Effects of long-range transported air pollution from vegetation fires on daily mortality and hospital admissions in the Helsinki metropolitan area, Finland

Abstract

Introduction: Fine particulate matter (PM_2.5) emissions from vegetation fires can be transported over long distances and may cause significant air pollution episodes far from the fires. However, epidemiological evidence on health effects of vegetation-fire originated air pollution is limited, particularly for mortality and cardiovascular outcomes.

Objective: We examined association between short-term exposure to long-range transported PM_2.5 from vegetation fires and daily mortality due to non-accidental, cardiovascular, and respiratory causes and daily hospital admissions due to cardiovascular and respiratory causes in the Helsinki metropolitan area, Finland.

Methods: Days significantly affected by smoke from vegetation fires between 2001 and 2010 were identified using air quality measurements at an urban background and a regional background monitoring station, and modelled data on surface concentrations of vegetation-fire smoke. Associations between daily PM_2.5 concentration and health outcomes on i) smoke-affected days and ii) all other days (i.e. non-smoke days) were analysed using Poisson time series regression. All statistical models were adjusted for daily temperature and relative humidity, influenza, pollen, and public holidays.

Results: On smoke-affected days, 10µg/m³ increase in PM_2.5 was associated with a borderline statistically significant increase in cardiovascular mortality among total population at a lag of three days (12.4%, 95% CI -0.2% to 26.5%), and among the elderly (≥65 years) following same-day exposure (13.8%, 95% CI -0.6% to 30.4%) and at a lag of three days (11.8%, 95% CI -2.2% to 27.7%). Smoke day PM_2.5 was not associated with non-accidental mortality or hospital admissions due to cardiovascular causes. However, there was an indication of a positive association with hospital admissions due to respiratory causes among the elderly, and admissions due to chronic obstructive pulmonary disease or asthma among the total population. In contrast, on non-smoke days PM_2.5 was generally not associated with the health outcomes, apart from suggestive small positive effects on non-accidental mortality at a lag of one day among the elderly and hospital admissions due to all respiratory causes following same-day exposure among the total population.

Conclusions: Our research provides suggestive evidence for an association of exposure to long-range transported PM_2.5 from vegetation fires with increased cardiovascular mortality, and to a lesser extent with increased hospital admissions due to respiratory causes. Hence, vegetation-fire originated air pollution may have adverse effects on public health over a distance of hundreds to thousands of kilometres from the fires.

Keywords: Air pollution; Hospital admissions; Mortality; Particulate matter; Vegetation fire.