Size distribution of airborne particle-bound polycyclic aromatic hydrocarbons during rice straw open burning in Hanoi, Vietnam

Abstract

This study dealt with size distribution of airborne particle-bound polycyclic aromatic hydrocarbons (PAHs) during rice straw open burning (RSOB) and non-RSOB period in Hanoi. Two sampling campaigns for PAHs associated with airborne particles of six different sizes (PM0.1, PM0.1-0.5, PM0.5-1, PM1.0-2.5, PM2.5-10, PM> 10) were conducted at three sampling sites in Hanoi during 2018–2020. The average concentrations of total particle-bound PAHs were higher during RSOB period (11.7 ± 5.3 ng m−3) than during non-RSOB period (10.1 ± 5.4 ng m−3), and concentrations were significantly higher at the near-RSOB site (11.0 ± 4.9 ng m−3) than at the far-RSOB site (7.1 ± 3.4 ng m−3). Of the various PAHs, the average concentration of benz[a]anthracene (BaA) and benzo[a]pyrene (BaP) bound to PM0.1 and PM1-2.5 exhibited the greatest significant difference in between the near- and the far-RSOB site. The size distributions of total PAHs were unimodal with the maximum concentration in accumulation mode at all sampling locations. The four-ring PAHs shifted to slightly larger particles during the RSOB period (1.34–1.5 μm) compared to the non-RSOB period (0.87 μm) or with the distant site (1 μm). The concentrations of 5- and 6-ring PAHs remained stable in smaller particles, peaking at 0.8 μm. Diagnostic ratios implied biomass burning contributes to PAHs emissions in all sampling sites, while vehicular emission are the significant emission source in the far-RSOB site. This result provides a comprehensive understanding of the size distribution of particle-bound PAHs in the air during RSOB, and useful information for the intergrated air quality management in RSOB regions.