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.