4.1 Analysis of land use land cover change
Land use land cover data a regenerated for 1999, 2011 and 2022 with eight classes, namely, built-up area, mining area, vegetation, agricultural land, barren land, river, reservoir/lakes/pond sand river sand (Fig. 4).
It showed a sharp increase of mining area(open-cast) from 1630.53ha to 7943.51 ha (0.93–4.51%) during 1999–2022 period of time (Fig. 5). This was associated with a significant areal increase of built-up areas from 34293.87 ha to 56502.85 ha (19.48–32.08%). A steep fall of vegetation coverage from 23129.01 ha to 11800.78 ha (13.14–6.7%) is also noticed as well as the decrease of agricultural land from 100666.44 ha to 83045.80 ha (57.15–47.15%).
4.2 Analysis of Land Surface Temperature
As per the change analysis of LST in ADDA, the land surface temperature (Fig. 6) is found to gradually increase from 1999 to 2022 in winter months of January- February. The temporal change of land surface temperature is shown to be closely associated with the rapid change land use land cover pattern (Fig. 4). For all the maps, dark red tone depicts the highest Land Surface Temperature and sky blue tone depicts lowest Land Surface Temperature.
In 1999, Sonepur Bazari, Khottadih, and Mohanpur open cast mining areas has shown highest LST value (27⁰C-28⁰C) and its surrounding areas showed LST values around 25⁰C. The Narayankuri, Banshra OC, New Kenda, and parts of BCCL, IISCO Coal field showed medium LST range from 23⁰C to 26⁰C and LST of their surrounding area was 21⁰C respectively. Besides, there were many discontinued OC where work was in disruption, generally had shown LST around 14⁰C.
On the other hand, active mining belts are found to show a rise in temperature in 2011 (around 34˚C). It mainly has shown temperature hot spots over Sonepur Bazari OCP (Open Cast Pit), Gourandi, Gourandi-Begunia, Jambad, Bonjemehari, with LST values ranging from 32⁰C up to 34⁰C where as its surrounding areas has shown an average LST value of 30⁰C.The Mohanpur, Khottadih, New Kenda, Banshra OCP and part of BCCL, IISCO Coal fields have shown LST value from 27⁰C to 32⁰C. The LST of their surrounding areas hovered along 25⁰C. The LST value found to be around 16⁰C in discontinued open cast mines.
This distribution of land surface temperature over the coal mining regions of ADPA has shown more increased value of LST in 2022 than the previous years. The highest temperature retrieved is near about 39˚C.In 2022, the temperature hot spots are found over Gourandi, Gourandi-Begunia, and Sonepur Bazari OCP showing the highest LST from 36⁰C to 38⁰C. The possible cause behind this increase is likely the rapid growth of open cast mine areas. Its surrounding areas has shown LST values of nearly 34⁰C.Besides these prime areas, Mohanpur, Khottadih, Dabor, Bonjemehari, Madhabpur, Jambad, New Kenda, North Searsole OCP, and parts of IISCO, and BCCL Coalfields have shown medium LST ranging from 34⁰C to 36⁰C.The LST of Narayankuri, Nimcha-Amkola,Madhabpur,Dalurbandh,Itapara,Banshra, and Bhanora-West OCP has shown values within the range of 26⁰C to 28⁰C.The high-temperature pixels are also found to be distributed in some non-mining areas, probably due to the presence of industries and built-up areas in the vicinity. Besides, there are many discontinued open cast coal mine where work is in the disruption. The coal mines, which are no longer functioning, has shown a moderate to lower LST values ranging between 16˚C to 19˚C.
Land Surface Temperature was measured by using an infrared thermometer (LASER-GM320) in the field to validate the process of deriving LST values from satellite derived data at the end of February in 2022. According to the field measurements, Land surface temperature is highest at Gourandi-Begunia OCP (42⁰C) and the lowest value is found at Khottadih OCP which is 36⁰C (Fig. 7).
The spatial cross-profiles of LST across the ADPA represents sharp increase of temperature temporally, however the spatial pattern of hotspots is almost static (Fig. 8).
Along the cross profile A-B in 1999 (Fig. 8-B-ab), Mohanpur OCP displays LST value about 23⁰C, which is highest in the line. In 2022, (Fig. 8-B-ab1) Mohanpur OCP of Salanpur colliery area shows highest LST value which is about 26⁰C. The LST of rural and semi urban area in the cross-profile A-B showed a value around 18⁰C to 20⁰C in 1999 which experienced a rise in 2022 by 2⁰C.
Along the cross section C-D, Sripur, Satgram, Kunustoria, Kajora colliery has shown LST value up to 28⁰C in 1999 (Fig. 8-B-cd), which increased to 34⁰C in 2022 (Fig. 8-B-cd1). The LST of urban areas such as Asansol Municipal Corporation, Raniganj Municipality and Kulti Municipality show LST ranging from 20⁰C to 26⁰C and the industrial areas like Durgapur show LST values ranging between 27⁰C to 30⁰C in 2022.
Cross profile E-F represents the LST value of Salanpur coalfield area as26⁰C in 1999(Fig. 8-B-ef), which abruptly rises to38⁰C in 2022 (Fig. 8-B-ef1). Kenda, Kunustoria, Kajora colliery are found to experience LST of nearly 18⁰Cto 22⁰C in 1999 which again, experienced a rise in 2022 by3⁰C. LST of adjacent villages are found to be around 16⁰C in 2022.
Hence, the cross profiles reveal an abrupt increase in LST in the areas where the mining area has increased at least 4.51% from 1999 to 2022 (Fig. 9). Besides the legal mining operations, there are many instances of the unauthorized digging of opencast mines, which is noted during the field visit of the study region. We observed that few parts of LST are spatially decreased from 1999 to 2022, but with respect to, noted that the LST are increased with time in certain location of mine OCPs and most of areas in 2022 (Fig. 8). The most important reason for increasing LST is found to be the coal fire and loading-unloading of the overburden of Opencast mines. Instances of coal fire were documented at Bonjemehari, Ramnagar, Ambad, Sangramgarh [13]. Sonepur Bazari, Khottadih, Churuliya, Kamarkhola, Belbadh, Sitalpur, Khayerbandh, Jamuria, and Dhadka [18]. Sometimes, the heat produced is not dissipated completely due to the poor supply of air in a confined space and thus, increases the land surface temperature. An excessive amount of over burden can also be a possible cause of increasing LST in mining areas.
Though the mining activity may not be the sole contributor for increasing LST over the area, an attempt is made to see the correlation between the overall expansion of the Open-cast mining area in 1999,2011 and 2022 and the changing annual average value of LST for those years. The Pearson correlation coefficient value between them is proved to be very strong with an R2 value of 0.87 (Fig. 9).
4.3 Analysis of Aerosol Optical Depth
Another environmental impact of opencast mining is the change in Aerosol Optical Depth (AOD). AOD indicates the optical clarity of the atmospheric air column, with higher values indicating more scattering and absorption by particles and chemicals in the atmosphere [20]. Hence, the study also has attempted to analyze the impact of extensive opencast mining of the ADPA region on the distribution of AOD. Change of Aerosol Optical Depth has been observed from the period from 2001 to 2022 for the winter season (Fig. 10).
In 2001, the value is found to be higher in urban and industrial areas of Jamuria block, Andal block, and Faridpur-Durgapur block (0.36–0.42). Sonepur Bazari, Khottadih, and Mohanpur OCP however, have shown higher AOD around 0.37. Narayankuri, New Kenda, Banshra OCP have shown comparatively lower AOD (nearly 0.29). Whereas, the AOD of discontinued OCPs has shown values ranging between 0.20 to 0.21.
In 2011, the maximum AOD value in this area is found to be 0.68 (Fig. 10). The value is lower in the western part and higher in the eastern part. The values have reached highest in the urban industrial zones (0.56–0.68). Among all the OCMs, Sonepur Bazari, Khottadih, Banshra, Narayankuri, New Kenda OCP have shown AOD values ranging from 0.60 to 0.68. Mohanpur, Gourandi, Gourandi-Begunia OCP and part of the BCCL coal field have shown comparatively lower AOD (0.56–0.58) and the AOD of discontinued OC lingered around 0.37.
In 2022, these values increased further with a maximum value of 0.85. AOD is found to beat a higher level in the south and south west parts. Though the hotspots are found mostly over the same urban and industrial belts, this time, Sonepur Bazari, Khottadih, New Kenda, North Searsole, Banshra, Nimcha- Amkola, Narayankuri, Madhabpur, Jambad OCM has also shown values as high as 0.78. Madhabpur, Kalipahari, BCCL, Itapara, Mohanpur, Gourandi, Gourandi-Begunia and Bhanora West OCM have shown valuesaround0.71. In 2022, the AOD of Discontinued OCPs has shown values nearly about 0.66 because of the less initiative taken towards the regrowth of the vegetation cover. Sometimes AOD change sits characteristics with the changes in wind directions, wind speed, rainfall, and the amount of water vapour present in the atmosphere.
Figure 11. Correlation between Areal changes of Mines (Ha in %) and Aerosol Optical Depth
Here, the areal increasing trend of the mining area (2001, 2011, 2022) has shown a high positive correlation with the increasing rate of Aerosol Optical Depth with an R2 value of 0.96 (Fig. 11).
4.4 Spatial distribution of Suspended Particular Matter (PM10)
Atmospheric visibility is highly influenced by the quantity of Suspended Particulate Matter (PM10) present in the air. PM10 particles are less than 10 microns in diameter.PM10 data is retrieved from CPCB website (https://cpcb.nic.in/) [31] and therefore spatially distributed through inverse distance weighting (IDW) interpolation method. The point data is fetched for nine stations, over ADDA region. As wind direction and speed plays a major role in the distribution of air pollution, here the analysis also has used these data alongside PM10 distribution. In the year 2011, when the average PM10 of ADPA has shown an average value of 175–271 µg/m3 (Fig. 12), the wind direction was from the south (S), south-south-west (SSW), northwest (NW), and west-north-west (WNW).
In 2020, when the average value of PM10 over ADPA region was 175–271µg/m3, the wind direction was quite same like 2011, only with an additional flow of wind from southwest (SW) direction.
The PM10 values of the year 2011 is found to be ranging from 91 to 271 µg/m3.Satgram OCP, Kunustoria OCP, Asansol Municipality, Durgapur Municipality,Raniganj is found to represent high value of PM10 (179–271µg/m3). whereas SonepurBazari, Kenda,Kajora,Pandaveswar, Jhanjra and Bankola area has shown medium PM10 (156–171µg/m3) value. Salanpur OC and part of the BCCL coalfield area has shown low PM10 (133–153µg/m3) and Kanksa forest area has displayed very low value of PM10 (91–128µg/m3).
In 2020, the highest value of PM10 is found to be 115µg/m3, though the increase in the higher limit was not significant.This time the higher concentration is found to be spread over a large area over the western portion of ADDA region where most of the industries and OCMs were active. Sonepur Bazari, Salanpur, Sripur, Kajora, Kunustoria, Kenda, Satgram, Kunustoria, Kenda, Sodepur, Pandaveswar, Jhanjra were and part of BCCL coal field areas fall sunder the high PM10 zone with values starting from 110 to nearly 115µg/m3. The Kanksa forest area has showing the lowest amount of PM10 like 2011 (100–104µg/m3).
4.5 Spatio-Temporal variation of differentparticulate matter and gaseous pollutants
The most important emissions during coal mining and through active mine fires are generally the particulate matter (PM), sulfur dioxide (SO2), nitrogen dioxide (NO2) and heavy metals. The maximum value of PM10 is found as 151 µg/m3 in February 2019 and the minimum concentration of PM10 was 31 µg/m3 in September 2018 at Asansol during the time period. The maximum concentration of PM10 was 160µg/m3 in December 2018 and the minimum concentration of PM10 was 20 µg/m3 in September 2018 at Durgapur. The permissible limit of PM10 concentration is 100 µg/m3 in a 24 hours of time-weighted average (https://cpcb.nic.in/) [31].The maximum concentration of SO2 was 22 µg/m3 (February 2019) and the minimum concentration of SO2 was 3 µg/m3 (July 2018) at Asansol whereas, the maximum concentration of SO2 was 16 µg/m3 (February 2019) and the minimum concentration of SO2 was 5 µg/m3 (July 2018) at Durgapur. The permissible limit of SO2 concentration is 80 µg/m3 in a 24 hours of time-weighted average (https://cpcb.nic.in/) [31]. The maximum concentration of NO2 was 98 µg/m3 (February 2019) and the minimum concentration ofNO2 was 19 µg/m3 (July 2018) at Asansol. On the other hand, the maximum concentration of NO2 was 80 µg/m3 (February 2019) and the minimum concentration of NO2 was 36 µg/m3. (September 2018) at Durgapur. The permissible limit of NO2 concentration is 80 µg/m3 in a 24 hours of time-weighted average (https://cpcb.nic.in/)[31].
The temporal variation of air pollution is also controlled by the meteorological parameters like wind direction,rainfall,water vapour,relative humidity, and temperature.As both Durgapur and Asansol are located nearby,the meteorological control is almost similar over those two places.Both of the places show a very high level of PM10 and NO2, especially in the winter season.This is possibly a direct effect of the open-air mining activities especially drilling, blasting, over burden loading and unloading,coal loading and unloading, haulroads, transportroads, stockyards, exhausts from heavy earth moving machinery, exposed overburden dumps,exposed pit faces,presence of fire, coal handling plants,crushing of coal to a convenientsize in the feeder breaker etc.
4.6 Relationship between Aerosol Optical Depth (AOD) and PM10
The PM10 and MODIS AOD data are found to be strongly related to each other in ADPA region (Fig. 14). So, AOD can be a good indicator of the near-surface PM10 concentrations in Asansol and Durgapur areas in future studies. The increase in PM10 concentration is found to be always followed by an increase in the AOD value, which is clearly observed in open cast mining areas.
The correlation coefficient of the linear regression between AOD and PM10 shows an R² value of 0.77 which indicates that positive relationship between AOD and PM10 in winter season in Asansol block.
The correlation coefficient between AOD and PM10 shows an R² value of 0.65 in Durgapur region which indicates a strong positive relationship between those two parameters. The dust of coal mines can be the probable cause of increasing the PM10 in ADDA region which in turns has increased the value of AOD over the years.
4.7 Comparison of the concentration of PM10 in Asansol between2019 and 2020 featuring the lockdown period
This research has assessed the air quality changes during pre-lock down and lock down period in Asansol city and tried to evaluate the maximum reduction of Suspended Particulate Matter (PM10) during the COVID-19 lockdown period.
The lockdown period mainly lasted from 24.03.2020 to 31.05.2020. In March 2019, the maximum PM10 in the atmosphere was127µg/m3, which fell down to 94µg/m3 in March2020.InApril2019, the maximum value of PM10in Asansol was223µg/m3andit reduced to 101µg/m3 in the same month in 2020. In May2019, the maximum PM10 concentration was179µg/m3, which reduced to 111µg/m3in May 2020. From the start of June 2020, however, the pollutant concentration again showed a rise with the progression of unlock periods. In the end of the year 2020, the PM10 concentration level nearly became similar with the values from its previous year. ReductionintheconcentrationofPM10in 2020 lockdown period probably happened because of the closure of on-road vehicle emission and industrial activities, and shut down of malls, shops etc. which restricted the public transport. Still, the PM10 values had not reduced significantly in this region compared with the other parts of the country due to the continuous activity in coal-mining regions as coal is the major power source of India [2].
4.8 Effect of Particulate matter on human health in ADDA region
Asansol-Durgapur Development Authority region is one of the most polluted areas in West Bengal due to the coal mining industry, heavy industries, and rapid urbanization. Coal dust is a major risk factor for the health of occupational coal miners [3]. The activities responsible for pollution around coal mine areas are drilling, blasting, coal and overburden loading, exposed overburden dumps, haul roads, transport roads, stock yards, exposed pit faces, presence of fire, exhausts from heavy earth moving machinery [11]. The blocks of Paschim Bardhaman, especially the ADDA region have been suffering from air pollution-induced diseases from a long time.
In the time-frame of 2017-18, it is found that the percentage of respiratory diseases are well related with particulate matter concentration (Fig. 17). Asansol and Faridpur-Durgapur blocks have shown the greatest number of patients suffering from respiratory diseases (66.14% and 28.49% respectively) where the level of PM10 is also higher (195 µg/m3 and 156 µg/m3 respectively). Peng et. al [34] has also found similar results in their study.
The common respiratory diseases that are mostly observed in the locality of Paschim Burdwan are Chronic Obstructive Pulmonary Disease (COPD), asthma, skin infection, eye irritation, chronic colds, and coughs, teeth corrosion, found from the respondents. The majority of them reported the problems of different lung diseases. Children and elder persons are found to be most affected in surrounding areas. This affects people adversely, especially women, including hair loss [35]. As those airborne pollutants also mixes with the water, there is a chance of spreading pneumoconiosis, asbestosis, silicosis, and siderosis disease in the locality [20].