Novel approaches to characterize environmental noise pollution and its sources in rapidly developing cities: Application to the sub-Saharan African city of Accra, Ghana

Abstract

Background: Cities in sub-Saharan Africa (SSA) are growing at a faster rate than in any other continent. Numerous transport, industrial, and commercial sources of environmental noise pollution may be present, however, little is known about the levels and patterns of noise and its sources in SSA cities.Methods: We deployed an extensive monitoring campaign to characterize the space-time patterns of environmental noise and identify sources in the city of Accra, Ghana. We measured and analyzed sound level data and audio from ~150 locations that were monitored for either 7-days (n=140 locations) or 1-year (n=10 locations) from April 2019 to May 2020. We calculated metrics of environmental noise including A-weighted 24hr, day, and night sound levels (LAeq24hr, Lday, Lnight), and an event-based metric called the Intermittency Ratio (IR, % of event-based sound energy). Audio recordings were analyzed for types of sounds (i.e., sources) using a pre-trained neural network.Results: Most residential areas (95% of site-days) exceeded the national noise guidelines (Day 55; Night 48 dBA). Commercial, business, and industrial areas had the highest median Lday (69 dBA [Interquartile range (IQR) 59, 76]) and Lnight (63 dBA [IQR 58, 67]) and the lowest median percent of event-based sound (46% [IQR 30, 57]), while the inverse was true for peri-urban background areas. The most predominant sources of sound in the city were from road transport, animals, human speech, and outdoor music (present 75%, 24%, 23%, and 12% of the time, respectively), and these sounds varied between location and time with animal sounds occurring most often in background areas at night and road transport sounds in commercial, business, and industrial areas.Conclusion: Noise levels in Accra are higher than in most high-income country cities and should be prioritized as an environmental health risk in stronger policies and regulation.