A study of nitrogen dioxide (NO(2)) periodicity over the United Arab Emirates using wavelet analysis

NO(2) and nitric oxide (NO) are the most reactive gases in the atmosphere. The interaction of NO(x) molecules with oxygen, water and other chemicals leads to the formation of acid rain. The presence of NO(2) in the air affects human health and forms a photochemical smog. In this study, we utilize wavelet analysis, namely, the Morlet wavelet, which is a type of continuous wavelet transform, to conduct a spectral analysis of the periodicity of nitrogen dioxide (NO(2)). The study is conducted using data from 14 weather stations located in diverse geographic areas of the United Arab Emirates (UAE) over a period of two years (2019 and 2020). We explain and relate the significance of human activities to the concentration level of NO(2), particularly considering the effect of the COVID-19 lockdown to the periodicity of NO(2). The results show that NO(2) concentrations in desert areas such as Liwa and Al Quaa were unaffected by the lockdown period (April–July 2020) resulting from the COVID-19 pandemic. The other stations in the urban areas of Abu Dhabi city, Al Dhafra and Al Ain, showed a reduction in NO(2) during the lockdown. NO(2) is more highly concentrated during winter seasons than during other seasons. The periodicity of NO(2) lasted from a few days up to 16 days in most regions. However, some stations located in the Al Dhafra region, such as Al Ruwais and the Gayathi School stations, exhibited a longer period of more than 32 days with a 0.05 significance test. In the Abu Dhabi region, NO(2) lasted between 64 and 128 days at the Al Mafraq station. The correlation between the NO(2) concentration across several ground stations was studied using wavelet coherence.