The department's Air Pollution Control Program develops multiple plans to meet federal standards for six criteria pollutants: lead, ozone, particulate matter, carbon monoxide, nitrogen dioxide and sulfur dioxide. These plans constitute one main state implementation plan (SIP).
The EPA reviews pollutant standards every five years. Sometimes, a review results in a tightened standard. When this happens, the multi-step process to draw up a new SIP begins again. It's not uncommon for work on the old and new standards to overlap. The department considers input from all stakeholders when developing a SIP.
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