SWI: Standards Weighted Intake
In christiaanpauw/AQoffset: Makes calculation needed for air quality offsetting

Calculates the total effective intake of pollutants by using standardisation

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SWI(conc, NAQS = NULL, pop = people, ap = "Annual", Q = 8, idpos = 1,
  polpos = 3, aveperiodpos = 2, cyclepos = 5, sep = "_",
  verbose = FALSE)

`conc`	Raster. The concentration of every pollutant
`NAQS`	Data frame of the National Air Quality Standards
`pop`	Raster. The number of people in each grid cell
`ap`	Character verctor. "Annual" or "Daily"
`Q`	Numeric. Breathing rate in m3 per person per day
`idpos`	Numeric referring to the ID position
`polpos`	Numeric referring to the position of the pollutant.
`aveperiodpos`	Numeric referring to the average period position.
`cyclepos`	Numeric referring to the cycle position.
`sep`	Character vector containing the seperator to be used.