pb > Ni > Cu > Cd. The mean values of As, Cd, Cr, and Cu were determined to be 32.5 ± 18.3, 0.33 ± 0.07, 45.8 ± 11.9, and 21.9 ± 7.42 mg Kg⁻¹, respectively. These levels are higher than their standard levels in Thailand, namely 10.0, 0.16, 45.5, and 21.5 mg Kg⁻¹, respectively. Principal component analysis (PCA) revealed that the primary origins of heavy metal contamination are predominantly attributed to residential settlements and agricultural areas. The hazard quotient (HQ) was used to estimate the non-carcinogenic risk of exposure to heavy-metal-bound surface sediments for both children and adults. The results showed that the HQ values for both groups were less than 1.0 (HQ < 1.0), indicating no risk. Moreover, assessment of the long-term risk for ingestion of toxic metals indicated no risk (<10⁻⁶) based on the lifetime cancer risk (LCR). However, the LCR values of As and Cr were 5.3 × 10⁻⁶ and 2.5 × 10⁻⁶, respectively, demonstrating the most elevated LCR among the hazardous metals in terms of children’s exposure. Therefore, it is possible that children living in agricultural areas and participating in activities around the study area may be exposed to elevated concentrations of As and Cr.

Open biomass burning (BB) has contributed severely to the ambient levels of particulate matter of less than 2.5 μm diameter (PM_2.5) in upper northern Thailand over the last decade. Some methods have been reported to identify the sources of burning using chemical compositions, i.e., ions, metals, polycyclic aromatic hydrocarbons, etc. However, recent advances in nuclear techniques have been limited in use due to their specific instrumentation. The aims of this study were to investigate the sources of ambient PM_2.5 in Chiang Mai city using stable carbon (δ¹³C) and nitrogen isotopes (δ¹⁵N). The mean concentrations of total carbon (TC) and total nitrogen (TN) in PM_2.5 were 12.2 ± 5.42 and 1.91 ± 1.07 μg/m³, respectively, whereas δ¹³C and δ¹⁵N PM_2.5 were −26.1 ± 0.77‰ and 10.3 ± 2.86‰, respectively. This isotopic analysis confirmed that biomass burning was the source of PM_2.5 and that C₃ and C₄ plants contributed about 74% and 26%, respectively. These study results confirm that the stable isotope is an important tool in identifying the sources of aerosols.