Microplastic pollution in coastal surface seawater of Southern Vietnam.

Microplastics have recently emerged as a significant environmental concern due to their direct impacts on marine ecosystems. Vietnam, with its 3260-km coastline, faces an elevated risk of microplastic pollution due to various coastal anthropogenic activities. This study explored microplastic distribution in coastal surface seawater in the Southern Vietnam regions of Tien Giang, Can Gio, and Vung Tau. A total of 45 samples were collected in April, 2019, and the results showed that microplastics present at all sampling sites, with the abundance varying from 0.074 ± 0.109 pieces/m3 in Can Gio to 0.56 ± 0.35 pieces/m3 in Tien Giang. Estuarial sites showed higher abundances for all regions. Most microplastics were under 2.8 mm, fragmented, and primarily white or transparent. Polypropylene, polyethylene, and ethylene-vinyl acetate were the dominant polymers. This research indicates the urgency of further investigations to comprehensively understand the influence of wind patterns and other environmental factors on microplastic distribution.

Estimating alcohol and tobacco consumption of university students and urban population in Ho Chi Minh City by wastewater analysis.

The quantitative measurement of urinary biomarkers in wastewater has emerged as a robust tool for estimating alcohol and tobacco consumption in populations. In this study, we applied the wastewater-based epidemiology (WBE) approach to compare alcohol and tobacco use between university students and urban inhabitants in Ho Chi Minh City, Vietnam. Ethyl sulfate and cotinine serve as markers for alcohol and tobacco use, respectively. Our findings reveal that urban inhabitants aged 15 and above consume 1.56 ± 0.23 mL of pure ethanol and 2.8 ± 0.33 mg of nicotine per day, while university students consume 0.69 ± 0.13 mL of pure alcohol and 1.2 ± 0.2 mg of nicotine per day. This indicates that, on average, students consume less alcohol and tobacco compared with urban adults. A Monte Carlo simulation indicated that, on average, university students in our study smoke 1.5 cigarettes per day, while urban residents aged 15 and above smoke 4.3 cigarettes per day. Considering the smoking prevalence, a student smoker in this study consumes 6.5 cigarettes per day, a level high enough to establish addiction. On the other hand, alcohol use estimation is significantly lower than previous survey-based reports, likely due to degradation within on-site septic tanks. Future research should aim to extend the sampling period to capture seasonal variations and improve the understanding of tobacco and alcohol consumption patterns. The results from this study are crucial for decision-makers in Ho Chi Minh City to develop effective public health strategies and interventions. PRACTITIONER POINTS: Wastewater-based approach is applicable to estimate the tobacco consumption in Ho Chi Minh City. Each current smoker in the urban area of Ho Chi Minh City smokes nearly a package a day. The estimated consumption for student smokers in U-town is 6.5 cigarettes per day, a level high enough to establish addiction. The existence of septic tanks within Vietnam's drainage systems prevents reliable estimation of alcohol consumption for the entire population.

In-depth analysis of ambient air pollution changes due to the COVID-19 pandemic in the Asian Monsoon region.

The COVID-19 pandemic has given a chance for researchers and policymakers all over the world to study the impact of lockdowns on air quality in each country. This review aims to investigate the impact of the restriction of activities during the lockdowns in the Asian Monsoon region on the main criteria air pollutants. The various types of lockdowns implemented in each country were based on the severity of the COVID-19 pandemic. The concentrations of major air pollutants, especially particulate matter (PM) and nitrogen dioxide (NO2), reduced significantly in all countries, especially in South Asia (India and Bangladesh), during periods of full lockdown. There were also indications of a significant reduction of sulfur dioxide (SO2) and carbon monoxide (CO). At the same time, there were indications of increasing trends in surface ozone (O3), presumably due to nonlinear chemistry associated with the reduction of oxides of nitrogens (NOX). The reduction in the concentration of air pollutants can also be seen in satellite images. The results of aerosol optical depth (AOD) values followed the PM concentrations in many cities. A significant reduction of NO2 was recorded by satellite images in almost all cities in the Asian Monsoon region. The major reductions in air pollutants were associated with reductions in mobility. Pakistan, Bangladesh, Myanmar, Vietnam, and Taiwan had comparatively positive gross domestic product growth indices in comparison to other Asian Monsoon nations during the COVID-19 pandemic. A positive outcome suggests that the economy of these nations, particularly in terms of industrial activity, persisted during the COVID-19 pandemic. Overall, the lockdowns implemented during COVID-19 suggest that air quality in the Asian Monsoon region can be improved by the reduction of emissions, especially those due to mobility as an indicator of traffic in major cities.

Study on the concentration, composition, and recovery rate of bacterial bioaerosols after rainfall in Ho Chi Minh City.

Aerosolized microorganisms have become an important factor in assessing air quality. To determine the characteristics of bacterial bioaerosols in air and rainwater, as well as calculate the recovery rate of bacteria after rains in Ho Chi Minh City, our study was performed using the SKC Biostage sampler for airborne bacteria and Plate Count Agar (PCA) medium for bacterial concentration. Subsequently, the study determined the bacterial community composition at the phylum and order levels using the 16S rRNA (16S metabarcoding) method. Before the rain, bacterial concentrations in the air ranged from 263.39 ± 21.00 to 277.39 ± 78.99 CFU/m3, and in rainwater 264.89 ± 51.17 to 285.72 ± 28.00 CFU/m3. Following rains, the bacterial concentrations decreased to their lowest levels within the first 1-2 h and gradually increased thereafter, reaching their peak after 9 h for heavy rain and after 12 h for light and moderate rains. The bacterial bioaerosols recovery rate was determined to be 100% for light and moderate rains and 94.6% for heavy rain. The change in bacterial concentration after rainfall showed a positive correlation with temperature (r = 0.85) and CO2 concentration (r = 0.70) and a negative correlation with relative humidity (r = - 0.79). Bacterial composition analysis revealed that the Actinobacteria, Firmicutes, and Proteobacteria phyla were dominant and characteristic of the humid tropical climate in Vietnam. Notably, Firmicutes were the most prevalent phylum both before and after rains. The increased prevalence of certain bacterial orders, particularly Staphylococcus, could contribute to the spread of pathogens, particularly foodborne pathogens. In addition to rain, relative humidity contributed to reducing bacterial bioaerosols concentration and their recovery rate after the rain.

Long-Range Atmospheric Mercury Transport from Across East Asia to a Suburban Coastal Area in Southern Vietnam.

Exports of atmospheric mercury (Hg) from continental East Asia, a major Hg emitter in the globe, have been reported by several studies in neighboring countries such as Japan and Korea. Nonetheless, studies concerning this topic in Southeast Asia (SEA) countries are still limited. Accordingly, gaseous elemental mercury (GEM) has been measured from Can Thanh High School (CTHS), a suburban coastal site in southern Vietnam to study its characterization and discover the evidence of Hg trans-boundary transport from regional sources (e.g., East Asia). Data collected in July, August, and October 2022 were used in this study, and the overall GEM concentration was 1.61 ± 0.32 ng m-3. The GEM levels were higher in October than in July and August, potentially due to the discrepancy in air mass transport patterns induced by tropical monsoon and source origins of Hg. MERRA-2, backward trajectories, and CALIPSO images revealed the trans-boundary air pollution from continental East Asia to southern Vietnam, evidenced by significantly elevated (> 30%) atmospheric Hg concentrations as well as other air pollutants when the plume arrived at CTHS. Furthermore, our results also imply that atmospheric Hg exported from East Asia could influence large areas in SEA, suggesting the need for more studies in various SEA countries in the upcoming future. This study illustrated the influence of regional Hg emissions on local atmospheric Hg pollution and provided data to improve knowledge of the Hg biogeochemical cycle in SEA.

Wearing masks as a protective measure for children against traffic-related air pollution: A comparison of perceptions between school children and their caregivers in Ho Chi Minh City, Vietnam.

BACKGROUND: Traffic-related air pollution (TRAP) problems are unlikely to be solved in the short term, making it imperative to educate children on protective measures to mitigate the negative impact on their health. Children and their caregivers may hold differing views on wearing a face mask as a safeguard against air pollution. While many studies have focused on predicting children's health-protective behaviours against air pollution, few have explored the differences in perceptions between children and their caregivers. OBJECTIVES: To examine this, we conducted a study that compared the health beliefs of two generations and evaluated the factors that influence the use of masks by children to reduce air pollution exposure. METHODS: The study was conducted in 24 secondary schools and involved 8420 children aged 13-14 and their caregivers. We used a Health Belief Model (HBM)-based instrument containing 17-item self-administered health beliefs questionnaires to gather data. The results were analysed using hierarchical logistic regression to determine the probability of children frequently wearing masks to protect against TRAP. RESULTS: Our study showed both children and caregivers recognised that several factors could influence mask-wearing among children: discomfort or difficulty breathing while wearing a mask and forgetting to bring a mask when going outside; perceived threats of the poor quality of air and children's respiratory health problems; and cues to mask use (i.e., seeing most of their friends wearing facemasks and ease of finding masks in local stores). However, only children were significantly concerned with public perception of their appearance while wearing a mask. Females were more likely to wear masks, and caregivers with higher levels of education were more likely to encourage their children to wear masks. Children who commuted to schools by walking, biking, or motorbiking were also more accepting of mask-wearing than those who travelled by car or bus. CONCLUSIONS: Children and their caregivers hold different perceptions of wearing masks to protect against air pollution. Children are more susceptible to social judgements regarding their appearance when wearing a mask.

Evaluating major anthropogenic VOC emission sources in densely populated Vietnamese cities.

Volatile organic compounds (VOCs) play an important role in urban air pollution, both as primary pollutants and through their contribution to the formation of secondary pollutants, such as tropospheric ozone and secondary organic aerosols. In this study, more than 30 VOC species were continuously monitored in the two most populous cities in Vietnam, namely Ho Chi Minh City (HCMC, September-October 2018 and March 2019) and Hanoi (March 2019). In parallel with ambient VOC sampling, grab sampling was used to target the most prevalent regional-specific emission sources and estimate their emission factors (EFs). Emission ratios (ERs) obtained from ambient sampling were compared between Vietnamese cities and other cities across the globe. No significant differences were observed between HCMC and Hanoi, suggesting the presence of similar sources. Moreover, a good global agreement was obtained in the spatial comparison within a factor of 2, with greater ER for aromatics and pentanes obtained in the Vietnamese cities. The detailed analysis of sources included the evaluation of EF from passenger cars, buses, trucks, motorcycles, 3-wheeled motorcycles, waste burning, and coal-burning emissions. Our comparisons between ambient and near-source concentration profiles show that road transport sources are the main contributors to VOC concentrations in Vietnamese cities. VOC emissions were calculated from measured EF and consumption data available in Hanoi and compared with those estimated by a global emission inventory (EDGAR v4.3.2). The total VOC emissions from the road transport sector estimated by the inventory do not agree with those calculated from our observations which showed higher total emissions by a factor of 3. Furthermore, the inventory misrepresented the VOCs speciation, mainly for isoprene, monoterpenes, aromatics, and oxygenated compounds. Accounting for these differences in regional air quality models would lead to improved predictions of their impacts and help to prioritise pollution reduction strategies in the region.

Burden of asthma-like symptoms and a lack of recognition of asthma in Vietnamese children.

OBJECTIVE: Lack of recognition of asthma in childhood results in unmet asthma treatment needs and leads to the risk of sub-optimal respiratory health. The present study assessed the prevalence of asthmatic under-recognition in middle school children in Vietnam. METHODS: We conducted a school-based survey among 15,112 Vietnamese children. Most of them are aged from 13 to 14. Schools and students were recruited using multi-stage sampling. Respiratory symptoms were collected via self-report using a standardized tool from the International Study of Asthma and Allergies in Childhood. Under-recognition of asthma was defined as a presence of at least one asthma-like symptom but a negative response to having ever asthma. Associations were investigated using logistic regression. RESULTS: Prevalence of asthma-like symptoms was 27.3% and prevalence of physician-diagnosed asthma was 8.5%. Over 80% of symptomatic children were not diagnosed with asthma. Under-recognition of asthma was found more in girls (adjusted odds ratio; aOR = 1.75; 95%CI: 1.54 to 1.98). CONCLUSIONS: Asthma is significantly under-recognized in Vietnamese middle-school children. Urgent action is required to improve the recognition of asthma in Vietnam.

Atmospheric particulate-bound mercury (PBM10) in a Southeast Asia megacity: Sources and health risk assessment.

Particulate-bound mercury (PBM) is a global environmental concern owing to its large dry deposition velocities and scavenging coefficients, both of which drive Hg into terrestrial and marine ecosystems. PBM observation studies have been widely conducted over East Asia, but comparable studies in Peninsular Southeast Asia (PSEA) remain scarce. This is the first study reporting PBM concentrations for Ho Chi Minh City (HCMC), the biggest metropolitan area in Vietnam. A total of 222 samples were collected in 2018 and contained an average PBM10 (particulate matter - PM with diameter ≤10 µm) concentration and Hg mass fraction (i.e. PBM/PM) of 67.3 ± 45.9 pg m-3 and 1.18 ± 1.12 µg g-1, respectively. Although PBM concentration was lower than those reported in Chinese megacities, the Hg mass fraction was similar to those in China, suggesting strong enrichment from anthropogenic Hg emissions in HCMC. Traffic-induced particulate emission and deposition processes were major factors governing PBM temporal variation at our site. In addition, the prevailing southwest monsoon winds brought air masses that passed through industrial areas and were associated with a higher Hg mass fraction. Statistically significant positive correlations (R2 = 0.11-0.52, p < 0.01) were observed for PBM with PM and the Hg mass fraction, indicating similar PM and Hg sources or oxidized Hg adsorption onto PM via gas-particle partitioning. Moreover, PCA results revealed a higher contribution of primary sources than secondary sources to PBM concentration variability in HCMC. A health risk assessment indicated that the PBM concentrations at HCMC posed minimal non-carcinogenic risks (HI < 1) for children and adults, but dermal contact may act as an important exposure route since lightweight clothing is common among residents. This PBM dataset over PSEA, a region with high atmospheric Hg emissions, provides a valuable resource for the Hg scientific community to improve our understanding of Hg biogeochemical cycle.

Characteristics of Microplastics and Their Affiliated PAHs in Surface Water in Ho Chi Minh City, Vietnam.

Microplastic pollution has become a worldwide concern. However, studies on the distribution of microplastics (MPs) from inland water to the ocean and their affiliated polycyclic aromatic hydrocarbons (PAHs) are still limited in Vietnam. In this study, we investigated the distribution of MPs and PAHs associated with MPs in canals, Saigon River, and Can Gio Sea. MPs were found at all sites, with the highest average abundance of MPs being 104.17 ± 162.44 pieces/m3 in canals, followed by 2.08 ± 2.22 pieces/m3 in the sea, and 0.60 ± 0.38 pieces/m3 in the river. Fragment, fiber, and granule were three common shapes, and each shape was dominant in one sampling area. White was the most common MP color at all sites. A total of 13 polymers and co-polymers were confirmed, and polyethylene, polypropylene, and ethylene-vinyl acetate were the three dominant polymers. The total concentration of MPs-affiliated PAHs ranged from 232.71 to 6448.66, from 30.94 to 8940.99, and from 432.95 to 3267.88 ng/g in Can Gio sea, canals, and Saigon River, respectively. Petrogenic sources were suggested as a major source of PAHs associated with MPs in Can Gio Sea, whereas those found in Saigon River and canals were from both petrogenic and pyrogenic sources.

Characteristics of polycyclic aromatic hydrocarbons in ambient air of a tropical mega-area, Ho Chi Minh City, Vietnam: concentration, distribution, gas/particle partitioning, potential sources and cancer risk assessment.

This is the first investigation on overall characteristics of 25 polycyclic aromatic hydrocarbons (PAHs) (15 PAHs regulated by US-EPA (excluding naphthalene) and 16 PAHs recommended by the European Union) in ambient air of Ho Chi Minh City, Vietnam. Their levels, congener profiles, gas/particle partitioning, potential sources of atmospheric PAHs (gas and particulate phases), and lung cancer risks in the dry and rainy seasons were examined. The ∑25 PAH concentration in the dry and rainy seasons ranged from 8.79 to 33.2 ng m-3 and 26.0 to 60.0 ng m-3, respectively. Phenanthrene and Indeno[123-cd]pyrene were major contributors to gaseous and particulate PAHs, respectively, while benzo[c]fluorene was dominant component of the total BaP-TEQ. The ∑16 EU-PAH concentration contributed to 13 ± 2.7% of the total ∑ 25 PAH concentration; however, they composed over 99% of the total ∑ 25 PAH toxic concentration. Adsorption mainly governed the phase partitioning of PAHs because the slope of correlation between logKp and logP0L was steeper than - 1. Vehicular emission was the primary source of PAHs in two seasons; however, PAHs in the dry season were also originated from biomass burning. Assessment of lung cancer risk showed that children possibly exposed to potential lung cancer risk via inhalation.

Comparative study on water-soluble inorganic ions in PM2.5 from two distinct climate regions and air quality.

Recently, air quality has significantly improved in developed country, but that issue is of concern in emerging megacity in developing country. In this study, aerosols and their precursor gas were collected by NILU filter pack at two distinct urban sites during the winter and summer in Osaka, Japan and dry and rainy seasons in Ho Chi Minh City (HCMC), Vietnam. The aims are to investigate the contribution of water-soluble inorganic ions (WSIIs) to PM2.5, thermodynamic characterization and possible formation pathway of secondary inorganic aerosol (SIA). The PM2.5 concentration in Osaka (15.8 µg/m3) is lower than that in HCMC (23.0 µg/m3), but the concentration of WSIIs in Osaka (9.0 µg/m3) is two times higher than that in HCMC (4.1 µg/m3). Moreover, SIA including NH4+, NO3- and SO42- are major components in WSIIs accounting for 90% and 76% (in molar) in Osaka and HCMC, respectively. Thermodynamic models were used to understand the thermodynamic characterization of urban aerosols. Overall, statistical analysis results indicate that very good agreement (R2 > 0.8) was found for all species, except for nitrate aerosol in HCMC. We found that when the crustal species present at high amount, those compositions should be included in model calculation (i.e. in the HCMC situation). Finally, we analyzed the characteristics of NH4+- NO3-- SO42- system. A possible pathway to produce fine nitrate aerosol in Osaka is via the homogeneous reaction between NH3 and HNO3, while non-volatile nitrate aerosols can be formed by the heterogeneous reactions in HCMC.

Atmospheric concentrations and gas-particle partitioning of PCDD/Fs and dioxin-like PCBs around Hochiminh city.

Atmospheric PCDD/Fs and dl-PCBs samples were collected in Hochiminh city, Vietnam to address the effect of meteorological parameters, especially rainfall, on the occurrence and gas/particle partitioning of these persistent organic pollutants. The results indicate that PCDD/Fs and dl-PCBs concentrations in industrial site are higher than those measured in commercial and rural sites during both rainy and dry seasons. In terms of mass concentration, ambient PCDD/F levels measured in dry season are significantly higher than those measured in rainy season while dl-PCB levels do not vary significantly between rainy and dry seasons. The difference could be attributed to different gas/particle partitioning characteristics between PCDD/Fs and dl-PCBs. PCDD/Fs are found to be mainly distributed in particle phase while dl- PCBs are predominantly distributed in gas phase in both rainy and dry seasons. Additionally, Junge-Pankow and Harner-Bidleman models are applied to better understand the gas/particle partitioning of these pollutants in atmosphere. As a results, both PCDD/Fs and dl-PCBs are under non-equilibrium gas/particle partitioning condition, and PCDD/Fs tend to reach equilibrium easier in rainy season while there are no clear trend for dl-PCBs. Harner-Bidleman model performs better in evaluating the gas/particle partitioning of PCDD/Fs while Junge-Pankow model results in better prediction for dl-PCBs.

Atmospheric PCDD/F concentration and source apportionment in typical rural, Agent Orange hotspots, and industrial areas in Vietnam.

Vietnam has a double burden of dioxin from both industrial sources and historical sources. To evaluate the concentration of PCDD/Fs in ambient air in different areas of Vietnam and their possible sources, atmospheric samples were collected from three areas namely Son La (rural area) and Da Nang (harbor - Agent Orange hotspot area), and Ho Chi Minh City (metropolitan - industrial city). Vapor and solid phases of PCDD/Fs were collected and analyzed following the TO-9A sampling method. Principal Component Analysis and Positive Matrix Factorization model were applied to characterize the possible source. The average concentrations of PCDD/Fs were found to be 21.3 ± 13 fg I-TEQ/m3 in Son La (n = 32), 65.2 ± 34 fg I-TEQ/m3 in Da Nang (n = 16) and 139 ± 84 fg I-TEQ/m3 in Ho Chi Minh City (n = 8). The findings of this study targeted open burning (42%) and biomass burning (51%) as the major emission sources of PCDD/Fs in ambient air of Son La, Vietnam. Major possible sources of PCDD/Fs in Da Nang could be transportation activities (64%), however, the other factor (36%) was suspected to be contaminated with 2,3,7,8-TeCDD from Agent Orange. Most of PCDD/Fs emitted in Ho Chi Minh City related to industrial activities (93%).

Characteristics of ammonia gas and fine particulate ammonium from two distinct urban areas: Osaka, Japan, and Ho Chi Minh City, Vietnam.

Continuous and simultaneous measurements of ammonia gas (NH3) and fine particulate ammonium (PM2.5NH4+) were performed in two distinct urban areas: Osaka, Japan, and Ho Chi Minh City (HCMC), Vietnam. Measurements were performed using a new online instrument. Two measurement periods were conducted during February 11-March 12, 2015 (cold period), and July 1-September 14, 2015 (warm period), at the urban site in Osaka, while 17 days of measurements, from May 21 to June 8, 2015, were conducted at the urban site in HCMC. The average NH3 concentration at the HCMC site was much higher than that at the Osaka site. The differences in the NH3 levels between the two cities are a result of their different emission sources. Traffic emission is a significant contributor to the NH3 levels within the urban area in Osaka. Conversely, the contribution of traffic emission to the NH3 levels in the HCMC urban area is negligible. With a population of around 8.5 million people living in the urban area of HCMC, the high NH3 level is due to human sources and poor waste management systems, especially because of the high temperature (30 °C) and dense population of the city (density up to 42,000 inhabitants per km2). In contrast to the NH3 levels, the highest PM2.5NH4+ level occurred during the cold period at the Osaka site, and the average level at this site was higher than that at the HCMC site. The availability of atmospheric acids, low temperature, and high humidity facilitates the formation of ammonium. Our results indicate that NH3 plays a key role in secondary inorganic aerosol formation; therefore, it contributes to a significant amount of PM2.5 at the Osaka site. In contrast, the high levels of PM2.5 observed at the HCMC site are likely from road traffic emission, mainly motorcycles, rather than secondary inorganic aerosol formation.

Air pollution and risk of respiratory and cardiovascular hospitalizations in the most populous city in Vietnam.

Air pollution has become an alarming issue in Vietnam recently; however, there was only one study so far on the effects of ambient air pollution on population health. Our study aimed to investigate the short-term effects of air pollutants including PM10, NO2, SO2, and O3 on respiratory and cardiovascular hospitalizations in Ho Chi Minh City (HCMC), the largest city in Vietnam. Data on hospitalization from the two largest hospitals in HCMC and daily records of PM10, NO2, SO2, O3 and meteorological data were collected from February 2004 to December 2007. A time-series regression analysis with distributed lag model was applied for data analysis. Changes in levels of NO2 and PM10 were strongly associated with hospital admissions for both respiratory and cardiovascular diseases (CVD); whereas levels of SO2 were only moderately associated with respiratory and CVD hospital admissions and O3 concentration was not associated with any of them. For a 10µg/m(3) increase of each air pollutant, the risk of respiratory admissions increased from 0.7% to 8% while the risk of CVD admissions increased from 0.5% to 4%. Females were found to be more sensitive than males to exposure to air pollutants in regard to respiratory diseases. In regard to CVD, females (RR, 1.04, 95% CI, 1.01-1.07) had a slightly higher risk of admissions than males (RR, 1.03, 95% CI, 1-1.06) to exposure to NO2. In contrast, males (RR, 1.007, 95%CI, 1-1.01) had a higher risk of admission than females (RR, 1.004, 95%CI, 1.001-1.007) to exposure to PM10. People in the age group of 5-65year-olds had a slightly higher risk of admissions caused by air pollutants than the elderly (65+years old) except for a significant effect of PM10 on the risk of cardiovascular admissions was found for the elderly only.

Comparison of particle-phase polycyclic aromatic hydrocarbons and their variability causes in the ambient air in Ho Chi Minh City, Vietnam and in Osaka, Japan, during 2005-2006.

A comparative study of polycyclic aromatic hydrocarbons (PAHs) associated with particulate matter (TSP) in the ambient air in an urban area in Ho Chi Minh City, Vietnam and in Osaka, Japan was carried out from 2005 to 2006. The objective of this study was to investigate the environmental levels, emission sources, seasonal variations and health risk of eleven PAHs in the two cities, especially Ho Chi Minh City where air pollution is becoming a serious concern. The results showed that the concentrations of TSP and total PAHs were significantly higher in Ho Chi Minh City than levels in Osaka. The concentrations of 5- and 6-ring PAHs (BeP, BbF, BkF, BaP, BghiP and InP) were much higher in TSP samples in Ho Chi Minh City than in Osaka, accounting for 82% and 51% of total PAHs, respectively. These PAHs are known to be highly carcinogenic and mutagenic in humans. Vehicular emission is suggested as one of the main pollution sources of PAHs in both cities. Motorcycles and gasoline automobiles are suggested as the main emission sources of PAHs in Ho Chi Minh City, whereas diesel automobiles are the primary source in Osaka. Seasonal variations of PAHs were observed in this study; higher concentrations of PAHs were found in the rainy season (May-December) and lower concentrations corresponded to the dry season (February-April) in Ho Chi Minh City, while higher concentrations of PAHs were observed in the winter (November-January) in Osaka. The number of sunshine hours was an important meteorological factor affecting seasonal variations of PAHs in Ho Chi Minh City, while the temperature was a main factor causing the variations of PAHs in Osaka. The high BaP equivalent concentration of 5- and 6-ring PAHs even in the ambient air is an alarming signal for harmfulness to human health and environmental quality in Ho Chi Minh City.