Impact of climate change on tropospheric ozone and its global budgets

Abstract

Abstract.We present the chemistry-climate model UM CAM in which a relatively detailed tropospheric chemical module has been incorporated into the UK Met Office's Unified Model version 4.5. We obtain good agreements between the modelled ozone/nitrogen species and a range of observations including surface ozone measurements, ozone sonde data, and some aircraft campaigns.Four 2100 calculations assess model responses to projected changes of anthropogenic emissions (SRES A2), climate change (due to doubling CO 2 ), and idealised climate change-associated changes in biogenic emissions (i.e. 50% increase of isoprene emission and doubling emissions of soil-NO x ). The global tropospheric ozone burden increases significantly for all the 2100 A2 simulations, with the largest response caused by the increase of anthropogenic emissions. Climate change has diverse impacts on O 3 and its budgets through changes in circulation and meteorological variables. Increased water vapour causes a substantial ozone reduction especially in the tropical lower troposphere (>10 ppbv reduction over the tropical ocean). On the other hand, an enhanced stratosphere-troposphere exchange of ozone, which increases by 80% due to doubling CO 2 , contributes to ozone increases in the extratropical free troposphere which subsequently propagate to the surface. Projected higher temperatures favour ozone chemical production and PAN decomposition which lead to high surface ozone levels in certain regions. Enhanced convection transports ozone precursors more rapidly out of the boundary layer resulting in an increase of ozone production in the free troposphere. Lightning-produced NO x increases by about 22% in the doubled CO 2 climate and contributes to ozone production.The response to the increase of isoprene emissions shows that the change of ozone is largely determined by background NO x levels: high NO x environment increases ozone producCorrespondence to: G. Zeng (guang.zeng@atm.ch.cam.ac.uk) tion; isoprene emitting regions with low NO x levels see local ozone decreases, and increase of ozone levels in the remote region due to the influence of PAN chemistry. The calculated ozone changes in response to a 50% increase of isoprene emissions are in the range of between −8 ppbv to 6 ppbv. Doubling soil-NO x emissions will increase tropospheric ozone considerably, with up to 5 ppbv in source regions.

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

“…Stevenson et al, 2006;Zeng et al, 2008;Kawase et al, 2011;Morgenstern et al, 2013;Young et al, 2013). For the ozone burden, Kawase et al (2011) also find increases under RCP4.5 and 8.5 in sensitivity tests that are similar to the CC4.5 and CC8.5 runs of this study.…”

“…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.…”

Key drivers of ozone change and its radiative forcing over the 21st century

“…The current best estimate of annual and global mean LNO x emissions is 5 ± 3 Tg(N) yr -1 , with chemistry-climate models suggesting LNO x emissions sensitivity to climate change of ~ 4-60 % K -1 (Schumann and Huntrieser, 2007). Although more recent modelling studies find LNO x emissions climate sensitivity lying at the lower end of the above estimate (Zeng et al, 2008;15 Banerjee et al, 2014), results from a multi-model activity suggest large uncertainty in the magnitude and even the sign of future projections response due to different parameterizations (Finney et al, 2016). Most LNO x emissions occur in the mid-upper tropical troposphere over the continents, where photochemical production of ozone is most efficient in the troposphere -i.e.…”

“…For example, the RCP8.5 emission scenario refers to the total 8. Previous research has investigated impacts on ozone abundances and 30 distributions associated to future changes in climate, ODSs and ozone precursor emissions in a processed-based approach (Collins et al, 2003;Sudo et al, 2003;Zeng and Pyle, 2003;Zeng et al, 2008;Zeng et al, 2010;Kawase et al, 2011; al., 2016). Other modelling studies focused on the radiative effects of mainly tropospheric ozone changes under future emission scenarios in a non processed-based fashion (e.g.…”

Future changes in surface ozone over the Mediterranean basin in the framework of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx)

“…3a). Figure 3b (Lelieveld and Dentener, 2000;Zeng et al, 2008;Langner et al, 2012;Lacressonnière et al, 2012;Safieddine et al, 2014). A minimum in surface ozone is simulated over the NorthWestern Europe region, which corresponds to a VOC-limited regime in summertime, unlike the MB which is characterized by a NO x -limited regime as shown by Beekmann and Vautard (2010).…”