re given below:</p><ul><li><p>nugget: \(I\)</p></li>
<li><p>none: \(0\)</p></li>
</ul><p>In short, the nugget effect is modeled when <code>nugget_type</code> is <code>"nugget"</code>
and omitted when <code>nugget_type</code> is <code>"none"</code>.</p>
<p>Dispersion and random effect initial objects are specified via
<code><a href="https://usepa.github.io/spmodel/reference/dispersion_initial.html" class="external-link">spmodel::dispersion_initial()</a></code> and <code><a href="https://usepa.github.io/spmod