Variability of Surface Air Temperature and Relative Humidity at a Tropical Site in Osogbo, Nigeria

Abstract

The warmness experienced at the lowest strata of the Earth’s atmosphere is largely caused by the increase in air temperature and relative humidity due to the greenhouse gases (GHGs). Consequently, this has a significant impact on health conditions and is detrimental to human fitness. However, changes in response to the climatic forcing within the boundary layer has substantial impacts on temporal trends of the atmospheric parameters. Therefore, this study utilized eight weeks (8) PurpleAir data (May 1 to June, 30, 2022) acquired from African Centre for Space Science and Technology Education (UN-ARCSSTE-E), NASRDA situated at the Osun State University, Campus, Osogbo, Osun-State to study the variation of surface air temperature, relative humidity and the nexus in the variability. The data collected were sampled at 2 s interval and the dataset was reduced to 30 30-minute averages for each day and the statistical analyses were carried out using Micro Cal Origin software and Open-Air project for R-statistics. The results showed that at night, the air temperature had a similar relationship with relative humidity, it was still lower than the optimum temperature zone, say, (24-30°C). Additionally, two relative humidity peaks were observed in the early morning and at night, aligning with two low points (troughs) in surface temperature. These low temperatures were primarily due to nighttime cooling and loss of heat through long-wave radiation. The relative humidity peaks observed in the early morning were attributed to intensified convective activities. Also, the atmosphere was noticed to be more stable at night with reduced turbulence. This stability impedes vertical mixing, allowing moisture to accumulate near the surface, thereby contributing to the higher relative humidity observed during nighttime hours. Correlation analysis between temperature and relative humidity showed that from week 1 to week 8, surface air temperature had a cumulative decrease of 1.32oC while relative humidity had a cumulative increase of 4.25% at Osogbo. On average, 3.21% increase in relative humidity had a correlation of 1oC decrease in surface air temperature at Osogbo.