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Volume : 44

Part : 2

Proceedings of the Institute of Acoustics

 

 

Objective and perceived acoustic environments during the COVID-19 lockdown: An overview of evidence

 

Angel M. Dzhambov1, Medical University of Plovdiv, Plovdiv, Bulgaria

 

ABSTRACT

 

The COVID-19 pandemic took a heavy toll on population health directly, but also triggered profound changes to social life, daily mobility patterns, and activity spaces. At the beginning, public health measures for limiting the spread of the virus mandated home confinement and limited outdoor activities, which in turn reshaped typical acoustic environments for many people. This overview provides a synopsis of the evidence of changes to residential noise exposure and perceived soundscape quality and components across different contexts. Most studies reported sound level reductions in the range of 4-10 dB. Reductions were larger on weekends compared with weekdays, and in previously socially active areas compared with traffic-dominated locations. People had a clear preference for the new lockdown soundscapes. Traffic noise levels reportedly declined across various settings, allowing for natural sounds, hitherto masked, to become more prominent.

 

Keywords: confinement; pandemic; soundscape; traffic noise

 

1. INTRODUCTION

 

The shut-down of non-essential businesses and restriction of human movement imposed by many governments during the initial stages of the SARS-CoV-2 virus pandemic in 2020 caused major disruptions to social life and traffic flows all over the globe [1], so much so that the Earth underwent the “longest and most prominent global anthropogenic seismic noise reduction on record” [2]. Traffic noise and social sound levels reportedly declined across various settings, allowing for natural sounds, hitherto masked, to become more prominent. On the other hand, prolonged home confinement made indoor sounds, such as mechanical sounds, human voices, and noise generated by neighbors, even more relevant for the well-being of building occupants. These profound changes to sound typologies made possible unprecedented experiments to better understand the implications of these “lockdown soundscapes” [3]. This overview provides a synopsis of the evidence of changes to residential noise exposure and perceived soundscape quality and components across different contexts.

 

2. METHODS

 

The author performed a rapid review of published literature up until March 23 2022. Electronic database searches were limited to MEDLINE and Scopus. In addition, searches in Google, reference lists of included publications, and the personal records of the author retrieved additional study records. Keywords used in different combinations were “pandemic”, “covid”, “confinement”, “soundscape”, and “noise”. Only publications in English describing empirical studies were considered. The studies included in this review focus on the change in objectively measured or perceived soundscape components in any environment during periods of strict lockdown, confinement, or restrictions related to the COVID-19 pandemic. However, underwater soundscapes or distinctive soundscapes (e.g., church bell and festival sound studies) were not considered due to time constraints.

 

3. RESULTS AND DISCUSSION

 

3.1. Urban Noise Levels

 

Four Spanish studies reported similar reductions and patterns in sound level change. In Barcelona, data from 70 sensors showed reductions during the lockdown (vs. pre-lockdown in 2020) of 5.6 dB LAeq, 4.4 dB L10, and 10 dB L90, and an increase in L10-L90 by 5.6 dB [4]. The reduction in LAeq was largest in areas previously hosting nightlife (9 dB), followed by commercial and restaurants areas (7 dB), and dense traffic areas (5 dB). When comparing sound levels to the same period in 2018/2019, reductions were slightly lower (2.5 dB LAeq, 1.5 dB L10, 6.5 dB L90), and L10-L90 was increased by 4.9 dB. The greatest reduction of over 7 dB was seen on Fridays and Saturdays. Thirty one monitoring stations in Madrid documented an average reduction during the lockdown of 4-6 dB Lday, Levening, Lnight [5]. Here too, sound levels were reduced more on weekends due to the absence of leisure and commercial activity, especially in previously socially active areas, where the drop reached 11.2 dB. During weekends the activity started earlier in the morning and ended earlier in the afternoon. Of note, a seemingly counterintuitive rise in Lnight at one location was explained by the presence of a field hospital nearby. In Girona, nightlife areas also experienced the greatest reduction in sound levels, followed by commercial and restaurants areas, and dense traffic areas. Reductions were more pronounced on weekends and at night. For example, at a nightlife location, the weekend reduction in Lnight was 11 dB compared with 5 dB on weekdays [6]. Reductions in Lnight were 10-15 dB in the quiet area on weekend evenings and 8-12 dB in restaurant areas. Conversely, the traffic location saw smaller 2- and 8-dB reductions in Lnight on weekdays and weekends, respectively. These three Spanish studies [4-6] observed a novel soundmark at 8 p.m. due to the daily applause that people gave from balconies and windows in support of healthcare workers. Lenzi et al. set up a monitoring station at Plaza de las Escuelas (Basque Country) where multiple sources contributed to soundscape [7]. Psychoacoustic indicators were calculated from audio recordings, and recorded sounds were annotated by experts. Mean LAeq was 55.9 dB during the first lockdown phase, 53.6 dB during the strict lockdown that followed, and 53.1 dB during the easing of restrictions. Despite these small differences, the soundscape of this place underwent considerable changes. Natural sounds increased and human sounds decreased during phase 2, and retuned to baseline in phase 3, while technological sounds continued to decrease. During the strict lockdown, there was a decrease in eventfulness and loudness and an increase in pleasantness. Upon easing the lockdown, street life and sounds returned to baseline, which precipitated an increase in acoustic complexity and acoustic richness.

 

Pagès et al. used data from a network of low-cost sensors in Milan and Rome [8]. They found an average reduction of 7.3-7.6 dB Lden, reaching a maximum of 11.7-12.8 dB in Milan. In Rome, these figures were 5.2-5.4 dB and 8.8 dB, respectively. The authors noted increased detection of anomalous noise events, especially during weekends, due to unmasking.

 

Aletta et al. carried out binaural recordings at 11 locations in London and observed an average decrease in LAeq, L10, and L90 of about 5.4 dB [9]. However, these reductions varied across London (1.2 dB to 10.7 dB LAeq), with the largest reductions in previously active areas dominated by human sounds, followed by previously traffic-dominated areas, and quiet areas. L10 and L90 showed lower values during the pandemic at previously busy sites, but changes were minimal or absent in quiet areas. Loudness was reduced by 0.7-11.2 sone. Of note, presence of water features affected other soundscape descriptors, exemplified by the major reduction in sharpness at one location where a previously active fountain did not function during the lockdown, while the opposite was seen at another location where sharpness did not change as a nearby waterfall kept functioning. Another UK study was set up around a school in Guildford [10]. The location was on a heavily trafficked conjunction where both traffic and human sounds were prominent. Upon lockdown ease, lockdown sound levels increased by 2-3 dB throughout the week, with daytime noise, Lday, having the largest increase by up to 5 dB.

 

Hornberg et al. used data from 22 monitoring locations with different land use in Ruhr, Germany [11]. The mean overall sound level dropped by 5.1 dB, but that varied across land use classes. Urban forests, green spaces, and residential areas experienced a decrease of 5.9 dB each, while traffic locations only saw a 3.9 dB reduction. Diurnal sound level dynamics during the pandemic closely followed pre-pandemic patterns, although the curve was shifted towards lower absolute levels. The two curves came closest at around 6 am (Δ 1.7 dB) and were farthest apart at 9 pm (Δ 7.7 dB). Like in the other studies [4-6], largest reductions in LAeq were measured on weekends, in particular Sundays (6.5 dB), while on Saturdays the reduction was smaller (3.8 dB). Interestingly, the anticipation of the restrictions, reinforced by media coverage of the pandemic, led to a drop of LAeq already before the lockdown came into effect, with the exception of the week before the lockdown, when news about possible supply shortages caused many people to rush to do final errands [11].

 

Similarly, in Kanpur, India, sound level changes were not uniform across land uses [12]. Sensors in commercial and industrial areas registered a 6 dB reduction in LAeq, while in two quiet areas the corresponding reductions were 8 and 18 dB, and two residential areas saw the largest reductions (13 and 23 dB). During the lockdown, there was a peak in sound level at around 8-9 am and a smaller peak in the evening.

 

Across five measurement sites in Buenos Aires [13], average reduction were 2.3 dB (1.4-4.7 dB) for Lden and reached 4.1 dB (2.7-6.9 dB) for Lnight. The maximum daytime reduction was 4.7 dB at a traffic site, while the smallest at another location, where public bus traffic persisted, was 1.4 dB. In Lima, aircraft Lden at the airport was reduced by 7.1 dB [14]. At night, reductions were larger (10.6 dB), compared with daytime (4.4 dB) and evenings (5.4 dB). This nighttime decrease was mostly due to the reduced number of distinct noise events (11.5 dB lower L10 at night).

 

A case study was reported from Sweden, where no lockdown was established, as the country took a softer approach towards the pandemic [15]. Sound levels were measured at one location at a building façade at the corner of a busy crossroad in central Stockholm. The authors reported a peak drop of more than 4 dB in April 2020. Again, the reduction was more pronounced during the weekend (3 dB) than on weekdays (1.9 dB).

 

In the Boston area [16], a 1–3 dB reduction in LAeq during the lockdown was registered in protected urban areas close to the city center. However, there was a 4–6 dB increase in another area that was close to a highway. The latter finding was explained by the greater vehicle speeds that were possible on that section of the highway as a result of lessened traffic congestion during the lockdown.

 

Major reductions in road network (7.6 dB) and airport noise levels (21.5 dB Lden) in France and 9 dB lower noise levels in Barcelona were also reported (Bruitparif and Ajuntament de Barcelona, cited by [9]).

 

3.2. Perceived Urban Soundscapes

 

Online surveys were conducted to understand how people perceived lockdown soundscapes in different contexts. Torresin et al. [17, 18] conducted a survey on indoor soundscapes in 464 Londoners. In terms of the appropriateness of the indoor sonic environment for the activities performed at home, more than half of respondents reported that it was very/perfectly appropriate for working from home and relaxation. In terms of soundscape dimensions, spaces appropriate for relaxation had high comfort, whereas spaces appropriate for working from home had high comfort and low content scores (more private and under control rooms) [17]. Different sounds contributed differently to the dimensions of comfort and content and the importance of different sounds depended on the activity performed and circumstantial factors [18]. Well-being was associated with more comfortable soundscapes with lower content.

 

In 323 Bulgarian university students who spent over 20 hours/day at home, self-rated health was associated with less perceived mechanical sounds and natural sounds – natural sounds related to stronger feelings of being away from stressors and demands, while the opposite association was found with mechanical sounds [19]. Human sounds and music had no apparent effect [19]. In general, people reported noticing more natural sounds and less mechanical and traffic noise during the lockdown, and expressed higher preference for lockdown soundscapes. In a nationwide Argentinean survey (n=1371), perceived mechanical sounds dropped by 58-73%, biological sounds increased by 29-53%, environmental increased by 24-39%, and human increased by 1-12% [20]. Biological sounds showed the greatest increase in big cities. 74.5% of the participants perceived the acoustic environment as more pleasant during the lockdown, where previously louder places near the house showed a higher percentage of preference for the new acoustic environment. People’s emotional appraisal of the acoustic environment was dominated by irritation before the lockdown and by tranquility and happiness during the lockdown. In Catalonia, Spain, people also preferred the lockdown soundscape [21]. Overall satisfaction increased from 16.4% pre-lockdown to 63.4% during lockdown, and then dropped to 27.3% post-lockdown. During lockdown, the soundscape was described with adjectives like “exciting”, “calming”, and “pleasant”, but post-lockdown, participants reported a decrease in perceived bird (-16%) and neighbor (-10%) sounds, and some increase in traffic sounds (4-7%).

 

Similarly, across Italy, road traffic noise and mechanical sounds in the dwelling were reduced in 38% and 15%, respectively, while natural sounds increased in 13% [22]. This corresponded to decreases in noise annoyance (e.g., 23% for road traffic), perceived improvement in sound quality, and increased appropriateness of the sonic environment. Another Italian study combined an online survey (n=200) with recordings made by 50 participants using smartphone apps [23]. The majority of participants reported that they realized how much the acoustic environment had changed during lockdown and half had started paying attention to it, discovering previously unnoticed sound layers. Making recordings had helped participants realize the effects of the lockdown.

 

Other surveys combined questionnaire data with field measurements. Data from 21 monitoring stations across five cities in France showed an average reduction of 4-6 dB Lden, reaching up to 10 dB at four locations [24]. These reductions were more pronounced on weekends in Lyon, Aix, Saint-Etienne and Toulouse, while in Grenoble the trend was opposite. Throughout the day, reductions were uniform with one exception where the reduction during the night was larger (> 10 dB). This study also surveyed a large sample of 3242 people and found major decreases in noise annoyance, most pronounced in suburban areas and in Nantes conurbation (participants from Nantes lived next to an airport, which became largely inactive during the lockdown). Perceived traffic noise dropped considerably and natural sounds increased by some 50%, resulting in an overall perceptions of “calm”, “pleasant”, and “peaceful” soundscape.

 

Mitchell et al. [25] included 1136 participants in a field survey in 2019 and 86 participants in a subsequent online listening experiment in 2020. The study took place at 13 locations (11 in London and 2 in Venice) varying in typology. Binaural recordings were made twice, in 2019 and in 2020. A model was trained on the questionnaire responses from 2019, which was then used to develop soundscape predictions for pleasantness and eventfulness during lockdown from the acoustic data collected in 2020. Various classic and psychoacoustic indicators were calculated to enhance the predictions. In terms of sound levels, all locations experienced a reduction in LAeq reaching 5.2-10.5 dB. There was a general decrease in predicted eventfulness, while predicted changes in pleasantness were mixed across locations. Pleasantness increased in previously traffic-dominated locations, but not in human- and natural-dominated locations. Specifically, reductions in LAeq improved pleasantness only when the baseline sound level exceeded 60–65 dB. Locations, which had the most human sounds pre-pandemic, showed the greatest predicted reduction in eventfulness, but changes to psychoacoustic parameters like sharpness could cancel out the reduction in eventfulness. Participants perceived natural sounds as more dominant and human sounds as less dominant during the lockdown.

 

Aumond et al. [26] combined measurements from 15 sensors with sound recognition analysis in a small-scale survey (n=31) in France. There was a general decrease in LAeq of 5-10 dB, reaching 15 dB at one location. The reduction was more pronounced at traffic sites, and in one residential area there was a slight increase. Sound recognition analysis found a drastic reduction of road traffic and an increase of bird songs. Weekly dynamics were interesting, as on Wednesdays, when children had the afternoon off, sound levels were not so much reduced. In the afternoons and during the weekends, a quiet area saw an increase in human sounds. This study also looked at soundscape dimensions and found that pleasantness was associated with more bird sounds and less traffic noise, while eventfulness was positively associated with traffic noise.

 

In an international survey, 75% of respondents reported a significant reduction and improvement in outdoor sound levels [27]. Measurements at four locations in Italy (2 close to railways, 1 to a hospital), showed Lden levels in the range 43.3-67.2 and Lnight 38.4-57 dB, but no direct comparisons with measurements from previous time points were possible.

 

Across Spanish provinces [28], perceived sound quality at home also improved during the lockdown, resulting in a 20% drop in noise annoyance compared with pre-lockdown. That is, an almost twofold decrease of annoyance due to penetrating sounds. Participants also took audio recordings using smartphone apps. An average reduction of over 30 dB was registered, with 10 dB reductions in Lday and Levening, in Cordoba. As the restrictions were relaxed, sound levels and loudness increased.

 

Istanbul, Turkey, is an idiosyncratic case, as the country had declared partial lockdown during weekdays and a total holiday curfew (May 2020) [29]. Two measurement locations were selected (1 building on a main road and 1 in a housing estate near a greenspace). On weekdays (partial lockdown), sound levels were 2.1-2.4 dB lower than in 2017. However, during the holiday curfew, there was a 7.8 dB reduction at one building, but a 5 dB increase at the other. This increased sound level during the Ramadan holiday was explained by parks being closed and people instead gathering in the greenspace around their building. Previously noisier environments benefited more in terms of decline in noise annoyance of occupants, irrespective of their stress and anxiety levels during the pandemic. Specifically, annoyance due to traffic decreased, while annoyance by indoor noises (but not neighbors) increased.

 

3.3. Greenspace Soundscapes

 

Some studies were set up in green spaces, such as protected areas, parks, and urban green areas [30-33]. Users (n=109) of a walking and cycling path bordering a major highway in Antwerp, Belgium, were surveyed during the pandemic but in a period when the lockdown restrictions had already been lifted and sound levels had returned to pre-pandemic levels [31]. Highway noise emerged as dominant followed by traffic noise from other roads, while human and natural sounds were slightly noticeable, and railway and aircraft noises were mostly absent. Individual differences played a role in soundscape perception, as those who were more concerned about the pandemic were also more noise sensitive to natural and traffic sounds and attributed more importance to environmental quality than in the pre-pandemic period. In a Chinese study comparing pre-post visitor perceptions of a national park, post-lockdown visitors reported higher stress levels and the high stress group was more sensitive to natural soundscapes [32]. The authors examined how perceived restorativeness dimensions related to each other and found that in the high stress group the effects of perceived extent and fascination on compatibility were more pronounced.

 

In an international online survey of 3109 participants from Spain, England and Ireland, over 90% of participants reported improvement in outdoor natural sounds and traffic during the 1st wave of the pandemic [33]. Perceived improvement in natural sounds was greater among respondents from Spain and Ireland and in those who lived in urban areas.

 

Derryberry et al. specifically explored how the lockdown restrictions affected vocalization of the white-crowned sparrow in the San Francisco Bay Area [30]. Overall, there was a 7.4 dB LAeq reduction in sound levels in urban and 3.6 dB in rural areas; background noise (L90) dropped by 7 dB in urban and 1.4 dB in rural territories. That allowed birds to sing at lower amplitudes, vocal performance improved, and communication distance doubled, especially in urban areas.

 

3.4. Summary of Findings

 

Most studies reported sound level reductions in the range of 4-10 dB. A long-term reduction of traffic noise by “as few as” 5-10 dB could materially decrease the population-level risk of noise annoyance [34], sleep disturbance [35], cardio-metabolic diseases [36, 37], mental disorders [38], and adverse pregnancy outcomes [39]. Therefore, these changes would not be trivial for the global burden of disease, if they could be sustained after the pandemic. Some distinct temporal and spatial patterns emerged during the lockdown: 1) reductions were larger on weekends compared with weekdays, owing to the absence of active social life and leisure sounds; 2) previously socially active areas, especially those hosting nightlife, experienced larger reductions (sometimes two-fold) compared with traffic-dominated locations. These findings should be taken with a grain of salt though. Heterogeneity stemming from the diversity in contexts (e.g., severity of lockdown restrictions, measurement sites), sound sources, measurement procedures and setup, and reference periods against which lockdown data were compared, makes it difficult to derive a “pooled effect”. As a positive development, one can note that several studies employed a range of classic and psychoacoustic indicators. That answers a call for better operationalization and standardization of soundscape description to more fully understand human response to sounds [40].

 

Surveys showed that people had a clear preference for lockdown soundscapes. Traffic noise levels reportedly declined across various settings, allowing for natural sounds, hitherto masked, to become more prominent. While the focus of this review was mostly on changes in the acoustic environment, rather than on associated health outcomes, some of the soundscape surveys found benefits to well-being and perceived health. This is in line with a meta-analysis on health effects of natural sounds – water sounds were particularly associated with positive health and affective outcomes, and bird sounds, with lower stress and annoyance, especially in comparison to noise [41]. Besides shifting the balance between unwanted and wanted sounds, the pandemic silenced soundmarks embedded in local culture, such as outdoor festivals and religious sounds, and replaced them with novel ephemeral soundmarks, like the 8 o’clock applause for healthcare workers [1].

 

3.5. Limitations of the Review

 

The author carried out a rapid and non-systematic review of the literature, which may have missed pertinent studies. The electronic searches were restricted to two formal databases using a limited set of keywords. Coastal/underwater and idiosyncratic soundscape studies were not included. Neither the risk of bias in the studies included, nor the overall certainty of evidence were evaluated. Therefore, this review can be seen as a stepping stone to a comprehensive scoping review of the evidence. An extended version of this review is underway and will be published as a stand-alone peer-reviewed full-length paper.

 

4. CONCLUSIONS

 

Multiple studies that leveraged data from noise monitoring stations or conducted measurements found potentially important reductions of 4-10 dB in outdoor sounds levels. These changes were not uniform across different locations and depended on land use typology, dominant noise source, and other contextual factors.

 

The pandemic has provided us with the unique opportunity to appreciate, in a tangible way that would have otherwise been impossible, how urban soundscapes can change for the better. Now, the question is whether we will simply snap-back to our pre-COVID mindset or will make use of the momentum generated by the discourse on how much better sonic environments can become for both humans and wildlife.

 

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1 angelleloti@gmail.com; angel.dzhambov@mu-plovdiv.bg