Day Time Seasonal Variation of Ozone and Its Association with Methane at Different Pressures over Barrow, Alaska

This study has explored the seasonal day time variations of the two most important trace gases involved in global warming i.e., Methane (CH 4 ) and Ozone (O 3 ). Since solar activities also play a vital role in the formation of ozone, and hence solar flux data is also consulted in the present paper. Here we have discussed, day hours seasonal variation of O 3 , solar flux and CH 4 at different pressures for four different seasons i.e., winter, summer, autumn and spring. We have evaluated the correlation between O 3 , solar flux and CH 4 over an American station “Barrow, Alaska” for a period of 18 years and conclude that in every season of the year, CH 4 shows linear increment with a good significance level above 95%. The autumn season shows a good correlation between solar flux and O 3 with a maximum value of 0.53 in October and a minimum value of 0.34 in November month. In the winter season, CH 4 shows linear increment with a significance level above 95% at every pressure height. We also conclude that O 3 shows an increment trend in March and April months, but its negative trend is found in May month of the spring season.


Introduction
Climate change is one of the major challenges for mankind and nature, which is affecting our lives [1]. The change in climate has been categorized as various seasons of the year. A season is a period of the year that is classified by special climate conditions. Each has its own temperature and weather patterns that repeat yearly, but this variation depends on many factors. Changes in the climate badly affect the earth's atmosphere and hence have a severe impact on humans [2]. The lifespan of the earth is becoming smaller day by day due to human pollution [3]. In recent years, global surface temperatures are generally increasing which gave rise to many studies [4] [5] [6]. Methane (CH 4 ) and ozone (O 3 ) are the two most important gases involved in global warming [7], after carbon dioxide (CO 2 ). The concentrations of both of these gases have increased substantially during the industrial era [8]. Many studies have been done on ozone seasonal variation [9] [10]. Oxidation of methane is responsible for the large amount of ozone formation in the troposphere, which shows that both the gases are relatable to each other [11]. Methane data trends have developed many studies [12] and hence developed our interest too. This shows that correlation between the ozone and methane is an important aspect [13]. The chemically active climate gases ozone and methane are responsible for changes in the current climate and will affect the future climate also [14] [15]. Methane is one of the well-mixed green house gases; however, small regional variations in the atmospheric methane concentrations occur throughout the atmosphere. The source of it is divided into two categories i.e., natural and anthropogenic sources. Most of the world's methane emissions come from natural sources, such as wetlands and lakes. The remaining is derived from anthropogenic activity. Global background surface ozone concentrations have roughly doubled since preindustrial times [16], because of increases in emissions of nitrogen oxides (NO x ) and methane [17], and are projected to continue to increase [18] [19]. One of the research work estimated that the reduction of about 20% of current global anthropogenic methane emissions, will reduce ozone mixing ratios globally by about 1 ppbv and prevent almost 30,000 premature mortalities globally in 2030 and about 370,000 mortalities between 2010 and 2030.
It is well known that solar ultraviolet (UV) radiation plays an important role in ozone generation [20]. Changes in solar activity influences climate, weather, seasons and other atmospheric properties. The photochemistry is driven by solar radiations [21]. Nearly all the earth's energy derives from the sun, and it is therefore natural to study about links between variations in the sun's irradiance and changes in the atmosphere [22] [23] [24]. The 10.7 cm solar radio flux (F10.7) is one of the most frequently used indices of solar activity, and it is expressed in solar flux units (sfu) [25]. In reference [26], observed that there is a declining trend in total column ozone at Karachi and Mt. Abu with a significance level of over 95%. They also observed on the basis of long term data set of 25 years that there is a higher magnitude of 4 to 10 DU per decade in September to December months, and a lower magnitude of 2 to 4 DU per decade in pre summer months.
The carbon monoxide and ozone show an increasing trend over the maximum months of the year  in "Tutuila", whereas the sun spot number shows decreasing trend throughout the year. It was found that the ozone shows an increasing trend and its value is found to be maximum in the month of December, whereas in November month, the value was found to be negative [27].
In the present paper, we have discussed ozone, solar flux and methane and the Zou studied about the seasonal variation in total ozone over the Tibetan Plateau and found the low ozone concentrations over the large scale topographies of the Tibetan Plateau, the Rocky Mountains, and the Andes Mountains. The total ozone in Tibet was found to be lowest in October and highest in March month.
On the basis of zonal mean total ozone, the largest ozone deficiency over Tibet was found in the month of May, while smallest deficiency during November to January months. Also it was found that the ozone deficiencies are negatively correlated to the heat flux from the surface to the air in Tibet and the correlation coefficient was −0.97 [28].
The same type of study of surface ozone and its precursor gas was done at Anantapur, a semi-arid region. In this study the ozone levels were found to be highest during the winter and summer period and lowest during the monsoon period. The increment rate of ozone was found to be highest around the local time 09:00 hour, and it is about 4.7 ppbv/h, and the maximum rate of decrement was observed during the evening time and this rate of decrement was observed to be about −3.0 ppbv/h [29].
The study about the seasonal variation in surface ozone and its precursor gases was also done at Ahmedabad, India, which is an urban site. This study showed the diurnal variations of Ozone, NO x and CO. In this study the high levels of ozone were observed, and it exceed to 80 ppbv. It was found that the day time ozone production is basically due to the photo-oxidation of the precursor gases.
The boundary layer processes and meteorology also play an important role in the variability of these gases. The study showed that increment in the average amount of ozone is larger during daytime than the night time. The diurnal variations in NO x and CO are due to combined effects of local emissions. It was found that the annual variation in average ozone concentrations varies from August to November month. The minimum value 12 ± 2 ppbv is found in August month to a high value of about 30 ± 3 ppbv during November. Also the concentration of ozone concentrations was observed to be maximum during autumn and winter months and this higher value is due to higher amounts of precursor gases. Also during these months, the solar radiation was minimum.
Actually, the higher levels of precursors during these two seasons are due to large scale transportation from the continents and lower boundary layer heights.
They also try to correlate the ozone and precursor gases and found that both are anti-correlate with each other [30].

Dataset and Site Description
As in the present study we try to establish a relation between solar flux, ozone and methane so we required sufficient data of any station, therefore we chose an

Methodology
For the comparative study and for analyzing the data, we have selected the ap-

Variation in Winter Season
The   Figure 1. It has been observed from the slopes of corresponding CH 4 data that for each set of different pressures, the value is showing linear increment with good significance level above 95% in every month of this season. In December month the maximum growth is found for CH 4 at 300 hPa pressure and minimum for CH 4 at 100 hPa pressure and the maximum and minimum values are 4.6309 and 1.8476 respectively. Similarly for January month the maximum increment is 3.4548 which is for CH 4 at 400 hPa pressure and minimum is 1.4057, which is for CH 4 at 100 hPa pressure. In the same way for February month the maximum and minimum value is found to be 4.1621 and 1.3233 corresponding to 400 and 100 hPa pressure. Hence for CH 4 we see that for each three months minimum increment is at the lowest pressure of 100 hPa. The variation of solar flux is also shown for winter season against the year in the same figure, and       and August months. It has been observed from the slopes of corresponding CH 4 data that in summer season value is showing linear increment with good significance level of above 95% in each three month of this season. In June month the maximum slope is 4.0452, which is for CH 4 at 400 hPa pressure and minimum slope is 1.5243 for CH 4 at 100 hPa pressure. Similarly in July month the maximum slope is 4.3365 for CH 4 at 400 hPa pressure and minimum slope is 1.8020, which is for CH 4 at 100 hPa pressure. August month shows the maximum slope of 4.4681, and minimum slope of 1.6567 for CH 4 at 400 hPa and 100 hPa pressure respectively. If we observe the variation of O 3 then it is found that the slope is negative in all three months of the summer season with significance level above 80% in June month. The variation of the solar flux is also negative for all three months with maximum slope −1.4897 in July month with significance above 80% and minimum slope −2.1254 in June month with good significance level above 90%.   Observations also show that slope of O 3 is negative in all three months of the season with significance level above 80% in October month and above 90% in November month. Solar flux value is also found to be negative for all three months with maximum slope of −1.5088 in November month with significance level above 70% and minimum slope of −1.7834 in September month with good significance level above 90%.

Variation in Autumn Season
In observing Table 1 we see that the correlation between solar flux and O 3 in

Conclusions
The current study shows the seasonal variation in ozone and methane and on the basis of this study the following conclusions were carried out: • In winter season we observed the linear increment with a good significance level above 95%. The maximum growth is found for methane at 300 hPa and   On the basis of above outcome, we conclude that, the minimum slope of CH 4 is at the lowest pressure of 100 hPa and it increases with an increase in pressure heights up to 400 hPa, but further starts decreasing at 500 hPa pressure i.e., slope is increasing with increase in pressure height to some extent only, and also for each season slope is showing linear increment. It was also observed that the value of methane is found to be minimum in winter season and maximum in autumn season at every pressure height. Further we observe that in each season of the year significance level for CH 4 data is really good i.e., above 95%. For ozone and solar flux we concluded that its value is decreasing with a negative slope for every season. Studying about every season for 18 years we conclude that autumn Atmospheric and Climate Sciences season shows a good correlation between O 3 and solar flux with a significance level above 95% and also there is a good correlation between solar flux and CH 4 with a significancy above 90% in autumn season.