Heatwave events and concurrent ozone concentrations between 2006 and 2022 at two sites in southern and northern Spain

Hotter-than-usual days are becoming more common, such that heat waves are expected to increase in intensity, frequency, duration, and spatial extent in Spain. Within this framework, this paper looks at the combined effects of extreme temperatures and air pollution in two cities in Spain, Córdoba and Valladolid, over the period 2006-2022. Synoptic patterns and air mass movement were analysed during the eleven coincident heat waves at both locations in order to study what impact orography and local meteorology have on ozone concentrations. Weak flow conditions were the most frequent synoptic pattern in the Iberian Peninsula during heat waves. Moreover, west and local circulations characterised the main air trajectories at low levels (500 m agl), while southwest maritime advections and African air mass transport were more frequent at higher levels (1500 and 3000 m agl) in Córdoba and Valladolid, respectively. On average, maximum ozone values were higher in Córdoba (105.1 µg m^-3) than in Valladolid (80 µg m^-3) and were strongly correlated with extreme temperatures at both locations (r up to 0.8, p-value < 0.05). Mean temperature in Córdoba was 31.9 °C, with the maximum value reaching 43.7 °C, while temperatures in Valladolid were lower (28.3 °C and 37.3 °C, respectively). Calculation and assessment of some indices helped to understand the impact of extreme events. Caution actions based on the Heat Index characterised heat wave periods. Moderate risk was the general Air Quality Health Index feature recorded and reached a very high risk of unhealthy air quality in the June 2022 event in Córdoba.