Abstract
Introduction: Continuous monitoring provides real-time data which is helpful for measuring air quality; however, these systems are often very expensive, especially for developing countries such as Vietnam. The use of low-cost sensors for monitoring air pollution is a new approach in Vietnam and this study assesses the utility of low-cost, light-scattering-based, particulate sensors for measuring PM2.5 concentrations in Ho Chi Minh City.
 Methods: The low-cost sensors were compared with both a Beta attenuation monitor (BAM) reference method and a gravimetric method during the rainy season period of October to December 2018.
 Results: The results showed that there was a very strong correlation between two low-cost sensors (R = 0.97, slope = 1.0), and that the sensor precision varied from 0 to 21.4% with a mean of 3.1%. Both one-minute averaged data and one-hour averaged data showed similar correlations between sensors and BAM (R2 = 0.62 and 0.69, respectively), while 24-hour averaged data showed excellent agreement (R2 = 0.95, slope = 1.05). In addition, we also found a strong correlation between those instruments and a gravimetric method using 24-hour averaged data. A linear regression was used to calibrate the 24-hour averaged sensor data and, once calibrated, the bias dropped to zero.
 Conclusion: These results show that low-cost sensors can be used for daily measurements of PM2.5 concentrations in Ho Chi Minh City. The effect of air conditions, such as temperature and humidity, should be conducted. Moreover, technical methods to improve time resolution of lowcost sensors need to be developed and applied in order to provide real-time measurements at an inexpensive cost.
Highlights
Continuous monitoring provides real-time data which is helpful for measuring air quality; these systems are often very expensive, especially for developing countries such as Vietnam
Sensor precision was calculated via the coefficient of variation (CV) of the raw outputs: CV = Cs/Cm, and with acceptable CV values being smaller than 10% 7
These results suggest that the two low-cost sensors can be treated when monitoring PM2.5 concentrations
Summary
Continuous monitoring provides real-time data which is helpful for measuring air quality; these systems are often very expensive, especially for developing countries such as Vietnam. The use of low-cost sensors for monitoring air pollution is a new approach in Vietnam and this study assesses the utility of low-cost, light-scattering-based, particulate sensors for measuring PM2.5 concentrations in Ho Chi Minh City. There are a variety of methods used for determining the concentration of particles in the atmosphere Both gravimetric and continuous methods 2,3 such as impactors (gravimetric method), tapered element oscillating microbalances and beta attenuation monitors are widely used, while instruments such as the DustTrak and SidePak use light scattering to obtain particle mass concentrations. These methods are often time-consuming or expensive, especially for continuous monitoring devices
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