Abstract
Abstract. This study quantifies future changes in tropospheric ozone (O3) using a simple parameterisation of source–receptor relationships based on simulations from a range of models participating in the Task Force on Hemispheric Transport of Air Pollutants (TF-HTAP) experiments. Surface and tropospheric O3 changes are calculated globally and across 16 regions from perturbations in precursor emissions (NOx, CO, volatile organic compounds – VOCs) and methane (CH4) abundance only, neglecting any impact from climate change. A source attribution is provided for each source region along with an estimate of uncertainty based on the spread of the results from the models. Tests against model simulations using the Hadley Centre Global Environment Model version 2 – Earth system configuration (HadGEM2-ES) confirm that the approaches used within the parameterisation perform well for most regions. The O3 response to changes in CH4 abundance is slightly larger in the TF-HTAP Phase 2 than in the TF-HTAP Phase 1 assessment (2010) and provides further evidence that controlling CH4 is important for limiting future O3 concentrations. Different treatments of chemistry and meteorology in models remain one of the largest uncertainties in calculating the O3 response to perturbations in CH4 abundance and precursor emissions, particularly over the Middle East and south Asia regions. Emission changes for the future Evaluating the CLimate and Air Quality ImPacts of Short-livEd Pollutants (ECLIPSE) scenarios and a subset of preliminary Shared Socioeconomic Pathways (SSPs) indicate that surface O3 concentrations will increase regionally by 1 to 8 ppbv in 2050. Source attribution analysis highlights the growing importance of CH4 in the future under current legislation. A change in the global tropospheric O3 radiative forcing of +0.07 W m−2 from 2010 to 2050 is predicted using the ECLIPSE scenarios and SSPs, based solely on changes in CH4 abundance and tropospheric O3 precursor emissions and neglecting any influence of climate change. Current legislation is shown to be inadequate in limiting the future degradation of surface ozone air quality and enhancement of near-term climate warming. More stringent future emission controls provide a large reduction in both surface O3 concentrations and O3 radiative forcing. The parameterisation provides a simple tool to highlight the different impacts and associated uncertainties of local and hemispheric emission control strategies on both surface air quality and the near-term climate forcing by tropospheric O3.
Highlights
Tropospheric ozone (O3) is an air pollutant at both regional and global scales
The surface O3 response in these models was calculated from simulations with reductions in tropospheric O3 precursor emissions across the four major Northern Hemisphere emission regions (Europe, North America, east Asia and south Asia). The parameterisation using these results provided a fast and simple tool to predict future surface O3 concentrations for the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (RCPs), highlighting the importance of future changes in emissions and CH4 abundance for surface O3 concentrations and quantifying the associated uncertainty
We describe improvements and extensions to a simple parameterisation of regional surface O3 responses to changes in precursor emissions and CH4 abundances based on multiple models
Summary
Tropospheric ozone (O3) is an air pollutant at both regional and global scales. It is harmful to human health (Brunekreef and Holgate, 2002; Jerrett et al, 2009; Turner et al, 2016; Malley et al, 2017), whilst affecting climate (Myhre et al, 2013) and causing damage to natural and managed ecosystems (Fowler et al, 2009; United Nations Economic Commission for Europe (UNECE), 2016). Predicting source–receptor relationships for O3 is complex due to large natural background sources, formation of O3 from local emissions, non-linear chemistry and intercontinental transport processes (TF-HTAP, 2010) It is uncertain how the interaction of local and regional emission controls with global changes (e.g. of methane and climate) could affect O3 concentrations in the near-term future (2050s) (Jacob and Winner, 2009; Fiore et al, 2012; von Schneidemesser et al, 2015). The parameterisation is extended to estimate changes in tropospheric O3 burden and its impact on O3 radiative forcing It is used with the latest emission scenarios from Evaluating the CLimate and Air Quality ImPacts of Short-livEd Pollutants (ECLIPSE) V5a (Klimont et al, 2017, 2018) and the sixth Coupled Model Intercomparison Project (CMIP6) (Rao et al, 2017) to explore how source–receptor relationships change in the future, informing the future direction of emission control policies. We conclude by suggesting how this approach could be used to inform future emission policy in relation to O3 concentrations
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