NOx: Friend or Foe?

NOx is what it sounds like, noxious gases made of nitrogen and oxygen that are released during fossil fuel combustion. NOx is short for nitrogen oxides, which includes a bunch of different gases, including nitrogen dioxide (NO2), which can damage your throat and lungs, and nitrous oxide (N2O), also known as laughing gas, which is a potent greenhouse gas. NOx comes from smokestacks and tailpipes.

But NOx is noxious in another way--it reacts with sunlight to form ground-level ozone, which is plaguing the Denver metro area in the summertime (see the picture below).

Yet the relationship between NOx isn't exactly linear. In some cases, NOx can actually reduce ozone. NOx is the reason that the ozone monitor in downtown Denver consistently has the lowest ozone readings in the metro area. When NOx goes up, ozone goes down in downtown Denver, and vice-a-versa.

It's this crazy relationship that has some folks resisting the idea of reducing NOx here in Denver to keep people safe from ozone. Reduce NOx, they say, and you'll increase ozone.

It's not that simple, though.

Sure, in some cases, reducing NOx will increase ozone, but the increases are never substantial. In downtown Denver, ozone concentrations rarely, if ever, rise above 70 parts per billion, which is far below the current health standard of 80 parts per billion.

Not only that, but to the extent NOx may decrease ozone, the effect is extremely local. While NOx may decrease ozone in downtown Denver, it sure doesn't decrease ozone in Highlands Ranch, Boulder, Golden, or Fort Collins. All these places suffered through bouts of unhealthy ozone this past summer.

And finally, study after study shows that reducing NOx helps reduce ozone, especially over large areas. One study found that the blackouts in the northeast back in 2003 decreased ozone across Pennsylvania by about 50%. That's because NOx emissions from coal burning power plants ceased.

But don't get us wrong, reducing NOx alone won't solve Denver's ozone woes. At a forum last week, atmospheric scientist Jana Milford made clear that it's going to take both reductions in NOx, as well as volatile organic compounds, or VOCs, which are also key ozone forming pollutants.

In the past, the State of Colorado has written off NOx reductions as a way to reduce ozone in Denver. This needs to change. In our struggles to keep ozone below unhealthy levels, reducing NOx from smokestacks and tailpipes is going to be key to keeping the region healthy.