EFFECT OF AIR POLLUTION ON DETERMINATION OF THRESHOLD TEMPERATURES FOR HEAT AND COLD WAVES IN SPAIN

Current scientific evidence shows that the weather conditions which cause heatwaves in Spain are also linked to factors that contribute to increased air pollution from NO₂, O₃ and PM. Both air pollution and temperature affect the same diseases and vulnerable groups. Extreme temperatures prevention plans do not take the effects of air pollution into account. We conducted an ecological time series study of Spain's 47 provinces (2014-2023), daily all-cause mortality (ICD-10: A00-R99) was used. Using the Haugh-Pierce methodology, mortality anomalies were correlated with the daily maximum/minimum temperature at which they occurred, thereby determining the heat/cold waves temperature (Tthreshold). Two scenarios were considered: (i) including only univariate models; and (ii) adding the daily average concentrations of the pollutants as control variables. Among the 45 provinces with both heat-wave threshold estimates available, the median difference between pollutant-controlled and uncontrolled thresholds was 0.4 °C (Q1-Q3: 0.1 to 0.7 °C; bootstrap 95% CI: 0.2 to 0.6 °C). Among the 42 provinces with both cold-wave threshold estimates available, the median difference was -0.3 °C (Q1-Q3: -0.6 to 0.0 °C; bootstrap 95% CI: -0.4 to -0.1 °C). This implies that epidemiological thresholds are sensitive to pollution adjustment; including the effect of air pollutants when determining temperature thresholds would enable more precise activation of heat/cold wave prevention plans. This study shows that to improve early warning systems, it is essential to ensure that the impact of different environmental stressors on health are separately characterised.