Effects of elevated humidity on stratospheric ozone content in the tropics

Abstract

This study examines the effects of elevated humidity on stratospheric ozone content in the tropics, a case study of Nigeria. The specific stations in Nigeria studied with their co-ordinate include Makurdi (7.7°N 8.5°E), Maiduguri (11.9°N 13.2°E), Kano (12.0°N 8.5°E), Port-Harcourt (4.9°N 7.0°E) and Lagos (6.5°N 3.4°E). Using monthly mean stratospheric ozone data from Earth Probe Total Ozone Mass Spectroscopy (EPTOMS) together with humidity and temperature data from the Nigerian Meteorological Agency (NIMET), studies were carried out over the five stations for a period of fifteen years (1998-2012). The results show that elevated humidity cools the stratosphere, slowing down the rate of chemical reactions that destroy ozone, thereby resulting to more ozone amount. Ozone variation is latitude dependent with more variations in station observed in the north. Using Spearman’s Rank Correlation Coefficient analysis, it was equally observed that ozone and temperature are strongly anti-correlated in Port Harcourt, Makurdi and Lagos stations (r = -0.8531, -0.7832, and -0.8759, respectively); and positively correlated in Maiduguri and Kano stations (r = 0.3776 and 0.4965, respectively). The positive correlation may be attributed to the high dehydration of water vapor in those stations. Results also revealed that ozone and humidity are positively correlated (r = 0.9073, 0.9021, 0.7133, 0.7552, and 0.7692), for Port Harcourt, Makurdi, Maiduguri, Lagos, and Kano. Both ozone and humidity attain maximum during wet season and minimum during the dry season in Nigeria. The implication of more humidity in the wet season is due to the evaporation of raindrops and surface puddles. The implication of more ozone concentration in the wet season may be attributed to the transportation of ozone from the influence of Brewer-Dobson Circulation (BDC). Again it was found out that temperature and humidity are negatively correlated. Consequently, our findings show that, at elevated humidity, the surface temperature is low with more stratospheric ozone content. Key words: Humidity, stratospheric ozone, temperature, rainfall.