CLIMATOLOGY OF OZONE EXCEEDENCES IN THE ATLANTA METROPOLITAN-AREA - 1-HOUR VS 8-HOUR STANDARD AND THE ROLE OF PLUME RECIRCULATION AIR-POLLUTION EPISODES
Jcs. John et Wl. Chameides, CLIMATOLOGY OF OZONE EXCEEDENCES IN THE ATLANTA METROPOLITAN-AREA - 1-HOUR VS 8-HOUR STANDARD AND THE ROLE OF PLUME RECIRCULATION AIR-POLLUTION EPISODES, Environmental science & technology, 31(10), 1997, pp. 2797-2804
This work compares the relative frequencies of and meteorological cond
itions most conducive to exceedences of the current 1-h/120-ppbv natio
nal ambient air quality standard for ozone and the proposed revised st
andard based on daily maximum 8-h averages. Chemical and meteorologica
l data gathered from 1987 through 1993 in Atlanta, GA, are used to det
ermine the daily maximum 1-h and 8-h average ozone mixing ratios at ea
ch local monitoring site, during the ozone season for each year. The n
ature of the highest among the maxima and the concurrent local meteoro
logical conditions are examined. We find a high degree of correlation
between the daily maximum 1-h and 8-h averages(R-2 = 0.92) in Atlanta,
with an 8-h daily maximum concentration of 98 ppbv being climatologic
ally equivalent to a 1-h daily maxima of 120 ppbv. Over the 7-year per
iod investigated, exceedences of 8-h-averaged concentrations of 70, 80
, and 90 ppbv were about 5, 3, and 2 times more frequent in Atlanta th
an exceedences of the current 1-h/120-ppbv standard. Meteorological co
nditions that fostered Atlanta's most severe 1-h and 8-h maximum ozone
pollution events over the period were quite similar. The majority of
the most extreme 1-h and 8-h events were associated with multiple-day
episodes with very stagnant meteorological conditions and a recirculat
ion and recooking of Atlanta's plume on consecutive days. These events
, called ''plume recirculation'' episodes, are distinct from other mul
tiple-day episodes that were characterized by fairly steady winds, lit
tle or no recirculation, and more modest O-3 concentrations. Plume rec
irculation episodes are among Atlanta's most severe O-3 exceedences an
d therefore were chosen by the State of Georgia for urban airshed mode
ling in its most recent State Implementation Plan (SIP) and will likel
y remain the focus in future SIPs even if a new 8-h standard is promul
gated.