Nitro-polycyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons in particulate matter in an urban area of a tropical region: Ho Chi Minh City, Vietnam

Urban air pollution in many cities of the developing world in Asia, particularly in Vietnam, is increasing significantly. Atmospheric particulate matter pollution is dangerous to the health of millions of people and is a particular concern. In this study, two nitro-polycyclic aromatic hydrocarbons (nitro-PAHs), 1-nitropyrene (1-NP) and 2-nitrofluoranthene (2-NF) and several polycyclic aromatic hydrocarbons (PAHs)—highly carcinogenic and mutagenic compounds—were quantified in particulate matter (PM) collected at three ambient air sites (VNU, ITTE and DOSTE) in an urban area of Ho Chi Minh City, Vietnam, between January 2005 and March 2006. The DOSTE site was close to ground level on a street with a high traffic density. 2-NF was more abundant than 1-NP at all sampling sites. Concentrations of 1-NP and PAHs at the traffic site (DOSTE) were higher than those at the other sites (VNU and ITTE). The daytime/nighttime distribution of 2-NF and the 2-NF/1-NP ratios were used to evaluate the gas-phase formation of 2-NF and its formation route. The average ratios of 2-NF/1-NP at the VNU and ITTE sites were much higher than those at the DOSTE site, suggesting that the gas-phase reactions are an important source of 2-NF in the ambient air. The higher nighttime concentration of 2-NF observed at the VNU and ITTE sites and the converse result observed for the traffic site indicates that an NO3 radical-initiated reaction is the dominant route for 2-NF formation in ambient air, while the majority of 2-NF at the traffic site may be attributed to OH radical-initiated reactions.