Spatial modelling and inequalities of environmental noise in Accra, Ghana

Abstract

Noise pollution is a growing environmental health concern in rapidly urbanizing sub-Saharan African (SSA) cities. However, limited city-wide data constitutes a major barrier to investigating health impacts as well as implementing environmental policy in this growing population. As such, in this first of its kind study in West Africa, we measured, modelled and predicted environmental noise across the Greater Accra Metropolitan Area (GAMA) in Ghana, and evaluated inequalities in exposures by socioeconomic factors. Specifically, we measured environmental noise at 146 locations with weekly (n = 136 locations) and yearlong monitoring (n = 10 locations). We combined these data with geospatial and meteorological predictor variables to develop high-resolution land use regression (LUR) models to predict annual average noise levels (LAeq_24hr, L_den, L_day, L_night). The final LUR models were selected with a forward stepwise procedure and performance was evaluated with cross-validation. We spatially joined model predictions with national census data to estimate population levels of, and potential socioeconomic inequalities in, noise levels at the census enumeration-area level. Variables representing road-traffic and vegetation explained the most variation in noise levels at each site. Predicted day-evening-night (L_den) noise levels were highest in the city-center (Accra Metropolis) (median: 64.0 dBA) and near major roads (median: 68.5 dBA). In the Accra Metropolis, almost the entire population lived in areas where predicted L_den and night-time noise (L_night) surpassed World Health Organization guidelines for road-traffic noise (L_den <53; and L_night <45). The poorest areas in Accra also had significantly higher median L_den and L_night compared with the wealthiest ones, with a difference of ∼5 dBA. The models can support environmental epidemiological studies, burden of disease assessments, and policies and interventions that address underlying causes of noise exposure inequalities within Accra.

Keywords: Environmental noise; Intermittency ratio; Land use regression; Road-traffic noise; Socioeconomic status; Sub-Saharan Africa.

Fig. 1

Locations of rotating and fixed measurement sites in the Greater Accra Metropolitan Area (GAMA). The GAMA, Accra Metropolis, and Tema boundaries are from the Ghana Statistical Service, road-network and water-body shapefiles are from OpenStreetMap (2019).

Fig. 2

Predicted noise levels in the Greater Accra Metropolitan Area. Predictions were made for a fixed height of 4 m off the ground onto an ~50 m × 50 m grid of the city and calculated from the 24 surfaces of long-term hourly averages. Grey areas on the map represent areas excluded from prediction as they are out of sample (e.g., water bodies, forest/grassland). Legend: LAeq_24hr (dBA): 24-h equivalent continuous A-weighted noise level; L_den (dBA): Day-evening-night equivalent continuous A-weighted noise level. L_den was calculated with respect to day-time: 6am-6pm (13 h); evening: 7pm–9pm (3 h); night-time: 10pm-5am (8 h); L_day (dBA): Day-time equivalent continuous A-weighted noise level (6am-9:59 pm); L_night (dBA): Night-time equivalent continuous A-weighted noise level (10:00pm-5:59 am).

Fig. 3

Cumulative densities of the proportion of the Accra Metropolis population living in enumeration areas (EA) with varying noise levels. The solid grey vertical line and the dashed black vertical line shows the L_den and L_night limits for road-traffic noise based on WHO guidelines for the European region, respectively (World Health Organization, 2018).

Fig. 4

Distribution of enumeration area (EA) L_denand L_nightacross quintiles (20% increments) of EA socioeconomic status (SES) in Accra Metropolis. SES: EA median log equivalized household consumption. The upper and lower limits of the black box represent the interquartile range of the distribution and the horizontal line within the box represents the median. Each colored point represents an EA average noise level (dBA).