Accounting for Mobility in Air Pollution Exposure Estimates in Studies on Long-Term Health Effects.

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Citation abstract

INTRODUCTION: Large-scale epidemiological studies investigating long-term health effects of air pollution can typically only consider the residential locations of the participants, thereby ignoring the space-time-activity patterns that likely influence total exposure. People are mobile and can be exposed to considerably different levels of air pollution or air pollution mixtures when inside versus outside, commuting, recreating, or working. Neglecting these mechanisms in exposure assessment may lead to incorrect distributions of exposure over the population, which may, subsequently, lead to incorrect exposure-health relations in epidemiological studies. In this study, we investigated whether a more sophisticated mobility-enhanced exposure assessment would lead to different exposure predictions and health effect estimates compared with using a residential-based exposure.

METHODS: Agent-based modeling (ABM 3 ) was used to model mobility patterns in Switzerland and the Netherlands based on travel survey information. Hourly air pollution surfaces of nitrogen dioxide (NO 2 ) and fine particulate matter (PM 2.5 ) developed separately for the Netherlands and Switzerland, for weekdays and weekends, were overlaid with the ABM data to extract exposures. These air pollution exposures were assigned to two adult cohorts in Switzerland - the Swiss Cohort Study on Air Pollution and Lung and Heart Diseases in Adults (SAPALDIA) and the Swiss National Cohort (SNC) - and the European Prospective Investigation into Cancer study adult cohort in the Netherlands (EPIC-NL). Exposures were assigned based on (1) residential address location only (residential-based) and (2) residential and work address locations plus mobility (mobility-enhanced). In the case of SAPALDIA, known work address locations were available and additionally used. Associations with health outcomes (natural and cardiovascular mortality, coronary and stroke events, blood pressure, and lung function) in the three cohorts were investigated. To evaluate the performance of the ABM, we collected GPS readings from 489 participants in Switzerland and 189 participants in the Netherlands in tracking campaigns. The participants recorded GPS readings, using both a wearable GPS recording device and a mobile phone app while also recording their time-activity in the app diary.

RESULTS: We successfully developed mobility-enhanced exposures for over 3 million participants, including an assessment of uncertainty. We found a good agreement between exposures estimated with the app and the GPS tracker, supporting the scalability of the approach. We evaluated the ABMs with GPS and time-activity data collected independently in tracking campaigns that included almost 700 participants from selected areas in the two countries. For these participants, the exposures based on GPS measurements versus those derived from ABM showed a moderate to good agreement (R 2 = 0.52-0.81). Within the three cohorts, when compared with exposure based on only the residential location, the mobility-enhanced exposure showed very high correlations (R > 0.95). Finally, the epidemiological analyses revealed very small differences in the associations across health outcomes for the different exposure estimates (mortality in SNC; cardiovascular morbidity and mortality in EPIC-NL; and lung function and blood pressure in SAPALDIA) within the three cohorts. In SAPALDIA, where the work address was known for a subset of individuals, a further comparison using the estimated work address in the ABM indicated little difference in mobility-enhanced exposures.

CONCLUSIONS: Our results suggest that the assessment of air pollution exposure at the residential address in epidemiological studies generally does not lead to substantial bias in health effects estimates. If time-activity patterns in other study areas differ greatly from the patterns analyzed in our study, differences between residential and activity-enhanced exposures may be larger. Despite the good agreement between residential and work locations, exposure research should continue to strive toward improving exposure assessment in large-scale epidemiological studies to minimize exposure misclassification.