Muhandisī-i Bihdāsht-i Muḥīṭ (Feb 2024)
Investigating the revertability of air pollution in Isfahan after precipitation
Abstract
Background: The ever-growing population and the industrialization of societies have led to an increase in environmental pollution, especially water and air pollution. In recent decades, air pollution in large cities has become a serious challenge that threatens the health of society. On the other hand, the water deficiency and the drying up of rivers, lakes and wetlands have led to an increase in dust production around cities, which in turn has worsened air pollution. Climatic factors also have an impact on changes in air pollution. Precipitation is one of the phenomena that can abruptly reduce air pollution, and air quality remains in a favorable state for some time after precipitation ceases. The aim of this study is to investigate the time when air pollution returns to the conditions before the occurrence of precipitation. Methods: Currently, air pollution in the Isfahan metropolitan area is measured at 9 air quality monitoring stations by the Transportation and Traffic Department of Isfahan Municipality. In this study, Faiz station, which is located in an area with high traffic volume in terms of vehicle traffic, was selected among these 9 stations, which are scattered throughout Isfahan. In this study, the air pollution of Faiz station was evaluated based on the concentration of pollutants according to the standards of the US Environmental Protection Agency. Finally, the influence of precipitation on air pollution in the study area was examined. Results: looking at the CO concentration in the air, it was observed that the maximum time of reversal of baseline pollution after precipitation is associated with the precipitation events of March 11, February 1 and March 10 with 46, 37 and 31 hours, respectively. For PM2.5 concentrations, the maximum reversibility of pollution was recorded on May 3, January 27 and January 15, with the reversibility of this pollutant to baseline pollution being 59, 51 and 49 hours, respectively. For NO2, the maximum reversibility of pollution was recorded on March 10 and 7, which respectively 64 and 47 hours after the end of the precipitation, the amount of NO2 returned to its baseline value. As for the pollutant SO2, the effect of the precipitation of November 6 on SO2 lasted until about 3 days later, so that according to the available data, the amount of SO2 is lower than the baseline pollution at all hours of November 7. Conclusion: The results show that in terms of CO in the air, there was good air quality in 99% of the cases recorded at the Faiz station and average air quality in 1% of the cases, and that in terms of SO2 in air, there was good air quality in about 99.8% of the cases recorded and average air quality in about 0.2% of the recorded cases. The study of the NO2 concentration in the air showed that 98% of the recorded cases classified in good air quality and 2% in average air quality. As for PM2.5 concentration, 26% of the time was in good condition, 48% in average air quality, 18% in unhealthy air quality for sensitive groups, 7% in unhealthy air quality and 1% in very unhealthy air quality. It should be mentioned that the PM2.5 concentration reached a hazardous air quality condition in some hours. Finally, the results of this study showed that on some days the occurrence of precipitation had no significant effect on the reduction of air pollution, while on other days precipitation caused a significant reduction in air pollution and air pollution had not reached the baseline level even after 215 hours. It is possible that after the rain stopped, other factors such as wind were effective in keeping air pollution low.
