Not all VOCs are ozone forming as close to half of VOCs come from biogenic or natural sources like trees and vegetation. For this reason and because of VOC diversity, industries and environmental regions tend to focus more on NOx reductions to reduce ozone. The Texas Air Quality Study recently suggested that NOx reductions would be the most efficient way to reduce ozone in the Houston-Galveston region. Nonetheless, the region's SIP requires a 25% reduction in VOCs by November 15, 2007 to meet the ozone standard. .
Nitrogen Oxides (NOx) are the most significant ingredient in the formation of ozone. NOx is the term used to represent a "group of highly reactive gases, all of which contain nitrogen and oxygen in various amounts." The pollutant is formed when fuels are "burned at high temperatures", of which diesel engines and industry fuels are culpable. Since 1970, the emissions of six principle pollutants have decreased but NOx has increased by 10% in this same period due to economic growth. .
Since NOx can be transported long distances, the EPA suggests that emissions be dealt with in a regional rather than a local manner. In the Houston-Galveston area, these emissions are dealt with by eight joint counties. In this region, industrial NOx emissions account for 55% of NOx, while motor vehicles are responsible for 44%. This data contrasts significantly from the national average where NOx primarily comes from motor vehicles (49%), and industrial, commercial, residential, and utilities account for 46% of NOx emissions. .
Ozone Adverse Effects.
NOx and ozone have several adverse effects on society. The primary concerns surrounding NOx emissions are health concerns (asthma & respiratory). In particular, diesel emissions containing NOx and particulates trigger pre-existing respiratory conditions. Ozone also affects lung tissue sufficiently to reduce lung function, contributing to particle inhalation, which occurs "deeply into sensitive parts of the lungs.