Influence of the rainfall and temperature oscillation on air quality in Kathmandu valley: The wavelet analysis.

In this study, wavelet analysis and traditional cross-correlation analysis (TCA) have been employed to explore the temporal characteristics of the Air Quality Index (AQI) (PM2.5) and its relationships with meteorological factors, air temperature, and rainfall in the capital city of Nepal, Kathmandu, during 2017 - 2020. The temporal variation of monthly averaged (AQI) (PM2.5) revealed that the air quality was unhealthy in winter, improved in summer, and subsequently became unhealthy again in autumn and spring. We also noticed that the lowest AQI (PM2.5) was recorded in 2020, which is due to the COVID-19 pandemic lockdown. By analyzing the time-frequency relationship of (AQI) (PM2.5) with air temperature and rainfall, using Cross Wavelet Transform (XWT), we observed the interannual, seasonal, and monthly common periodicity between them. The coherency of XWT is then tested by using Wavelet Transform Coherence (WTC), which showed a negative correlation of AQI (PM2.5) with rainfall and air temperature, while an anomaly was seen among AQI (PM2.5) and temperature as they were positively associated for a few months in 2017, 2018, and 2020. Moreover, the results of cross-correlation and multiresolution analysis (MRA) are consistent with wavelet analysis, indicating the driving effect of air temperature and rainfall on (AQI) (PM2.5). [ABSTRACT FROM AUTHOR]