The length of each vector represents the wind speed. In the second chronological image, lead air concentrations are once again illustrated. This time, cumulative wet deposition and 3-hour rainfall amounts are superimposed. Note that for dry deposition, the maximum amount was near 20 grams per hectare while for wet deposition, the maximum at one 40 km grid cell was in excess of 70 grams per hectare. The air concentrations appear in shades of blue.
Rainfall appears in shades of green, and wet deposition in purple.
During this particular month, note that little rainfall occurred when the air flowed across St. Louis from the dry north, northwest, and west. On the other hand, moisture carried by southerly winds from the Gulf of Mexico often triggered rainfall events as the St. Louis plume was transported northward and eastward. As a result, the cumulative wet deposition pattern shows maximum values to the north and northeast of St. Louis. Near the end of the month, a significant wet deposition episode occurs across Iowa when the air concentrations were high and the rainfall was moderate in intensity. The final image compares the cumulative patterns of dry and wet deposition amounts.