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New Hampshire Department of Environmental Services

Summary of Ozone Events - Exceedance Day Episode Analyses

For each day that an ozone monitor exceeds the standard, NHDES documents 1) the level of peak ozone concentration, 2) the time of the peak ozone concentration, and 3) the interpreted wind direction at the time of the exceedance. A short written summary describes downward short wave radiation (ultraviolet radiation) and wind direction streamlines for the hours in which the peak ozone concentration occurred at each monitor. High levels of downward short wave radiation efficiently drive the ozone formation chemistry. When radiation levels are low however, ozone formation is slow. Therefore, a day with low radiation levels, and high ozone concentrations, might be concluded as a day when ozone transport into the area was considerable. Streamlines indicate the general wind flow patterns over an area at a particular moment in time. They give a good indication of near-field sources of ozone and its precursors, and they also portray verification of the seabreeze phenomenon.

Backwards trajectory analyses are also described for each monitor, which trace the course the air traveled leading up to the peak ozone concentration. Trajectories give a longer-range estimation of possible source regions of ozone and its precursors. It is important to note, that these trajectories provide a reasonable approximation to where the airmass may have been prior to arriving in New Hampshire. However, the uncertainty of the path grows with increasing time lapse from arrival in New Hampshire. Trajectories passing over the Atlantic Ocean also have increased uncertainties.



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NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
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