Spatio - Temporal Trace Gas and Trace Metal Foot Prints in an Industrial and Marine Scenario

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Figure 1. Location Sketch of sampling sites

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The sampling site specifications chosen are ample enough to provide a complete appropriation about the declining air quality. Six sampling sites are selected in Kochi metropolis which represents different segments of the region. Both E1 and E2 represent estuarine sites. Marine aerosols and anthropogenic aerosol due to human activities deteriorate the environment severely. Industries and automobiles release toxic chemicals to the atmosphere. Biogenic emissions still worsen the situation. Oil refineries are a major source of tarry organic particulate matter in all these sites. Agricultural activities in some areas produce sugar like material which makes the pollutant an adhesive character and sticky nature. R1 and R2 are two riverine sites. At R1 automobiles are the major source for both particulate and trace gases. Fossil fuel burning and construction work liberate pollutants and add to the already existing polluted atmosphere. The fresh water source may release reduced nitrogen species and sulphur compounds to the environment. R2 is an industrially populated region and augmented with industrial emissions. Though fossil fuel burning and automobile release are present to a slight extend, it contribute to the deterioration of the environment. The coastal site C1and C2 makes difference that sea salt contamination is maximum in their pollutant discharge. A detailed description of the pollution sources in the study area is given in the Table 1. The map of the study area is given in Figure 1. The pollution sources are related to fisheries and retting of coconut husk. The selected sites are in the vicinity of estuarine, riverine and coastal areas so that the input from these aquatic sources into the troposphere could also be encountered. The categorization of sites into these three different sets is on the firm understanding that each specific site has its own characteristic emanation. This study is the first attempt of this sort in this area.

2.2. Sampling Procedure

The sampling is done using high volume sampler of model APM 415 (Envirotech) maintaining the flow rate at 1 m³per minute. The inlet is placed 3 meters above the ground level. For sites without surrounding obstructive vegetation, topography or buildings, a minimum height of 2 meters above ground level is recommended. For continuously measured aerosol parameters, one-hour time resolution is appropriate with measure of the central value (arithmetic mean) and variability (standard deviation) reported for each parameter for each hour. Continuous monitoring is performed in the month of May (2010) and January (2011) for three hours. The gaseous pollutants like sulphur dioxide (SO₂), nitrogen dioxide (NO₂) and ammonia (NH₃) are monitored by collecting them in impingers with suitable absorbing media attached to the sampler. Nuclepore glass fibre filter paper of size 20x25 cm is used as collection substrate for particulate matter (PM₁₀). The impactor collects the particulate matter (PM₁₀ ) the atmosphere with an upper break up of 10 micrometer according to the specification. The collection substrate is pre-conditioned, desiccated and accurately weighed in an electronic balance before and after sampling. The blank filters are also kept at the same condition. After sampling the substrates and gases are brought back and kept in refrigerator for further analysis.

2.3. Analytical Procedure

Gaseous pollutants are analyzed by wet chemical methods and quantified by spectrophotometer. The samples in the absorbed medium are estimated colorimetrically. Sulphur dioxide is estimated using modified West and Geake method ^[24]. In brief, the gas is collected in an impinger containing 20 ml absorbing medium, sodium tetra chloro mercurate. It is treated with sulphamic acid, acid bleached p-rosaniline hydrochloride and the absorbance is measured at 560 nm. Nitrogen dioxide is determined using modified Jacob and Hochheiser method ^[12] in which the gas is collected in alkaline sodium arsenite and colour development is done by adding sulphanilamide and N [1-Napthyl ethylene diamine dihydrochloride] with the absorbance at 540 nm. Ammonia is estimated by Indophenol-blue method ^[16]. The exposed filter paper is acid digested using a mixture of nitric and perchloric acids in the ratio 5:1 for trace metal quantification. The analysis is performed using ICP-AES (Inductively Coupled Plasma –Atomic Emission Spectroscopy) and the concentration of elements like Fe, Al, Cu, Cd, Zn and Pb are estimated.

3. Results and Discussions

3.1. Variation in Particulate Matter

The meteorological parameters under consideration include wind speed, wind direction, temperature and humidity. From the wind rose plot (Figure 2 and Figure 3), it is observed that the prevailing wind at Kochi is south west in winter while in summer it is from North -Northwest. The average temperature in summer is 29°C and winter 27°C. Throughout the sampling period there exists moderate precipitation. The relative humidity is more in winter than summer and continuous rainfall is observed in almost all the months from May (2010) to January (2011). All these factors influence the nature of particulate matter composition and dispersion of gases. The PM₁₀ concentration in the samples varies notably from summer to winter and is enhanced in winter season. Higher value at the sites C1 and C2 can be attributed to sea salt loading in both the seasons. The lofty value of PM₁₀ in winter seasons at E1 and E2 is due to the anthropogenic activities, low wind velocity, low temperature and relatively stable atmospheric conditions with low dispersion rate and earlier reports also supports ^[21]. Gas-to-particle conversion may be effective due to photochemical reaction, increase in coagulation and resuspension may add onto the above cited fact. The trend is represented in Figure 4.

Figure 2. Prevailing SW wind in January

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Figure 3. Prevailing W-NW wind in May

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Figure 4. Variation of Particulate Matter in Summer and Winter

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Figure 5. Variation of Trace Gases in Summer and Winter

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3.2. Quantification of Gases

The main sources of atmospheric acidity are the gaseous emissions of SO₂ and NO₂, generated by civil and industrial activities ^[18]. In the atmosphere, both SO₂ and NO_x are subjected to chemical transformation by oxidants, which lead to formation of sulphuric acid containing aerosol and gaseous HNO₃ ^[19]. These two products then react further under typical conditions with NH₃and have a neutralizing effect producing both sulphate and nitrate in the aerosol phase as ammonium sulphate and ammonium nitrate. These chemicals can be deposited to the earth’s surface by either dry or wet deposition process and the chemical transformation process can be referred to as gas-to-particle conversion and involves many factors, viz. meteorological parameters, site characteristics. ^[6]. The present study reveals the elevated concentration of SO₂in the winter season. The average concentrations of SO₂at the commercial city centers Sydney, Prague, Cairo, Frankfurt, Tokyo, Nairobi and Manila are 62.6, 154.3, 39.0, 80.7, 55.1, 214.8 and 56.5 μg/m³ respectively ^[25]. A peak value of 126 μg/m³ is observed at site R2 in winter season. The industrial belt zones which release SO₂ into the atmosphere as a byproduct is the major reason. The mean concentration varies from 6.4 μg/m³ to 35.9 μg/m³ (summer) and 14.74 μg/m³ to 126.9 μg/ m³(winter). NO₂ in winter and summer season is found high at R1 and R2. The mean NO₂concentration reported for the cosmopolitan cities like Delhi, Calcutta, Chennai, Mumbai are 37.4, 167.4, 16.2 and 30.7 μg/m³ respectively ^[4].In the present study site the concentration varies from 6.46 μg/m³ to 23 μg/m³ (summer) and 3.15 μg/m³ to 52.48 μg/m³in winter. The site, R1, rural in action hitherto, there is a major roadway connecting to different districts and busy with vehicular traffic throughout the times. The study behavior by Avnish Chauhan ^[2] also proposes that the concentrations of pollutants are higher in winter. NH₃ is the most prevalent gaseous base found in the atmosphere, and is, therefore, fundamental in determining the overall acidity of, precipitation, cloud-water and atmospheric aerosols ^{[14, 15, 22]}. NH₃ is emitted by a variety of sources such as soil, sludge, animal waste, automobiles and agricultural processes ^[20]. Ammonia decreases in the order E1> E2> C1> R2> R1> C2 in the summer season. The site, E1 encompasses estuarine character along with harbor activities are foregoing. Biogenic waste enhances the richness of ammonia in the estuarine premises. The major transport of ammonia and sulphur to the industrial site R2 is through water ways from the Wellington Island, a place near to E1. Hence ammonia can be distributed entirely over the available space and might be one of the reasons for its high fortification in respective site. Conversely in winter, ammonia is considerably high at R2 (Figure 5). Some of the major thriving industries which manufacture ammonia, caprolactum, ammonium Sulphate, urea, sulphuric acid etc are located near to this site. In winter due to low temperature, the dispersal may be low and in all the sites ammonia is profoundly enhanced in this season. The comparatively higher temperature though frequent rain can cause dissociation and volatilization of ammonium salts enriching the environment. The site R2 which is in an industrial belt is experimentally proved to be heavily polluted in winter which is in accordance with our expectation.

3.3. Quantification of Trace Metals

The measured metal concentrations are graphically presented in Figure 6. The winter season represents the maximum concentration of trace metals. It might be due to persistent ground level inversion conditions during this time. Organic and inorganically bound species both in particulate and soluble form intensify the existing dangerous situation. The concentration of Cd and Pb are below the detectable limit, however Pb is observed at an average of 0.03μg/m³ in all the sites during the summer season. The low value shows the control adaptive measures taken for Pb. The major source of Pb to the atmosphere comprises from petrol combustion. The non-leaded petrol is using now-a-days which reduces the amount of Pb considerably. A slight detection in summer can be attributed to emission of Pb into the atmosphere over past decades which have initiated to considerable increase of Pb in soil along the road side. ^{[3, 13]}. Fe and Al vary from 0.38 to 0.84 μg/m³ and 0.17 to 1.81μg/m³ in summer. The winter season with concentration (Fe) 1.5 to 109.85 μg/m³ and (Al) 3.67 to 155.3 μg/m³ shows a high input of these metals. Fe and Al have both crustal and anthropogenic point sources. Earlier reports show that the crustal elements are found to have high concentration in summer ^[1]. Al levels are elevated in summer than Fe especially in site E2. The site topography enlightens to the fact that one of the largest container terminal (Vallarpadam Terminal Container) resides near to it and is commissioned in 2010. Frequent construction works are taking place and prevailing W–NW windblown in the season might have a role in dispersing the pollutants. The winter season representing a higher input can be attributed for the stable conditions and low dispersion rates but at the same time anthropogenic activities are intense and construction related work in the harbor areas leads to aggregation of pollutants in and around the place where the source is located. Similar type of observations have been reported ^{[1, 11]}. Zn varies from 0.05 to 0.38 (summer) and 0.75 to 4.36 (winter). The spatial distribution of copper is enhanced in summer season than in winter. This fortification is high in site E2 (0.58 μg/m³) and may be due to coal ash resuspension ^[3] and from industrial sources.

Figure 6. Variation of Trace metals in Summer and Winter

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3.4. Enrichment factor (EF)

The distribution of trace elements vary from place to place, depending upon the regions selected. However it is possible to predict whether the given element is enhanced or reduced using a parameter called Enrichment Factor (EF). The Enrichment Factor is the ratio of the concentration of any trace metal or ion to Fe in the sample divided by the corresponding ratio in crustal material ^[23]. If the EF <10, trace metal in aerosol has crustal origin and If vice versa they are derived from some other sources. The enrichment factor is calculated for each metal, using iron as the normalizing element. EF= (Cmetal / C iron) spm / (Cmetal / C iron) crust, where EF is the enrichment factor, (Cmetal / C iron) spm is the ratio of concentration of metal to concentration of iron in aerosol, and (C metal / C iron) crust is the ratio of the metal to iron in the earth crust. The results of EF factor reveal that except Al all other elements have EF values greater than 10. This indicates other than aluminum; rest of all elements has significant anthropogenic sources. The order of EF values are in the order Cu> Zn> Pb> Al. The Enrichment factors for elements at the site R2 are found to be higher especially in winter season. The atmospheric stability in winter compared to summer facilitate the pollutants, especially hygroscopic, adhesive type and deliquescent, to remain as an aggregation. The site R2 is an industrial belt area, covering small and large scale industries which are run by state and centralized organizations. This region can be considered to be a cesspool of toxic metals surrounding in ambient air.

Table 2. Correlation Analysis of Trace Metals in summer and winter

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