Figure 1.   Geographic distribution of sulfur emission fluxes: (a) Anthropogenic emissions of sulfur (SO₂ plus primary sulfate) and (b) biogenic sulfur (DMS plus H₂S) emissions. The latitude band structure of the oceanic DMS emissions given by Bates et al. [1992] is still apparent after distribution proportional to coastal zone color scanner (CZCS) data and reallocation to the model grid, introducing discontinuities in these emissions. Note logarithmic scale; white denotes areas with no emissions.

Figure 2.   Synoptic analysis at the 500 and 925 hPa surfaces for April 15 1800 UT. The arrows point to areas of zonal flows and a cutoff low in the 500 and 925 hPa panels and to an omega block in the 500 hPa panel. Cooler colors (blue, green) represent lower values of the height of the surface, hotter colors (yellow, red) represent higher values of this height.

Figure 3.   Illustration of wind flows around anticyclonic and cyclonic circulations. In the Northern Hemisphere, low height (low pressure, cool color) contour is always to the left of the wind vector, cyclonic circulations are counterclockwise, and anticyclonic circulations are clockwise.

Figure 4.   Isentropic analysis for April 1 0000 UT at the 295°K, 300°K, 305°K, 310°K, and 320°K surfaces. The potential temperature is constant at all points on each chart, and the contours represent constant barometric pressures. The colors denote the sulfate mixing ratio on the isentropic surface. Gray areas denote the intersection of isentropic surfaces with the ground; white areas denote regions where the sulfate mixing ratio was <0.01 ppb. Arrows indicate wind velocity; scale arrow indicates maximum velocity.

Figure 5.   Isentropic analysis for April 3 0000 UT. As in Figure 4.

Figure 6.   Isentropic analysis for April 4 0000 UT. As in Figure 4.

Figure 7.   Isentropic analysis for April 5 0000 UT. As in Figure 4.

Figure 8. Sulfur (SO₂ + sulfate) column burden on April 5, 1987, 0600 UT and April 6, 1987, 0600 UT. From top to bottom: SO2 column burden, sulfate column burden, total sulfur column burden, and sulfate fraction of the total column burden. Black symbols denote location of site (22.5°W, 37.5°N) chosen for detailed analysis of sources and formation mechanisms of sulfur species.

Figure 9. Sulfate column burden on April 5, 1987, 0600 UT and April 6, 1987, 0600 UT. From top to bottom: primary, secondary by gas-phase formation, and secondary from aqueous-phase conversion. Black symbols denote location of site (22.5°W, 37.5°N) chosen for detailed analysis of sources and formation mechanisms of sulfur species.

Figure 10. Sulfate column burden on April 5, 1987, 0600 UT and April 6, 1987, 0600 UT. From top to bottom: derived from biogenic sources, derived from North American sources, derived from European sources, and derived from all sources in the model domain. Black symbols denote location of site (22.5°W, 37.5°N) chosen for detailed analysis of sources and formation mechanisms of sulfur species.

Figure 11. Time series of the percent contribution from each formation mechanism to the sulfate burden in five longitude bands: (a) 100°W to 65°W, (b) 65°W to 40°W, (c) 40°W to 20°W, (d) 20°W to 0°, and (e) 0° to 30°E. NA refers to anthropogenic sources west of 30°W, Eu refers to anthropogenic sources east of 30°W; Bio refers to biogenic sources.

Figure 12. Vertical profiles of (left) SO₂ and (middle) sulfate concentrations derived from emissions in different source regions, and vertical profiles of (right) sulfate concentrations resulting from different formation processes for April 5, 1987, 0600 UT to April 6, 1987, 0600 UT at location 22.5°W, 37.5°N. Note increase in abscissa range for each panel.