The concentration of NOx cannot be obtained by just using one NOx pad.

NOx is a mixture of NO and NO2, so there is no alpha value for NOx.

We must use both NO2 and NOx pads simultaneously for sampling, and the two pads are then analyzed separately.

The concentrations obtained are then both used in the analytical formula shown in the protocol.

The calculation for NO is done by subtracting NO2 from NOx.

To determine the concentration of NOx, one must use one NO2 and one NOx pad on each side of same sampler.