Building and optimising an automatic monitoring system network for outdoor PM_2.5: a case study of Ho Chi Minh City

PM_2.5 exposure data are important for air quality management. Optimal planning and determination of locations where PM_2.5 is continuously monitored are important for urban areas in Ho Chi Minh City (HCMC), a megacity with specific environmental problems. Objectives of the study to propose an automatic monitoring system network (AMSN) to measure outdoor PM_2.5 concentrations in HCMC using low-cost sensors. Data related to the current monitoring network, population, population density, threshold reference standards set by the National Ambient Air Quality Standard (NAAQS) and the World Health Organisation (WHO), and inventory emissions from various sources, both anthropogenic and biogenic, were obtained. Coupled WRF/CMAQ models were used to simulate PM_2.5 concentrations in HCMC. The simulation results were extracted from the grid cells, from which the values of points exceeding the set thresholds were determined. The population coefficient was calculated to determine the corresponding total score (TS). Optimisation of the monitoring locations was statistically performed using Student's t-test to select the official locations for the monitoring network. TS values ranged from 0.0031 to 3215.9. The TS_min value was reached in the Can Gio district and the TS_max value was reached in SG1. Based on the t-test results, 26 initial locations were proposed for a preliminary configuration, from which 10 optimal monitoring sites were selected to develop the AMSN of outdoor PM_2.5 concentration measurements in HCMC towards 2025.