Implemented quarantine due to the ongoing novel coronavirus (agent of COVID-19) has an immense impact on human mobility and economic activities as well as on air quality. Since then, and due to the drastic reduction in pollution levels in cities across the world, a large discussion has been magnetized regarding if the lockdown is an adequate alternative counter-measure for enhancing air quality. This paper aimed at studying the Air Quality Index (AQI), PM2.5, and tropospheric NO2 levels in three lockdown phases (before, during, and after) among 21 cities around the world. Simple before/after comparison approach was carried out to capture the declining trend in air pollution levels caused by the lockdown restrictions. The results showed that the frequency distribution for NO2 is more variable than that for PM2.5, and the distribution is flatter from 2020 to the baseline 2018-2019 period. Besides, AQI, in most of the cities, has varied from high to mild pollution during the lockdown and was moderate before. Although during the lockdown, a reduction of 3 to 58% of daily NO2 concentrations was observed across the cities, an increase was detected in three cities including Abidjan (1%), Conakry (3%), and Chengdu (10%). Despite this mixed trend, the NO2 time series clearly showed the effect of the unlocking phase where the NO2 levels increased in almost all cities. Similarly, PM2.5 concentrations have increased in the post-lockdown period, with 50% of the cities reporting significant positive differences between the lock and the unlock phase. Then, the levels of PM2.5 were higher at the pre-lockdown phase than at any other time exhibiting a “U” shape. In addition, during Ramadan, it was noted that altered patterns of daily activities in some Islamic cities have a significant negative impact on air quality.

For over three decades, Iraq has suffered from climate variability and desertification. Rainfall rates have decreased with abnormal high-temperature degrees, recurrence of dust storms has been increasing and many agricultural areas have turned into barren land. In this article, to study these climatic variations and detect important climate indices in Iraq, ten indices (total rainfall, average temperature, maximum temperature, minimum temperature, number of days of dust rising, number of days of dust storm, relative humidity, atmospheric pressure at sea surface level, total evaporation and wind speed) were investigated at 24 meteorological stations in Iraq for 30 years. January in winter, July in summer and annual rates of climate indices were analysed through a factor analysis method. As a result, total rainfall, minimum, maximum and average temperature were found as the strongest indices of the two seasons in Iraq. However, in the annual rates, the total rainfall indicator ranked last in the second component of the factor analysis. The contour lines for the factors of rainfall and maximum temperature offered a clear guide to patterns of the characteristics in winter, summer and annual rates. The northern regions were characterized by high values of rainfall in winter in comparison to the central and southern parts of Iraq. However, high temperatures were found in Baghdad and the southern regions in summer, which showed more than 45 ∘ C.

The CALPUFF atmospheric transport model was used to estimate ambient air concentrations of SO2, CO, NO2, and PM2.5, in a 256 km 2 region surrounding the Daura oil refinery in Baghdad, Iraq during a six-month period in the summer for 2013 and the winter of 2014. The CALPUFF modeling system includes a meteorological processor (CALMET), a Lagrangian puff atmospheric transport model (CALPUFF), and a post processor (CALPOST). Source term and meteorological data, including surface and upper air observations, were pre-processed and formatted for CALMET and CALPUFF using FORTRAN programs. Monthly emission rates and stack parameters for twelve stack sources were included in the model. Winds out of the northwest predominated, followed by winds out of the north and the west. The urban regions with the highest pollutant concentrations in the study domain were the Daura Express Highway located south and southeast of the facility, and the refinery employee residences located west of the facility. These areas were closest to the Daura oil refinery. Predicted pollutant concentrations showed that SO2 and CO were higher than NO2 and PM2.5, for the study period because emission rates of SO2 and CO were greater than NO2 and PM2.5. Monthly dispersion patterns were similar among the pollutants and exhibit plumes in the predominant wind direction. Winter generally had the highest predicted pollutant concentrations compared to the summer months.

In this study, the concentrations of sulfur dioxide (SO2) were emitted from the Daura oil refinery units and their effect on the surrounding areas of the refinery were investigated, and also, study the atmospheric stability effective by using the Screen View model, and check the effect of the wind speed and direction on the spread of pollutants. As indicated during this study, the physical factors of the sources of pollution, such as the height of the chimney, its diameter and the surrounding environmental conditions, contributed to the increase in the concentration of contaminants. It was generally observed that the concentration of SO2 increased by increasing the rates of airflow and ambient temperature. This work was prove the influences of weather conditions in the transmission and spread of pollutants such as wind speed, wind direction, atmospheric stability and ambient temperature, but the effect of ambient air temperature was lower than others variables. When the distance increases between the plume and the source of pollution, a heat exchange takes place with the surrounding atmosphere, the difference between the temperature of the emitted gas and the surrounding atmosphere decreases and the buoyant force increases. This leads to a lack of vertical movement that disperses the contaminants. In addition, the concentration of the pollutants decreases with the distance increases from the source of the pollution. In the present work, emission rate of SO2, and stack gas exit velocity calculated for all stacks (point sources) of the twelve production units during August 2013, and February 2014 by using the actual amounts of fuel consumed in Daura refinery in this period.

Sulfur dioxide is one of the dangerous pollutant gases; it has many effects associated with longer exposures to respiratory illness, alterations in the lungs, cardiovascular disease, and premature death. In this study desulfurization techniques are applied to the burned fuel oil used in the Al-Daura refinery at two seasons (January represents winter and July represents summer) to reduce the emission of SO2. Method for desulfurization is based on oxidation (hydrogen peroxide) and solvent extraction techniques by N-methyl–2 -pyrrolidone (NMP) applied on crude fuel oil used in refinery, this method can remove about 75% of sulfur from fuel oil used to a supplied refinery in 2017. The total amount of burned fuel oil is 60011.6 and 40418 kg/hour (January–July) through 2017. The emission rate for SO2 is calculated before and after desulfurization suggested to apply and leads to reduce the average monthly rates from 6000 to 2100 and 2900–700µg/m3 at January-July at a distance of 1000 m from refinery point center. More reduction in farther distances in SO2 concentration reach to more than 35% resulted after applied desulfurization. This change in emission rate leads to modify the pollution spatial distribution of SO2 concentration according to the Gaussian model for the dispersion of pollutant around the refinery and with a distance reached to more than 10 km. Overall there is a significant change in the air quality of SO2 around Al-Daura refinery specifically in the southeast direction when this technique is applied.