Impact of advections of particulate matter from biomass combustion on mortality in Madrid

Background / Objective: Approximately 20% of particulate and aerosol emissions into the urban atmosphere are of natural origin (including wildfires and Saharan dust). During these natural episodes, PM10 and PM2.5 levels usually exceed WHO health protection thresholds. The objective is to evaluate the possible effect of advections of particulate matter from biomass fuel combustion on daily specific-cause mortality among the general population and the segment aged ≥75 years in Madrid. Materials and methods: Ecological time-series study in the city of Madrid from 01/01/2004 to 31/12/2009. The dependent variable analysed was daily mortality due to natural (ICD-10:A00-R99), circulatory (ICD-10:I00-I99) and respiratory (ICD-10:J00-J99) causes in the population, both general and aged ≥75 years. The following independent and control variables were considered: a) daily mean PM2.5 and PM10 concentrations (Madrid Municipal Air Quality Monitoring Grid) ; b) maximum daily temperature (State Meteorological Agency); c) daily mean O3 and NO2 concentrations; d) advection of particulate matter from biomass combustion (http://www.calima.ws/), using a dichotomous variable; and, e) linear trend and seasonalities. We conducted a descriptive analysis, performed a test of means and, to ascertain relative risk, fitted a model using autoregressive Poisson regression and stratifying by days with and without biomass advection, in both populations. Results: Of the 2192 days analysed, biomass advection occurred on 56, with mean PM2.5 and PM10 values registering a significant increase during these days versus those without advection. PM10 levels displayed a significant effect on natural-cause mortality on days with advection, while PM2.5 levels displayed a significant effect on all-cause mortality on days without advection. PM10 had a greater impact on organic mortality with advection (RRall ages=1.035 [1.011-1.060]; RR≥75years=1.066 [1.031-1.103]) than did PM2.5 without advection (RRall ages=1.017 [1.009-1.025]; RR≥75years=1.012 [1.003-1.022]). Among specific causes, respiratory -though not circulatory- causes were associated with PM10 on days with advection in ≥75-year age group. Conclusion: PM10 levels, rather than PM2.5 levels, were associated with an increase in natural-cause mortality on days with advection of particulate matter from biomass combustion, particularly in the ≥75-year age group. Expected trends in terms of population ageing and an increasing number of fires (consequence of climate change) mean that measures must be adopted to minimise the health impact in such situations