Ozone Transport

Elevated concentrations of ozone, often above the national ambient air quality standard for photochemical oxidants, have been measured in both urban and rural areas of Connecticut. One such episode took place on June 10, 1974. Ozone levels, after stabilizing at values slightly above the standard (i.e., 80 to 110 ppb; Connecticut generated ozone concentrations), rose sharply late in the afternoon reaching concentrations as high as 310 ppb (almost 4 times the standard) in Hartford. The trajectory of the air mass, which arrived in Hartford at the time of maximum O₃ occurence, had its origin in the metropolitan New York area during the early morning rush hour on the episode day. This illustrates that the advective transport of O₃ and O₃ precursors into Connecticut from New York are probably responsible for a significant portion (approximately two-thirds) of the elevated O₃ concentrations measured throughout Connecticut on days when winds are from the south-southwest direction. The fact that peak O₃ levels occur late in the afternoon, several hours after maximum sunlight intensity, reinforces the conclusion that excessive O₃ concentrations developed as O₃ and ozone precursors were generated in the vicinity of New York City and then drifted inland into Connecticut on the afternoon sea breeze.

It appears to be unrealistic to develop a hydrocarbon control strategy for Connecticut in order to meet the photochemical oxidant ambient air quality standard when O₃ and/or ozone precursors ad-vectively transported into the State cause oxidant levels to exceed the standard. The complete cessation of all anthropogenic hydrocarbon emissions in Connecticut would not necessarily assure that the standard would be attained here. The implication is that a regional (i.e., the eastern part of the United States) hydrocarbon control strategy is needed to reduce adequately ozone formation and transport so as to allow Connecticut to meet the current oxidant standard.