Drivers of the tropospheric ozone budget throughout the 21st century under the medium-high climate scenario RCP 6.0

Abstract

Abstract. Because tropospheric ozone is both a greenhouse gas and harmful air pollutant, it is important to understand how anthropogenic activities may influence its abundance and distribution through the 21st century. Here, we present model simulations performed with the chemistry-climate model SOCOL, in which spatially disaggregated chemistry and transport tracers have been implemented in order to better understand the distribution and projected changes in tropospheric ozone. We examine the influences of ozone precursor emissions (nitrogen oxides (NO x ), carbon monoxide (CO) and volatile organic compounds (VOCs)), climate change (including methane effects) and stratospheric ozone recovery on the tropospheric ozone budget, in a simulation following the climate scenario Representative Concentration Pathway (RCP) 6.0 (a medium-high, and reasonably realistic climate scenario). Changes in ozone precursor emissions have the largest effect, leading to a global-mean increase in tropospheric ozone which maximizes in the early 21st century at 23 % compared to 1960. The increase is most pronounced at northern midlatitudes, due to regional emission patterns: between 1990 and 2060, northern midlatitude tropospheric ozone remains at constantly large abundances: 31 % larger than in 1960. Over this 70-year period, attempts to reduce emissions in Europe and North America do not have an effect on zonally averaged northern midlatitude ozone because of increasing emissions from Asia, together with the long lifetime of ozone in the troposphere. A simulation with fixed anthropogenic ozone precursor emissions of NO x , CO and non-methane VOCs at 1960 conditions shows a 6 % increase in global-mean tropospheric ozone by the end of the 21st century, with an 11 % increase at northern midlatitudes. This increase maximizes in the 2080s and is mostly caused by methane, which maximizes in the 2080s following RCP 6.0, and plays an important role in controlling ozone directly, and indirectly through its influence on other VOCs and CO. Enhanced flux of ozone from the stratosphere to the troposphere as well as climate change-induced enhancements in lightning NO x emissions also increase the tropospheric ozone burden, although their impacts are relatively small. Overall, the results show that under this climate scenario, ozone in the future is governed largely by changes in methane and NO x ; methane induces an increase in tropospheric ozone that is approximately one-third of that caused by NO x . Climate impacts on ozone through changes in tropospheric temperature, humidity and lightning NO x remain secondary compared with emission strategies relating to anthropogenic emissions of NO x , such as fossil fuel burning. Therefore, emission policies globally have a critical role to play in determining tropospheric ozone evolution through the 21st century.

Drivers of changes in stratospheric and tropospheric ozone between year 2000 and 2100

“…CCM studies that have imposed increases in methane according to the RCP scenarios show large increases in tropospheric ozone, particularly at RCP8.5, which would greatly oppose the effects of emission controls on global, tropospheric ozone (e.g. Young et al, 2013;Revell et al, 2015).…”

“…During the 21st century, changes in climate, ozonedepleting substances (ODSs) and emissions of ozone precursor species are expected to be major factors governing ozone amounts and its distribution in the stratosphere and free troposphere and at the surface (e.g. Johnson et al, 1999;Jonsson et al, 2004;Hauglustaine et al, 2005;Zeng et al, 2008;Fiore et al, 2012;Revell et al, 2015). With the projected decline in ODSs following the Montreal Protocol, the relative contribution of very short-lived substances (VSLSs) to the halogen loading of the stratosphere is expected to increase.…”

“…The analysis focuses on changes between 2000 and 2100 under the RCP4.5 and 8.5 climate forcing scenarios. Note that future methane emissions are highly uncertain and changes in its abundance, particularly at RCP8.5, will likely have large tropospheric and stratospheric impacts (Randeniya et al, 2002;Fleming et al, 2011;Revell et al, 2012Revell et al, , 2015Young et al, 2013) that are not the focus of this study. Instead, we wish to isolate other drivers of ozone changes, in particular, the role of a change in mean climate state at RCP8.5, without the assumption of a large increase in methane abundance.…”

Surface Ozone Concentration and Its Relationship with UV Radiation, Meteorological Parameters and Radon on the Eastern Coast of the Baltic Sea

“…Ozone is a toxic air pollutant that is both necessary and harmful to life on earth. The ozone layer in the stratosphere serves as the main barrier protecting us from harmful UV radiation [1,2], therefore the ozone layer decomposition is a global problem that needs to be solved by reducing emissions of the materials destroying the ozone shield (chlorine fluoride hydrocarbons and some other organic halogen formations) into the atmosphere [3].…”

An upper-branch Brewer–Dobson circulation index for attribution of stratospheric variability and improved ozone and temperature trend analysis

“…To investigate temperature and ozone variability in the stratosphere and mesosphere at all latitudes, without data gaps, we simulate historical ozone and temperature variations using the chemistry-climate model (CCM) SOlar Climate Ozone Links (SOCOL, version 3; Stenke et al, 2013) in specifieddynamics mode, whereby the vorticity and divergence of the wind fields and temperature, and the logarithm of surface pressure are "nudged" using the ERA-Interim reanalysis (Dee et al, 2011(Dee et al, ) between 1983(Dee et al, and 2012 (Revell et al, 2015), except for the solar irradiance input, for which we use the Spectral And Total Irradiance REconstruction -Satellite era (SATIRE-S) model (Krivova et al, 2003;Yeo et al, 2014). In the following we focus on temperature and ozone variables; the former is nudged, while the latter is simulated by the CCM SOCOL.…”