Keywords

1 Introduction

Carbon dioxide is a trace gas in the earth’s atmosphere of which exchange occurs between the major environmental reservoirs such as the oceans and the biosphere. Being the most abundant greenhouse gas in the atmosphere (besides water vapour) atmospheric CO2 contributes most significantly to global climate change (Bolin et al. 1986; Houghton et al. 1996). The great industrial demands for energy promoted to release vast quantities of carbon dioxide into the earth’s atmosphere since the beginning of the industrial revolution. Monitoring of atmospheric CO2, as conducted constantly since the late 19th century, showed a steady and continuous increase in its concentrations. Because of the increasing human activities, its atmospheric concentration increased from 280 ppm in pre-industrial revolution to current level of 380 ppm (IPCC 2007). According to IPCC (2001), atmospheric CO2 concentrations increased by 31 % over the last 250 years. The average increase rate of CO2 was maintained at 1.4 ppm year−1 for the period 1960–2005 (IPCC 2007). The rate of its increase in the last 10 years (1995–2005) is estimated to be 1.9 ppm year−1 to show the highest growth rate since its direct measurements from 1950s (IPCC 2007).

Carbon dioxide levels recorded at various locations around the world consistently show a direct link with fossil fuel combustion (Denning et al. 1995; Colombo et al. 2000). Other sources of atmospheric CO2 include plants, animals, microbial respiration, ocean emission, and land use change. As such, fossil fuel combustion and cement production have increased carbon dioxide emissions by 70 % in the last 30 years (Prentice et al. 2001; Marland et al. 2006). As the increase in atmospheric greenhouse gas concentrations is the main cause of global warming , it is predicted to affect trend of climate change in both regional and global scales. Detailed information concerning the source/sink of greenhouse gases and their emission strengths has been one of the major goals of global climate study. Because the distribution of CO2 is subject to geographical and temporal variations (Keeling 1961; Pales and Keeling 1965; Inoue and Matseuda 1996), model predictions with a relatively wide geographical coverage were not necessarily useful to accurately quantify CO2 exchange on a global scale (Massarie and Tans 1995; Keeling et al. 1995). By considering such limitations, numerous attempts have been made to build a database of CO2 to cover diverse environmental conditions (Levin 1987; Levin et al. 1995; Schmidt et al. 1996). For instance, a continuous measurement of CO2 (and the related isotopic carbon ratios) has been reported in the Krakow region, Poland (Kuc 1991) or in the K-puszta region of Hungary (Haszpra 1995). However, despite the importance of CO2 data acquisition, relatively little is known about its distribution on hilly areas of the world. This paper reports the results of CO2 measurements made in the atmosphere of Dokriani Bamak lying in the high altitude region of the Northwest Himalaya, India. The purpose of this study is to primarily evaluate the carbon dioxide concentration levels and its temporal variabilities in the hilly region of Garhwal Himalaya at Dokriani Bamak, India. The results of this study will provide some insights into the environmental behaviour of CO2 in mountainous environs.

2 Materials and Methods

The concentration data of CO2 were collected using infrared CO2 gas analyzer (LI- 820, LI-COR, USA). Air was drawn at a flow rate of 1 L min−1 through air filter (Balston 25 µm) attached to non-CO2 absorbing Teflon tubing into the gas analyzer. Sampling interval was set to 30 s, and the data were recorded every 2 h by a data logger (LI-1400, LI-COR, USA). The incoming air was passed through a column of magnesium perchlorate to eliminate the possible interference due to water vapour. The CO2 gas analyzer was calibrated prior to measurement by checking span and zero values with CO2 calibrant gas (505 ppm). The measurement range of CO2 by the NDIR analyzer was 0–1,000 ppm with an accuracy of <2.5 % and a total drift of <0.4 ppm/°C at 370 ppm. The CO2 values recorded at two hourly intervals were converted into daily or monthly for the analysis of its temporal variabilities at different intervals.

3 Results and Discussion

3.1 General Pattern of Temperature and CO2 Distribution at Study Site

The present study was conducted at Dokriani Bamak, a high altitude area situated in Uttarkashi district of Uttarakhand Himalayan region in India (Fig. 1).

Fig. 1
figure 1

Location map of the study site

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Carbon dioxide concentrations were recorded at the Base camp of Dokriani Bamak (altitude of 3,600 m above mean sea level, Latitude 30° 50′–30° 52′N, Longitude 78° 47′–78° 50′E). The study area is accessible only during the summers i.e. May to November. During rest of the months the area is inaccessible due to heavy snow. So the temperature data were only measured during the growing season. Average temperature recorded during the year was 4.7 °C and during the growing season (May–October 2005) was 6.8 °C. Concentrations of CO2 in air were monitored at 1.5 m above the ground at two hourly intervals (for up to 9 h: 0600 to 2200 h (local time) throughout the study period (May to November 2005 except September 2005). The concentration data of atmospheric CO2 have been collected continuously from various locations in the world since its measurements at Antarctica and Mauna Loa observatory (Hawaii) in 1958. In India, CO2 was monitored for the first time in the air and soil layers near the ground in the year 1941 (Mishra 1950): The study was conducted to measure CO2 in the open as well as crop fields. The longest monitoring of atmospheric CO2 in India was first made at Cape Rama, a maritime site located in the west coast of India for a 10 year period (1993 and 2002: Bhattacharya et al. 1997). The results of this study are the first attempt to continuously measure atmospheric carbon dioxide in the hilly region of Dokriani Bamak, Uttarkashi, Uttarakhand. In Table 1, the basic statistical parameters of CO2 data monitored in this study are presented. The overall mean value of CO2 measured in this study was 383.5 ± 2.8 ppm.

Table 1 Statistical summary of atmospheric CO2 recorded at Dokriani Bamak, Uttarkashi
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3.2 Diurnal Variation in Carbon Dioxide Levels

To assess the diurnal variation of CO2, the data obtained above the ground at every 2 h intervals are plotted and examined in many respects. In Fig. 2a, the CO2 concentrations for each 2 h interval are compared diurnally using all data sets. The CO2 levels at this site maintained a diurnal pattern that is consistent enough to show the highest values (393.8 ppm) in the night time (2200 h) and lowest values (376.5 ppm) in the afternoon (1200 h) with the relative amplitude of 4.5 %. Figure 2b depicts the diurnal pattern of CO2 between different months of the year 2005. The differences in hourly CO2 concentration levels varied significantly between minimum (373.7 ppm in August) and maximum values (400.6 ppm in June) across the months. If the strengths of diurnal variation were compared by relative amplitude (RA) values between different months, the RA values ranged from 2.55 (May) to 5.95 % (June). The diurnal cycle of CO2 is generally known to exhibit a maximum at night (or morning) and a minimum during the daytime (Schnell et al. 1981; Baez et al. 1988; Yi et al. 2001). A nighttime maximum of CO2 in rural areas has been attributed to respiration by plants (and animals) and its emissions from soils. In contrast, daytime minimum is explained by photosynthesis (Spittlehouse and Ripley 1977; Baez et al. 1988; Nasrallah et al. 2003). Such phenomenon can also be explained partially by the changes in meteorological conditions, as the height of the mixing layer increases under stronger solar radiation (Aikawa et al. 1995).

Fig. 2
figure 2

Diurnal variation in the atmospheric CO2 using all hourly measurements for a all data sets and b monthly data sets of CO2

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Many previous studies based on long-term monitoring of CO2 also indicated that CO2 fluctuates both diurnally and seasonally (Woodwell 1978; Keeling et al. 1984; Fung et al. 1987). The average relative amplitude in this study was found as 6.95 % between the daytime drawdown and night time buildups of CO2. This RA value is smaller than those measured in the Savannah regions (21.6 %) and tropical rain forests (25.4 %) (Schnell et al. 1981), urban area of Basel city (Switzerland) with 15.5 % (Vogt et al. 2006), and urban area of Chicago with RA values of 9.02 % (Grimmond et al. 2002). The RA value of the present study is however comparable to that measured from four different sites in Phoenix (2.85–7.86 %: Day et al. 2002). Differences in the magnitude of RA values may be ascribable to such factors as the strength of biospheric photosynthesis, respiration, mixing conditions, and emissions from anthropogenic sources (Pales and Keeling 1965; Inoue and Matsueda 1996). Considering the magnitude of diurnal fluctuations in the study area, such variability CO2 may have significant implications on the vegetation of the region due to its impact on the plant photosynthesis (Veste and Herppich 1995).

4 Comparison with Previous Studies of CO2 Concentration

In an attempt to understand the factors controlling the distribution of CO2 under various environmental conditions, we examined our monitoring data obtained from the mountainous area of Garhwal Himalaya, India with those reported from other parts of the world. Table 2 summarizes the yearly carbon dioxide values, measurements conditions, detection method, and amplitude of CO2 data for all comparable data sets. For this comparative analysis, all the reference data were basically taken from the data sets of year 2006 from the WMO global atmosphere watch, world data centre for greenhouse gases (WDCGG).

Table 2 Comparison of the mean CO2 concentration measured from all different stations around the world
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The annual mean concentrations of CO2 for all the recording stations except Romania (368.3 ppm) were well above the global background concentrations of CO2 (380 ppm). Figure 3 depicts the absolute concentrations and relative amplitude of CO2 measured from all stations examined for comparative purposes. The mean CO2 concentration for India, Himalaya during the study year was higher (383.5 ppm), when compared to the stationary stations in Australia (379.1 ppm), Norway (383.07 ppm), Austria (381.7 ppm), Mt. Kenya (379.6 ppm) and Romania (368.3 ppm) stations. The relative amplitude of the CO2 values for all the comparative data can be estimated as the difference between the maximum and minimum values (amplitude) over mean. The relative amplitude of our study site was found to be more or less similar (4.50 %) to the RA recorded at Finland (4.68 %), Mongolia (4.43 %), Russia (4.58 %) and Kazakhstan (4.15 %).

Fig. 3
figure 3

A comparison of a absolute concentration (ppm) and b relative amplitude (%) of CO2

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Figure 4 shows the comparison of the monthly mean values of CO2 measured at different stations over the globe. Pallas-Sammaltunturi (Finland) and Mt. Kenya (Kenya) represent the global CO2 concentration sites, whereas all the other stations for regional CO2 concentration. Among all the sites shown in the Table 2, a number of stations including Sonnblick, Deuselbach, Fundata, Ulaan Uul, Sary taukum, etc. represent mountainous sites. All of these stations are stationary, while they are free from direct effect of any known anthropogenic sources. The annual mean CO2 concentration for mountainous sites, if derived using all those data sets, was much lower or similar (384.2 ppm, range: 381.7–386.2 ppm) than that of our study (383.5 ppm). If the relative amplitude values are compared between all mountainous sites (3.41–4.43 %), their values are quite analogous to our results (4.50 %).

Fig. 4
figure 4

Month- to- month variation of CO2 in all stations selected for comparison

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5 Conclusion

In the present study, the temporal variations in the atmospheric carbon dioxide in the mountainous area of Dokriani bamak were investigated using the data sets collected from May to Nov 2005 except September. The diurnal variation of CO2 was characterized by relative enhancement in the night. As the green plants intensively absorb atmospheric CO2 (through photosynthesis), the concentrations of CO2 are maintained in the least level during the daytime. When the diurnal variations are assessed across different months, the patterns confirmed the combined effect of biogenic and meteorological factors. It should be stressed here that the mean carbon dioxide concentration during the growing season in Dokriani bamak were higher (383.5 ppm) than the global mean atmospheric CO2 value of around 380 ppm. The present work is the first preliminary report covering continuous monitoring of CO2 in the mountainous region of Garhwal Himalaya, India. According to our analysis, it may be important to explain the possible cause of the high CO2 levels in this clean area. As the troposphere baseline data of CO2 concentration were not measured over the Himalayan region previously, precise measurements of atmospheric CO2 are needed for an extended period. Such efforts can offer more insights into the factors governing the CO2 concentration under diverse environmental settings.