Differential Cardiopulmonary Health Impacts of Local and Long-Range Transport of Wildfire Smoke

Abstract

We estimated cardiopulmonary morbidity and mortality associated with wildfire smoke (WFS) fine particulate matter (PM_2.5) in the Front Range of Colorado from 2010 to 2015. To estimate WFS PM_2.5, we developed a daily kriged PM_2.5 surface at a 15 × 15 km resolution based on the Environmental Protection Agency Air Quality System monitors for the western United States; we subtracted out local seasonal-average PM_2.5 of nonsmoky days, identified using satellite-based smoke plume estimates, from the local daily estimated PM_2.5 if smoke was identified by National Oceanic and Atmospheric Administration's Hazard Mapping System. We implemented time-stratified case-crossover analyses to estimate the effect of a 10 µg/m³ increase in WFS PM_2.5 with cardiopulmonary hospitalizations and deaths using single and distributed lag models for lags 0-5 and distinct annual impacts based on local and long-range smoke during 2012, and long-range transport of smoke in 2015. A 10 µg/m³ increase in WFS was associated with all respiratory, asthma, and chronic obstructive pulmonary disease hospitalizations for lag day 3 and hospitalizations for ischemic heart disease at lag days 2 and 3. Cardiac arrest deaths were associated with WFS PM_2.5 at lag day 0. For 2012 local wildfires, asthma hospitalizations had an inverse association with WFS PM_2.5 (OR: 0.716, 95% CI: 0.517-0.993), but a positive association with WFS PM_2.5 during the 2015 long-range transport event (OR: 1.455, 95% CI: 1.093-1.939). Cardiovascular mortality was associated with the 2012 long-range transport event (OR: 1.478, 95% CI: 1.124-1.944).

Keywords: epidemiology; long‐range transport; morbidity; mortality; smoke; wildfires.

Figure 1

Map of study domain with major population centers by population density, major interstates, and study grid.

Figure 2

MODIS satellite true‐color image and NOAA Hazard Mapping System (HMS) smoke polygons (gray) and active fires (red triangles) for 2012 High Park Fire (Colorado, panels a [Aqua satellite] and b); 2012 Waldo Canyon Fire (Colorado, panels c [Aqua satellite] and d); 2012 Pacific Northwest Fires (panels e [Terra satellite] and f); and 2015 Pacific Northwest Fires (panels g [Aqua satellite] and h). Source: NASA Worldview and NOAA HMS website.

Figure 3

Average daily WFS PM_2.5 in µg/m³ for Front Range counties within the exposure grid from January 2010 to September 2015.

Figure 4

Single daily lag effects of a 10 µg/m³ increase in WFS PM_2.5 on odds of respiratory and cardiovascular hospitalizations. Models adjusted for lagged temperature and ozone on the same day of lagged WFS exposure.

Figure 5

Distributed lag effects of a 10 µg/m³ increase in WFS PM_2.5 on odds of respiratory and cardiovascular hospitalizations. Models adjusted for lagged temperature and ozone on the same day of lagged WFS exposure.

Figure 6

Cumulative effect of same day exposure to lag day 3 of exposure of a daily 10 µg/m³ increase in WFS PM_2.5 on the risk for a cardiopulmonary inpatient hospitalization for El Paso County (Waldo Canyon Fire, 2012), Larimer County (High Park Fire, 2012), all Front Range counties, 2012, and all Front Range counties, 2015.

Figure 7

Cumulative effect of same day exposure to lag day 3 of exposure of a daily 10 µg/m³ increase in WFS PM_2.5 on the risk for a cardiopulmonary inpatient hospitalization for all Front Range Counties, by early season (May 1 to Jul 31) and late season (Aug 1 to Oct 31), 2012 and 2015 wildfire seasons.

Figure 8

Cumulative effect of same day exposure to lag day 3 of exposure of a daily 10 µg/m³ increase in WFS PM_2.5 on the risk for a cardiopulmonary mortality for each WFS event.

Figure 9

Cumulative effect of same day exposure to lag day 3 of exposure of a daily 10 µg/m³ increase in WFS PM_2.5 on the risk for a cardiopulmonary mortality for all Front Range Counties, by early season (May 1 to Jul 31) and late season (Aug 1 to Oct 31), 2012 and 2015 wildfire seasons.