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View Diary: Towards Zero Emissions: The Methane Cycle   (43 comments)

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  •  Actually (0+ / 0-)

    Tropospheric OH comes mostly from photolysis of formaldehyde and HONO in combination with the ozone reaction with alkenes.  The rest of your comment is mostly correct.

    •  Eh??? (0+ / 0-)

      Primary OH source is O1D (from photolysis of ozone) and water.  Formaldehyde (which comes mostly from methane oxidation) may be significant in the upper troposphere.  HONO may be important in high NOx regions near the surface, especially shortly after sunrise. Ozone and alkenes may be important in regions with high ozone and alkene loadings (but it depends on alkene).  All that said, ozone and water is where the bulk of the action is.

      •  It is a source (0+ / 0-)

        but I don't think it is the primary one in the troposphere.  In the stratosphere you are right.  But, tropospheric ozone is actually not the biggest source of tropospheric OH.  The realization of that has been fairly recent.  I think that is the way it is in the latest version of Atmospheric Chemistry by Finlayson-Pitts, and Pitts anyways.

        •  I think you might want to double check (0+ / 0-)

          I'm sure F-P&P (or Seinfeld and Pandis, or Jacob) don't say that!

          •  It takes (0+ / 0-)

            wavelengths below 300 nm to produce 1DO.  That happens a lot in the stratosphere, but ozone protects us down here.  Most ozone photolysis in the lower troposphere is 3PO which is not high enough in energy to abstract hydrogen from water.  It is not that important for this discussion though.  I am sure you will agree that most of it does not come from cosmic rays, unless  you are counting sunlight.

          •  You are right (0+ / 0-)

            In that overall in the atmosphere (1D)O from ozone is the most important source when you include the upper troposphere and stratosphere, and that is what counts for the overall lifetime of methane.

            •  Tell you what (0+ / 0-)

              Take any surface data set and see for yourself. Even at the surface JO1D is high enough to dominate production for normal amounts of ozone.  HOx is easy even though there are a gazillion reactions because you can assume it's at steady state.  If you need a mechanism just ask. If the UCR in your handle refers to UC Riverside, ask F-P herself.

              (BTW, the relative contribution of formaldehyde, acetone, and peroxides compared to ozone/water is largest in the UT: it's very dry up there.  Stratosphere is drier, of course, but there's even less in the way of OVOC, peroxides up there)

              •  Just checked FP+P (0+ / 0-)

                 It says that (1D)O dominates in the remote regions and is important in polluted areas.  I take that to mean it does not dominate there.  I was wrong to omit that reaction as a source of OH.  It is important.  Thanks for the correction.  btw, FP is at UCI now, not UCR and has been there for some time.  I based my statements on comments I heard from a professor at UCR about polluted air and the dominant sources of OH.  Also, an additional source we did not cover is HO2 + NO, a reaction we happen to be doing at the moment and even H2O2 photolysis which we are using to indirectly produce HO2.  Air pollution gets quite complicated doesn't it?

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