Abstract
Abstract. Large-scale changes in ozone precursor emissions affect ozone directly in the short term, and also affect methane, which in turn causes long-term changes in ozone that affect surface ozone air quality. Here we assess the effects of changes in ozone precursor emissions on the long-term change in surface ozone via methane, as a function of the emission region, by modeling 10% reductions in anthropogenic nitrogen oxide (NOx) emissions from each of nine world regions. Reductions in NOx emissions from all world regions increase methane and long-term surface ozone. While this long-term increase is small compared to the intra-regional short-term ozone decrease, it is comparable to or larger than the short-term inter-continental ozone decrease for some source-receptor pairs. The increase in methane and long-term surface ozone per ton of NOx reduced is greatest in tropical and Southern Hemisphere regions, exceeding that from temperate Northern Hemisphere regions by roughly a factor of ten. We also assess changes in premature ozone-related human mortality associated with regional precursor reductions and long-range transport, showing that for 10% regional NOx reductions, the strongest inter-regional influence is for emissions from Europe affecting mortalities in Africa. Reductions of NOx in North America, Europe, the Former Soviet Union, and Australia are shown to reduce more mortalities outside of the source regions than within. Among world regions, NOx reductions in India cause the greatest number of avoided mortalities per ton, mainly in India itself. Finally, by increasing global methane, NOx reductions in one hemisphere tend to cause long-term increases in ozone concentration and mortalities in the opposite hemisphere. Reducing emissions of methane, and to a lesser extent carbon monoxide and non-methane volatile organic compounds, alongside NOx reductions would avoid this disbenefit.
Highlights
Tropospheric ozone has been observed to have increased in polluted regions since preindustrial times, while the global ozone background has increased (Vingarzan, 2004)
The results show that the 10% reduction in nitrogen oxides (NOx) emissions in IN causes the greatest number of avoided mortalities, with 93% of that benefit occurring in IN itself
Large numbers of avoided mortalities result in IN from NOx reductions within the same region because of the high population density and because it has the largest decrease in the population-weighted annual average ozone (Fig. 1b); NOx reductions in IN reduce ozone throughout the year, while reductions in NA, EU, FSU, and EA increase the population-weighted ozone in the Northern Hemisphere (NH) winter (West et al, 2009)
Summary
Tropospheric ozone has been observed to have increased in polluted regions since preindustrial times, while the global ozone background has increased (Vingarzan, 2004). West et al.: Long-range ozone transport – Part 2: Steady-state mortality a net positive radiative forcing from global NOx emission reductions (Fuglestvedt et al, 1999; Wild et al, 2001) and surface NOx reductions in all world regions (Naik et al, 2005; Berntsen et al, 2005). Reductions of NOx from four different world regions have been shown to cause long-term ozone increases that are comparable to the direct short-term ozone decreases due to inter-continental transport, while combinations of NOx, NMVOC, and CO reductions have much smaller long-term influences due to compensating effects on OH and CH4 (Fiore et al, 2009). We present the sum of the short-term and long-term changes in surface ozone air quality – the net steady-state change for sustained NOx reductions – and its importance for the ultimate effect on the long-range transport of ozone between all nine world regions. We present methods of assessing changes in premature human mortality due to changes in ozone, and the avoided mortalities for each world region, for both the shortterm change in ozone air quality and the steady-state change
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