Associations of traffic-related air pollution and greenery with academic outcomes among primary schoolchildren

Background: There is preliminary evidence that greenery/greenspace around schools may be positively associated with children's cognitive development and academic outcomes, whereas traffic-related air pollution (TRAP) may have a detrimental effect. Few studies have examined pathways between both exposures and academic outcomes. This study aimed to assess associations between greenery, road traffic density (a proxy for TRAP) surrounding primary (elementary) schools, and academic achievement of primary schoolchildren in Melbourne, Australia.Methods: This cross-sectional study examined mean academic scores in Years 3 and 5 for primary schools (n = 851) in Greater Melbourne. Scores were from the 2018 'National Assessment Program - Literacy and Numeracy' (NAPLAN) in five domains: 'Reading'; 'Writing'; 'Spelling'; 'Grammar & Punctuation' and 'Numeracy'. Greenery was measured within school boundaries and surrounding Euclidean buffers (100, 300, 1000 and 2000 m) using the Normalized Difference Vegetation Index (NDVI). Measured TRAP proxies were weighted road density (WRD) within the buffers and distance to a major road. Generalised Linear Models were used to examine associations of greenery and TRAP with academic scores (adjusted for school socio-educational status), and to identify mediating pathways.Results: Greenery was positively associated with Reading scores in Year 3 (all buffers except 2000 m) and in Year 5 (all buffers), with Numeracy in Years 3 and 5 (all buffers) and with Grammar & Punctuation in Year 5 (all buffers). WRD was inversely associated with Reading scores in Year 5 (all buffers), with Numeracy in Year 3 (all buffers) and Year 5 (300 and 1000 m buffers), and with Grammar & Punctuation in Year 3 (100 and 300 m buffers) and Year 5 (all buffers). Distance to a major road was not associated with any score. TRAP partially mediated associations of greenery within 300 m with Numeracy in Year 3 and Grammar & Punctuation in Year 5, and within 2000 m for Reading in Year 5.Conclusions: Preliminary evidence indicated that greenery around primary schools was positively associated with Reading, Numeracy and Grammar & Punctuation scores, with TRAP mediating some associations. Further research is required to improve TRAP exposure assessment around schools to verify these findings and inform town/school planners and educators regarding optimal school locations and environments for promoting learning