Analyzing Temporal-Spatial Distribution of CO Pollutants during COVID-19 Epidemic (Case Study: Khuzestan Province, Isfahan, Tehran)

To prevent the spread of COVID-19 epidemics, restrictions such as "quarantine" have been imposed worldwide led to significant changes in the environment, especially the air. The purpose of this study is to investigate the temporal-spatial distribution of pollutants (CO) and the effect of corona constraints on it. For this purpose, CO data was extracted from MERRA-2 satellite with monthly and spatial time steps of 0.5 x 0.625 with time coverage of 2015-20. Then, the data distribution was analyzed by ArcGIS software. In this study, in order to measure the effect of applying corona restrictions on the level of CO pollutants, the data related to the period of applying corona restrictions (July 2020) were compared with the corresponding months in the base period (July 2015-2019), then the control effect of synoptic systems and atmospheric factors for the distribution and dispersion of this pollutant were studied in the provinces that had maximum of this pollutant in Iran. The results showed that the monthly average of this pollutant decreased not only in the provinces that had the maximum CO anomaly, but also over the whole atmosphere of Iran. The results of synoptic factors of geo-potential height and vertical air movement at the level of 500 hPa showed that in both periods, synoptic conditions were the same above the atmosphere of Tehran, Isfahan and Khuzestan provinces, so the studied synoptic factors have no role in this decrease. Examining the factory closure and the average condition of vehicle traffic in some of the busiest roads of these provinces, a decrease in transportation was also observed. The decrease in CO during periods of economic restrictions can be seen as a positive message of COVID-19 for air quality.
Extended Abstract
1-Introduction
The first case of acute respiratory syndrome was appeared in Wuhan, the capital of Hubei Province and China's sixth most populous city (December, 2017), and later spread rapidly in China and other countries. Due to the spread of this disease in more than 110 countries, on February 1^st, 2017, a public health emergency was declared internationally. It was on February 13^th, 2017, the disease was named COVID-19 or SARS-CoV-2. On March 23 of the same year, the World Health Organization changed the prevalence of the disease from epidemic to pandemic. In Iran, the first cases of COVID-19 were officially confirmed on February 20^th, 2017.  In Iran, cases of this disease were first observed in Qom and 15 days later, were reported from other 31 provinces of Iran. As the number of patients increased, preventive measures to control the COVID-19 pandemic were taken by the Iranian government and the "Stay Home" campaign was launched.
2-Materials and Methods
In this paper, long-term space-time methods obtained from the MERRA-2 model satellite were applied in order to measure the air quality of Iran. The model Modern-Era Retrospective Analysis for Research and Applications (Version 2), known as the MERRA-2 model, is one of the most reliable models for various researchers of climatology, the environment, etc. that helps make the best use of satellite observations. In this study, the average July data obtained from the average daily variable of carbon monoxide have been used for the entire geographical region of Iran (N90-E180-S90-W180) with emphasis on Tehran, Isfahan and Khuzestan provinces. NAEP / NCAR data were also used to investigate the effect of synoptic conditions on the quantity and quality of pollutants.
3- Results and Discussion
Covid-19 epidemic not only affects health and the economy, but also has consequences on various aspects of life such as air quality. In order to evaluate these effects on air quality, the amount of CO above the Iranian atmosphere was monitored by satellite monitoring at the base period (July 2015 to 2019) showing a decrease in the period of corona constraints (July 2020). This decrease was also seen in the provinces with the highest anomalies of this pollutant. Considering that the annual production of carbon monoxide is about 260 million tons and 60% of it enters the atmosphere due to human activities, especially incomplete fossil fuels and 40% due to natural processes and more than 70% of carbon monoxide emissions are producing in the air during transport operations and the movement of vehicles. Therefore, it is obvious that the average concentration of this pollutant in the atmosphere will fluctuate by reducing human activities and transportation through applying corona restrictions. In urban areas, fluctuations in monoxide gas, in addition to being dependent on transportation and factory activities, are also affected by synoptic conditions. The study of the synoptic conditions of both periods indicates the dominance of the subtropical high pressure stack and the dynamic behavior of the resulting stack over the mentioned provinces in both periods. The study of omega and rainfall in both periods also showed the establishment of the same synoptic conditions. Therefore, this reduction is independent from the studied synoptic conditions and is related to the restrictions imposed by the Iranian government, which has led to a reduction in traffic and industrial activities, a reduction in the emission of pollutants from vehicles, and so on.
 
4- Conclusion
A review of data on July CO emissions showed that the average monthly CO emissions in the Iranian atmosphere decreased during the application of the corona restrictions. This decrease in July 2020 that coincided with the corona wave and the intensification of corona restrictions was about ppbv5. Due to the role of industry and fixed resources, transportation and home-business activities in CO emissions, CO concentrations have decreased significantly in Khuzestan, Tehran and Isfahan provinces following the application of corona restrictions. In order to investigate the control effect of synoptic systems and atmospheric and transport factors on the distribution and dispersion of this pollutant in the provinces that had the highest pollutant, omega maps and geo-potential height of 500 hPa were examined determining precipitation factor. The studied atmospheric factors had fixed conditions in both periods and were not involved in this decrease. Therefore, it is obvious that the restrictions imposed by the Iranian government have played a role in this reduction. Because of the imposed restrictions, the average daily traffic of vehicles including passenger cars, vans and small trucks and minibuses, ordinary and three-axle trucks, buses, trailers and trucks; in some high-traffic axes, it decreased in all three provinces during July 2020 compared to 2015-2019. Therefore, the decrease in CO level along with the application of corona constraints can be considered as a result of the positive effect of COVID-19 on air quality.