Current Status of Fine Particulate Matter (PM2.5) in Vietnam's Most Populous City, Ho Chi Minh City

This paper provides insights into fine particulate matter pollution in the urban atmosphere of Ho Chi Minh City (HCMC), the most populous city in Vietnam Fine particulate matter (PM2.5) samples were collected daily at five exposed sites from March 2017 to March 2018. PK10 data (daily) and real-time PM2.5 (hourly) data were recorded concurrently at a roadside site. Daily particulate pollutant levels (i.e., PM2.5 and PMio) were determined using the gravimetric method using an impact sampler, and real-time PM2.5 data were measured using a continuous monitor. The measured PM2.5 concentrations varied from 10.4 to 110.8 mu g m(-3), with an annual mean of 36.3 +/- 13.7 mu g m(-3). All annual mean concentrations at the exposed sites exceeded the value limits of the Vietnamese standard (25 mu g m(-3)) and World Health Organization air quality guideline (10 mu g m(-3)), indicating high health risk at these sites. Although the sampling sites varied in their exposure levels, they exhibited very strong correlations and low differences in PM2.5 levels. Diurnal variation with a pronounced peak 2 hours after the morning rush hour was observed. This peak is likely attributable to not only primary sources (e.g., traffic-related sources) but also secondary aerosol formation. The urban atmosphere of HCMC was affected by strong local emission sources, as evidenced by the pronounced peak during morning rush hour as well as the significant negative correlation between PM(2.5)and wind speed. In addition, monthly PM2.5 levels exhibited remarkable seasonal variability, with the lowest and highest levels observed during the rainy and dry seasons, respectively. However, elevated PM2.5 levels were observed during the months with heavy rains, highlighting the influence of strong emission sources, likely the biomass burning of rice straw residues in the Mekong Delta area.