Long-term monitoring of the concentration of carbon black pollutants in Iran using NASA/MERRA-2 base model data

The atmosphere is a dynamic and complex natural gas system whose pollution kills humans more than others. Air pollution occurs when large amounts of suspended particles or harmful substances enter the atmosphere. Suspended particles with a diameter of fewer than 2.5 µm (PM2.5) are among the most important air pollutants. Black carbon (BC) particles are one of the most important and dangerous components of PM2.5 suspended particles. The aim of this study was to analyze the behavior and time-space distribution of BC pollutants in Iran using the data of the MERRA-2 base model during a statistical period of 40 years (1980-2019). 

In this study, black carbon data in NetCDF format with initial monthly and spatial time steps of 0.5° x 0.625° were first extracted from the Earth data website. After extracting the data, qualitative control, pre-processing and, processing operations were performed. Then, the calculations were performed on monthly and seasonal matrices (on 740 pixels or networked points) using the facilities that the user's software applications ArcGIS, Grads, and Origin pro provide. In the last step, steps were taken to create raster, vector, charts layers and, information tables and the desired outputs were prepared.

The use of MERRA-2 base model data has provided very good results of the spatio-temporal distribution of BC in Iran. The results of the study showed that the monthly and seasonal differences were significant. In terms of monthly differences, the highest amount of BC was estimated in December and the lowest in June. Among the seasons, the highest and lowest levels of BC were related to the winter and summer. Spatially, the highest distribution of BC was observed in the western half of Iran, especially in the metropolises of Tehran and Ahvaz. Analysis of the time series of BC concentrations in the Iranian atmosphere showed that the concentration of this pollutant increased during the statistical period and this increase occurred especially from 2000 AD onwards. Also, in the study of meteorological parameters affecting the concentration of BC, the results showed a significant positive correlation between the concentration of BC and air pressure and a significant negative correlation with wind speed.

The results showed a clear understanding of the concentration of BC in the Iranian atmosphere. We showed that BC pollution is affected by some meteorological parameters such as air pressure and wind speed. In general, regardless of the mechanisms of development, nature, and emission of this pollutant in different parts of Iran, the behavior of the concentration of this pollutant in the context of time indicates the warning of its danger in large parts of Iran. Therefore, it is necessary to take the necessary management and executive measures to reduce this pollution, especially in metropolitan areas with high concentrations of BC.