The impact of changing exposure to PM2.5 on mortality for US diplomats with multiple international relocations: a modelling study.

Background: Current evidence linking long-term exposure to fine particulate matter (PM_2.5) exposure and mortality is primarily based on persons that live in the same residence, city and/or country throughout the study, with few residential moves or relocations. We propose a novel method to quantify the health impacts of PM_2.5 for United States (US) diplomats who regularly relocate to international cities with different PM_2.5 levels.

Methods: Life table methods were applied at an individual-level to US mortality statistics using the World Health Organization's database of city-specific PM_2.5 annual mean concentrations. Global Burden of Disease concentration-response (C-R) functions were used to estimate cause-specific mortality and days of life lost (DLL) for a range of illustrative 20-year diplomatic assignments for three age groups. Time lags between exposure and exposure-related mortality risks were applied. Sensitivity analysis of baseline mortality, exposure level, C-R functions and lags was conducted. The effect of mitigation measures, including the addition of air purifiers, was examined.

Results: DLL due to PM_2.5 exposure for a standard 20-year assignment ranged from 0.3 days for diplomats' children to 84.1 days for older diplomats. DLL decreased when assignments in high PM_2.5 cities were followed by assignments in low PM_2.5 cities: 162.5 DLL when spending 20 years in high PM_2.5 cities compared to 62.6 DLL when spending one of every four years (5 years total) in a high PM_2.5 city for older male diplomats. Use of air purifiers and improved home tightness in polluted cities may halve DLL due to PM_2.5 exposure. The results were highly sensitive to lag assumptions: DLL increased by 68% without inception lags and decreased by 59% without cessation lags for older male diplomats.

Conclusion: We developed a model to quantify health impacts of changing PM_2.5 exposure for a population with frequent relocations. Our model suggests that alternating assignments in high and low PM_2.5 cities may help reduce PM_2.5-related mortality burdens. Adding exposure mitigation at home may help reduce PM_2.5 related mortality. Further research on outcome-specific lag structures is needed to improve the model.