Long-Term Characteristics of Atmospheric Ventilation over Abuja, Nigeria: Variability, Trends, and Extreme Events

Abstract

Atmospheric ventilation plays a critical role in determining the capacity of the atmosphere to disperse pollutants and maintain air quality in urban environments. However, long-term information on atmospheric ventilation characteristics over rapidly growing tropical cities remains limited. This study investigated the climatology, interannual variability, long-term trends, temporal stability, and extreme low-ventilation events associated with atmospheric ventilation over Abuja, Nigeria, using ERA5 reanalysis data from 2016 to 2025. Boundary-layer height (BLH), wind speed (WS), ventilation coefficient (VC), and 2-m air temperature (T2M) were analyzed using climatological, trend, variability, and extreme-event approaches. The results revealed pronounced seasonal variability in BLH and VC, indicating the strong influence of atmospheric mixing processes on ventilation conditions. Annual mean BLH ranged from 569.39 to 631.47 m, while VC varied between 835.63 and 959.86 m² s⁻¹ during the study period. Trend analysis showed a statistically significant increase in T2M of 0.091 °C yr⁻¹ with 0.028 p value, corresponding to approximately 0.9 °C of warming over the decade. In contrast, no significant long-term trends were observed in BLH, WS, or VC (p > 0.05), suggesting that atmospheric ventilation remained relatively stable despite increasing temperatures. Stability analysis indicated that BLH and VC exhibited coefficients of variation (CV) of 112.30% and 115.12%, respectively, compared with 48.88% for WS and 14.66% for T2M. The twenty lowest ventilation events were characterized by exceptionally shallow boundary layers and weak winds, with most occurring during nighttime and early-morning hours and concentrated between September and December. The findings demonstrate that atmospheric ventilation over Abuja is strongly influenced by boundary-layer dynamics and exhibits substantial temporal variability but limited long-term change. This study provides the first decadal assessment of atmospheric ventilation over Abuja and offers valuable information for air-quality management, environmental planning, and future climate-impact assessments in tropical urban environments.