How protective is China's National Ambient Air Quality Standards on short-term PM2.5? Findings from blood pressure measurements of 1 million adults

Although short-term exposure to fine particulate matter (PM2.5) air pollution has been shown to induce elevated blood pressure (BP), limited evidence is available regarding the association between ambient PM2.5 and BP levels in nationwide China and how the association may change. This study sought to explore acute BP changes with exposure to PM2.5 at levels below China's current National Ambient Air Quality Standards (NAAQS). Based on a spatiotemporal study of over 1 million adults, we linked BP measurements to daily estimates of PM2.5 from multiple sources (i.e. in situ observations, satellite measurements of aerosol and numeric simulations of air quality model) after adjusting for several individual-level covariates and further conduced the below-criteria models by restricting the analyses within subsets of individuals with short-term PM2.5 exposure below 75 mu g m(-3) (i.e. NAAQS of 24 h PM2.5 in China). We further explored variations in BP-PM2.5 associations by pollution level and for different demographic groups. With full adjustments, a 10 mu g m(-3) increase in PM2.5 was statistically significantly associated with a 0.049 mmHg (95% confidence interval, CI: 0.041, 0.057) increase in systolic BP, a 0.022 mmHg (95% CI: 0.017, 0.027) increase in diastolic BP and a 0.77% (95% CI: 0.62%, 0.92%) increased risk of hypertension (HPN). For both BP and HPN, the exposure-response curves were linear, with no threshold effects, at the low-concentration ends and sublinear at the high-concentration ends. Below the current NAAQS, the associations in population level remained statistically significant and were even stronger. A 10 mu g m(-3) increase in below-NAAQS PM2.5 was associated with a 1.95% (95% CI: 1.44%, 2.47%) increased risk of HPN. Specific subpopulations were more susceptible to PM2.5 exposure. These findings can help support decisions by policymakers to revise related environmental regulations to protect public health.