VOCs are emitted by products derived from petroleum, natural gas, coal, or wood and include gasoline, industrial chemicals, dry cleaning solvents, paints, and household cleaners. NOx is produced from burning fuels, including gasoline and diesel fuel. A bar chart in the lower-left of the Smog City screen shows the relative amount of VOC and NOx emissions from each emissions source category.
Human activity produces ozone-forming emissions in many ways.
Some emissions sources are easy to see, such as exhaust from automobiles or trucks. Others are nearly invisible, and may not be odorless, such as evaporating paint or lighter fluid used for backyard barbecues. In Smog City you can increase the population from zero to double the current population. The current population is based on a city of about one million people. Weather Controls Daily weather conditions strongly affect ozone levels.