Science at the Frontier (1992) / Chapter Skim
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8 Atmospheric Science: Research and Regulation: Science's Contribution to the Public Debate
8 Atmospheric Science: Research and Regulation: Science's Contribution to the Public Debate
Pages 178-198
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From page 178... ...
We need to think about the chemical coupling at the time we are devising regulations," he maintained. Aware of pressing environmental problems, atmospheric scientists work with a sense of urgency to sort out and understand the intricacies of complex physical interactions.
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From page 179... ...
The urgency that attends the problems of pollution, he thinks, confers a responsibility on atmospheric scientists to consider issues like cost-effectiveness and adverse impacts whenever their results might be central to a political debate, which in atmospheric science is very often. McRae has developed this awareness of the political arena as his model begun in graduate school at Caltech has evolved using a historical database of Los Angeles weather and pollutant data.
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From page 180... ...
Because of the severity of pollution in Southern California, McRae and his model have been drawn deeply into the political decision-making process. Alan Lloyd, another session participant and chief scientist for the South Coast Air Quality Management District in California, emphasized that "it is critical to have available a wide group of scientists and institutions that regulators can turn to for unbiased and impartial information." McRae credited the session's third participant, Arthur Winer, an atmospheric chemist at the University of California, Los Angeles, with "unraveling some of the very interesting things the chemistry going on at nighttime in the atmosphere." Winer brought to the symposium discussion his perspective as a longtime scientific advisor to California's regulators, and he also singled out as a challenge for atmospheric science the need "to arrest the declining numbers of really gifted young scientists" entering the field.
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From page 181... ...
REGULATION ARE THE CORRECT QUESTIONS BEING POSED? McRae and his colleagues have drawn some conclusions from their latest model that might influence regulators to redirect a current, major control strategy: the reduction of reactive organic gases.
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From page 182... ...
Regulating ROGs was not reducing ozone formation at all, because the role of NO had been misperceived and as a conseauence underestimated. - x ~ ~ Although, as Lloyd pointed out, "ozone levels in Los Angeles have been cut by about half over the last 15 years," the model indicated that in the rest of the country where NOX was not being regulated, uncontrolled emissions of NOX could confound the intended results of ROG reduction.
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From page 183... ...
The socalled ozone layer of the stratosphere with the heaviest concentrations develops at the altitudes it does because of a natural balance: higher up, above the stratosphere, the density of oxygen is such that liberated oxygen atoms encounter relatively few oxygen molecules to join to; lower down in the troposphere, insufficient light energy arrives due to the shielding effect of the ozone that has been created above. When McRae referred to engineers failing to "get the sign right"
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From page 184... ...
When liberated, a single chlorine atom can trigger a catalytic reaction and destroy thousands of ozone molecules, thus contributing to a breakdown of the Earth's protective ozone shield. Ozone as a Pollutant Ozone in the upper stratosphere is created largely by natural processes, and its presence serves a vital function.
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From page 185... ...
Hydroxyl radicals can be produced in several ways. When an ozone molecule absorbs a relatively high-energy photon, it dissociates to form molecular oxygen and a relatively long-lived, electronically excited atom known as the singlet D state (ID)
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From page 186... ...
Not only are more hydroxyl radicals produced, but newly formed nitrogen dioxide also pushes the numerator of the ozone equilibrium equation up, and along with it the concentration of ozone. Without these excess concentrations, it normally requires an ozone molecule to oxidize nitric oxide into nitrogen dioxide, but equation (12)
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From page 187... ...
Such chemical reactions can contribute to a cycle or chain reaction that intensifies the concentration of ozone, and hence increases smog. Knowing how to identify and apply the reactions is the important framework, but obtaining accurate measurements of these substanceswhich can exist in a transient condition, swirling around the atmosphere, in concentrations as small as a few parts per trillion presents a formidable challenge to atmospheric chemists.
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From page 188... ...
Sunlight drives most of the chemical reactions that atmospheric scientists model, and thus conventional wisdom held that nighttime with its absence of hydroxyl radicalsmight offer a respite from the creation of secondary pollutants. General pollution measurements taken after dark seemed to confirm that nighttime chemistry "was of minor importance," said McRae, who added that it "was even disregarded in some models." NO3 for example, is a trace nitrogen-containing radical with such small predicted concentrations (in the parts-per-trillion range)
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From page 189... ...
is produced in large quantities from the world's oceans but does not accumulate during the day because of the presence and interaction of the hydroxyl radical. Again, since the OH radical disappears at night, atmospheric chemists were unable to explain why .
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From page 190... ...
Since HONO is a photolytic species that readily breaks apart into the hydroxyl radical and nitric oxide during the day, Winer continued, "the accumulated nitrous acid that photolyzes at sunrise leads to a pulse of OH radicals that represents a kicking off of the next day's smog." In the fall and winter seasons in California when ozone and formaldehyde (which also photolyze to produce OH radicals) are reduced, this OH radical kickoff by nitrous acid can become a dominant source of OH radicals.
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From page 191... ...
Traditionally, in the past, scientists had a theoretical formulation and then went into the lab to verify it." But meteorology has always been difficult to fit into that tradition because one cannot simply design and conduct experiments in the laboratory of a real city. With advanced models like the one McRae has spent the better part of a decade developing and refining, however, atmospheric science is beginning to utilize the experimental method more as some of the hard sciences do.
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From page 192... ...
Writing about McRae and other scientists breaking new ground with computers, Robert Pool (1984) anticipated a theme that was to be visited during the Computation session at the Frontiers symposium: "Not only can computer experiments substitute for many of the studies normally done in a lab, but they also are allowing scientists to gather data and test hypotheses in ways that were closed to them before.
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From page 193... ...
But now that the model has earned its stripes as a predictor, it is the scientists who are defining the levels of various hypothetical pollutant emissions and the weather influencing them. The model then produces a vision of what such pollution and weather in Los Angeles would look like that has been captured in a video, produced by the Pittsburgh Supercomputing Center, called "Visualizing Los Angeles Air Quality." A second video called "Smog" was developed and produced by the National Center for Supercomputing Applications "to try to understand the physics and the chemistry," where the heart of McRae's work lies.
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From page 194... ...
REFRAMING THE LAWS OF POLLUTION CONTROL McRae's long history of involvement with colleagues in the field and regulators in Southern California, along with the demonstrable cogency of his methods and his model, have given him a role in recent regulatory reform. Said Lloyd, "His work gave technical credence to strong regulations that were needed to reduce emissions." The South Coast Air Quality Management District, said Lloyd, is well served by the views and resources provided by individuals like Winer and McRae, although Lloyd's premise is that "the scientists and the scientific community have to be more proactive." Thus, when the model McRae has spent nearly a decade developing and refining was finally put to the test, and its results suggested many fairly dramatic implications, the battle was just being joined.
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From page 195... ...
Given a mandated, numerical air quality goal, strategies to reduce ROG emissions to a level that leads to air that meets that standard have been evaluated for cost-effectiveness. The Empirical Kinetics Modeling Approach employs a simplified, singlecell trajectory formulation to model the impact of a number of possible ROG and NOX emission level combinations on the resultant ozone level, and then to derive a new ROG reduction goal.
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From page 196... ...
A number of surprising spatial patterns were observed for the first time, as this modeling technique revealed interactions and time-sensitive patterns for the targeted substances that had not been captured by previous models. In particular, the model demonstrated that changing relative emissions standards very often had the impact not of reducing peak ozone concentrations, but of merely moving them to a different region within the airshed.
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From page 197... ...
These suggest that only by considering numerous receptor sites throughout the region and over time, and evaluating at least PAN and inorganic nitrates in addition to ozone, can a strategy be developed that embraces the known major trade-offs. SCIENCE IN THE PUBLIC INTEREST Thus it can be seen from the work authored by Milford, Russell, and McRae that atmospheric scientists very often assume a strongly proactive stance about their conclusions.
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From page 198... ...
1989. A new approach to photochemical pollution control: Implications of spatial patterns in pollutant responses to reductions in nitrogen oxides and reactive organic gas emissions.
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