Drivers of divergent trends in tropospheric ozone hotspots in Spain, 2008–2019

Abstract

This study aimed to investigate the causes of contrasting ozone (O3) trends in Spanish O3 hotspots between 2008 and 2019, as documented in recent studies. The analysis involved data on key O3 precursors, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), among other species, along with meteorological parameters associated with O3. The dataset comprised ground-level and satellite observations, emissions inventory estimates, and meteorological reanalysis.

The results suggest that the increasing O3 trends observed in the Madrid area were mostly due to major decreases in NOx emissions from the road transport sector in this urban VOC-limited environment, as well as variations in meteorological parameters conducive to O3 production. Conversely, the decreasing O3 trends in the Sevilla area likely resulted from a decrease in NOx emissions in a peculiar urban NOx-limited regime caused by substantial VOC contributions from a large upwind petrochemical area. Unchanged O3 concentrations in other NOx-limited hotspots may be attributed to the stagnation of emissions from sectors other than road transport, coupled with increased emissions from certain sectors, likely due to the economic recovery from the 2008 financial crisis, and the absence of meteorological variations favorable to O3 production.

In this study, the parameters influencing O3 varied distinctively across the different hotspots, emphasizing the significance of adopting an independent regional/local approach for O3 mitigation planning. Overall, our findings provide valuable insights into the causes of contrasting O3 trends in different regions of Spain, which can be used as a basis for guiding future measures to mitigate O3 levels.