The second resource provided illustrates how crop yields increase with increased CO2 and drop with increased surface O3. Both gases are projected to increase, but these increases are not projected to be evenly distributed over the globe. Since CO2 is recognized as a greenhouse gas, its concentration cannot be allowed to rise indefinitely. Otherwise, the ensuining climate changes will cause crops to fail more frequently for the common reasons: drought, floods, storms, blight.

This suggests that concentrations of ozone precursors (VOC, NOx) must not rise indefinitely, either. The primary sources of VOCs are solvents (industrial processes, paints etc.) and ICEs without emissions control equipment. Two-stroke gasoline engines used in small to medium motorcycles, ATVs, jetskis, snowmobiles, leafblowers, chainsaws etc. are particularly gross polluters, but four-stroke motorcycles and light aircraft are also bad. These vehicle categories are presently subject to much higher emissions limits, or none at all.

NOx (i.e. NO, NO2, N20 et al.) is produced in all combustion processes, including caloric power plants, jet aircraft, ICEs, furnaces, wildfires etc.

For lambda=1 systems such as homogeneous gasoline injection, three-way catalysts reduce NOx to N2 and O2 almost completely once they reach operating temperature. Further reductions would be possible by pre-heating the catalyst prior to starting the engine.

For lamda>1 processes (e.g. diesel), volume ignition concepts (HCCI et al.) simply avoid flame fronts and the associated NOx production. Unfortunately. the high heat release rate limits applicability to part load scenarios. HC and CO emissions go up. For flame-based combustion, SCR technology is expensive but effective in reducing engine-out NOx compounds to N2 and O2. Proven in power plants, it is now being applied to new trucks in Europe, with large cars expected to follow soon. The snag is that you have to set up a distribution infrastructure for AdBlue, a 35% aequeous solution of pure urea. The alternative, NOx-store catalysts are not as effective nor do they last as long, which is why they have not made it into series production yet.

Aircraft jet engines release substantial amounts of NOx (chiefly N20, aka laughing gas) into the troposphere, mostly at high altitude. Ground-level emissions can be reduced a little by tractor-pulleys for taxiing (e.g. Frankfurt airport) but take-off and landing (thrust reversal!) account for the lion's share anyhow.

"Ozone is formed via the interaction of oxides of nitrogen (NOx) and sunlight."

Technically, it's NO2 (nitrogen dioxide) that is the ozone precursor form of NOx. NO2 photo-dissociates into nitric oxide (NO) and atomic oxygen (O). The resulting O combines with molecular oxygen (O2) to form ozone (O3). However, the NO that is left over from the initial photo-dissociation immediately reacts with ambient O3 to reform NO2 and O2. Thus there is no net ozone production just from the photo-dissociation of NO2. Volatile Organic Compounds (VOCs) play a significant role in ground-level ozone (GLO) production in that atmospheric decomposition of VOCs produces peroxy radicals (RO2 and HO2). These peroxy radicals oxidize NO into NO2, resulting in more NO2 for O3 formation and less NO for O3 depletion.