Calendar Year

Figure 7.2. Annual mean (flux-weighted) wet deposition at West Point, NY, National Atmospheric Deposition Program: (A) [SO42-], [NO3-] and [H+]; (B) [Cl-] and [Na+].

delivery of acids via precipitation declined appreciably at NY99 since the early 1980s (Fig. 7.2A). Similar temporal trends for other areas of the Hudson River basin are likely, reflecting reductions in acidic gas emissions from electricity generating stations within and upwind of the region. Data from West Point suggest an increase in mean annual pH from about 4.2 in the mid 1980s to about 4.4 in the late 1990s.

The largest source of Na+ and Cl- to West Point wet deposition is marine aerosols. Precipitation episodes that entrain primarily marine air, more common during the winter half of the year, tend to have higher concentrations of both these

0 0

Post a comment