VOC chemical climate and O3 variation: impact of emissions on regional O3 increment

Understanding the role of individual volatile organic compounds (VOCs) in the formation of surface ozone is important for the effective targeting of ozone mitigation strategies. The UK operates two European Monitoring and Evaluation Programme (EMEP) monitoring ‘supersites’ where concurrent measurement of 27 VOCs, NOx and ozone allows the relationships between these precursors and ozone to be explored. This work presents the relative contribution of measured VOCs on ozone formation at the ‘supersites’, including spatial variation across the UK, and temporal changes between 1999 and 2012. The study was undertaken using the impact-centred chemical climatology framework (Malley et al 2014) VOC concentrations are made up from both regional and local emissions. Regional components of ozone concentrations are distinguished from hemispheric background ozone and measured ozone concentrations which show depletion due to the local NOx environment. Increased VOC photochemical cycling is observed during periods of regional ozone formation, and the contribution of individual VOCs to this total measured VOC cycling is discussed. The drivers of this photochemical depletion, such as meteorology and emissions are evaluated. Back trajectories are coupled with gridded VOC emission maps to estimate the exposure of trajectories to VOC emissions for the four days prior to their arrival at the receptor site. These emissions are disaggregated into 11 broad source sectors, and their contribution is evaluated. Finally the implications of the level of source disaggregation available are discussed in terms of its limitations on VOC emissions speciation to estimate the exposure of receptor sites to individual VOCs.. Using the SNAP sector and the NFR code sector data, it is demonstrated that a greater level of source sector disaggregation would be beneficial for atmospheric model studies and policy determination.