An investigation of the meteorological effects on ozone during the 1995 OTAG episode in the northeast corridor

This study examined the behavior of ozone, its precursors and meteorology during the 1995 OTAG episode (i.e., 7--18 July 1995) at sites in the northeast corridor using PAMS data. Four urban sites (i.e., Washington DC, Baltimore, Philadelphia, and New York) and two non-urban sites (i.e., sites upwind and down wind of Baltimore) were used. The departures of ozone, of its precursors, and of various meteorological parameters from their average values on non-exceedance days in the June--July 1995 period were examined during the episode period. The authors found that when exceedances took place, temperatures and solar radiation were consistently higher than those found on the average non-exceedance day. Large positive temperature departures began to build up 24 to 48 hours after the large ozone buildup. The temperature departures reached a peak on 15 July in most cases which is when the ozone reached a peak, decreasing significantly thereafter, but remaining positive through the end of the period. The solar radiation departures were generally large and positive when the exceedances took place, indicating clear skies and significant amounts of solar energy available for the photo chemistry. The wind speed and direction were highly variable from site to site, producing no temporal ormore » spatial consistency in the flow pattern. The wind field was diffusive (i.e., governed by turbulence and not the synoptic pressure gradient), and not conducive of transport, particularly long-distance transport. Secondary mid-day maximums in the NO{sub x} distribution developed when a local wind minimum developed. Since the presence of the secondary maximums in the NO{sub x} distribution will undoubtedly affect the local chemistry, it was concluded that the local wind variations were affecting the local chemistry.« less