Characterization of Atmospheric Mercury in the High-Altitude Background Station and Coastal Urban City in South Asia

This study is performed to evaluate the potential sources and seasonal variation of atmospheric mercury (Hg) emissions from regional sources and other influences in India. To achieve this, using the gold amalgam technique with an automated continuous mercury vapour analyzer (TekranTM 2537B). To assess the total gaseous mercury in high altitude mountain peak station at Kodaikanal & coastal/urban air in Chennai region, the impact of changing weather conditions is also evaluated. To compare the past and recent reports of mercury at different locations in the world. The average total gaseous mercury value in Chennai is 4.68 ng/m 3 , which is higher as compared to Kodaikanal, where it is 1.53 ng/m 3 . The association between TGM with meteorological parameters in ambient air such as temperature, relative humidity, rainfall intensity, the direction of wind and velocity of was studied. The TGM concentration in India are compared with other nations, the TGM levels are similar to the east and Southeast Asian countries, and also Europe, Sub-Saharan Africa and North America are the averages and maximum concentration generally smaller. This research will help to establish more effective management approaches to mitigate the impacts of atmospheric mercury on the rural and urban environment.


Introduction
The Atmosphere hosts almost all emissions from every source on the Earth's surface, freshwater bodies, oceanic surface and anthropogenic emissions. In the atmosphere, mercury occurs in the following three primary forms: The gaseous elemental mercury (GEM), reactive elemental mercury or divalent mercury (RGM) and particulate mercury (PHg) [1,2]. There is a significant quantity of research which indicates that these elements in the environment, water and marine environments via a dynamic mixture of transport and transformation in natural and human (anthropogenic) [1,[3][4][5]. Mercury (Hg) stays as a natural substance with the biogeochemical cycle, which is involved in the Earth and is considered as a contaminant because of its long-range transport in the atmosphere [6,7].
At World level, about 50 to 70% of total mercury discharge is through anthropogenic exercises, including petroleum product ignition, smelting of metals, burning of urban waste, the release of smoke from coal-burning power plants [8,9]. In nature, mercury occurs in three unmistakable structures, GEM, RGM and PHg [10][11][12][13]. Among these three structures, RGM and PHg shift rapidly because of their characteristics such as high-water dissolvability and reactivity [14,15]. The lifetime of GEM is 0.5 to 2 years, which is sufficient for its transportation worldwide level [16][17][18]. It is reported that East Asian Nations are a standout amongst the most critical patrons of worldwide anthropogenic mercury discharge [19][20][21]. Total gaseous mercury (Hg0) evasion is approximated to be 2900 mg/year (range 1900-4200 mg/yr) from the ocean [22,23]. The ocean is therefore known to be the primary terrestrial Hg source worldwide, contrasted with approximately 2000 mg/yr from direct anthropogenic emissions. Hg usually occurs in geochemical reserves, but for several years human activities including mining and more recent burning of fossil fuels have increased the emission of Hg from the mineral source into the atmosphere [24,25]. The background means the concentration of TGM in the northern hemisphere (1.3-1.6 ng m −3 ), southern hemisphere (1.1-1.3 ng m −3 ) and tropic regions (0.8-1.1 ng m −3 ) respectively [26][27][28]. Various investigations have been completed worldwide on GEM mainly centred on the urban and rural locales, including mining and mechanical territories [29][30][31][32][33][34]. A thorough investigation of the air fluctuation, adding up to vaporous mercury and their relationship at the high-altitude station (Kodaikanal) of Southern India has been reported [35]. However, there is no complete investigation of the developed and developing urban regions of India and their contribution to TGM. This is the first research in India with a comparative and continuous observation of the temporal variations in TGM and its relationship to other meteorological parameters in urban and rural high-altitude stations. In general, the variation in mean seasonal concentration of TGM depends largely on meteorological variables. The study aims to investigate that during the day concentration of TGM is strongly change by solar radiation, evaporation and weather patterns. The main objectives of this study are to assess the Seasonal variability of atmospheric Total Gaseous Mercury (TGM) in highaltitude background station (Kodaikanal) and coastal urban city (Chennai) in India, to identify the potential sources and sinks of atmospheric mercury in the study areas and the influence of changing weather conditions on the atmospheric mercury distribution. Further, to compare the concentration of mercury in the past and recent findings of mercury at different locations around the world.

Materials and methods
In this study, monitoring sites are centrally located in high-altitude background station (Kodaikanal) and coastal urban city (Chennai) in South India (Figure 1). Kodaikanal is situated on a plateau on the southern ridge of upper Palani hill, at 2133 m (6998 ft) between the valleys of Parappar and Gundar. Such hills surround the Western Ghats mountains on the western side of South India. Kodaikanal region covering the whole of Kodaikanal taluk is located between 10° 7'56" N latitude and 10°26' and 77°15' East and 77°42' East longitude. Such hills shape the western Ghats on the west portion of South India's eastward slope. Kodaikanal is located on the east coast of the Western Ghats, at the southern end of the elevated hills of Palani of Dindigul district, in the state of Tamil Nadu. For a long time in Kodaikanal, despite reports of extensive mercury contamination, the closure of a mercury factory owned by the Indian Unilever company Hindustan Unilever became a big concern. There are 35,021 residents in Kodaikanal.

Sampling methods and materials
The Total Gaseous Mercury (TGM) estimation was carried out using a Tekran™ 2537B utilizing an in-situ automated ambient mercury vapour analyzer. Tekran mercury vapour analyzer (2537B) continuously measured the TGM every 5-minutes from January 2015 to December 2016 at high-altitude background station (Kodaikanal) and coastal urban city (Chennai) in South India. The meteorological information was acquired from computerized weather stations such as the Central Pollution Control Board (CPCB) Chennai station, Indian Meteorological Department and World weather online. Consistent informational collections of the above said parameters were recorded for each 15-minute interim and per day averages. Using a Mercury Vapor Automated Analyzer (Model No-Tekran 2537B), the addition of total gaseous mercury (TGM) was studied. To this achieve, using cold vapour atomic fluorescence spectroscopy (CVAFS) techniques and the minimum Environmental Sustainability -Preparing for Tomorrow 4 detection limit 0.1 ng/m 3 , which are described. When the ambient air was analyzed, a 47 mm Teflon filter was inserted in the whole measurement method of usage of the experiment. The flow rate is constant 1 L min -1 during all sampling periods. The implicit two gold cartridges, on the other hand, gather and thermally desorb mercury. The analyzer measured the Hg concentrations with intervals of 5 minutes automatically every 24 hours, and it was calibrated with its internal permeation sources. Present measurements at atmospheric TGM concentrations include other parameters, temperature, relative humidity, density, rainfall intensity, the direction of wind and velocity of the wind. The analyzer is automatically adjusted every 24 hours for each cartridge utilizing the internal ZERO and SPAN Permeation Processes. The peak areas for both cartridges during the calibration cycle are ensured during the ZERO process and under an error of less than ± 10% during the SPAN process. Computerized day-to-day alignments were performed every 24 hours (3.10 p.m. and 3.40 p.m.) using the instrument's internal adjustment source [35,36]. The periodical inner alignment expels both in traverse and zero that are caused for the most part by temperature and maturing of the fluorimeter light. The tested air was estimated in each five-minute time interim at a stream rate of 5 L min −1 . The detail of the inspecting air and the precision status of the instrument is clarified by Mao et al. The recognition furthest reaches of the TGM are< 0.1 ng m −3 . The precision of the estimation and the task is ± 5 %. Zero air was utilized as straightforward for the instrument. Airstream was gathered through PFA Teflon tube, which was tried with an aftereffect of around 100 % RGM passing proficiency (vacillation of RGM is once in a while < 2 %). However, this method is still the most accurate to date and is widely used for the observation of speciated Hg in ambient air.

Characteristics of TGM in the high-altitude background station in South India
In the meteorological variables at the high-altitude ground station at Kodaikanal, India continued measurement of total gaseous mercury (TGM= Gaseous Elemental Mercury (GEM) + Reactive Gaseous Mercury (RGM) was performed from Jan 2015 to December 2015). The mean concentration for TGM was 1.49 ng m −3 with a range of 1.1-2.10 ng m −3 is shown in Figure 2. The Global Mercury Observation System (GMOS) ground-based monitoring sites in India are also the highest altitude monitoring location in the GMOS network at Kodaikanal (South India). Such measurement positions constitute a major addition to the GMOS network and improve the understanding of atmospheric Hg species in this world region. The statistical summary of TGM concentration along with the meteorological parameters in the ambient air of Kodaikanal during the study period provided in Table 1. Figure 2 shows the hourly average, daily average, monthly variation of TGM concentration in high-altitude background station (Kodaikanal) in South India. The maximum hourly and daily average concentrations were 2.55 ng/m 3 and 1.95 ng/m 3 , respectively. The TGM concentration was occurring at every day for a month, evening time (3.00 am to 6.00 pm; the maximum concentration within the whole-time frame) it is shown in Figure 2. This finding was identical to previous observations of [37], at high altitude, remote area of the region of Mt. Changbai, northeast China. Mean annual TGM concentrations at the site of Kodaikanal were recorded at 1.52 ± 0.24 ng/m 3 ; between 0.77 ng/m 3 and 3.35 ng/m 3 . These observable values of mean TGM concentrations were strongly linked to previous observations [35]. The average TGM values in the study area have also been compared with those reported from the high-altitude rural areas, but lower than in the Asian coastal regions [30,38]. The highest monthly average TGM was reported in April 2015 (2.07 ng/m 3 ), while in July 2015 the lowest monthly average was 1.08 ng/m 3 . The TGM concentrations range from 0.7 to 2.0 ng/m 3 , accounted for approximately 96% of the overall TGM. The annual mean TGM values were usually higher during the day time (1.57 ng/m 3 ) compared tonight (1.08 ng/m 3 ) it shows in Figure 2. The day-night fluctuations in the TGM level may be induced by temperature variations and thus condensation levels and soil volatilization. A rural site with a similar altitude (~2800 m) in the south of France, where the estimation of TGM in the Pic du Midi Observatory [39], with equivalent techniques, recorded an average of 1.86 ± 0.27 ng/m 3 . The geogenic mercury emissions are almost ~0.5 kilotonnes per year (kt y −1 ) and re-emission of Hg ~1.6 kt y −1 from the sources of plants and biomass burning [40]. The mercury deposition can be influenced by organic substances complexation, binding to Fe-Mn oxides, hydrothermal pollutants, sulfide interaction and methylation, as well as world proximities such as river drainage, waste sources, etc. [9,10,19,41]. Meteorological conditions of high-altitude background station (Kodaikanal) in South India studied during the period under report are presented in Figure 3. The rose diagram graphically displays wind speed, and wind direction graph indicates that West, ENE direction has the maximum value of frequency fall in 20% with a wind speed range of 4-5 m/s at December to March. The minimum wind speed ranges 2-3 m/s falls in during May to November in Kodaikanal site (Figure 3). The relative humidity values increased from June to November; also, the TGM Environmental Sustainability -Preparing for Tomorrow 6 concentrations were decreased. But relative humidity values decreased from December to May; similarly, the TGM concentrations were increased. Between November and May (dry season), the TGM concentration difference was relatively higher than between June and August (wet season). The Correlation trends of TGM concentration and meteorological parameters in high-altitude background station (Kodaikanal) in South India it shows in Figure 3. There were major differences in the mean seasonal concentration of TGM, which mainly depends on weather conditions, and found to be the following: Summer > Winter > Northeast monsoon or Autumn > South-West monsoon or Spring it is given in Table 1. This research also showed that solar radiation, evaporation and rainfall strongly changed the daytime TGM concentration. The seasonal variation is influenced by meteorological conditions and other external sources [4,14]. The gaseous elemental mercury is an important pathway from soil to atmosphere at the forest and to the environment [19]. Also, in the Kodaikanal region, the mean annual TGM value in the Northern Hemisphere in Kodaikanal is well within the ranges of the recorded TGM background for the area (1.5-1.7 ng/m 3 ). These ground stations mainly track the remote background at high altitude sites and sea levels. The meteorological conditions are significantly influenced by the topsoils and vegetation to release mercury in nature environments [8,26]. The findings were also significantly affected by long-transport of improved Hg air masses from the eastern part of Gansu, the west of Shanxi, the west of Ningxia as well as northern India [37]. Furthermore, these studies have shown that natural source emissions in summer are higher than in winter.

Temporal variability of atmospheric mercury in Chennai coastal and urban region
Diurnal and monthly variation of TGM concentration and meteorological parameters in the coastal urban city (Chennai) in South India were estimated in-situ. In the overall monitoring period, day by day, TGM esteem ranges from 0.07 to 638.74 with a mean estimation of 4.68 ng/m 3 . The highest concentration of total  (Figure 4). The measured values of TGM are having a higher range than the Northern Hemisphere foundation concentration (1.50-1.75 ng/m 3 ) [9,42]. TGM concentration occurring at every day, night or early morning (2.00 am to 7.00 am; the maximum concentration within the whole-time frame) is shown in Figure 4. Similarly, TGM concentrations were higher in the early in the morning and midnight times reported by Schmolke et al. [36]. Such night-time maximums of TGM concentration [33,36,43,44] have been due to mercury releases in the night-time inversion layer from surface accumulations. The potential sources of TGM in the investigation ground are from coal-based power plants, vehicular discharge, and

Trends of TGM concentration and meteorological parameters in high-altitude background station (Kodaikanal) in South India.
Environmental Sustainability -Preparing for Tomorrow 8 squander burning [11,12,43]. The short-term measurements of TGM in china report recommend that the TGM ranges from 2.5 to 3.5 ng/m 3 for east beach front territories of China, 1.94 to 3.22 ng m −3 for Indochina peninsular regions [29]. Ci et al. [45] revealed that sea occasions are effectively engaged with the conveyance of the GEM along with the beachfront territories. Globally an average of 1.5 ng/m 3 of gaseous mercury is found in the atmosphere and Chennai; the average is 4.68 ng/ m 3 . The present-day a large source of atmospheric mercury obtains from the ocean the mostly in Hg0 (approximately ranges 1900-4200 Mg/year). The datasets of meteorological parameters versus TGM were plotted in Figure 5. Amidst the whole investigation time frame, the most extreme aggregate recurrence of wind rose was seen between 35 to 65° (NE) and 195 to 275° (SSE to WSW), and this focus is around 39% of the aggregate TGM outflow from the coastal urban city (Chennai) in South India Figure 5. TGM fluctuations were observed seasonally and diurnally, which suggested differences in source intensity, deposition processes and meteorological influences. The meteorological data set observed used to compare total gaseous mercury variation in the coastal urban city (Chennai) in South India, and it shows in Figure 5. The annual rose diagram graphically displays wind speed, and wind direction graph indicates that NE direction has the maximum value of frequency fall in 14% with a wind speed range of more than 5 m/s at Chennai urban environments. It is observed that when the temperature (27 centigrade) is low, the total gaseous mercury is found to be maximum (8.07 ng/m 3 ) for February ( Figure 5). olar radiation, temperature, relative humidity and the wind speed increased a month of April, but the TGM concentration was in declined it shows in Figure 5.
The TGM concentration was in positively correlated in barometric pressure and wind direction. The TGM concentrations continuously decreased in the following months, April to August; similarly, the barometric pressure and relative humidity also decreased ( Figure 5). The meteorological parameters play a vital role in regulating atmospheric total gaseous mercury concentrations [15,46]. The leading cause of pollution in megacities India is affected by the coal-fired power plants, transportation, industrial activity and also urban solid waste [47]. The peak concentration of total gaseous mercury was observed in Chennai urban environments during Winter as 5.64 ng/m 3 , and the lowest concentration occurred during South-West

Mercury assessment of South Asia and global perspective
The influence of seasonal shift is very predominant in high-altitude background station (Kodaikanal) and coastal urban city (Chennai) in South India. The meteorological parameters (Wind speed, wind direction, solar radiation, Atmospheric temperature, Relative humidity) and TGM focus were connected to decide the relationship connection between the informational indices of the monitoring sites. Total gaseous mercury concentration varies significantly with wind speed and wind direction and other meteorological parameters, a concentration which changes with the seasons as given in Table 1. China and India where less attention of recycling the waste and increased production of coal combustion, metals, chlorine, and cement production. In India imported mercury users of Chlor-alkali plants, thermometers, batteries, Hg-Zinc, Zn-Carbon, fluorescent lamps, thermostat switches, alarm clocks, and hearing aids a total mercury user of 129.32 (Mg) reported by Mukherjee et al. [47]. A total of 6500 tones year −1 , adapted from, was measured for mercury emissions from biomass combustion, geogenic activities, and soil/vegetation/ocean emissions. The atmospheric mercury emissions approximately one-third from the sources of anthropogenic emissions similarly, natural emissions 70% and Oceanic emissions from 36% [31]. The primary anthropogenic sources such as combustion of fossil fuels for 24% and coal-burning (21%) at worldwide estimated emissions [5]. The approximately 2320 Mg of mercury is released yearly to the worldwide atmosphere (31%) for the primary sources of anthropogenic emission [8]. The world's leading mercury reservoirs, a unit of the Earth's measurement system and still an ecosystem suffering from anthropogenic activity, encompass the atmosphere (4.4 to 5.3 Gt), the terrestrial environment (in particular soils: 250 to 1000 Gg) and aquatic ecosystems (e.g. oceans: 270 to 450 Gg) [48]. The sustainability of mercury monitoring networks is an essential factor affecting the effectiveness of monitoring efforts.
In a global mercury assessment in 2013, mercury reported to dental usage measured at roughly 270-341 tons in 2010 [49], which represents 10% of global consumption of mercury Figure 6. Recently, the United Nations Environment Programme (UNEP) report 2018 to estimate the anthropogenic sources of Environmental Sustainability -Preparing for Tomorrow anthropogenic sources in 2015 were about 2220 tons. Such sources constitute respectively 25 to 37 percentages of overall worldwide mercury emissions, measured at approximately 2000 tons. The TGM concentration in South Asia (India) are compared with other nations, the TGM levels are similar to the east, and southeast Asian countries and also Europe, Sub-Saharan Africa and North America are the averages and maximum concentration generally smaller. Mercury emission estimated (kg) in global in south Asia was in the second-largest nation in the worldwide it shows Figure 6 [49]. Recent assessments of emissions of mercury into the environment (the 2010 targets) indicate that the primary anthropogenic sources of mercury pollution into the environment are artisanal and small-scale gold mining and fossil fuels (primarily coal) for power plants and industrial boilers for the generation of heat and electricity. In India majority of mercury releases from coal-burning (89,444 kg) followed by non-ferrous metal production (22,536 kg), waste from products (13,692 kg), cement production (13,421 kg) non-ferrous metal production, combustion of fossil fuels and artisanal small scale gold mining was in less than 1000 kg etc. it shows in Figure 6 [49]. The most important natural sources and sources of re-emissions assessed within the GMOS project are oceans, which contribute 36% of the emission of mercury, followed by biomass (9%), deserts, metal and non-vegetation areas (7%), tundra and grassland (6%), forest (5%) and evasion after the events of mercury depletion (3%) [25,40]. The majority of mercury releases worldwide estimated by fossil fuel combustion (11%), small-scale gold mining (5%), non-ferrous metal production (4%), cement production (3%), caustic soda production (2%), waste incineration (2%) and pig iron production (1%) [8]. Total mercury emissions are dominant in Asian countries, particularly China and India, and this information on the above factors and detailed estimates for mercury can be found in AMAP/UNEP [49].
Mukherjee et al. [47] reported the mercury contamination in India its mainly from industrial mercury emissions from coal combustion, the iron and steel industry, non-ferrous metallurgical plants, chloralkali plants, cement industry, waste disposal and other minor sources (i.e. brick production). The largest contributors to the source categories are coal combustion (52%) and waste incineration (32%) as shown in Figure 6. In general, TGM concentrations in urban and suburban areas are higher than in rural areas [49]. Mercury emission estimated (kg) in global in south Asia was in the second-largest nation in the worldwide [49]. However, measurements from global urban sites, which are also situated in the same region Asia, showed less than half of the mean concentration from our site. One of the main reasons for our study area is located in the coastal region was that episodically diluting with cleaner marine air and TGM with oceanic bromine will reduce pollution [50]. The possible sources of TGM in India are coal-fired power plants, vehicular emission, manufacture of ferrous and non-ferrous metals, waste incinerating sites, domestic fuel use from residents within the Informal villages around the Landward side, and ocean origin sources. Also, The Asian countries emissions are dominated in the global anthropogenic mercury emissions [21]. Current estimations on mercury emissions and re-emissions of primary natural mercury, including, mercury leakage cases, were measured at 5207 tonnes year −1 , which accounts for approximately 70% of the GMOS programme [5]. This pollution estimate is accurately compared to the information given by Cohen et al. Various additional lines of study and measurement are necessary to improve inventories of mercury and improve the ability to assess control options.

Conclusions
India is known to be the second-highest mercury (Hg) contributor to the global Hg budget for the environment. The present study is focused on the hourly, daily, and seasonal variations of the TGM concentration and meteorological parameters investigated at high-altitude background station (Kodaikanal) and coastal urban city (Chennai) in India. The mean total gaseous mercury concentration in Chennai is 4.68 ng/m 3 , which is higher when compared to Kodaikanal, where it's approximately 1.53 ng/m 3 . TGM concentrations exhibit an obvious diurnal pattern at Chennai urban region. All peak values appear between 3:00 am, and 8:00 am in all the seasons. This is probably the result of the change in the height of the atmospheric boundary layer that occurs between day and night. This is in large relation to global averages, but slightly less than in semi-industrial/urban areas in India.
The reason behind the higher concentration of total gaseous mercury in Chennai region is the high pollution due to anthropogenic sources, for example, industrial and vehicular emissions, which essentially improves vaporous mercury and also significantly enhances the atmospheric mercury level. Among the seasons, concentrations of TGM were higher during winter season both in Chennai and Kodaikanal indicating dry air with lower humidity aggregates higher pollutants in an urban environment. Total gaseous mercury concentration during the winter season is observed to be maximum in both regions. The average TGM concentrations during four monitoring seasons were ordered as Winter > Summer > Autumn > Spring. The average TGM concentrations in Chennai during the four monitoring seasons were ordered as Winter (5.64 ng/m 3 ) > Summer (5.16 ng/m 3 ) > Autumn (4.59 ng/m 3 ) . From the results, it is clear that meteorological parameters play a vital role in the variation of total gaseous mercury. Factors such as the re-emission of concentrated mercury through Earth soils, vertical mixing and long-range transport influenced the seasonal variability of TGM at the monitoring sites. Moreover, it is clear that in the future if these meteorological parameters changes, it will change the concentration of total gaseous mercury in the observation regions. The present study can be extended by quantifying the total mercury emission from the earth systems and its impact on environments and human health in the Chennai urban region. There is a shortage of essential information and pollution factors for Asian countries to complete this analysis to address this situation. Recent work has used TGM and meteorological parameters, although the impact of wind speed, wind direction, and solar radiation on pollutant behaviour are well known, and these factors can be more easily approached in future research.