Source regions of summertime ozone and haze episodes in the eastern United States

During the summer of 1979, the mobile Atmospheric Research Laboratory (ARL) was sited near the Louisiana Gulf Coast to monitor the concentrations of air contaminants in air masses moving northward from the Gulf. Using the ARL data in conjunction with O₃ and visibility measurements across the entire eastern United States as well as synoptic meteorological data and satellite photographs, major source areas were identified. The haze which was observed on the Louisiana Gulf Coast appears to be primarily due to aged sulfate aerosols. The evidence presented strongly suggests that the sulfates were largely due to SO₂ emissions in the northeastern and midwestern United States. The haze initially formed over and downwind of these source areas and was transported to the Gulf Coast area. In the last two episodes, the haze was subsequently transported back to the Midwest source region. Elevated levels of O₃ were also associated with the haze. Again, the Northeast and Midwest appear to be the most significant source areas for the regional O₃ episodes. Occasionally, O₃ formed from emissions in the east Texas area also appear to affect a large portion of the Gulf Coast. In addition, each episode appeared to have a significant stratospheric air component based on⁷Be measurements. All three episodes followed the passage of upper levels troughs which produce stratospheric intrusions due to tropopause folding.