Water Soluble Ionic Species in the Atmospheric Fine Particulate Matters (PM2.5) in a Southeast Asian Mega City (Dhaka, Bangladesh)

Abstract

Atmospheric fine particulate matters (PM2.5) were collected with an Envirotech Instrument (Model APM 550) at the roof of Khundkur Mukarram Hussain Science Building, University of Dhaka, Bangladesh between January and February, 2013. PM2.5 samples were collected on Quartz fiber filters during day and night time. Water soluble ions (sulfate, nitrate, phosphate, chloride, bromide, sodium, potassium and calcium) were analyzed with Ion Chromatography (Model 881, Metrohm Ltd., Switzerland) and Flame photometer (Model PFP7, Jenway, UK). Average PM2.5 mass was 136.1 μg·m−3 during day time and 246.8 μg·m−3 during night time with a total average of 191.4 μg·m−3. Nighttime PM2.5 concentration was about double compared than that of daytime presumable due to the low ambient temperatures with high emissions from heavy duty vehicles. The 24-hour average PM2.5 mass (average of day and night) was about eight times higher than WHO (25.0 μg·m−3) and about three times higher than DoE, Bangladesh (65.0 μg·m−3) limit values. The total average concentrations of sulfate, nitrate, phosphate, bromide, chloride, sodium, potassium and calcium were 5.30, 7.75, 0.62, 0.16, 1.19, 1.30, 8.11, and 3.09 μg·m−3, respectively. The concentrations of the water soluble ions were much higher during nighttime than daytime except nitrate, bromide and potassium. Excellent correlations were observed between sulfate and nitrate, sodium and chloride, bromide and phosphate indicating joint sources of origin. Potassium, sulfate, nitrate and calcium are the most dominant species in PM2.5. Water soluble ionic components in Dhaka contributed about 15% mass of the PM2.5. Ratio analysis showed that sodium and chloride were from mainly sea salt. Potassium has varieties of sources other than biomass burning. Sulfate and nitrate are mainly from fossil fuel origin. This is the first study of the day and night variation of the water soluble ionic species at the fine particulate matters (PM2.5) in Bangladesh.