Variation of Ambient Air Quality Scenario in Chittagong City: A Case Study of Air Pollution

Abstract: The ambient air quality data for particulate matter as well as criteria of gaseous pollutants were assembled during December 2013 to December 2015 from the Continuous Air Quality Monitoring Station (CAMS) located at Agrabad, Chittagong. The observation showed that during AprilOctober, 24 hour average concentration of PM10 and PM2.5 were within the National Ambient Air Quality Standard (NAAQS) level but it increased occasionally by more than two and a half times during the whole nonmonsoon period (November-March). The highest values found of PM2.5 were 321.1 μg/m3 in January, 2013 and 220.34 μg/m3 in December 2015. Whether, the highest alarming concentration of PM10 was reported as 474 μg/m3 in January 2007. The other gaseous pollutants such as SO2, NO2, O3, CO and Hydrocarbons remain well within the permissible limit except dry non-monsoon period. The yearly average increase of Air Quality Index (AQI) value indicates the growth rate of air pollution in Chittagong city. The main responsible pollutant for air pollution is found PM2.5.


INTRODUCTION
Chittagong city stands on the right bank of the river Karnaphuly. There are several sources of air pollution in Chittagong city, among them unfit vehicles and industries are notable. The numbers of mostly reconditioned vehicles are increasing in every year. One third of these vehicles do not have any fitness certificate. Due to port facility, this city is attractive for the investors to build up industry. A number of 'Export Processing Zones (EPZ)' has been established by the local and foreign investors (BBS, 2010). Most of the industries are not following the environmental rules and regulations. Along with this many urban areas and shopping and recreational facilities are present within the boundary of the study area considered where human exposure to air pollution caused by vehicular induced turbulence. Though green landscape around Chittagong city and monsoon heavy rainfall helps to reduce the intensity of air pollution, a significant change in land uses and human intervention aggravate the degradation of air quality. The maximum temperature are between 29 °C and 35 °C in monsoon and minimum temperature are between 12 °C and 17 °C in winter. The total annual rainfall throughout the city varies between 2159 mm (85 inches) and 3048 mm (120 inches) rising sometimes to 3810 mm (150 inches). On average approximately 80% of the rainfall occurs during the May to September monsoon. During summer season, winds are generally from the southeast. Easterly and northeasterly winds prevail during the winter periods. The 2011 National census determined that the Chittagong city corporation area had a population of approximately 25,92,439 in approximately 558,097 households.
It is one of the most densely populated cities in the country and facing a high level of air pollution. High influx of people from rural areas, emissions from various kinds of diesel vehicles and badly maintained automobiles, biomass/coal burning for cooking and in the brick kilns, huge number of construction works, re-suspended road dust etc. is making Chittagong as one of the most polluted cities in the country. Not much research has been done on air quality of Chittagong, but the air quality of the city is comparable to capital city Dhaka, where according to a recent World Bank Report, it has been estimated that every year around 10,800 premature deaths along with several million cases of illness are being caused by the air pollution. Norwegian Institute of Air Research (NILU) conducted some research on air quality of Chittagong city.
Atmospheric pollution in urban areas is a major issue in many developing countries around the world. It is well recognized that air pollution has hazardous effects on human health causing respiratory diseases (Dockery andPope 1994, Dockery et al. 1989). Sulfur dioxide (SO2) and nitrogen dioxide (NO2) are important primary pollutants in the ambient air because of their adverse effects on human health and vegetation, their contributions to the acidification of the environment (Legge and Krupa, 1990) and the role of oxides of nitrogen (NO2) in the formation of photochemical oxidants. NO2 contributes to the buildup of tropospheric ozone (O3) and to the lifetime of greenhouse gases (Houghton et al., 1990) and thus be also a key species for global warming. Particulate air pollution can be generated by natural and anthropogenic activities. Anthropogenic sources can be stationary and mobile. It has been estimated in many countries that, traffic-related emissions constitute more than 50% of the total particulate air pollution (Protection, 1996).
Chittagong (latitude 22.22N, longitude 91.47E) has the largest port in Bangladesh, and is heavily trafficked, especially the central city area covering about 10 km2. The main road network in the city goes toward the port area and northward toward the industrial areas. These roads are also heavily trafficked, with persistent traffic jams most of the day. Trucks transporting goods between the port and the industrial areas constitute a significant part of the traffic, and the combination of the hilly nature of the area, the stop and start mode of the congested traffic, and the age and heavy loading of most of the trucks causes large emissions of black diesel smoke. Brick kilns are important source of building materials and pollution. Prior work in Dhaka has suggested a major role for brick kilns in producing air pollution there (Begum et al., 2004). Vehicular emissions, as well as biomass/coal burning for cooking and in the brick kilns around the city, are the main contributor to these emissions (Chaloulakou et al., 1999;Kassomenos et al., 1995). Ambient air quality standards for Bangladesh and WHO guideline shown in Notes: (a) Not to be exceeded more than once per year.
(b) The objective is attained when the annual arithmetic mean is less than or equal to 50 ug/m3. (c) The objective is attained when the expected number of days per calendar year with a 24-hour average of 15 μg/m3 is equal to or less than 1.
(d) The objective is attained when the expected number of days per calendar year with the maximum hourly average of 0.12 ppm is equal to or less than 1.

METHODOLOGY
The ambient air quality monitoring network Bangladesh consists of eleven (11)  Multiple gaseous / PM analyzers as shown in Figure 1 are used for Continuous gaseous monitoring. Gaseous PM analyzers were made by Environment S.A., France. UV Fluorescence was used as SO 2 analyzer; chemiluminescence was used as NO 2 analyzer, while NDIR principle was employed to analyze CO. CH4 and non CH4 were measured by Flame Ionization Detector. Particulate matter was analyzed by Beta Gauge analyzer and O 3 was measured by UV Fluorescence. All instruments were certified by USEPA.
An air quality index (AQI) is a number used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. As the AQI increases, an increasingly large percentage of the population is likely to experience increasingly severe adverse health effects.

Fig1. Air Quality Monitoring Equipment at Agrabad CAMS
The AQI is calculated using the mathematical expression:-

Ip = (Cp -BP Lo ) + I Lo
Where, IP = the index value for pollutant P; = the truncated concentration of pollutant P; = the breakpoint that is≥ ; = the breakpoint that is ≤ ; = the AQI value corresponding to ; = the AQI value corresponding to ;

RESULT & DISCUSSION
From the analysis it is clear that, the concentration of all pollutants are below their respective standard limit ( All the value found of SO2 and NO2 throughout the year 2013-2015 were within the standard limit. Figure 2 and figure 3 represent the maximum, minimum and average concentration of SO2 and NO2. Figure.2: 24 hour average NO 2 at CAMS, Chittagong (monthly average, maximum and minimum) Figure.3: 24 hour average SO 2 at CAMS, Chittagong (monthly average, maximum and minimum) The National Ambient Air Quality Standard for PM 2.5 is 65µg/m3 for 24 hour on average (Table  I) and for annual arithmetic mean the standard is 15 µg/m3. Figure 4 presented   The Daily Air Quality Index (AQI) is calculated for the year 2013-2015 considering six criteria pollutants (NO2, SO2, CO, O3, PM2.5, and PM10). The maximum AQI was found 371 in 10 January 2013 which classify as Hazardous. The responsible pollutants found for air pollution in Chittagong city is PM2.5. In almost all the cases, the concentration of PM 2.5 governed for AQI. The average AQI of the year 2013, 2014 and 2015 is 127, 132 and 133 respectively. This is the indication of increasing air pollution in Chittagong city. Figure 6 to figure 8 represent the daily AQI trend from 2013 to 2015.    The concentration of most responsible pollutants for AQI PM 2.5 considerably decrease in monsoon season, that's why the value of AQI remain below 100 which is categorized according to USEPA as moderate for health impact. The yearly average value of AQI for Chittagong city is above 100 which mean the environmental condition is unhealthy. Figure  The pollutants concentration largely depends on meteorological parameters. When the rainfall and wind speed is high specially in monsoon period the concentration of PM 2.5 slows down. The time series plot of PM 2.5 and metrological parameter presented in Figure 9 to 11, shows temporal (daily) variation of PM 2.5 concentration with the change of intensity of metrological parameter over the sampling period.

CONCLUSION
Chittagong City is experiencing several problems due to air pollution. Though the problem is not too much acute like other busy city but it will face worse condition in upcoming days if proper steps would not been taken. Particulate matter is being identified as the main pollutant of concern. Data from the monitoring station reveals that the pollution from particulate matters greatly varies with climatic conditions. While the concentration level comes down the limit value in the monsoon period (April-October), it goes beyond the limit during nonmonsoon time and sometimes even crosses three times during the non-monsoon period (November-March). The extent of pollution level during non monsoon period was found to be much higher than the standard level indicating alarming threat to the human health.
The highest values found of PM2.5 were 321.1 µg/m 3 in January, 2013 and 220.34 µg/m 3 in December, 2015 while other gaseous pollutants remain within the permissible limit. Emission from vehicles, domestic cooking, brick fields, industries, and building construction material and road dust are the main sources of pollution. It is also necessary to remove all unfit vehicles from the city for improving the air quality. Government should take proper initiative to control air pollution in order to improve health quality of the people of the city.