The COVID-19 global pandemic has necessitated some drastic measures to curb its spread. Several countries around the world instituted partial or total lockdown as part of the control measures for the pandemic. This presented a unique opportunity to study air pollution under reduced human activities. In this study, we investigated the impact of the lockdown on air pollution in three highly populated and industrious cities in Nigeria. Compared with historical mean values, NO 2 levels increased marginally by 0.3% and 12% in Lagos and Kaduna respectively. However, the city of Port Harcourt saw a decrease of 1.1% and 215.5% in NO 2 and SO 2 levels respectively. Elevated levels of O 3 were observed during the period of lockdown. Our result suggests that there are other sources of air pollution apart from transportation and industrial sources. Our findings showed that the COVID-19-induced lockdown was responsible for a decrease in NO 2 levels in two of the locations studied. These results presents an opportunity for country wide policies to mitigate the impact of air pollution on the health of citizens.

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The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), originating from the Wuhan region of China, has caused devastating damages across the world. The impact of SARS-CoV-2 (COVID-19) has been reported in global transportation (Abu-Rayash & Dincer, 2020) and power system (Gulati et al., 2021). The greatest impact has been on the global health system, overwhelming the health care facilities of many developed and developing countries (Armocida et al., 2020). COVID-19 infections could be asymptomatic, symptomatic or presymptomatic leading to severe forms which require intubation and can lead to death (Lee et al., 2020). For instance, older patients with more than one underlying medical condition (e.g., hypertension, obesity, diabetes, chronic kidney diseases etc.) are more predisposed to severe COVID-19 complications (Fang et al., 2020; R. T. CDC et al., 2020), although younger and healthier patients are more likely to respond faster to treatment (C. CDC et al., 2020;Wang et al., 2020). Multiple organ failure and cardiopulmonary complications, such as myopericarditis, pulmonary embolism and acute respiratory distress syndrome, represent some of the major complications of severe COVID-19. The COVID-19 outbreak has created a global health crisis. There are a total of 171,259,456 COVID-19 cases, 3,567,030 deaths worldwide as of 2 June 2021 (John Hopkins University, 2021) with Nigeria having the highest number of cases (166,534) and deaths (2,099) in West Africa. The first case of COVID-19 incidence was reported on 27 February 2020. Since then the reported confirmed cases increased considerably to about 1,350 cases before the end of the second month. Lagos State, Kano State and Federal Capital Territory (FCT) reported the highest number of cases in Nigeria. The Federal government of Nigeria and various State Governments imposed restrictive measures such suspension of all activities and religious gatherings, indefinite closure of public and private schools/institutions, extension of the travel ban to some countries, suspension of the

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Abstract-Radio refractivity values obtained for different heights (Ground surface, 50 m, 100 m and 150 m) over a tropical station, Akure, South-Western Nigeria using in-situ data over a period of five years has been investigated for chaos. Several chaos quantifiers such as entropy, Lyapunov exponent, recurrence plot were used. Determinism was detected in the time series studied at all the levels. Results obtained from the computation of radio refractivity show that the value of radio refractivity decreases with increasing altitude while chaotic quantifiers obtained at ground level and height 100 m are found to be more chaotic than the other two levels (50 m and 150 m).