Response of lightning NO_x emissions and ozone production to climate change: Insights from the Atmospheric Chemistry and Climate Model Intercomparison Project

Abstract

Results from an ensemble of models are used to investigate the response of lightning nitrogen oxide emissions to climate change and the consequent impacts on ozone production. Most models generate lightning using a parameterization based on cloud top height. With this approach and a present‐day global emission of 5 TgN, we estimate a linear response with respect to changes in global surface temperature of +0.44 ± 0.05 TgN K−1. However, two models using alternative approaches give +0.14 and −0.55 TgN K−1 suggesting that the simulated response is highly dependent on lightning parameterization. Lightning NOx is found to have an ozone production efficiency of 6.5 ± 4.7 times that of surface NOx sources. This wide range of efficiencies across models is partly due to the assumed vertical distribution of the lightning source and partly to the treatment of nonmethane volatile organic compound (NMVOC) chemistry. Careful consideration of the vertical distribution of emissions is needed, given its large influence on ozone production.

Global high-resolution simulations of tropospheric nitrogen dioxide using CHASER V4.0

“…Even over remote regions, a highresolution simulation has the potential to improve model performance through considering the effects of nonlinear chemistry in highly concentrated NO x plumes emitted from ships and lightning (Charlton-Perez et al, 2009;Vinken et al, 2011;Gressent et al, 2016). These NO x emission sources in remote regions have significant impacts on climate and air quality (Eyring et al, 2010;Holmes et al, 2014;Banerjee et al, 2014;Finney et al, 2016). It is thus important to clarify the importance of resolving small-scale sources and plumes within a global modeling framework for a better understanding of the global atmospheric environment and chemistryclimate system.…”

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.…”

“…Nevertheless, simulated present-day LNO x emissions of 4.8 ± 1.6 Tg(N) yr -1 lies within observationally-derived estimates, and 15 the model's LNO x sensitivity to climate of 10.8 % K -1 is at the upper end of the two standard deviation climate model range (8.8 ± 2 % K -1 ) (Finney et al, 2016). The net global tropospheric ozone responses to climate will be largely determined by the interplay between climate-induced ozone losses and lightning-induced ozone production.…”

“…However, present-day LNO x emissions have significant uncertainties and climate models do not agree even on the sign of the change due to different lightning parameterizations (Finney et al, 2016). Nevertheless, simulated present-day LNO x emissions of 4.8 ± 1.6 Tg(N) yr -1 lies within observationally-derived estimates, and 15 the model's LNO x sensitivity to climate of 10.8 % K -1 is at the upper end of the two standard deviation climate model range (8.8 ± 2 % K -1 ) (Finney et al, 2016).…”

“…A subset of eight models from the ACCMIP activity shows a small negative but not significant tropospheric forcing of −33 ± 42 mWm -2 , with few models reporting positive forcings . The impact of climate change on ozone forcing is surrounded by large uncertainties, which may be associated with chemistry-climate feedbacks and the lack 10 of confidence in the LNO x sensitivity to global mean surface temperature, due to different parameterizations and the vertical distributions of the emissions (Banerjee et al, 2014;Finney et al, 2016), as well as changes in the BDC (Butchart, 2014). For example, the climate change-induced net ozone forcing between 2000-2100 -following the future emission scenario RCP8.5 in an independent CCM -is of the 15 same order of magnitude but different sign (−70 mWm -2 ) (Banerjee et al, 2017).…”