Impact of rice straw open burning on local air quality in the Mekong Delta of Vietnam

Abstract

This study aims to investigate the characteristics of air pollutants emitted from rice straw open burning (RSOB) and their impacts on local air quality in the Mekong Delta. Field experiments were conducted for the winter-spring rice crops in 2018 and 2019 at thirteen different locations of four provinces representing for this area. Particulate matter (PM_2.5, PM₁₀ and TSP), PAHs, VOCs and primary gaseous pollutants (CO₂, SO₂ and NO₂) were investigated. It was observed that PM_2.5 is the major part of PM emission during RSOB. 16 US. EPA-listed particle-bound PAHs were quantified. Their total concentrations during RSOB in Vinh Long and Can Tho were 2750 ± 225 ng m⁻³ and 2867 ± 497 ng m⁻³ for TSP; 2402 ± 322 ng m⁻³ and 2583 ± 586 ng m⁻³ for PM₁₀, which are 809 times and 974 times higher than those in the background for TSP and PM₁₀, respectively. The proportion of PAHs in PM₁₀ is higher than that in TSP. The contents of individual PAHs in PM during RSOB increased significantly, especially the carcinogenic PAHs group increased from 21% to 33% compared to the background. These results reconfirm the ratios Fth/(Fth + Pyr), B[a]P/B[k]F and B[a]P/ $\sum 9\text{ PAHs}$ as diagnostic ratios to identify PAHs from RSOB. 10 VOCs including BTEX and halogenated compounds emitted from RSOB were determined. BTEX group was the most dominant, accounting for 73% of the total VOCs. The findings of this study are very important for further studies on RSOB for integrated air quality management in the region.