NCAQ Report to Congress: Review and Response

Airborne measurements of gaseous and particulate sulfur and nitrogen pollutants were made in southwestern Kentucky on the afternoon of October 21, 1979. Back-trajectory analysis indicates that the sampled air parcel moved over northern Florida, Alabama, and western Tennessee during the two days prior to sampling. Before moving over Florida, the air parcel was over the Atlantic Ocean for at least five days. Analytical long-range transport (LRT) model predictions based on anthropogenic emissions account for only about 75% of the airborne measured concentrations of 14.7 μg m^?3 for SO₂ and 4.8 μg m^?3 for SO₄ ^2?. The remaining 25 % is thought to be due to biogenic sulfur emissions from the extensive wetland areas along the Gulf Coast.

Forward-trajectory analysis indicates that the air parcel moved to the Adirondack Mountains of New York State 24 hours after sampling. Model predictions indicate that SO₂ and SO₄ ^2? mean layer concentrations at the Adirondacks were 24 and 16 μg^?3, respectively. Almost half of this sulfur was estimated to come from emissions in the heavily industrialized region along the Ohio River Valley.

Further comparisons used a measurement data base obtained in southeastern Canada and the state of Arkansas during August 1976. An air parcel was tracked for seven days as it entered the north central United States, stagnated over the lower midwest, and then moved to eastern Canada. Model predictions were in substantial agreement with regional SO₄ ^2? concentrations measured at a number of ground-level sites. Average SO₄ ^2? concentrations measured in central Arkansas on August 10, 1976 were 20 μ m^?3 vs. a modeled value of 19 μ m^?3. Average SO₄ ^2? concentrations measured in Nova Scotia four days later were 22 μg^?3 vs. a modeled estimate of 24 μg^?3.