The influence of ozone precursor emissions from four world regions on tropospheric composition and radiative climate forcing

Including the effect of O₃ on CO₂ uptake by vegetation likely makes these net RFs more negative by −1.9 to −5.2 mWm⁻²/Tg N yr⁻1, −0.2 to −0.7 mWm⁻²/Tg C yr⁻1, and −0.02 to −0.05 mWm⁻²/Tg CO yr⁻1. Net RF impacts reflect the distribution of concentration changes, where RF is affected locally by changes in SO₄²⁻, regionally to hemispherically by O₃, and globally by CH₄. Global annual average SO₄²⁻ responses to oxidant changes range from 0.4 ± 2.6 to −1.9 ± 1.3 Gg for NOx reductions, 0.1 ± 1.2 to −0.9 ± 0.8 Gg for NMVOC reductions, and −0.09 ± 0.5 to −0.9 ± 0.8 Gg for CO reductions, suggesting additional research is needed.

The 100-year global warming potentials (GWP₁₀₀) are calculated for the global CH₄ reduction (20.9 ± 3.7 without stratospheric O₃ or water vapor, 24.2 ± 4.2 including those components), and for the regional NOx, NMVOC, and CO reductions (−18.7 ± 25.9 to −1.9 ± 8.7 for NOx, 4.8 ± 1.7 to 8.3 ± 1.9 for NMVOC, and 1.5 ± 0.4 to 1.7 ± 0.5 for CO). Variation in GWP₁₀₀ for NOx, NMVOC, and CO suggests that regionally specific GWPs may be necessary and could support the inclusion of O₃ precursors in future policies that address air quality and climate change simultaneously.

Both global net RF and GWP₁₀₀ are more sensitive to NOx and NMVOC reductions from South Asia than the other three regions.