Assessment of outdoor-to-indoor noise attenuation levels for night-time residential noise exposure

Although people spend most of their night-time hours indoors, environmental noise exposure is typically assessed using outdoor levels. This study examined outdoor-to-indoor noise attenuation across 49 dwellings in Greater London using synchronized and unsupervised measurements, while noise levels were expressed via the A-weighted equivalent ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>L</mml:mi> <mml:mrow> <mml:mi>A</mml:mi> <mml:mi>e</mml:mi> <mml:mi>q</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ), maximum ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>L</mml:mi> <mml:mrow> <mml:mi>A</mml:mi> <mml:mi>m</mml:mi> <mml:mi>a</mml:mi> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ), and percentile ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>L</mml:mi> <mml:mrow> <mml:mi>A</mml:mi> <mml:mn>01</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>L</mml:mi> <mml:mrow> <mml:mi>A</mml:mi> <mml:mn>05</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>L</mml:mi> <mml:mrow> <mml:mi>A</mml:mi> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) noise indicators. Moderate-to-strong correlations between night-time outdoor levels and outdoor-to-indoor attenuation levels ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>r</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:math> – <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:mn>8</mml:mn> </mml:mrow> </mml:math> ) informed the development of multiple and mixed-effect linear regression models to estimate indoor noise levels based on outdoor levels. Mixed-effect models outperformed multiple linear models (RMSE: 0.7–4.9 vs 2.3–5.7 dB(A)), with outdoor levels accounting for most variability, and with additional contributions from the occupation status, window size, and room volume predictors. The estimated attenuation levels ranged from 20 to 26 dB(A), with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>L</mml:mi> <mml:mrow> <mml:mi>A</mml:mi> <mml:mi>e</mml:mi> <mml:mi>q</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> in line with the WHO recommended 25 dB(A) level. The proposed modeling approach enables estimates of indoor noise exposure, offering a more representative basis for night-time exposure–response assessments in the UK and similar urban settings.