This study aims to ascertain the oxidative potential (OP) of PM2.5 in Chiang Mai (CM) City, Northern Thailand. Chiang Mai suffers from severe air pollution, which poses a health risk. Dithiothreitol assay (DTT) was used to analyze the OP of 53 samples of PM2.5 filters collected between January and April 2021 using a medium-volume air sampler with a flow rate of 100 L/minute for 24 h every other day. We analyzed components of PM2.5, including carbonaceous content [i.e., organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC)], eight water-soluble inorganic ions (WSIIs), and twenty-one metal components.
Our study found that OPDTTv (volume-normalized DTT activity) in PM2.5 had an average of 0.13 ± 0.01 nmol/min/m3 and OPDTTm (mass-normalized DTT activity) had an average of 2.44 ± 0.24 pmol/min/μg. OPDTTv was moderately correlated with carbonaceous components (r = 0.44 − 0.50, p < 0.01), WSII components (r = 0.41 − 0.55, p < 0.01), and metal components (r = 0.40 − 0.48, p < 0.01). No significant positive correlation between thesePM2.5 components and the OPDTTm was found in this study. Interestingly, moderate positive correlations were observed between OPDTTv and potassium (K, K+) and WSOC, indicating that these sources were primarily derived from biomass combustion tracers and secondary organic aerosols, respectively. Moderate positive correlations were also observed between OPDTTv and secondary ions (NO3−, NH4+). The redox-active nature of NO3− produced by gases and free radicals led to OPDTTv associations with secondary ions. Furthermore, associations were found between OPDTTv and transition metals such as copper (Cu) and iron (Fe), which contribute to generating oxidative stress.
Our study showed that the OP of PM2.5 is dominated by carbonaceous components from burning biomass, secondary organic aerosols, and transition metals. Further OP studies of other chemical components in PM2.5 should also be explored to estimate more potential health risks.
Author Contributions
Conceptualization, T.S. and T.P.; methodology, P.P.; validation, S.K.; formal analysis, T.S.; investigation, T.P.; resources, Y.Z. and F.C.; data curation, N.T.; writing—original draft preparation, T.S.; writing—review and editing, T.P.; supervision, S.K., W.S., Y.Z. and F.C.; project administration, T.P.; funding acquisition, T.S. and T.P. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by Research Institute for Health Sciences (RIHES), Chiang Mai University (CMU) Grant Number 001/2566 to TS. PM2.5 sampling and PM2.5 chemical analyses essential for this research were funded by The National Research Council of Thailand (project: Determination of secondary aerosol sources of ambient PM2.5 in Chiang Mai city: A year-round campaign in 2021, project ID: 31249 to TP). Additionally, I was appreciated with Fundamental Fund 2566, Chiang Mai University are gratefully acknowledged for partially tuition fees during study in Master of Science in Health Sciences Research, School of Health Sciences Research (SHSR).
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author on reasonable request.
Conflicts of Interest
The authors declare no conflict of interest.
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