Air pollution poses worlds most serious environmental health threats towards people and their properties (Hoque et al., 2020; Mukta et al., 2020). Other environmental implications of air pollutants include global warming, acid rain, and effects on wildlife (Gauderman et al., 2004; Jansen et al., 2005; Epton et al., 2008). The principal air pollutants of concern are ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO), sulfur dioxide (SO2), methane (CH4), chlorine (Cl2), and particulates (PM2.5 and PM10), which are emitting due combustion of fossil fuels as well as biomass burning (Dianat et al., 2016; Khaefi et al., 2017; Hoque at al., 2020). Air pollution is a pressing issue for Bangladesh, which ranks 169th (out of 178 countries) at the Environmental Performance Index for Air Quality (APT, 2016). Here, main sources of air pollution include emission from faulty vehicles, especially diesel run vehicles, brick kilns and dust from roads and construction sites and toxic fumes from industries (Hoque et al., 2020; Mukta et al., 2020). According to the Department of Environment (DoE), the density of airborne particulate matter (PM) reaches 463 micrograms per cubic meter (µg/m3) in Dhaka city during the dry season (Dec-ember-March), which is the highest level in the world (Air Pollution Reduction Strategy for Bangla-desh, Final Report, 2012). Although, World Health Organization (WHO) air quality guidelines (2006) recommend a maximum acceptable PM level of 20 µg/m3, whereas cities with 70 µg/m3 are considered as highly polluted.

Poor ambient air quality is instigating damage to human health, agricultural production and materials (Mukta et al., 2020; Hoque et al., 2022b).  So, it is high time to create awareness and motivation about air pollution management and control all over Bangladesh. However, in different times air pollution issues have been considered, and often guided by the multinational agencies like the World Bank (WB), Asian Development Bank (ADB), United Nations Environment Program (UNEP), which have taken measures or have made schemes to minimize and limit air pollution. However, the Department of Environment (DoE), the Government agency funded with conserving the environment in Bangladesh, sought plans to create a policy which will reduce air pollution in Bangladesh under the framework of the Male declaration to regulate and avoidance of air pollution and its possible trans-boundary consequences for South Asia (Air Pollution Reduction Strategy for Bangladesh, Final Report, 2012). 

Air pollution is a major anthropogenic environmental concern that has recently gained prominence among all environmental issues in Bangladesh. According to a World Bank report, the economic cost of pollution of air in healthcare sector of Bangladesh alone is estimated annually as U.S. $132-583 for Dhaka city and U.S. $200-800 for the four biggest cities in Bangladesh, which contributes 0.7-3.0% of the countrys per year GDP (C. Brandon, Economic valuation of pollution of water and air in Bangla-desh: World Bank Workshop negotiations draft, 1997). Moreover, a 20 percent cutback from the current level of PM10 in Dhaka would save health costs of around 169-492 million annually (World Bank, 2006). In addition, among the megacities of the world, Dhaka leads the rankings, having 7000/yr cardiovascular mortality and 2100/yr excess cases of hospital admissions for COPD (Chronic Obstructive Pulmonary Disease) attributable to air pollution (Azkar et al., 2012; Gurjar et al., 2010).

Objectives of the study 

This study was conducted to satisfy the following objectives:

1)To find out the concentration level of CO, CO2, NO2, SO2, Cl2, CH4, PM2.5 and PM10 at the ambient air of Narsingdi Sadar. 

2)To show the spatial distribution of these pollutants by using Geographical Information System (GIS). 

3)To calculate AQI (Air Quality Index) for the study area.

Study area

Narsingdi is a district in central Bangladesh. It is situated north-east of Dhaka, capital  of Bangladesh. It belongs to the division of Dhaka. The district is renowned for its synthetic textile industry. The study was conducted in fifteen areas of Narsingdi Sadar (23°558.79"N and 90°433.80"E) of Dhaka division including Velanagar, Railway Station, Boro Bazar, Ghoradia, Brahmondi, Shaheprotap, Launch Ter-minal, Satirpara, Bus Terminal, Silmandi, Gangpar Bridge, Panchdona, Shekherchar, Madhabdi and Anondi.

Figure 1. Map of study area with sampling locations

Data collection 

The study was conducted from fifteen different locations of Narsingdi Sadar. The research was based on primary air quality data under the direct supervision of a supervisor. Primary data were collected by Aeroqual S500 (New Zealand), a portable air quality monitor during September 2022.

AQI calculation

In our study AQI is calculated by using following formula:

Here,

I: AQI (Air Quality Index)

C: the pollutant concentration

C low: the concentration breakpoint that is ≤ C

 C high: the concentration breakpoint that is ≥ C

 I low: the breakpoint Index narrating to C low 

I high: the breakpoint Index narrating to C high 

C low, C high, I low, I high are from the US EPA Pollutant Breakpoint.

Table 1: The US EPA pollutant breakpoint for calculating AQI.

Spatial distribution of PM2.5 in the study area

As shown in Table 2, the concentration of PM2.5 ranged from 16-58 µg/m3, average is 31.55µg/m3. However, this value is lower than the Nanjing, China 65.36 µg/m3 (Hasnain et al., 2021), Dhaka 77 µg/m3 (Khuda K.E., 2020) and Delhi 182.49 µg/m3 (Sethi et al., 2020) and higher than the previous study of Chittagong 21.2 µg/m3 (Hoque et al., 2022a). However, the spatial expansion of PM2.5 showed that the highest value of PM2.5 was observed 58 µg/m3 in Boro Bazar (Fig. 3). The sources of PM2.5 of this area may be associated with fossil fuel burning vehicles, road side construction and public gathering.

Table 2: Concentration of air pollutants in the study area.

Fig. 3: Spatial distribution of PM2.5 in the study area.

Spatial distribution of PM10 in the study area

As displayed in Table 2, concentration of PM10 ranged from 19-165 µg/m3, average 61 µg/m3. Interestingly, this value is lower than the Nanjing, China 102.75 µg/m3 (Hasnain et al., 2021), Dhaka 65.5 µg/m3 (Khuda K.E., 2020), Delhi 299.78 µg/m3 (Sethi et al., 2020) and higher than the previous study of Chittagong 57.3 µg/m3 (Hoque et al., 2022a). However, the spatial expansion of PM10 showed that the highest value of PM10 observed 165 µg/m3 in Anandi (Fig. 4). The sources of PM10 of this area may be associated with roadside construction, waste burning, dust from open land and grinding operation.distribution of CO in the study area

As demonstrated in Table 2, concentration of CO ranged from 0.0-1.7 ppm (avg. 0.22 ppm). In comparison, this value is lower than Nanjing, China 0.89 ppm (Hasnain et al., 2021), Dhaka 1.8 ppm (Khuda K.E., 2020), Delhi 2.51 ppm (Sethi et al., 2020) and Chittagong 1.2 ppm (Hoque et al., 2022a) of the previous study. However, the spatial expansion of CO showed that the highest value of CO observed in Shaheprotap of the study area (Fig. 5). The sources of CO of that area may be associated with incomeplate combustion of vehicular emission.

Fig. 4: Spatial distribution of PM10 in the study area.

Spatial distribution of NO2 in the study area

As given in Table 2, concentration of NO2 ranged from 5.72-5.75 ppm (avg. 5.74 ppm). Regrettably, this value is higher than the Nanjing, China 0.03 ppm (Hasnain et al., 2021), Dhaka 0.08 ppm (Khuda K.E., 2020), Delhi 0.06045 ppm (Sethi et al., 2020) and Chittagong 0.0244 ppm (Hoque et al., 2022a) of the previous study. However, the spatial distribution of NO2 showed that the highest value of NO2 observed 5.75 ppm in Bus Terminal (Fig. 6). The Spatial distribution of SO2 in the study area

As given in Table 2, concentration of SO2 ranged from 0.0-0.1 ppm (avg. 0.046 ppm). In comparison, concentration of SO2 is higher than Nanjing of China 0.005 ppm (Hasnain et al., 2021), Dhaka 0.016 ppm (Khuda K.E., 2020), Delhi 0.010 ppm (Sethi et al., 2020) and Chittagong 0.013 ppm (Hoque et al., 2022a) of the previous study. Fig. 7 showed the spatial of SO2 in the study area. As observed in Fig. 7, the highest value of SO2 observed 0.1 ppm in Madhabdi followed by Anandi, Gangpar Bridge, Silmandi, Launch Terminal, Railway Station and Brahmondi. The sources of SO2 of those areas may be associated with burning of sulfur containing fuels by locomotives, ships and motor vehicles.

Fig. 5: Spatial distribution of CO in the study area.

Fig. 6: Spatial distribution of NO2 in the study area.

Spatial distribution of CO2 in the study area

As displayed in Table 2, concentration of CO2 ranged from 571-693 ppm (avg. 614.93 ppm). However, the spatial distribution of CO2 showed that the highest value of CO2 observed 693 ppm in Railway Station. The sources of CO2 of that area may be associated with deforestation, land clearing for infrastructure, and degradation of soils.

Fig. 7: Spatial distribution of SO2 in the study area.

Spatial distribution of CH4 in the study area

As given in Table 2, concentration of CH4 ranged from 8-37 ppm (avg. 15.8 ppm). However, the spatial distribution of CH4 showed that the highest value of CH4 observed 37 ppm in Railway Station followed by Boro Bazar (20 ppm), Goradia (20 ppm), Bhramondi (19 ppm), Shaheprotam (18 ppm), Silmandi (15 ppm), Velanagar (15 ppm), Bus Terminal (14 ppm), Launch Terminal (13 ppm), Gang-par Bridge (13 ppm), Satipara (12 ppm), Pachonda (12 ppm), Madhabdi (11 ppm), Shekherchar (10 ppm), Anandi (8 ppm) (Fig. 9). The sources of CH4 of the study area may be associated with organic waste decomposition at the surrounding area of the Railway Station.

Fig. 8: Spatial distribution of CO2 in the study area.

As given in Table 2, concentration of Cl2 ranged from 0.02-0.04 ppm (avg. 0.028 ppm). Fig. 9 the spatial distribution of Cl2 in the study area. As shown in Fig. 9, that the highest value of Cl2 observed as 0.04 ppm in Anandi followed by Boro Bazar (0.03 ppm), Goradia (0.03 ppm), Shaheprotap (0.03 ppm), Velanagar (0.03 ppm), Launch Terminal (0.03 ppm), Gangpar Bridge (0.03 ppm), Madhabdi (0.03 ppm), Railway station (0.02 ppm),  Bhramondi (0.02 ppm), Silmandi (0.02 ppm), Bus Terminal (0.02 ppm), Satipara (12 ppm), Pachonda (0.02 ppm), Shekherchar (0.04 ppm) (Fig.  9). Sources of Cl2 of those areas may be associated with textile and dying industry, cooling hot water, bleaching activities and photochemical oxidation of different types of air pollutants. For workers who use Cl2, the U.S. Occupational Safety and Hazard Administration (OSHA) regulates the level of Cl2 in workplace air for safety. OSHA has set a permissible exposure limit (PEL) for Cl2 at 0.1 ppm. Fortunately, the highest value of Cl2 0.04 ppm in this study is lower than the OSHAs permissible limit 0.1 ppm.

Spatial distribution of CH4 in the study area

As given in Table 2, the concentration of CH4 ranged from 8-37 ppm (avg. 15.8 ppm). However, the spatial distribution of CH4 showed that the highest value of CH4 observed 37 ppm in Railway Station followed by Boro Bazar (20 ppm), Goradia (20 ppm), Bhramondi (19 ppm), Shaheprotam (18 ppm), Silmandi (15 ppm), Velanagar (15 ppm), Bus Terminal (14 ppm), Launch Terminal (13 ppm), Gang-par Bridge (13 ppm), Satipara (12 ppm), Pachonda (12 ppm), Madhabdi (11 ppm), Shekherchar (10 ppm), Anandi (8 ppm) (Fig. 9). The sources of CH4 of the study area may be associated with organic waste decomposition at the surrounding area of the Railway Station.

Fig. 9: Spatial distribution of CH4 in the study area.

As given in Table 2, concentration of Cl2 ranged from 0.02-0.04 ppm (avg. 0.028 ppm). Fig. 9 the spatial distribution of Cl2 in the study area. As shown in Fig. 9, that the highest value of Cl2 observed as 0.04 ppm in Anandi followed by Boro Bazar (0.03 ppm), Goradia (0.03 ppm), Shaheprotap (0.03 ppm), Velanagar (0.03 ppm), Launch Terminal (0.03 ppm), Gangpar Bridge (0.03 ppm), Madhabdi (0.03 ppm), Railway station (0.02 ppm),  Bhramondi (0.02 ppm), Silmandi (0.02 ppm), Bus Terminal (0.02 ppm), Satipara (12 ppm), Pachonda (0.02 ppm), Shekherchar (0.04 ppm) (Fig.  9). Sources of Cl2 of those areas may be associated with textile and dying industry, cooling hot water, bleaching activities and photochemical oxidation of different types of air pollutants. For workers who use Cl2, the U.S. Occupational Safety and Hazard Administration (OSHA) regulates the level of Cl2 in workplace air for safety. OSHA has set a permissible exposure limit (PEL) for Cl2 at 0.1 ppm. Fortunately, the highest value of Cl2 0.04 ppm in this study is lower than the OSHAs permissible limit 0.1 ppm.

Fig. 10: Spatial distribution of CH4 in the study area.

Calculation of AQI value of the study area

Table 3: Comparison of measuring air pollutants data with previous study.

The study measured the AQI values of the different locations of the study area based on PM2.5 concentration. Among all the study locations, this study found out that the highest AQI value 152 was observed in the Boro Bazar of the study area followed by Bus Terminal (129), Gangpar Bridge (117), Anandi (112), Ghoradia (102), Brahmondi (89), Panchdona (84), Satirpara (83), Shaherpotap (82), Silmandi (80), Railway Station (78), Madhabdi (78), Shek-her char (76), Launch Terminal (76), Velanagar (59). In this study measured AQI value of the study area were compared with published AQI value of US consulate (website aqicn.org/city/bd) and were very much comparable to the US consulate published data (Table 4).

Table 4: Comparison of calculated AQI value of the study area with published data.

According to AQI categories and colors, corresponding index values and cautionary statements for different levels of health concern, we have categorized every site of the study area based on air quality (Table 5). Launch Terminal, Satirpara, Panchdona, Shek-her char and Madhabdi are in moderate condition, where air quality is acceptable during the study conducted. However, there may be danger for people who are unusually sensitive to air pollution. Whereas, air quality of Boro Bazar, Ghoradia, Bus Terminal, Silmandi, Gangpar Bridge and Anandi are in unhealthy condition to the sensitive groups. Where peoples of sensitive categories may be experienced health effect, but general public are may not be affected.

Table 5: Air Quality Index and health concern of the study area.

As given in Table 5, air pollution of Velanagr, Railway Sation, Brahmondi, Shaheprotap

In this study, we measured concentration of major gaseous air pollutants (CO, CO2, NO2, SO2, Cl2 and CH4) and particulate matter (PM2.5 and PM10) by a portable sensory based air quality monitoring device (Aeroqual series 500). Average concentrations of air pollutants were as follows: CO (0.22 ppm), CO2 (614.93 ppm), NO2 (5.74 ppm), SO2 (0.0467 ppm), CH4 (15.8 ppm), Cl2 (0.30 ppm), PM2.5 (31.55 µg/m3) and PM10 (61 in µg/m3). The highest peak of CH4 was (37 ppm) measured in railway station. Whereas, highest concentration of Cl2 (0.30 ppm) was measured in Anandi. Interestingly, two waste dumping site were identified in the same study locations where highest CH4 and Cl2 were detected during the study. Average concentration of SO2 was measured 0.50 ppm, which is higher than those of Nanjing, Chaina and Dhaka. Extended concentration of SO2 emission in the study area maybe associated with sulfur containing coal burning in the brick field. The AQI values indicates that air pollution status in Velanagr, Railway Sation, Brahmondi, Shaheprotap, Launch Terminal, Satirpara, Panch-dona, Shekherchar and Madhabdi were in moderate condition where air quality is acceptable. Whereas, air quality status of Boro Bazar, Ghoradia, Bus Terminal, Silmandi, Gangpar Bridge and Anandi were unhealthy for sensitive communities of people.

The authors acknowledge the Research center of Mawlana Bhashani Science and Technology Univer-sity, Tangail, Bangladesh for their financial contri-bution to accomplish the research.

All the authors of this manuscript agreed that they have no confliction to make the manuscript publish-able.