Study of air pollution in Tabriz City by the use of Nitrogen Dioxide OMI sensor

Introduction
 Today, the unfavorable weather conditions are one of the critical problems in the world's major cities, which have many harms to humans and the environment. Nitrogen monoxide and nitrogen dioxide are important air pollutants. Nitrogen dioxide is a reddish-brown gas with a pungent odor. The most important human resources producing this pollutant are car exhaust and fixed sources such as fossil fuels, power plants, incinerators, and home heating appliances. In addition to human resources, nitrogen oxides are also produced by bacteria, volcanoes, and lightning. The city of Tabriz is one of the metropolises of Iran, and the increase in the population of the city, motor vehicles, consumption of fossil fuels, industrial activities, and improper use of heating devices and the existence of industrial factories has increased energy consumption in this city and many problems. It has created an environment for the residents of this city. The purpose of this paper is to study the trend of nitrogen dioxide as an indicator of air pollution from OMI data using linear fit after eliminating significant rotation periods on the time series of the average monthly nitrogen dioxide for the city of Tabriz.
Methodology
 In this study, the nitrogen dioxide data measured by the OMI satellite sensor and the wind data, the surface temperature and the horizontal visibility measured with the synoptic station during the years 2004 to 2016, contaminated with airborne nitrogen dioxide emissions in Tabriz city is being investigated. The seasonal mean and nitrogen dioxide, temperature, wind, and horizontal visibility, as well as the correlation between nitrogen dioxide and meteorological data, have been investigated to better understand the changes in air pollution. To understand the properties and behavior of the functions, they can be examined in frequency space. Least square spectral analysis can be used to investigate non-distant time series. Statistical tests can also be performed until the periodic intervals obtained from the spectral analysis are statistically validated. After the formation of the time series, the average monthly nitrogen dioxide level between the 2004 to 2016 intervals was observed using spectral analysis of least squares of periods of four, six, and twelve months, which were also statistically significant. To calculate the nitrogen dioxide trend, significant components are eliminated from the time series. After eliminating the significant components of the four, six, and twelve months of the nitrogen dioxide time series, the trend is calculated using linear fit on the remaining time series.
Results and discussion
 The results showed that the highest amount of nitrogen dioxide occurs in cold season and the lowest amount in hot seasons. The average nitrogen dioxide content in the spring, summer, autumn and winter seasons was equal to 2.13, 1.90 ×, 3.88 × and 5.36 × molecules per cm² and its mean value was calculated at 2.84 × molecules per centimeter square. Also, the highest amount of standard deviation of nitrogen dioxide occurs in winter, 10.4  and its lowest value in summer, 0.97 The study of temporal, wind, and horizontal visibility of Tabriz city for the measurement period 2004 to 2016 shows that nitrogen dioxide and temperature have a relationship. So that nitrogen dioxide has the highest amount in the early and the late months of the year when it is cold, and vice versa. 96 percent of the winds of the city of Tabriz have a speed of less than 0.5 meters per second, so called quiet winds and the prevailing winds of the eastern and northeastern cities. The correlation coefficient of nitrogen dioxide with wind and temperature was -0.49 and -0.32, respectively, indicating a greater significance of wind in the variation of this pollutant. One of the simplest ways to check the air quality is horizontal visibility. The correlation coefficient of nitrogen dioxide with horizontal visibility for Tabriz city is -0.09 and its value has not been significantly different during the year. The amount of nitrogen dioxide in each year for Tabriz was 1.05 × molecules per cm².
Conclusion
 Paying attention to the quality of life and environmental issues in the city of Tabriz is very important due to population growth and increasing urban life.  Air pollution caused by nitrogen dioxide in the cold seasons of the year was mostly due to temperature inversion. As a result, what plays a significant role in air pollution in this city is the increase in urbanization, the development of factories, and the excessive use of fossil fuels, power plants, and motor vehicles. Therefore, adequate measures must be taken to reduce air pollution in order to maintain the health of citizens and the environment. One of the factors reducing air pollution is green space, and the city of Tabriz does not have a great green space, so the lack of green space in this area is strongly felt and is very small compared to international standards.