Contributions of Ten World Regions to the Global Tropospheric Ozone Burden Change from 1980 to 2010: High Sensitivity to Emissions from South and Southeast Asia

Abstract:

In recent decades, emissions of ozone precursors have shifted toward the equator, as emissions in some high-income regions have decreased, while emissions have increased markedly from especially East and South Asia. This change in the spatial distribution of emissions is troubling because of the greater sensitivity of tropospheric ozone to emissions from tropical and subtropical regions.

Here we extend our earlier work that showed for the first time that the equatorward shift of emissions between 1980 and 2010 contributed more to the global ozone burden change than the increase in the global magnitude of ozone precursor emissions or the global methane increase. We investigate the importance of changes in emissions of ozone precursors from 10 world regions, as well as the global methane concentration change, in increasing the global tropospheric ozone burden from 1980 to 2010. The modeled global tropospheric ozone burden has increased by 28.1 Tg, with 26.7% (7.5 Tg) of this change attributed to the global methane increase. Southeast Asia (5.6 Tg) and South Asia (4.0 Tg) contribute comparably to the global ozone burden change as East Asia (5.6 Tg), even though NO_x emission increases in each region are less than one third of those in East Asia. This finding highlights the greater sensitivity of global ozone to emissions from Southeast Asia and South Asia. Emission decreases from North America, Europe, and the Former Soviet Union have led to ozone burden decreases of 2.8, 1.0, and 0.3 Tg. The greater sensitivity of the global ozone burden to emission changes in tropical and subtropical regions emphasizes the importance of controlling emissions in these regions for global ozone.