Why is NOx such a major concern in the U.S. and elsewhere? NOx consists of roughly 90% to 95% NO and perhaps 5% to 10% NO₂. Those associated with fossil fuel fired boilers and other furnaces are from the combustion of these fuels and these pollutants’ subsequent exposure to the atmosphere. These resulting emissions are considered harmful and particularly bad in heavy populated and industrialized areas. NOx is a precursor to ozone, which is a major pollutant. It’s also blamed for acid rain formation and the degradation of forests as well as crop destruction. Many papers have already been written about the chemistry involved, so no need to dwell on it here.

Needless to say, the orange brown haze resulting in smog in populated areas during hot summer days is unhealthy, and the result has been many federal and state laws governing the reduction of NOx from combustion processes of all types. The effort to reduce NOx emissions is accelerating throughout the world — witness the choking hot summer days in Mexico City, Beijing, and other major cities in the world, as well as major cities in the U.S. Much of the focus on NOx emissions and ozone levels in the U.S. started in populated areas of the Los Angeles basin of Southern California. While significant strides have been made to reduce NOx and ozone levels there, Los Angeles and Bakersfield still are considered among the worst in the nation. Strict emissions regulations first mandated in Southern California have spread like wildfire to other industrialized and populated areas of the U.S. suffering from air pollution.