Investigating changes in sound level before emergence of covid-19 and during the restrictions due to its outbreak in the city of Mashhad (Case study: Shohada Crossroads)

Increasing population growth and technological advancements in cities inevitably result in rising noise pollution levels. The emergence of the coronavirus disease worldwide, including Iran, has significantly altered people's daily lives. This has presented a unique opportunity to assess changes in sound levels. Therefore, this study aims to investigate sound level variations before the outbreak and during the COVID-19 restrictions at a pivotal intersection in Mashhad.

The initial segment of this study examined the sound equivalent level in April 2018 and 2019 without considering any specific circumstances at the Shohada crossroad. In the second segment, employing SPSS22 software and the Wilcoxon test, we compared the alterations in various sound level indicators before the disease prevalence (April 2018) and during the restrictions (April 2019).

The results of the first part of the study revealed that the hourly equivalent sound level (Leq) in April 2018 and 2019 was 70.48 and 70.39 dB, respectively. The results of the second part indicated a significant difference between the two periods under investigation in terms of equivalent sound levels. The maximum and minimum sound equivalent levels (LMax, Lmin) reduction during the disease outbreak compared to the pre-outbreak period was 0.16 and 0.08 dB, respectively. Additionally, during the night curfew hours (21-03) in April 2019, the sound equivalent level decreased by 0.09 dB compared to 2018. 

The findings of this study demonstrate that the equivalent sound level at the Shohada crossroad in Mashhad exceeded national standards before the disease prevalence. However, noise pollution levels have decreased due to decreased economic activities during the outbreak and the associated restrictions. Nonetheless, the equivalent sound level still surpasses the established standards, indicating that noise pollution at the mentioned intersection persists. Further research is warranted on this subject, encompassing traffic modeling, noise pollution emission inventories, establishing links between land use patterns and noise pollution, and the influence of weather conditions on sound levels.