Marine influence on chemical composition of aerosol in Thailand

Abstract

This study was focused on atmospheric aerosols covering aerosols over both continent and ocean. Continent’s aerosols were collected from two coastal cities, Bangkok and Chonburi, and one in-land city, Chiangrai. To investigate seasonal variation and air-sea-land influences on chemical composition of aerosols, metals, lead isotope and water-soluble inorganic ions were examined coupled with air mass trajectory analysis. The study was divided into 3 parts. The first part, PM2.5 samples were collected in Bangkok and Chonburi during January 2018 to April 2019. The results revealed the highest PM2.5 concentrations in NE monsoon, and the lowest in SW monsoon. During NE monsoon, Bangkok and Chonburi were influenced by coal combustion emission from China and Vietnam and natural background of crustal soil dust. While long-range transport of marine aerosols from Indian Ocean and the Gulf of Thailand (GoT), as well as coal combustion emission, ore processing and road traffic emission played important roles during SW monsoon winds. The chemical composition of PM2.5 during the inter-monsoon winds had similarity with the SW monsoon winds. In the second part, aerosols over Thai waters during SW monsoon (August to October 2018) were collected on board of M.V. SEAFDEC-2 and R.V. Dr. Fridtjof Nansen in the GoT and the Andaman Sea, respectively. For the GoT campaign, PM10-2.5 was also collected. The results indicated composition of both PM10-2.5 and PM2.5 were dominated by sea spray aerosols, especially PM10-2.5. Near-shore aerosols, both PM10-2.5 and PM2.5, have shown signals of the continent sources. Furthermore, these near-shore samples were influenced by anthropogenic activities. For the third part, PM2.5 was collected in Bangkok and Chiangrai during the biomass burning season (January to April 2019). The results indicated that the PM2.5 in Chiangrai was influenced by crustal dust, biomass burning, industrial source and refuse incineration mixed with road dust. While Bangkok aerosols contained natural background, elements mixed with those from industrial emission, coal combustion, traffic emission and sea spray. No long-range transport from forest fire in the north was found reaching Bangkok.