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Aims We investigated the effects of exposure to very low levels of particulate matter <2.5 µm (PM2.5) and nitrogen dioxide (NO2) on coronary calcium score (CCS) in asymptomatic adults who are free of coronary artery disease (CAD). Methods and results This study included 606 asymptomatic adults (49% men, aged 56±7 years) recruited from communities in three states of Australia during 2017–2018. CCS was measured using coronary computed tomography scan at recruitment. Annual PM2.5 and NO2 concentrations were estimated on the year before recruitment using statistical exposure models and assigned to each participant’s residential address. Medical history, physical measurements, biochemistry, and sociodemographic and socioeconomic status were also recorded. Median concentrations of PM2.5 and NO2 were 6.9 µg/m3 [interquartile range (IQR) 6.0–7.7)] and 3.1 ppb [IQR 2.2–4.5], respectively. Of the 606 participants, 16% had high CCS (≥100) and 4% had very high CCS (≥400). Exposure to higher PM2.5 (per µg/m3) was significantly associated with greater odds of having high CCS (OR 1.20, 95% CI 1.02–1.43) and very high CCS (OR 1.55, 95% CI 1.05–2.29). Similar associations were observed for NO2 and high CCS (OR 1.14, 95% CI 1.02–1.27) and very high CCS (OR 1.23, 95% CI 1.07–1.51). These findings were robust to adjustment for sociodemographic factors, traditional cardiovascular risk factors, renal function, education, and socio-economic status. Conclusions Ambient air pollution even at low concentration was associated with degree of coronary artery calcification among asymptomatic low cardiovascular risk adults, independent of other risk factors. These findings suggest that air pollution is one of the residual risk factors of CAD.