  We propose two simple fixes to the Ryden and McNeil ammonia flux model. These
are necessary to prevent estimates from becoming unphysical, which very often
happens and which has not yet been noted in the literature. The first fix is to
constrain the limits of certain of the model's parameters; without this limit,
estimates from the model are seen to produce absurd values. The second is to
estimate a point at which additional contributions of atmospheric ammonia are
not part of a planned expert but are the result of natural background levels.
These two fixes produce results that are everywhere physical. Some experiment
types, such as surface broadcast, are not well cast in the Ryden and McNeil
scheme, and lead to over-estimates of atmospheric ammonia.
