Status of atmospheric particulate matter and black carbon concentration at Ashuganj in Brahmanbaria

ARTICLE INFO Atmospheric particulate matter (PM) samples (both PM10 and PM2.5) were collected simultaneously from Midland Power Company Limited at Ashuganj, in Brahmanbaria to monitor the seasonal fluctuations of particulate matter and black carbon (BC) concentrations from air samples. Total eight samples were collected from January 2016 to December 2017 using two Air Metrics MiniVol samplers and the quantity of PM2.5 and PM10 was detected by weighing the filters before and after exposure. The concentration of PM (PM2.5 and PM10) and BC were analyzed at the laboratory of Chemistry Division, Atomic Energy Centre, Dhaka. The black carbon concentration from both PM2.5 and PM10 samples were also determined by reflectance measurement. The concentrations of PM2.5 varied from 12.2–145 μgm where mean value was 67.09 μgm. The mean concentration of PM10 was 103.64 μgm whereas the concentration ranged from 20.5–220 μgm. The ratios of PM2.5/PM10 fluctuated during different seasons, winter showed higher concentration and summer showed relatively lower concentration for both PM2.5 and PM10. Atmospheric dispersion due to increased wind speeds and wider mixing layer heights are recognized to be responsible for the lower PM concentrations in warmer months. The concentrations of BC in PM2.5 also varied from 2.44–33.4 μgm and BC in PM10 varied from 4.51–57.2 μgm, respectively. The concentrations of particulate matter exceeded the Bangladesh National Ambient Air Quality Standard. Article history: Received: 06 June 2018 Accepted: 11 August 2018


Introduction
Air pollution has become a public health concern in Bangladesh and regarded as one of the major environmental hazards in Bangladesh as well as worldwide.Globally, ambient air pollution caused by industries, cars and trucks and other sources caused 4.2 million deaths.Over 37,000 Bangladeshi peoples die annually from diseases related to air pollution, according to World Health Organization (WHO, 2016).Dhaka's air quality has been ranked as third most polluted in the world according to an air quality data compiled by the World Health Organization for mega cities with a population of 14 million or more (WHO, 2016).Atmospheric PM is of great concern to the public and to government agencies because of its significant impact on human health, visibility reduction, agriculture and atmospheric chemistry.Atmospheric PM is generally defined as a mixture of solid and/or liquid particles that remains individually dispersed in the air (Begum et al. 2012).Atmospheric PM ranges in size from a few nanometers to tens of micrometers (µm) in diameter (Seinfeld and Pandis, 2006).Commonly used indicators describing PM that are relevant to health refer to the mass concentration of particles with a diameter of less than 10 µm (PM 10 ) and of particles with a diameter of less than 2.5 µm (PM 2.5 ).
These particles are dominated by sulfates, nitrates, organic carbon (OC) and elemental carbon (EC).BC is a sooty black material and also product of incomplete combustion of fuels, emitted from traffic, industry and the burning of fossil fuels and biomass.BC is one of the constituents of fine PM (PM 2.5 ) which scatters and absorbs solar radiation entering the Earth's atmosphere.It is the component of airborne PM which mostly absorbs light and is viewed as a major contributor to climate change (Bond et al., 2013).PM 10 and PM 2.5 include inhalable particles that are small enough to penetrate the thoracic region of the respiratory system.PM 2.5 can travel deep into the lungs and become lodged there.Several epidemiological studies have shown that long-term exposure to PM for years is directly associated with mortality, mainly due to cardiovascular and respiratory diseases (Habre et al., 2014;Madrigano et al., 2013).Previous studies have indicated that the severe PM 2.5 pollution resulted in more than 3 million premature deaths around the world in the year of 2010 (Lim et al., 2012).From the above discussion, it was observed that although particulate matter has significant impact on human health, very limited work have been conducted upon it.Considering PM, most of the researches focused only in urban background (Hasan et al., 2016;Begum et al., 2015) and traffic areas (Jahida et al., 2014and Begum et al., 2012, 2008) whereas research related to PM focusing on Power Company limited has not been well reported so far.Therefore, this study was carried out to i) observe the PM concentration in midland power company Ltd. at Ashuganj, in Brahmanbaria and to ii) determine BC concentration within the atmospheric PM.

Sampling Location and Duration
Midland Power Company Limited is a 50 MW heavy fuel based Power Plant Company situated at Ashuganj, Brahmanbaria.Two PM samplers (One for PM 10 and other for PM 2.5 ) were set up in the north-corner of the plant (latitude 24°1'42.26"N;and longitude 90°59'17.22"E).In Bangladesh, the climate is characterized by high temperature, high humidity most of the year and distinctly marked seasonal variation of precipitation.According to meteorological condition, the year can be divided into four seasons, pre-monsoon (March-May), monsoon (June-September), postmonsoon (October-November) and winter (December-February) (Salam et al., 2003).Therefore, collected data considering the four seasons (Table 1).

Results and Discussion
Concentration of PM 10 and PM 2.5 The statistics of PM and BC concentrations during the sampling periods is given in Table 2.At the power plant site, PM 10 concentration in December is higher than the concentration of other months between the two sampling years 2016-2017 whereas PM 2.5 concentrations found higher in January as compared to other months (Fig. 1).During winter, the daily PM 2.5 and PM 10 concentrations were higher than the 24-h average Bangladesh National Ambient Air Quality Standard (BNAAQS), which were set at 65 and 150 (µgm −3 ), respectively (Table 3).Haque et al. (2015) conducted an experiment in Dhaka and found that the concentration of PM 10 and PM 2.5 was 428.49µgm -3 and 246.5 µgm −3 , respectively.Twenty four hour mean PM 2.5 concentration during the winter in Dhaka was 322 ± 69 µgm −3 in the traffic hotspot site and 254 ± 57 µgm −3 in the residential site whereas during the monsoon, 24-hr mean PM 2.5 mass in the Dhaka residential area was 57 ± 15 µgm −3 (Jacqueline, 2012).During monsoon the PM levels were found lowest at sampling site (PM 2.5 -45 µgm −3 and PM 10 -78 µgm −3 ).
Observed lower PM concentrations are due to washout of particles by rainfall.The winter season is characterized by dry soil conditions, low relative humidity, scanty rainfall and low northwesterly winds.The low wind speed and temperature in winter favors the accumulation of pollutants, while the high temperature in summer favors air convection and the dispersion of pollutants.Atmospheric dispersion due to increased wind speeds and wider mixing layer heights are recognized to be responsible for the lower PM concentrations in warmer months (Pecorari et al., 2013;Khan et al., 2016).Actually, the Air Quality Guidelines (AQGs) set by the World Health Organization are stricter than the EU air quality standards (Table .3).The AQGs set the limit value for PM 2.5 at 10 µgm -3 annual mean and 25 µgm -3 24-h mean, while the limit values for PM 10 is 20 µgm -3 annual mean and 50 µgm -3 24-h mean.These values are considered acceptable and achievable objectives to minimize adverse effects on human health.

Concentration of Black Carbon
BC is produced during incomplete burning.Fig. 2 shows the concentrations of BC in PM 10 and PM 2.5 fractions.The BC concentration is determined both in the fine and coarse fraction of the collected PM.
Between the years 2016 and 2017, the maximum concentration of BC in PM 10 found in December 2016 and minimum concentration found in September 2016.
The highest concentration of BC in PM 2.5 was 33.4 µgm −3 in January and the lowest was 2.44 µgm −3 in October.From the Figure it can be clearly said that PM concentration is predominantly higher in winter season and it gradually reduced in rainy season.The ratio of BC in PM 2.5 /PM 2.5 also showed higher concentration in winter (0.26 µgm −3 in December, 2017) may be due to lower relative humidity and lower wind speed in winter.This result is comparable to the work conducted by Jahida et al. (2014).

Ratio of PM 2.5 /PM 10
The calculated ratio of PM 2.5 /PM 10 gives an idea about the sources of the particulate pollution in the atmospheric air.The calculated ratio of PM 2.5 /PM 10 has been shown in Fig. 3.The ratio of PM 2.5 /PM 10 ranged between 0.35 to 0.89 µgm -3 with a mean value of 0.62 µgm -3 .From the ratio, it examined that about 62% of PM 10 is PM 2.5 .It was also observed that about 61% of PM 2.5 is black carbon.
From the Figure, it is obvious that the ratio is higher in winter compared to summer indicate that fine particles comprise a large fraction in PM 10.The reasons for high peak in concentration during the winter are influenced by seasonal fluctuation of emissions but also by meteorological effects (Islam et al., 2014).Higher ratios (>0.48) are generally associated with the emissions from combustion processes (such as 0.95 for vehicle exhausts) whereas smaller ratios (0.28<) indicating that a higher proportion of the emitted PM mass in the coarse mode and are associated with the emissions from more mechanical, non-combustion sources such as mining, quarrying and agriculture (Munir, 2017;AQEG, 2012).

Conclusion
In this paper the seasonal variation of atmospheric PM 2.5 and PM 10 and the concentration of black carbon during the recent two years (2016-2017) were analyzed from Midland Power Company Ltd. using Air Metrics MiniVol sampler.The quantity of PM 2.5 and PM 10 was detected by weighing the filters before and after exposure whereas, the black carbon concentration was determined by reflectance measurement using an EELtype Smoke Stain Reflect meter.Result showed that the concentration of PM 10 ranged between 20.5-220 µgm −3 where mean value was 103.64 µgm −3 and for PM 2.5 , the ranges vary between 12.2-145 µgm −3 whereas, mean value was 67.09 µgm −3 .Considering the concentration of particulate matter, it could be concluded that these values exceeded the Bangladesh National Ambient Air Quality Standard.Result also showed that the ratio of PM 2.5 /PM 10 ranged between 0.32-0.88whereas, the mean value was 0.62 µgm −3 which indicates that the most of the particles are form the fine fractions and are generally associated with the emissions from combustion processes.The ratio of BC in PM 2.5 /PM 2.5 fluctuated between 0.20 µgm −3 to 0.26 µgm −3 whereas, mean value was 0.23 µgm −3 that indicated BC highly contribute to increasing PM concentration in these sampling site.It can also be seen that there is a change in BC concentration in the ambient air over the period.

Fig. 2 .Fig. 3 .
Fig. 2. The variation of daily average value of BC in PM 10 and PM 2.5 respectively, from January 11, 2016 to December 30, 2017

Table 2 . Summary statistics of PM 10 , PM 2.5 , BC concentrations during the sampling periods
Fig. 1.Variation of the daily average value of PM 10 and PM 2.5 from January 11, 2016 to December 30, 2017