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Paul Crutzen, Brian Ridley, fred C. Fehsenfeld, Jack Calvert, Ralph J. Cicerone, plus Prof. Ken Hare

October 19, 1990 @ 10:00 am – 6:00 pm
Senate Chamber, N940, Ross Building, York University

Frontiers in Atmospheric Chemistry.

Title: Changes in the Oxidative Power of the Atmosphere Due to Human Activities by Paul Crutzen, Max-Planck-Institute for Chemistry Mainz, West Germany
Abstract: The measured changes in CH4 and CO concentrations, and enhancements in  NOx emissions by fossil and  biomass fuel burning  have  led  to  important changes  in  the  global distributions of ozone and  hydroxyl radicals.  As  part of  a European effort on the three-dimensional modelling of  tropospheric chemistry, estimates are made  on  the changes  which  have taken  place in  the global distributions  of  ozone  and  hydroxyl.

Since pre-industrial  times  we  find that  ozone concentrations have increased  in  the  northern hemisphere,  but  that  on  the  other  hand  global average  OH  concentrations  have  declined,  leading  to  a  buildup  of  trace gases  in  the troposphere. Brochure

Title: Measurements and Implications of Photochemically Active Trace Species in the Remote Atmosphere by Brian Ridley, The National Center for Atmospheric Research Atmospheric Chemistry Division Boulder, Colorado

Abstract: Much of the atmosphere over the Pacific Ocean region is still believed to be relatively free from direct anthropogenic influence and it therefore has some semblance of the background troposphere.  By area, the ocean represents roughly 35% of the earth’s surface.  Due to the remoteness of the region, measurements of some photochemically important trace species also present an interesting challenge.  In an effort to further our understanding of the abundances, budgets,  photochemical  transformations,  and  influence  of  long  range transport  processes,  a five week study was  conducted at the Geophysical Monitoring  for Climatic Change  (GMCC) station  at  the  11,000 ft  level  on  Mauna Loa,  Hawaii  in  the  spring  of  1988. During this experiment, called the Mauna Loa Observatory Photochemistry  Experiment (MLOPEX), a variety  of  photochemically related  trace  species including  NOx,  NOy,  HNO3,  NO3-, O3, NMHCs,  J(NO2),  HOOH,  H2CO,  PAN, organic nitrates  and  other peroxides  were continuously measured  in  addition to  many  other measurements that are routinely made at the GMCC  station.  Results from this experiment will be presented and will be compared with photochemical  models,  with  measurements  made  previously  from  aircraft  programs  in  the Pacific,  and  with  measurements  made  in  continental regions.  In particular, the ozone photochemical tendency, partitioning of total odd nitrogen and implications for the abundance of peroxyl and hydroxyl radicals will be discussed.
In addition, and because thunderstorms may be significant source of odd nitrogen species to the  global  free  troposphere,  some  results  from  recent  aircraft  flights  within the  anvils  of thunderstorms will be presented. Brochure

Title: Regional Ozone Production by Fred C. Fehsenfeld National Oceanic and Atmospheric Administration U.S. Department of Commerce
Abstract: Ozone plays a key role in tropospheric chemistry and global climatology.  In addition, ozone is a secondary pollutant, and elevated levels of ozone can damage forests and crops and may be harmful to human health.  For these reasons, ozone represents an important component of air quality problems in  urban  areas,  and  an  emerging  air  quality  problem  in  rural  areas.  Most ozone is formed photochemically from ozone precursors, the oxides of nitrogen, NOx, and non-methane hydrocarbons, NMHC.  However, these reactions are exceedingly complex, many  of  the  key  processes  poorly  understood,  and  the  rate  of  emission  of  the  important precursor  compounds  into the atmosphere uncertain.  For these reasons, understanding the process responsible for ozone production represents an important and challenging problem. Our present understanding of the processes that shape the regional ozone distribution will be briefly reviewed, and the sources of the key precursor compounds examined.  The implication of recent field measurement campaigns to the understanding of these processes will be discussed. Brochure

Title: Studies of the N02-NOS-N205 System by Jack G. Calvert Atmospheric Chemistry Division National Center for Atmospheric Research Boulder, Colorado
Abstract: The nitrate radical, NO3, through it reactions involving NO2 and N2O5,
NO3 + NO2 = N2O5                          (1)
is important in  controlling the levels of  active nitrogen and  the partitioning of  NO  and  NO2 in both  the troposphere and  the  stratosphere.  Measurements of NO3 in the atmosphere have not been successfully reconciled with attempts to model its concentration. This suggests that some fundamental rate and/or spectroscopic parameters may not be known with sufficient accuracy today.  The Atmospheric Kinetics and Photochemistry group (including G.S. Tyndall, J. J.  Orlando, C.A.  Cantrell, R.E.  Shetter) within NCAR have redetermined the cross sections of each  of  these  molecules, equilibrium constant  for  (1)  and  the  rate  coefficients for  both  the formation (2) and decomposition (3) of N2O5 as a function of pressure and temperature.
NO3 + NO2 + N2 \ N2O5 + N2              (2)
N2O5 + N2 \ NO3 + NO2 + N2              (3)
These rate data, combined with previous measurements over a more limited temperature and pressure  range,  provide  a  more  complete  data  set  which can  be  used  to  define  the falloff characteristics of the rate coefficients k2  and  k3 in atmospheric modeling. Comparisons of the ratio of rate coefficients k2/k3 at a given pressure and temperature with measured values of K1 allow a check in the consistency of the present data. Brochure

Title: Isotopes in Stratospheric Ozone by Ralph J. Cicerone Department of Geosciences, School of Physical Sciences University of California, Irvine
Abstract: Observations have shown that stratospheric ozone is isotopically heavier than it would be if it contained only statistical proportions of 16O, 17O, and 18O.
Attempts to predict and/or explain the isotopic ratios have failed; no model accounts for the observed enrichments of heavy oxygen despite a growing number of studies from theory and laboratory experiments.  An explanation of the isotopic data is desirable even if it would not greatly alter our views of stratospheric photochemistry.  I will review what is known and attempt to isolate several likely possible mechanisms whose investigation could resolve the problem. Brochure


Updated on August 6th, 2014.