Commuter Exposures to In-Transit PM in an Urban City Dominated by Motorcycle: A Case Study in Vietnam

Exposure to in-transit particulate matter (PM) has negatively affected human health but is barely reported in an urban area dominated by motorcycles. This study aimed to investigate the personal exposure and inhaled dose of PM for commuting modes in Ho Chi Minh City (HCMC), Vietnam. To do this, we conducted simultaneously sampled trips between on motorcycle without and with facemasks, car, and bus. Measurements were performed using portable PM monitors across representing routes in HCMC. In total, we conducted 1086 km in length of paired mode trips. The result shows that motorcyclist was exposed to the highest PM concentrations followed by bus and car commuters. A facemask worn by a motorcyclist while riding was consistent in reducing the in-transit PM exposures (e.g., similar to 33-43% lower in PM2.5), and surgical facemask had higher PM removal efficiency than that of cloth facemask (p < 0.01). Ratios (I/O) for PM1 ranged from 0.31 for car/motorcycle to 0.77 for motorcyclecloth facemask/motorcycle, and PM10 tend to have the lowest ratios. However, bus/motorcycle ratios show the opposite trend with the highest ratio obtained for PM10 due to the effect of a stop-and-go pattern during bus trips. Compared to ambient PM2.5 concentration, in-transit PM2.5 concentration on motorcycle has a good correlation with those measured at the urban station. In conclusion, our work suggests that motorcycle should be urgently restricted in megacities (like HCMC) to protect human health. Policy makers should also pay attention to intransit PM exposure in public transport mode for future urban transport planning.