Quantifying and mapping exceedances of ozone flux-based critical levels for vegetation in the UK in 2018

The amended National Emissions Ceilings Directive (NECD; Directive (EU) 2016/2284, amendment of Directive 2003/35/EC) of the EU is aligning emission reduction commitments with those for the UN Convention on Long-range Transboundary Air Pollution (LRTAP), with the long-term objective to reduce air pollution to at or below the Convention’s critical levels and loads for ecosystems.
With respect to monitoring air pollutants, Article 9 of the Directive states that ‘Member States shall ensure the monitoring of negative impacts of air pollution upon ecosystems based on a network of monitoring sites that is representative of their freshwater, natural and semi-natural habitats and forest ecosystem types, taking a cost-effective and risk-based approach’. In order to comply with the requirements of Article 9, Member States may use the optional indicators listed in Annex V. To meet the requirements of Annex V of the amended NECD Directive by reporting on exceedances of flux-based critical levels for ozone, we mapped the modelled exceedances for vegetation for the year 2018. Authors followed the same approach as previously used in an initial scoping study for the year 2015 (Mills et al., 2017), and subsequent studies investigating ozone impacts for the years 2014-16 (Sharps et al., 2019), and 2017 (Sharps et al., 2020). The critical level exceedance data and ozone impacts on crop yield, annual increment of tree biomass and flower numbers in grassland were mapped and quantified by UK country using the latest flux-based methodology for wheat, potato, broad-leaf woodland, conifers and flowering of wild plants.