Space-time characterization of community noise and sound sources in Accra, Ghana

Abstract

Urban noise pollution is an emerging public health concern in growing cities in sub-Saharan Africa (SSA), but the sound environment in SSA cities is understudied. We leveraged a large-scale measurement campaign to characterize the spatial and temporal patterns of measured sound levels and sound sources in Accra, Ghana. We measured sound levels and recorded audio clips at 146 representative locations, involving 7-days (136 locations) and 1-year measurements between 2019 and 2020. We calculated metrics of noise levels and intermittency and analyzed audio recordings using a pre-trained neural network to identify sources. Commercial, business, and industrial areas and areas near major roads had the highest median daily sound levels (LAeq_24hr: 69 dBA and 72 dBA) and the lowest percentage of intermittent sound; the vice-versa was found for peri urban areas. Road-transport sounds dominated the overall sound environment but mixtures of other sound sources, including animals, human speech, and outdoor music, dominated in various locations and at different times. Environmental noise levels in Accra exceeded both international and national health-based guidelines. Detailed information on the acoustical environmental quality (including sound levels and types) in Accra may guide environmental policy formulation and evaluation to improve the health of urban residents.

Figure 1

Median sound level and intermittency metrics for rotating and fixed site locations in the GAMA. For the color legend scales, a bracket means that the value in the range is included and a parenthesis means that the value in the range is not included. Road network is from OpenStreetMap and the Greater Accra Metropolitan Area (GAMA) and Accra Metropolitan Area (AMA) boundary from Ghana Statistical Service. A waterbody is depicted on the map in light blue. LAeq_24hr: A-weighted equivalent continuous 24-h sound level; L_day and L_night: A-weighted equivalent continuous sound level in the day and night-time; IR_24hr: 24-h Intermittency Ratio.

Figure 2

Cumulative density (distribution) functions (CDF) of 1-min sound levels (dBA) across a 24-h day period in the Greater Accra Metropolitan Area. Data from rotating sites. Blue lines represent time periods in the nighttime and early morning (8 pm–8 am) and red and orange lines represent periods in the daytime (8 am–8 pm). CBI: Commercial, business, industrial areas; LAeq: 1-min A-weighted equivalent continuous sound level; dBA: A-weighted decibels.

Figure 3

Prevalence of sound sources within land use areas and varying sound levels (LAeq_1min) in the Greater Accra Metropolitan Area. Data from rotating sites. The percentage of site-time that each sound source was present was calculated from the data within each land use area and sound level interval separately.

Figure 4

Diurnal patterns of the percentage of site-time that detected road-transport, animal and insect, human speech, outdoor music and nature sound sources were present for each hour of the day and within land use areas in the Greater Accra Metropolitan Area. Data are from rotating sites, but fixed sites had similar trends.