The association of residential greenery with noise annoyance depends on transport source and environmental context: Insights from the large-scale NORAH study.

A growing body of literature highlights residential greenery (green vegetation in general and/or greenspaces) as a means to reduce negative health effects of transportation noise. A recent study using the Swiss nation-wide SiRENE survey data revealed that residential greenery was associated with reduced road traffic and railway noise annoyance, but increased aircraft noise annoyance. While the findings on road traffic and railway noise annoyance were expected, those on aircraft noise annoyance were unexpected. The aim of the current study therefore was to test the generalizability of the latter findings with data from the cross-sectional German NORAH study, which covers four major German airport regions with records of 26,607 individual participants. We complemented the NORAH data set with the metric "normalized difference vegetation index (NDVI)" for greenery and a metric for public greenspaces, and reanalyzed the associations of annoyance with residential greenery and noise exposure. Overall, we found road traffic noise annoyance to decrease with increasing greenery for day-evening-night-levels (L) of up to around 60 dB, but to increase at higher L. For aircraft noise annoyance, in contrast, the opposite was true, with a turning point at around 55 dB L. For railway noise, no consistent trend was observed. Our results thus confirm the findings from the SiRENE survey for road traffic and aircraft noise annoyance, except that residential greenery was found to be a moderator. Our study also shows that whether and how residential greenery is associated with noise annoyance depends on the noise source, noise level and environmental context.