Global Sources of Local Pollution An Assessment of Long-Range Transport of Key Air Pollutants to and from the United States (2010) / Chapter Skim
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2 Ozone
2 Ozone
Pages 35-66
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From page 35... ...
. Using health impact functions derived from the published literature, they estimate that if the standard had been attained, roughly 800 premature deaths, 4500 hospital and emergency department admissions, 900,000 school absences, and > 1 million minor restricted-activity days (per year averaged over the three years studied)
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From page 36... ...
. Different national and international standards are noted as well as bitmap image estimates for northern midlatitudes of the preindustrial background (i.e., O3 abundances with all anthropogenic emissions of NOx, CO, VOC, and CH4 cut off, and before current climate and stratospheric O3 change)
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From page 37... ...
bitmap image line) with all North American EPA policy relevant background (PRB, lowest red emissions cut off, and the background (blue line)
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From page 38... ...
Defining Background and Baseline Ozone The ultimate background level for tropospheric ozone existed before humans began to alter the atmosphere. In this preindustrial atmosphere tropospheric O3 sources included stratospheric intrusions; lightning NOx; natural surface emissions of CH4, CO, and VOCs; and wildfires.
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From page 39... ...
. There remains uncertainty in this value, yet when we combine the limited historical observations with our proven chemical knowledge of the formation of O3 and the model studies, we have high confidence that current baseline levels of tropospheric O3 in the Northern Hemisphere are much greater than the natural preindustrial levels.
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From page 40... ...
are caused primarily by a combination of regional emis sions and unfavorable meteorology. These are augmented by a changing baseline and episodic events caused, for example, by wildfires, lightning NOx, occasional stratospheric intrusions, as well as distant anthropogenic emissions.
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From page 41... ...
Comprehensive reviews of Northern Hemisphere O3 trends have been presented by Vingarzan (2004)
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From page 42... ...
While evidence generally shows that more regions of the Northern Hemisphere have increasing O3 baselines than have constant or decreasing ones, the magnitudes and specific patterns are not fully understood or simulated in chemical-transport models. Changes in natural variability, which can influence, for example, the stratospheric flux of O3 into the troposphere, could be a contributing factor.
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From page 43... ...
. Direct boundary layer transport from Asia is not a major contributor to the North American baseline because of the unfavorable circulation and the fast chemical loss of ozone under moist, sunlit conditions.
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From page 44... ...
, also provide high-resolution vertical profiles that can be used to identify pollution plumes, but not map their extent or transport in the same way as satellites. Brief, intensive field campaigns involving a range of in situ measurements and mobile lidars are often able to map out tropospheric ozone and provide important detail on tropospheric O3 plumes, including precursors, vertical profiles, and their dilution into the baseline levels.
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From page 45... ...
that are reasonably well simulated by the model results, shown bitmap image on the right (Wild et al., 2004b)
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From page 46... ...
. Seasonally, the TCO follows the Northern Hemisphere industrial pollution in the July and the Southern Hemisphere biomass burning source of O3 in November.
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From page 47... ...
Plumes of anthropogenic CO pollution can be seen leaving Asia and crossing the Pacific Ocean, and those of Alaskan and Canadian forest fires can be seen crossing North America and the Atlantic Ocean towards Europe. bitmap image SOURCE: Provided by D
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From page 48... ...
. Spring import of enhanced O3 levels into western North America has been identified in analysis of surface data and aircraft measurements during various campaigns focused on quantifying transport of polluted air masses from Asia to North America (e.g.
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From page 49... ...
can be transported between continents and are observed downwind of the major industrial regions and large wildfires in North America, Europe, and Asia. They are observed in the free troposphere over impacted regions but rarely at the surface due to dilution in the boundary layer.
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From page 50... ...
were found to be larger in spring and fall, with largest responses to reductions in NOx emissions. Import sensitivities (defined as the ratio in surface O3 response to a 20 percent decrease in the three foreign source regions vs.
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From page 51... ...
The April and July monthly means new from the ensemble of 14 HTAP models along with the standard deviation of bitmap image the ensemble are plotted. Peak levels of imported O3 can be seen over the west coast of North America, with higher values in spring than in summer.
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From page 52... ...
ozone enhancements varied between 1 to 5 ppb but sometimes as high as 10 ppb for particular events. The recent HTAP results based on ensemble model results show less variability and lower enhancements since these estimates provide an estimation of average increases in baseline O3 due to different source regions and not due to particular events.
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From page 53... ...
These results help demonstrate that production over any one region (e.g.,d Bitmappe North America) can include long-range transport of distant sources of O3 precursors as well as local emissions (Kotchenruther et al., 2001)
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From page 54... ...
and chemical and physical processing,including transport of plumes into downwind receptor regions where mixing into the boundary layer is important. Comparisons with data collected during dedicated aircraft campaigns are able
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From page 55... ...
Baseline O3 levels in the Northern Hemisphere are ele vated by current anthropogenic emissions of NOx, CO, and VOCs. Multimodel studies calculate that a 20 percent reduction in these emissions from any three of the four major industrial regions of the Northern Hemisphere will reduce surface O3 in the fourth region by about 1 ppb on average (i.e., a baseline enhancement)
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From page 56... ...
and health impact functions. A health impact function is used to calculate avoided deaths in a population, using baseline mortality rates, the modeled O3 changes, and a concentration-response factor.1 For cardiopulmonary deaths the concentration response function 1 More specifically, premature mortalities avoided due to the O3 concentration change are calculated as: ΔMort = y0 (-exp– βΔX )
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From page 57... ...
The avoided nonaccidental mortality is also evaluated and shown to be larger, since it includes cardiopulmonary mortality. As shown in Tables 2.1 and 2.2, 20 percent reductions of anthropogenic NOx, nonmethane VOCs, and CO emissions in NA were estimated to avoid more deaths outside NA than within (68-76 percent of resulting avoided deaths in the Northern Hemisphere [NH]
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From page 58... ...
A preliminary study finds that about 500 premature cardiopulmonary deaths could be avoided annually in North America by a combined 20 percent reduction in NOx, CO, and VOC emissions from the other three major Northern Hemisphere industrial regions and, correspondingly, about 1800 in Europe. The uncertainty in these estimates is large, at least ± 50 percent, and reflects uncertainties in modeling both O3 change and health effects.
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From page 59... ...
. The climate-change impact on AQS violations will lessen if NOx emissions decrease (Wu et al., 2008b)
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From page 60... ...
Projected climate change will lead to a warmer climate with shifts in atmospheric circulation. All of these changes have the potential to affect air quality, for better or worse: • higher water vapor abundances associated with a warmer climate drives down baseline O3 abundances due to the more rapid photochemical destruction of O3 in the marine boundary layer and the tropics;
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From page 61... ...
Ensure that the climate models include global atmospheric chemistry so that the model ensembles run for climate change assessments can also be used to evaluate changes in air quality. Analyze the climate statistics that are specific to air pollution: boundary layer height, stagnation episodes, intercontinental trans port, stratosphere-troposphere exchange, lightning, wildfires, and other natural emissions of O3 precursors.
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From page 62... ...
Combining the evidence from observations and models and including our basic knowledge of atmospheric chemistry there is high confidence that human activities have raised the baseline levels of tropospheric O3 in the Northern Hemisphere by 40-100 percent above preindustrial levels. Much of this increase can be directly attributed to anthropogenic emissions of ozone precursor species (CH4, NOx, CO, VOCs)
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From page 63... ...
Baseline O3 levels in the Northern Hemisphere are ele vated by current anthropogenic emissions of NOx, CO, and VOCs. Multimodel studies calculate that a 20 percent reduction in these emissions from any three of the four major industrial regions of the Northern Hemisphere will reduce surface O3 in the fourth region by about 1 ppb on average, but with large spatial and seasonal variation.
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From page 64... ...
Projected climate change will lead to a warmer climate with shifts in atmospheric circulation. All of these changes have the potential to impact air quality for better or worse: • Higher water vapor abundances associated with a warmer cli mate drives baseline O3 abundances down due to the more rapid photochemical destruction of O3 in the marine boundary layer and the tropics.
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From page 65... ...
Test and improve the simulation of air quality, including pollution episodes in both global and regional climate models. Ensure that the climate models include global atmospheric chemistry so that the model ensembles run for climate change assessments can also be used to evaluate changes in air quality.
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