Study of Surface Ozone over an American Station for a Period of 3.5 Decade

In this research paper we have evaluated the relation between surface Ozone (O3), Sun Spot Number (SSN) and Carbon Monoxide (CO) over an American station “Tutuila” for the long period of 35 years (1980-2015). It was analyzed that CO and O3 show an increasing trend over the maximum months of the year, whereas SSN shows decreasing trend throughout the year. We have concluded that, for O3 the increasing trend is found to be maximum in the month of December, whereas surprisingly just a month before it i.e., in November, the value was negative. We also analyze here the CO data for the same period. It is observed that the CO increases from January to June. Its increment is found to be minimum in January month and maximum in the month of April. After it, the CO shows the decay trend from July to September, and then again increases from October to December months. NO2 data of 11 years is also studied here and concluded that, the variation observed in March month is very small and is positive. In the same way, a positive trend is observed for NO2 data in June month, but in rest all the months the value is negative.


Introduction
The Earth's atmosphere is split into 5 layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere (Perevedentsev et al., 2019). Many of the human activities are badly affecting the atmosphere (Lu et al., 2018), and the stratosphere layer is a matter of great concern which is harmful to human itself (Anwar et al., 2016). It has been observed from past studies that concentrations of ozone in the upper stratosphere have increased in the last 15 years (Rozema et al., 2005). Depletion of the ozone layer by chlorine and bromine species has been a major environmental issue (Sivasakthivel & Reddy, 2011). The ozone layer, which absorbs and scatters the solar UV radiations, lies in this region (Brenna et al., 2019). The ozone layer is a naturally occurring gas in the region of the stratosphere, where ozone particles are accumulated (Wargan, 2018). But the thickness of the ozone layer varies with altitude and seasonal change (Davis et al., 2017). Life is protected from UV rays by the stratospheric ozone layer, which acts as a shield or sunscreen (Park et al., 2020). Surface ozone is a highly efficient greenhouse gas; its global warming potential is about 1200-2000 times that of CO 2 . Ozone is produced in the troposphere by photochemical oxidation of CO (Minschwaner et al., 2010), CH 4 , and Non-Methane Volatile Organic Carbons (NMVOCs) in the presence of NO x (Minschwaner & Manney, 2015). Loss of ozone in troposphere takes place through chemical reactions and dry deposition.
As an important greenhouse gas, O 3 is making significant contributions to climate change. The concentration of photochemical oxidants can be decreased by controlling their precursors such as: nitrogen oxides NO x (NO and NO 2 ) and Volatile Organic Compounds (VOCs) etc. (Ravishankara et al., 2009). Sunspots are areas that appear dark on the surface of the sun because of some temperature variation (Solanki, 2003). They are electrically charged gases that generate areas of powerful magnetic fields. These are regions of reduced surface temperature caused by concentrations of magnetic flux. Sunspots usually appear in pairs. The amount of solar activities changes with the stages in the solar cycle (Willett, 1962).
Observational evidence for a relation between atmospheric total ozone amount and sunspot number (SSN) has been presented and debated for more than two decades (Angell, 1989).
Generally, ozone production depends on several factors such as temperature, solar activity, wind, speed, and direction (Fleming et al., 2020). This work represents the influence of solar activity. However, previous studies have shown that ozone formation totally depends on the activities taking place on sun such as sunspots, solar winds, etc., which can alter the concentration of ozone (Arsenovic et al., 2018). They affect human health and have an impact on climatic change. One of the various problems caused by air pollution in urban areas is photochemical oxidants. The formation of ground-level ozone depends on several factors like, the intensity of solar radiation, the concentrations of NO x and VOCs, and also on the ratio of NO x to VOCs (Qin et al., 2004). Variability of ground air temperature, wind speed and direction, relative humidity, and precipitation associated with climate change have the potential to affect the distribution and deposition of O 3 . Nitrogenous compounds emitted by humans in a small amount like NO, N 2 O and NO 2 are considered to be most responsible for the depletion of the ozone layer (Zoran et al., 2020). Nitrous oxide is also a greenhouse gas, so reducing its emission from man-made sources would be good for both the ozone layer and climate. A study on Arctic and Antarctic ozone depletion has helped us in understanding ozone depletion more clearly (Solomon et al., 2014;Tilmes et al., 2005;Dameris et al., 2021;Bernhard et al., 2020). The main causes of ozone depletion are chlorofluorocarbons (CFCs), HCFCs and halons, apart from it CO and NO x also affect the stratospheric and tropospheric ozone, so here in the present study our main focus is only on the CO and NO x . Since the stratospheric ozone is formed by molecular ozone in the presence of solar UV radiation and hence solar activity i.e., the sunspot number, which represents how the sun is active, plays a major role. So, we have discussed the relation between ozone, sunspot number, NO 2 and CO data. This paper explores the interactions between these gases and stratospheric ozone.

Data Set and Site Description
For the present study, we required sufficient long-term data for a station, so we choose an American station "Tutuila" (Figure 1). A sufficient amount of ozone data for this station is available on https://www.esrl.noaa.gov/ this data were actually collected at ground by earlier researcher and hence the ozone data, which we used here is surface ozone, and now data is worldwide available on net. So here we called it ground based satellite ozone data. It means in our present study

Methodology
For analyzing the data, we have selected one American station "Tutuila" and downloaded ozone data of the years 1980 to 2015 from the above-mentioned site. This data includes everyday hourly ground base ozone data. For better comparative study, SSN, CO, and NO 2 data are also downloaded for the same period of the same station from their respective sites.
All the raw data downloaded was in grid form, which we have converted into the appropriate form. Further, we have calculated the monthly mean for every year data and got 12 data values i.e., one for each month. After it, we have plotted the monthly mean values of all the three substituent (O 3 , CO, SSN) against the years, so that the variation in all the three substituent can be easily concluded. The results obtained from each graph i.e., the slope and correlation coefficient for each month are collected and mentioned them in tabulated form.
Similar graphs for NO 2 data are also drawn. The result and conclusion obtained based on this study are given in the next section.

Result and Discussion
The monthly mean variation in CO, O 3 , SSN with years are shown in Figure 2.
This variation is for 35 years i.e., from 1980 to 2015.
It is observed from these figures and Table 1    From Table 2 respectively. The variation observed in March is very small and it is found to be positive i.e., 1.4481E12. In the same way, a positive trend is also observed in NO 2 data in June month and its growth rate is 3.4360E12. On the basis of correlation between O 3 and NO 2 it is found that there is not a particular relation between

Conclusion
On the basis of present study, in which we analyzed a data of about 35 years raging from 1980 to 2015 of Tutuila (American station) we can conclude that CO and O 3 show an increasing trend over the maximum months of the year, whereas SSN shows decreasing trend throughout the year.
Ozone shows the maximum increasing trend in December month, whereas in the previous month of it i.e., in November month it shows a negative trend.
If we see the CO data for the same period then it is observed that the value of it increases from January to June and its value is found to be minimum in January month and maximum in the April. The decaying trend of CO is observed from July to September, and after it i.e., from October to December months it again increases, but its growth rate is very small.
The analyzed 11 years data of NO 2 concluded that, the variation observed in March month is very small and is positive. In the same way, a positive trend is observed for NO 2 data in June month, but in rest all the months the value is negative. The correlation between O 3 and NO 2 shows that both are negatively correlated in some months and positively correlated in some other months. The negative correlation value between these two gases is found to be physically accepted only in the month of February and July, and positively physically accepted value in the month of August only.