Temporal variation of SO 2 and NO 2 concentrations around Parichha Thermal Power Plant , India

The present study was based on monthly variation of ambient air pollution in the village located within a radius of 3 km from the Parichhna thermal power plant (Jhansi, India). Parichha thermal power plant consumes annually 3.4 million tons of coal and the annual production capacity of the plant is 2.78 billion KWh. The thermal power plant uses approximately 10,000 tons of coal and emits large amount of air pollutants like fly ash, sulphur dioxide and oxides of nitrogen. Results revealed that the range of gaseous pollutants showed slight variation within the sampling dates during the four months under study. Although the average monthly concentration SO2 (21±2.88 μg/m) and NO2 (44±5.10 μg/m) was within the permissible limits given for industrial and residential areas, however, they are toxic on long term basis both for human health and nearby agricultural fields. The concentration of the SO2 ranged between 17 to 28 μg/m, while the concentration of NO2 ranged between 34 to 51 μg/m, during the study period. It is important to note that the values of the pollutants reported are after all the mitigative measures and preventive control equipments installed and working in the thermal Power plant. It has also been revealed that concentration of both gases was found to be consistently higher in the morning hours (8.00 to 10.00 h) compared to afternoon hours (12.00 to 14.00 h) throughout the study period.


INTRODUCTION
Thermal power plants are major sources of air pollution.Three major air pollutants emitted from these plants are Sulphur dioxide (SO 2 ), Sulphur trioxide (SO 3 ), Oxides of nitrogen (NO 2 , NO 3 ) and Suspended Particulate Matter (SPM).The amount of pollutants emitted from any power plant depends upon the type of the fuel used, burning method and type of control equipment.These pollutants settle in ambient air.Coal is re-emerging as the dominant fuel for power generation in various power plants (Patel and Patel, 2006).In India, coal is the only natural resource and fossil fuel available in abundance for different large and small scale industries.Consequently, it is used widely as fuel for thermal power plants producing electricity and also as a thermal energy source (Mishra, 2004).In India, power generation has increased greatly in recent years to meet the demand of the increasing population (Jamil et al., 2009).The capacity of power generation has increased tremendously from 1362MW in 1947to 147,403 MW in 2008.India has installed capacity for electricity generation to about 90,000 MW, of which more than 70% is produced by coal based thermal power plants.Coal is the only fossil fuel available in abundance; hence its usage will keep growing for another 2 to 3 decades at least, till there is an improvement in renewable energy sources.Availability of coal in India is of poor quality such as petcock, lignite, bituminous etc., used in power plants in which the percentage of sulphur have 6.0, 4.0 and 3.8%, respectively; also with very high ash content and low calorific value.It has been found that metallurgical industry like steel plants use good quality coal but the coal supplied to thermal power plants is of the worst quality.
A number of the coal mines are owned by private companies and they do not wish to invest on quality improvement (Mishra, 2004).The thermal power plants during the combustion of coal emits mainly carbon dioxide (CO 2 ), sulphur oxides (SO x ), nitrogen oxides (NO x ), chlorofluorocarbon (CFC), other trace gases and airborne inorganic particulates such as fly ash and suspended particulate matter.The two important emissions of thermal power plants that have been taken under consideration for the present study are SO x and NO x.

SO x
Sulphur dioxide is one of the main products released from the combustion of sulphur containing compounds in most energy fuels having significant environmental concern.The term SO x is a generic term describing emissions of SO 2 and SO 3 .It is predictable that just about 93% of the global SO 2 emissions are emitted in the northern hemisphere and the left over 7% are emitted in the southern hemisphere (WHO, 1979).The utmost anthropogenic sources of SO 2 consequence is from the burning of fossil fuels and from the smelting sulphide ores (Weil and Sandler, 1997).Presently SO 2 is the main issue pertaining to air pollution problems in developing countries, where it contributes both to urban pollution and to regional acid depositions (Cofala et al., 2004).Among man-made sources, fuel combustion (coal) in stationary sources accounts for 74%, industries 22% and transportation 2% of the total SO x (De, 2012).A significant feature of SO 2 is that once it is emitted into the atmosphere it can be converted through complex oxidation reactions into fine particulate sulfate and removed from the atmosphere by wet or dry deposition (De, 2012;Skinder et al., 2014).SO 2 can be oxidized in the atmosphere to form sulphate aerosols that contribute to acid deposition (Holleman and Wiberg, 2001).Thus elevated level of SO 4 2− concentrations in rain water are due to strong SO 2 emissions from coal fired thermal power plants (Demirak, 2007).Yaseen et al. 7

NO x
This represents composite atmospheric gases, nitric oxide (NO), and nitrogen dioxide (NO 2 ), which are primarily involved in air pollution.Nitric oxide (NO) is a colourless, odourless gas, but NO 2 has a reddish-brown colour and pungent suffocating odour (De, 2012).The formation of NO is favoured at high temperature, usually attained during much combustion process involving air (1210 to 1763°C).The second reaction is also favoured at temperatures of about 1100°C, but the amount of NO 2 formed is usually less than 0.5% of the total NO x at 1100°C.It is also formed by photolytic reaction; further man-made sources annually release 5×10 7 tons of NO x (De, 2012).The NO 2 levels depend mainly on chemical reactions and not on direct emissions (Mayer, 1999).It is considered that coal-fired power plants and vehicles are the nation's largest sources of nitrogen oxides and NO x produced in high temperature combustion processes (Memon, 2000;Emberson et al., 2001;Skinder et al., 2014).NO x is emitted from a variety of natural and anthropogenic sources (Al-Khalaf, 2006).Nitric oxide (NO) is by far the most important nitrogen containing species emitted into the atmosphere on a mass basis from human activities involving motor traffic, brick kilns and combustion in thermal power stations, in homes or industrial processes (Williams, 2000;Kumar and Joseph, 2006;Ali and Athar, 2006;Skinder et al., 2014).NO x levels were found to be stabilized in residential and industrial zones but increased alarmingly at commercial zones representing higher traffic activities (Goyal et al., 2006).Moreover, NO x concentration has been found to be at its peak during late hours of the day due to high traffic density of public and commercial vehicles (Jain and Saxena, 2002).NO 2 levels were also higher in the post monsoon season followed by winter and pre-monsoon seasons (Goyal et al., 2006).
A chemical reaction in atmosphere converts primary pollutants into secondary air pollutants.Sulfur dioxide and nitrogen dioxide goes under oxidation process and gets converted to particulate sulfate and particulate nitrates and are important features of urban air photochemistry.The rates for the formation of sulfate and nitrates in the atmosphere through conversion mechanisms are of considerable interest.It is because the conversion rates are important factors in controlling the concentrations of NO 2 and SO 2 .Thus, concentration of gases decreases on temporary basis as these are transformed into secondary products.Moreover, the rate of the conversion of nitrogen oxides to nitrate affects ozone formation and ultimate fate of the nitrogen oxides in the atmosphere.The environmental effects of these secondary pollutants are associated with acidification of precipitation, visibility reduction and its deleterious effects on human health (Khoder, 2002;Skinder et al., 2014).

Study site
The present study was carried out around Parichha thermal power station.It is situated in Jhansi district of Uttar Pradesh, India.Jhansi district lies in the Bundelkhand region.Jhansi has an area of 45.22 sq Km and a population of about 4.70 million, situated at a height of about 255 m above mean sea level (asl).Jhansi district lies between 25° 27'4"N to 25° 28'4"N latitude and 77° 38' 28"E to 77° 40' 12"E longitude in the semi arid region of the country.The power station is owned by the central government and is a coal fired station located near the National highway on the northern bank of Betwa river in Jhansi district.The power station is surrounded by villages such as Badagawn, Goramachiya, Chirgawn etc., and as per latest census report Parichha has a total population of around 2000.The average annual rainfall ranged between 800 to 930 mm in summer, furthermore, humidity during morning hours was 40 to 50% and for the rest of the day 15 to 20%.The maximum temperature during summer is 45°C and the minimum temperature is 25°C.While in winter, maximum temperature is 23°C and the minimum temperature is 4°C.It has limited vegetative cover and most of the land is used for agricultural practices.

Estimation of gaseous pollutants
Gaseous pollutants (SO2 and NO2) samplings were carried out every fortnightly.The gaseous pollutants were absorbed in appropriate absorbents prepared and placed in the impingers.A handy air sampler (model, PEM-HAS IB) was employed for collecting the gaseous pollutants.This model has a set of two borosilicate glass impingers (35 ml) to collect two different gaseous pollutants separately at a time.The flow rate of the air was adjusted at 1.5 L per minute (LPM).On each sampling date the instrument was ran twice for two hours between 8.00 to 10.00 h and 12.00 to 14.00 h.The impingers were covered by ice while in operation: transportation and storage of collected samples in the laboratory before the analysis.All the samples were analyzed within 3 h of the collection of the samples.

Determination of sulphur dioxide in air
The method for measuring SO2 was adapted from West and Gaeke (1956).In this method, air-exposed samples are treated in a solution of potassium tetrachloro-mercurate (TCM).A dichlorosulphitomercurate complex is formed, which subsequently reacts with pararosaniline and formaldehyde to form the intensely coloured pararosaniline methylsulphonic acid.The absorbance of the coloured solution was measured with spectrophotometer at 560 nm, and the concentration of SO2 was determined based on a calibration curve.

Determination of nitrogen dioxide in the atmosphere
The principle of NO2 measurement in atmospheric samples was described by Jacob and Hochheiser (1958).Ambient nitrogen dioxide (NO2) is collected by bubbling air through a solution of sodium hydroxide and sodium arsenite.The concentration of nitrite ion (NO2 -) produced during sampling is determined colorimetrically by reacting the nitrite ion with phosphoric acid, sulfanilamide, and N-(1-naphthyl)-ethylenediamine di-hydrochloride (NEDA) and measuring the absorbance of the highly colored azo-dye at 540 nm.

RESULTS AND DISCUSSION
Monthly variation of ambient air pollution in the village located within a radius of 3 km from the Parichhna thermal power plant has been presented in the Table 1.Results revealed that the range of gaseous pollutants showed slight variation within the sampling dates during the four months under study.Sulphur in coal cannot be destroyed; it can only be converted from one form to another.During the combustion process, sulphur reacts with oxygen and formed SO 2 and SO 3 (Buecker, 2006;Patel and Patel, 2006).The average monthly concentration of SO 2 (21±2.88µg/m 3 ) and NO 2 (44±5.10µg/m 3 ) was within the permissible limits given for industrial and residential areas, Table 2.The concentration of the SO 2 ranged between 17 to 28 µg/m 3 .While the concentration of NO 2 ranged between 34 to 51 µg/m 3 .Although, the reported values of SO 2 and NO 2 lie within the limits, however, they are toxic on long term basis.It is important to note that the values of the pollutants reported are even after all the mitigative measures and preventive control equipments installed and working in the thermal power plant.It is considered that coal fired power plants and vehicles are the nation's largest source of nitrogen oxides (NO x ) and is produced in high temperature combustion processes (Memon, 2000;Emberson et al., 2001).While Sulphur dioxide is a prime pollutant which is released directly to the atmosphere from domestic and industrial processes, particularly those using petroleum and coal combustion (Wellburn, 1998;Emberson et al., 2001).
A temporal variation in SO 2 and NO 2 concentration was observed in all the sampling dates shown in Figures 1  and 2. Concentration of both gases was found to be consistently higher in the morning hours (8.00 to 10.00 h) throughout the study period compared to afternoon hours (12.00 to 14.00 h).The concentration of SO 2 during 8.00 to 10.00 h ranged between 19 µg/m 3 (15 th April) to 28 µg/m 3 (15 th March).Corresponding concentration of SO 2 on the same sampling dates during 12.00 to 14.00 h ranged between 17 µg/m 3 (15 th April and 14 th May) and 25 µg/m 3 (15 th March).Similarly, the concentration of NO 2 during 8.00 to 10.00 h ranged between 42 µg/m 3 (30 th June) to 52 µg/m 3 (29 th May).Consequent concentration of NO 2 on the same sampling dates during 12.00 to 14.00 h ranged between 36 µg/m 3 (30 th June) and 45 µg/m 3 (15 th March).Results also revealed that concentrations of SO 2 were lower than the NO 2 as shown in the Figure 3.These results are in consonance with the results of Cerón-Bretón et al. (2013).
The present study shows that the concentration of gases (SO 2 and NO 2 ) were found to be consistently higher in the morning hours throughout the study period compared to afternoon hours, it is because as the temperature increases, photochemical reactions transform NO 2 into secondary air pollutants which may lead to reduction of NO 2 in the afternoon hours  ( Finlayson-Pitts and Pitts, 1993) as it receives solar radiations and the ozone is produced (Tang, 2009;Elampari et al., 2010).It has also been discussed that temperature has also significant effect on SO 2 concentrations (Salam et al., 2008).Due to the increasing temperature photochemical activities increase and also in the presence of ozone concentration (formed due to NO x ), which increase the oxidation of SO 2 and its conversion rate to sulfate (Spicer, 1986;Khoder, 1997;2002).Temporal variation of SO 2 and NO 2 concentration during the day, tally with the activities producing this pollutant such as thermal power plants; although the main source of SO 2 and NO 2 are thermal power plants, there are other sources as traffic flow, burning of agricultural biomass and other domestic or residential    activities.The results revealed that the values of SO 2 (within the vicinity of Parichha Thermal Power Plant) were lower than the concentration of NO 2 ; this variation might be attributed largely due to the proximity of the sampling site to the National High Way connecting Jhansi and Kanpur.The selected sampling sites were located just a few 100 m from the National High Way as the thermal power plant is located nearer to this highway.It is the fact that vehicular emissions contribute more NO 2 than SO 2 (Williams, 2000;Jackson, 2005a;Kumar and Joseph, 2006;Ali and Athar, 2006).Similarly, the concentration of SO 2 from motor vehicles is very low as compared to stationary sources (Williams, 2000).Thus this pattern is consistent with the observed temporal variation of NO 2 and SO 2 in the current study.
Due to continuous and long lasting emission of SO 2 and NO 2 , which are the principal pollutants of coal based power plants, affecting surrounding structures, buildings, monuments of historic importance and metallic structures very badly due to corrosive reactions (Acid rain).Renowned example of this is the victimized Taj Mahal in the city of Agra which is being deteriorated due to these toxic gases (Butler et al., 2002;Dene, 2002;Pokale, 2012).Health effects caused by exposure to high levels of SO 2 include breathing problems, respiratory illness, changes in the lung's defenses and worsening respiratory and cardiovascular diseases (Skinder et al., 2014).People with asthma or chronic lung or heart diseases are the most sensitive to SO 2 (Prasad et al., 2010).The coal fired Parichha Thermal Power Plant besides emitting gaseous pollutants also emits huge quantity of fly ash particles which are deposited on surrounding agricultural lands and consequently deteriorates the soil quality in addition to vegetation (Kumari, 2009).

Conclusion
The present study showing that the concentration of gases (SO 2 and NO 2 ) was found to be consistently higher in the morning hours throughout the study period compared to afternoon hours.This temporal variation of SO 2 and NO 2 concentration during the day, tally with the activities producing this pollutant such as thermal power plant, traffic flow, burning of agricultural biomass and other domestic or residential activities, and it is necessary to note that the values of the pollutants reported in this study are even after all the mitigative measures and preventive control equipments installed and working in the thermal Power plant.So the government agencies related to pollution control should keep this into consideration for the proper monitoring of air quality in the coal based power plants to prevent environment from degradation.

Figure 1 :Figure 1 .
Figure 1: Time-series and bimonthly variation for SO 2 concentrations during the sampling period around Pariccha Thermal Power Plant in the Year 2008 Figure 1.Time-series and bimonthly variation for SO2 concentrations during the sampling period around Parichha Thermal Power Plant in the Year 2008.

Figure 2 :
Figure 2: Time-series and bimonthly variation for NO 2 concentrations during the sampling period around Pariccha Thermal Power Plant in the Year 2008

Figure 2 .
Figure 2. Time-series and bimonthly variation for NO2 concentrations during the sampling period around Parichha Thermal Power Plant in the Year 2008.

Figure 3 :Figure 3 .
Figure 3: Comparison of SO 2 and NO 2 Concentrations around Pariccha Thermal Power Plant in the Year 2008 Figure 3.Comparison of SO2 and NO2 concentrations around Parichha Thermal Power Plant in the Year 2008.

Time weighted average Concentration in ambient air Industrial, residential, rural and other areas Ecologically sensitive area (Notified by Central Government)
Annual Arithmetic mean of minimum 104 measurements in a year at a particular site taken twice a week 24 hourly at uniform intervals.**24hourly or 8 hourly or 1 hourly monitored values, as applicable, shall be complied with 98% of the time in a year.2% of the time, they may exceed the limits but not on two consecutive days of monitoring. *