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The ambient air monitoring of PCDDs/PCDFs and dl-PCBs using passive air samplers in a residential urban area in Hanoi between 2012-2020 was deteminated. The seasonal variations of PCDD/PCDF and dl-PCB levels in ambient air in three periods: between Spring 2012 and Autumn 2015, from Winter 2015 to Autumn 2018, and between Winter 2018 and Autumn 2020 are similar to a V-shape with the highest peak in winter, then decreasing gradually in spring, bottoming in summer and rising again in autumn. The upward temporal trends of PCDD/PCDF and dl-PCB pollution, and total TEQD/F&DL, total TEQD/F and total TEQDL has been confirmed over time. The concentrations of total PCDFs were dominant and were approximately 1.0 to 9.3 times higher and 2.4 times higher on average than total PCDDs. Total dl-PCBs were 5.8 to 38 times higher and 17 times on average higher than the total toxic PCDDs/PCDFs. The PCDD/PCDF congeners contributed 83% to 95% of the total TEQ value. The phenomenon of temperature inversion not only causes seasonal air pollution but also increases the concentration of PCDDs/PCDFs and dl-PCBs with a narrower range but at a higher average levels.

Passive air sampling (PAS) method has been successfully developed using isotope standards 13C-labeled PCDDs/PCDFs as surrogates on the PUF disks from the beginning of sampling to monitor PCDDs/PCDFs from different sources of pollution, with very different levels of PCDDs/PCDFs in ambient air in the actual conditions of monsoon tropical climates with hot, wet weather and high temperatures in Vietnam. The 13C-labeled PCDD/PCDF surrogates acted as quantitative standards in the seasonal PAS process (spring, summer, autumn, winter) in the North and/or every 3 months in the dry and rainy seasons in the Central. At least 96.9% of all surrogates had the retention efficiencies of 17% to 185% on PUF disks, which were equivalent to that required by US EPA 1613B method for the recovery efficiencies only at sample preparation. This development method was shown to be reliable with 91.6% of the total PCDD/PCDF congeners which their relative percent differences (RPDs) between PCDD/PCDF concentrations on the PUF disks of field duplicates were not exceed 40% and an average RPD of only 7.4% to 30.5% for both PAS process and laboratory analysis.