Comments on Ozone variance in time and space

Elevated ozone over the north-central OTAG states during clean days

Bullet #4: The significance of this observation is not clear. Nor is it that it is in any way related to sources of ozone precursors. Landscape
effects and titration with NO can have a major influence on "minimum value" statistics. For example, the density of trees and the complexity
of terrain differ between the Midwest and other regions. Surface ozone data collected in small clearings and low-lying areas may be
substantially influenced by local deposition. This type of information should be factored into anaylyses of ozone patterns in the OTAG
domain.

Submitted by Eric Edgerton on 4/14/97 RecID: EricEdgerton1

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Pattern of Ozone

Bullet #2: From the perspective of rural sites, this statement does not bear out. There may be a step function somewhere around the
Mississippi River, and another at the OTR, but in between these extremes there is little variation from west to east. The picture may also
vary with latitude of the west-east slice and the intersection of urban areas along the way. Another consideration, of course, is the particular
statistic of interest. If attainment is the issue, very different results are obtained when the 1-hr standard is compared with the proposed
8-hour standard. For the mostly rural CASTNet network (n=40), all sites outside the OTR and at least 40 kilometers from a major city are in
attainment vis-a-vis the 1-hour standard. Most sites in the northeast and the Midwest are non-attainment vis-a-vis the proposed 8-hour
standard.

Submitted by Eric Edgerton on 4/14/97 RecID: EricEdgerton

Re: Pattern of Ozone - another view

The (40, mostly rural, and for the most part uniquely sited) CASTNet ozone sites provide an invaluable compliment to the
existing network of roughly 800 ozone monitors (relatively few of which are located in downtown urban centers). A unique
feature of CASTNet siting criteria (which are predominantly influenced by non-ozone considerations that have to do with
complex dry deposition calculation limitations) is that most (but not all)CASTNet sites tend to be on "ridgetops" - at varying
elevations. So while most CASTNet sites are "rural", their density is sparse, their period of record is short and their siting
charisterics are varied relative to ambient ozone gradients and to the larger, denser, older network of AIRS sites. To say that these
40 sites show a pattern which is different than those 800 sites, and that therefor the 800 should be disregarded is not logical.

Submitted by Richard Poirot on 4/14/97 RecID: RichardPoirot1

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The following statement seems over-stated: " It is therefore implied that urban areas are causing the highest 1-hour daily maximum ozone concentrations as well as the highest variation in ozone concentration (90th - 10th percentile difference)." If this were true, we could all go home. What about rewording to the effect that: "...urban areas are making substantial local contributions to the highest 1-hour daily maximum..."


Submitted by Richard Poirot on 2/22/97 RecID: RichardPoirot

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Volume I: Executive Summary--Ozone variance in time and space

Add The urban influence can be enhanced when urban areas of influence overlap or result from nighttime transport in front of sentence It is therefore...

Submitted by Jeffrey West on 2/18/97 RecID: JeffreyWest

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