The concentration of mercury and sulfate downwind of a coal-fired power plant stack at ground level over four years is shown in the table below. Determine (a) the average and standard deviation of the metal concentrations in air with distance from the stack, (b) plot the average concentrations with distance from the stack as either one or two scatter plots with lines, include error bars indicating the standard deviation for each point and (c) determine the distance downwind where the concentration of Hg and SO₄^2- is of greatest concern. Be sure to include labels and units on all axes, a plot legend, and use the correct number of significant digits. If necessary, plot the data on a secondary axis.

Distance downwind from stack (km)	Hg (ng/m3)				SO42- (ug/m3)
	Year 1	Year 2	Year 3	Year 4	Year 1	Year 2	Year 3	Year 4
0.1	440	80	1400	800	2	3	3	2
0.5	3000	1100	3500	2200	54	120	110	120
1.2	6200	5200	9100	8500	880	1200	780	970
1.7	35000	43000	63000	58000	160	180	90	150
3	15000	20000	31000	15000	59	47	61	56
7	7200	5800	7500	6600	2	3	2	1