Abstract
Abstract. Non-methane volatile organic compounds (NMVOCs) influence air quality and global climate change through their effects on secondary air pollutants and climate forcers. Here we simulate the air quality and radiative forcing (RF) impacts of changes in ozone, methane, and sulfate from halving anthropogenic NMVOC emissions globally and from 10 regions individually, using a global chemical transport model and a standalone radiative transfer model. Halving global NMVOC emissions decreases global annual average tropospheric methane and ozone by 36.6 ppbv and 3.3 Tg, respectively, and surface ozone by 0.67 ppbv. All regional reductions slow the production of peroxyacetyl nitrate (PAN), resulting in regional to intercontinental PAN decreases and regional NOx increases. These NOx increases drive tropospheric ozone increases nearby or downwind of source regions in the Southern Hemisphere (South America, Southeast Asia, Africa, and Australia). Some regions' NMVOC emissions contribute importantly to air pollution in other regions, such as East Asia, the Middle East, and Europe, whose impact on US surface ozone is 43%, 34%, and 34% of North America's impact. Global and regional NMVOC reductions produce widespread negative net RFs (cooling) across both hemispheres from tropospheric ozone and methane decreases, and regional warming and cooling from changes in tropospheric ozone and sulfate (via several oxidation pathways). The 100 yr and 20 yr global warming potentials (GWP100, GWP20) are 2.36 and 5.83 for the global reduction, and 0.079 to 6.05 and −1.13 to 18.9 among the 10 regions. The NMVOC RF and GWP estimates are generally lower than previously modeled estimates, due to the greater NMVOC/NOx emissions ratios simulated, which result in less sensitivity to NMVOC emissions changes and smaller global O3 burden responses, in addition to differences in the representation of NMVOCs and oxidation chemistry among models. Accounting for a fuller set of RF contributions may change the relative magnitude of each region's impacts. The large variability in the RF and GWP of NMVOCs among regions suggest that regionally specific metrics may be necessary to include NMVOCs in multi-gas climate trading schemes.
Highlights
Non-methane volatile organic compounds (NMVOCs) are chemically reactive gases emitted worldwide from natural and anthropogenic sources
We evaluate the sensitivity of air quality and radiative climate forcing (RF) to NMVOC emission location, and the corresponding NMVOC global warming potential (GWP), which may support the inclusion of NMVOCs in multi-gas emission trading schemes for climate
The global annual average net RF for the global 50 % NMVOC reduction is estimated as −9.73 mW m−2 or 0.21 mW m−2 (Tg C yr−1)−1
Summary
Non-methane volatile organic compounds (NMVOCs) are chemically reactive gases emitted worldwide from natural and anthropogenic sources. NMVOCs impact air quality and climate by contributing to tropospheric photochemistry (e.g., ozone (O3) production) and aerosol formation Because of their influence on short-lived climate forcers (e.g., O3, methane (CH4), aerosols), NMVOC reductions could help slow the near-term rate of climate change (Shindell et al, 2012). Previous studies have shown that the RF and global warming potential (GWP) of NMVOCs, like other short-lived O3 precursors, depend on emissions location given their short lifetime in the troposphere (Naik et al, 2005; Berntsen et al, 2006; Forster et al, 2007; Fry et al, 2012), but few studies quantify the range among different source regions. Using global models of chemical transport and radiative transfer, we simulate the air quality and net RF impacts, via changes in O3, CH4, and SO24−, of halving all anthropogenic NMVOC emissions together, globally and from 10 regions, as was done for CO emissions by Fry et al (2013). Future studies could evaluate the impacts of measures on multiple species, or combine the results presented here with those for co-emitted species to determine the net effect of emission control measures (Shindell et al, 2012)
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