Q73. If a non-Acid Rain unit combusts coal or other solid fossil fuel and has gas monitors installed but does not have a stack flow monitor, is installation and certification of a stack flow monitor required?

A73. If the unit and the currently installed gas monitors meet all six conditions specified in §98.33(b)(4)(ii), then the Tier 4 methodology must be used, and a flow monitor must be installed and certified prior to the applicable deadline specified in §98.33(b)(5). (See §98.34(c).)