Abstract
Abstract. Observations and models demonstrate that ozone and its precursors can be transported between continents and across oceans. We model the influences of 10% reductions in anthropogenic nitrogen oxide (NOx) emissions from each of nine world regions on surface ozone air quality in that region and all other regions. In doing so, we quantify the relative importance of long-range transport between all source-receptor pairs, for direct short-term ozone changes. We find that for population-weighted concentrations during the three-month "ozone-season", the strongest inter-regional influences are from Europe to the Former Soviet Union, East Asia to Southeast Asia, and Europe to Africa. The largest influences per unit of NOx reduced, however, are seen for source regions in the tropics and Southern Hemisphere, which we attribute mainly to greater sensitivity to changes in NOx in the lower troposphere, and secondarily to increased vertical convection to the free troposphere in tropical regions, allowing pollutants to be transported further. Results show, for example, that NOx reductions in North America are ~20% as effective per unit NOx in reducing ozone in Europe during summer, as NOx reductions from Europe itself. Reducing anthropogenic emissions of non-methane volatile organic compounds (NMVOCs) and carbon monoxide (CO) by 10% in selected regions, can have as large an impact on long-range ozone transport as NOx reductions, depending on the source region. We find that for many source-receptor pairs, the season of greatest long-range influence does not coincide with the season when ozone is highest in the receptor region. Reducing NOx emissions in most source regions causes a larger decrease in export of ozone from the source region than in ozone production outside of the source region.
Highlights
We estimate the influence of a 10% reduction in anthropogenic nitrogen oxide (NOx) emissions from each of these nine regions individually, considering the effects on surface ozone air quality within that region and in all other regions
For the source regions NA and EA, as well as for EU and FSU for some receptor regions, these results show that while the greatest changes in ozone production occur in the summer, the conditions for transport to other Northern Hemisphere (NH) receptors are more prevalent at other times of year
We analyze the effects of 10% reductions in anthropogenic emissions of NOx from nine world regions on the long-range transport of ozone
Summary
Tropospheric ozone is a pervasive air pollutant that affects human health, crop productivity, and natural ecosystems. Other studies have addressed the pathways for the export of pollution from or import to populated regions of interest (Stohl, 2004), including the export from the USA (Liang et al, 1998), Europe (Duncan and Bey, 2004; Duncan et al, 2008), and Asia (Newell and Evans, 2000; Phadnis and Carmichael, 2000; Mauzerall et al, 2000; Heald et al, 2003; Liu et al, 2003; Kunhikrishnan et al, 2004; Liu et al, 2005), and the import of pollution to Europe (Stohl and Trickl, 1999; Trickl et al, 2003; Stohl et al, 2003; Derwent et al, 2004, 2008), the US (Fiore et al, 2002, 2003; Lin et al, 2008), and Asia (Kunhikrishnan and Lawrence, 2004; Kunhikrishnan et al, 2006; Holloway et al, 2008) Because these studies have used different models under different conditions with different experimental designs, it is difficult to compare the results to quantify the relative strength of ozone transport between different source and receptor regions (Task Force on Hemispheric Transport of Air Pollution, 2007). This paper presents only the direct short-term changes in ozone air quality due to emission reductions (i.e., CH4 concentrations are not allowed to adjust fully to changes in OH); long-term changes in ozone air quality via CH4 are analyzed in the companion paper to this study (West et al, 2009), as are the consequences for premature human mortality due to exposure to ozone air pollution
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