Influence of monsoonal driving factors on the secondary inorganic aerosol over ambient air in Dhaka

• Main Authors: Norazman, Nur Hidayah, Khan, Md Firoz, Ramanathan, Sharanya, Shah, Syazwani Mustapa Kama, Jani, Siti Jariani Mohd, Joy, Khaled Shaifullah, Islam, Kazi Naimul, Jeba, Farah, Salam, Abdus, Yoshida, Otoha, Kawashima, Hiroto
• Format: Article
• Published: Amer Chemical Soc 2021
• Subjects: QD Chemistry
• Online Access: http://eprints.um.edu.my/34454/
• Institution: Universiti Malaya

Secondary inorganic components significantly contribute to the modification of ambient aerosol properties by forming haze or reducing visibility. This study characterizes the water-soluble components in PM2.5 and explores secondary inorganic aerosol (SIA) over the air in Dhaka, Bangladesh, throughout 2019. PM2.5 samples were collected on a 24 h basis using a high-volume air sampler, and water-soluble inorganic compositions were measured using an ion chromatograph (IC). The observed PM2.5 may pose potential health risks given that their 24 h mean exceeds the ambient air quality guidelines proposed by the World Health Organization (WHO) and the Department of Environment (DoE) of Bangladesh. Among the ions, SO42-, Ca2+, and NO3- were identified as the predominant species that account for 51, 20, and 11% of all soluble components, respectively. The soluble ions in PM2.5 were relatively higher in the summer monsoon (13.26 +/- 6.12 mu g/m(3)), possibly due to a combination of rampant anthropogenic activities and the pre-monsoonal meteorology. Humid summer plays a significant role in increasing the amount of SIA through the liquid-phase oxidation of precursor gases. Therefore, scavenging of ions may potentially occur (23% from the overall mean of ions) during the long rainy monsoon season over Dhaka. The anthropogenic origins of PM2.5, such as transportation, industry, and construction dust, are widely present in natural sources all over Dhaka. Dust was more sensitive to enriched PM(2.5 )than ions from a seawater origin. Excluding winter data, K+ may significantly resuspend from urban dust over Dhaka. The elements and molecular tracer technique reveal that the potential reactive ions (e.g., Cl-, SO42-, and NO3-) were more sensitive to anthropogenic human activities in Dhaka air than to seawater and terrestrial soil. The influence of converting vehicle fleets into compressed natural gas (CNG) run and upgrading kiln technology on increasing SO42- aerosol in Dhaka is yet to be investigated.