Models have difficulty reproducing recent observed trends in surface O 3 driven by changes in precursor emissions, natural sources, stratospheric influx and transport patterns ( Parrish et al., 2014). The underlying cause is differences in OH, which depends on humidity, sunlight and O 3, and on a wide range of chemical and dynamical processes.ДЇor O 3, on the other hand, the abundance, seasonality and spatial variation are represented relatively well in models under present-day conditions, but observed changes in surface O 3 since the preindustrial era are thought to be underestimated ( Stevenson et al., 2013), although there is continuing uncertainty surrounding preindustrial levels ( Tarasick et al., 2019). This prevents them from simulating the observed atmospheric build-up of CH 4 correctly or attributing its causes reliably and leads to substantial uncertainty in the impact of future emission changes on global climate ( Stevenson et al., 2013 IPCC, 2013). The relatively short lifetime of these gases makes them attractive targets for emission controls ( Shindell et al., 2012), but scientific uncertainties associated with the processes that govern their abundance and distribution has hindered the implementation of effective control policies.Д¬urrent global chemistryвЂ“climate models representing the co-evolution of atmospheric O 3 and CH 4 show differences in CH 4 lifetime of almost a factor of 2 ( Wild, 2007 Voulgarakis et al., 2013). CH 4 is an O 3 precursor and O 3 is a major source of OH, which controls the oxidation of CH 4 and many other trace gases.ДЄt the surface O 3 contributes to poor air quality and is damaging to human health, crop yields and natural ecosystems ( Monks et al., 2015). The atmospheric abundance of both gases has increased substantially due to anthropogenic activity, and their fates are strongly coupled through the short-lived hydroxyl (OH) radical. Methane ( CH 4) and ozone ( O 3) are the second and third most important greenhouse gases contributing to climate change since the preindustrial era ( IPCC, 2013).

Processes driving tropospheric composition change.ДЄtmospheric photochemistry and transport processes play important roles in the Earth system by controlling the impact of natural and anthropogenic trace gas emissions on air quality and global climate. Improvements are required while providing valuable new insight into the This approach allows us to identify key areas where model Substantial differences in the sensitivity of OH to primary and secondary We show a clear sensitivity of tropospheric ozone toДЄtmospheric humidity and precursor emissions which is similar for the models,Д«ut find large differences between models for methane lifetime, highlighting Important climate-relevant variables, poorly characterised processes and Models to quantify the sensitivity of ozone and hydroxyl radicals (OH) to Gaussian process emulation with three independent global chemistry-transport The main causes of diversity in current models. Sensitivity analysis provides a valuable method of identifying and quantifying

Identifying the weaknesses in process understanding or representation thatД¬ould lead to improved models and to better scientific understanding. Show substantial diversity in results that reflect underlying uncertainties,Д«ut little progress has been made in explaining the causes of this or in Of the observations required to constrain them. Physical and dynamical processes governing atmospheric composition, on theДЄpproximations needed to represent these numerically, and on the limitations These models are imperfect as they rely on our understanding of the chemical, Quality and climate depend heavily on chemistryвЂ“climate models thatДЄllow us to investigate the effects of changing emissions and meteorology. Projections of future atmospheric composition change and its impacts on air

Apsim global sensitivity analysis