My background is Environmental Science. I used to work in the Environmental Consulting side. What happens is a company gets permits to emit up to the limit. In many many years of testing result from customers all over the place I never saw any test results that came close to their limits. Most places (in whatever industry) only emitted a fraction of their permit levels. The goo you get on you from a seat at the movies is more dangerous than industrial discharges now-a-days. (lots of fecal bacteria there)