### Question
What does modification mean?


### Answer
**Modification** has the following meaning in *42 U.S.C. § 7412*:

> any physical change in, or change in the method of operation of, a major source which increases the actual emissions of any hazardous air pollutant emitted by such source by more than a de minimis amount or which results in the emission of any hazardous air pollutant not previously emitted by more than a de minimis amount

#### Citation:
  - *42 U.S.C. § 7412*
  - Heading: **CHAPTER 85-AIR POLLUTION PREVENTION AND CONTROL > SUBCHAPTER I-PROGRAMS AND ACTIVITIES > Part A-Air Quality and Emission Limitations**

