Spatiotemporal patterns and socioeconomic inequalities of noise and sound sources in Accra, Ghana

Abstract

The urban environment is made up of mixtures of mechanical, human, animal, and natural sounds with diverse acoustical qualities. Epidemiological evidence has shown that noise pollution - generally understood as loud, unwanted sound – can have adverse effects on multiple health states and outcomes. In growing sub-Saharan African (SSA) cities, noise pollution is an emerging public health concern. Yet limited local information on spatiotemporal variations and inequalities of sound environments is a barrier to the formulation and evaluation of environmental policies and management strategies.

My PhD research helps fills this data and information gap in a growing sub-Saharan African metropolis. I characterised and modelled the spatiotemporal patterns and socioeconomic inequalities of the outdoor sound environment and its sources in Accra, Ghana.

I designed and implemented a large-scale 1-year measurement campaign (April 2019 - June 2020) to collect data on sound sources and levels with audio recorders and sound level meters at 146 representative road-side locations (136 weeklong and 10 yearlong) in the Greater Accra Metropolitan Area (GAMA, ~5 million people, 1500 km2). To detect different types of urban sounds, such as road-transport, air-transport, music, human speech, nature, and animals, I applied a pre-trained deep learning acoustic classifier to the audio recordings. I used descriptive statistics and land use regression (LUR) methods to characterise and predict trends in sound levels (dBA), sound intermittency (Intermittency Ratio: % of sound energy from events) and the presence of different types of sounds (i.e., sources) across space and multiple time scales. I then linked aggregated census data at the enumeration area level (i.e., small census tracts) to estimate population exposures to, and socioeconomic (SES) inequalities in, the urban sound environment in Accra Metropolis, the main city area (~2 million people). SES metrics included household consumption, higher educational attainment, and unemployment.

Road transportation was the most identified source of environmental noise and was pervasive throughout Accra Metropolis. However, mixtures of different sound types were prevalent in different places and times of the day, such as animal and insect sound in peri-urban as well as higher SES areas in Accra Metropolis. Additionally, outdoor music and human speech sounds were more common in lower SES, high-density residential neighbourhoods, particularly during the daytime. Nature-based sounds were relatively uncommon, but more prevalent in peri-urban areas.

Measured and model predicted day-evening-night (Lden) and night-time (Lnight) equivalent continuous sound levels surpassed local1 and international2 guidelines almost everywhere in the GAMA, with significant spatial variations in magnitude. In Accra Metropolis, enumeration area Lden and Lnight followed a socioeconomic gradient; the lowest SES enumeration areas had higher median Lden and Lnight compared with higher SES areas. Furthermore, areas in the GAMA which had both high Lnight (≥ 50 dBA) and intermittent night-time sound (IRnight ≥ 50%), were predominantly found in the city’s poorest residential neighbourhoods.

The measured sound environment did change throughout the city during periods of extreme disruption or planned traditional festivals. Significant reductions in measured sound levels were observed during the COVID-19 pandemic lockdown (~ 6 dBA median reduction) in April 2020. Reductions were also observed at two of the long-term high-density residential sites during an annual 1-month ban on ‘drumming and noise making’ preceding the celebration of the Homowo festival (~ 3 dBA median reduction).

Sound levels in Accra Metropolis were generally higher than in cities in North America and Europe, and similar to a major city in South America, with estimates from either LUR or propagation-based models. Stronger noise policy is needed to ensure that permissible limits, which are in place to safeguard public health, are met. Furthermore, equitable city-level actions and interventions in relation to urban infrastructure (e.g., road-networks, buildings, parks) and services (e.g., transportation) are needed to reduce noise from specific sources and improve sound environments in Accra that could also have broader benefits for health and wellbeing.