Sources of surface O₃ in the UK: tagging O₃ within WRF-Chem

Abstract

Abstract. Tropospheric ozone (O3) concentrations depend on a combination of hemispheric, regional, and local-scale processes. Estimates of how much O3 is produced locally vs. transported from further afield are essential in air quality management and regulatory policies. Here, a tagged-ozone mechanism within the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) is used to quantify the contributions to surface O3 in the UK from anthropogenic nitrogen oxide (NOx) emissions from inside and outside the UK during May–August 2015. The contribution of the different source regions to three regulatory O3 metrics is also examined. It is shown that model simulations predict the concentration and spatial distribution of surface O3 with a domain-wide mean bias of −3.7 ppbv. Anthropogenic NOx emissions from the UK and Europe account for 13 % and 16 %, respectively, of the monthly mean surface O3 in the UK, as the majority (71 %) of O3 originates from the hemispheric background. Hemispheric O3 contributes the most to concentrations in the north and the west of the UK with peaks in May, whereas European and UK contributions are most significant in the east, south-east, and London, i.e. the UK's most populated areas, intensifying towards June and July. Moreover, O3 from European sources is generally transported to the UK rather than produced in situ. It is demonstrated that more stringent emission controls over continental Europe, particularly in western Europe, would be necessary to improve the health-related metric MDA8 O3 above 50 and 60 ppbv. Emission controls over larger areas, such as the Northern Hemisphere, are instead required to lessen the impacts on ecosystems as quantified by the AOT40 metric.

Implementation of an On-Line Reactive Source Apportionment (ORSA) Algorithm in the FARM Chemical-Transport Model and Application over Multiple Domains in Italy

“…A key aspect of these methods is constraining the sum of the concentration's contributions from the different sources always to be equal to the total concentration due to all the sources [22]. The Ozone SA Technology (OSAT, [23]), the Particle SA Technology (PSAT, [22,24,25]) within the CAMx model, the tagged species SA algorithms within CMAQ, such as TSSA [26,27] and ISAM (Integrated SA Method, [28]), the SIA SA algorithm [21], the ozone (O 3 ) tagging within WRF-Chem [29,30], the UCD/CIT model SA of nitrogen oxides (NO X ), and volatile organic compounds (VOCs) [31] are some examples of TAG methods. In Europe, several tagged species methods were developed and/or applied in state-ofthe-art CTMs (DEHM, [32]; LOTOS-EUROS, [33]; CMAQ-ISAM, [34]; CAMx-PSAT, [35]; WRF-Chem, [36]).…”