a. Point estimates and 95% confidence intervals for PM
. Positive associations were observed for PM2.5 and SDNN, HF and LF. A negative association was observed for the LF/HF ratio. The largest increase observed wasa 7.7% (95% CI: 2.3 to 13.3) increase in HF per IQR 90-min PM2.5 (8.34 μ g/m3). Figure 1b. Point estimates and 95% confidence intervals for CO and CO2. The largest declines in SDNN were 4.2% (95% CI: 1.8 to 6.5) per IQR 30-min CO (10 ppm) and 4.1% (95% CI: 1.8 to 6.3) per IQR 60-min CO2 (104 ppm). Figure 1c. Point estimates and 95% confidence intervals for NO¬2 and NOx. The associations for CO, CO2, NO2 and NOx (which were all correlated) were similar with statistically significant associations observed for SDNN and, in a few instances, the LF/HF ratio, but not HF or LF. The influence of averaging period differed for each pollutant. The largest declines in SDNN for each pollutant were a 3.9% (95% CI: 1.7 to 6.1) per IQR 60-min NO2 (155ppb), and 4.4% (95% CI: 2.2 to 6.5) per IQR 30-min NOx (240 ppb). Figure 1d. Point estimates and 95% confidence intervals for ozone and formaldehyde. Associations increased in magnitude and significance with increasing averaging periods for all HRV parameters except the LF/HF ratio. The largest effects were observed for HF, including a 16% (95% CI: 9.0 to 23.4) decline per IQR 90-min ozone (65 ppb) and a 12% (95% CI: 3.1 to 20.3) decline per IQR 90-min formaldehyde (34 ppb).