Convert pressure from PPM to Pascals

## Arguments

- ppm
Pressure value in umol/mol of class `units`

- P
Atmospheric pressure value in kPa of class `units`

## Value

Value in Pa of class `units`

## Details

$$\mathrm{Press}(kPa) = \mathrm{Press}(ppm) P(kPa)$$
$$\mathrm{Press}(Pa) = 1000 \mathrm{Press}(kPa)$$

## Examples

```
ppm = set_units(400, "umol/mol")
P = set_units(101.325, "kPa")
ppm2pa(ppm, P)
#> 40.53 [Pa]
```