4. Sulfur dioxide emissions: Consider the boundary layer over the Bay Area to be a well-mixed box with horizontal dimensions 100 km x 100 km and vertical dimension 2 km. (It's safe to assume uniform pressure and temperature as well). On average, the wind blows from west to east across the box at 4 m s. To prepare a top-down emission estimate, you fly a small plane along the western (incoming) and eastern (outgoing) edges of the box and measure average SO2 mixing ratios of 0.2 ppb (west) and 0.4 ppb (east). Assume a chemical lifetime of 2 d and dry deposition velocity of 0.5 cm s? for SO2 as the only loss processes aside from outflow, and emissions as the only source aside from inflow. a) Sketch a diagram for the sources and sinks of SO2 in the Bay Area, then calculate the overall lifetime of SO2 over the Bay Area, the individual lifetimes against outflow and deposition, and the relative contributions of each loss process b) Calculate the emission rate of SO2 in the Bay Area needed to balance the boundary layer SO2 budget and compare this top-down emission estimate to the EPA's bottom-up estimate of 13 Gg y? (in 2010)