How is O3 GHG gas created by human activity causing climate change?

Question

Please help me undestand these.

Greenhouse gases from human activity directly are: $\ce{CO2}$, $\ce{CH4}$, $\ce{NO2}$, $\ce{O3}$, and the $\ce{F}$-gases.

Wikipedia agrees: https://en.wikipedia.org/wiki/Greenhouse_gas

• It is clear that $\ce{CO2}$ and $\ce{NO2}$ is mainly from burning fossil fuel. Solution to decrease climate change effects: burn less (preferable zero) fossil fuel

• CH4 is mainly coming agriculture and landfills. Solution to decrease climate change effects: less meat, less landfill (recycle, waste incineration)

• F-gases are used in refrigerator, spray, various cooling devices. Solution to decrease climate change: no sprays, using diffent gases in cooling devices.

But where is $\ce{O3}$ (ozone) coming from? I know it is varios layer of the stratosphere, and protects us from UV. But what kind of human activity makes the $\ce{O3}$ in such amount that $\ce{O3}$ is classified as GHG (Greenhouse gas?) How we can prevent generating $\ce{O3}$, in that way we can decrease $\ce{CO2}$, $\ce{CH3}$, $\ce{NO2}$ and $\ce{F}$-gases?

Also I don't understand if $\ce{O3}$ is a GHG, then why the percentage in GHG is missing from most statistics, including inourworldindata.org?

https://ourworldindata.org/greenhouse-gas-emissions

(See this chapter: By gas: how much does each contribute to total greenhouse gas emissions?)

While other reseaches show as a major GHG, but there is no percentage:

https://www.acs.org/content/acs/en/climatescience/greenhousegases/whichgases.html

(Seek for the graph at this text: Source: Figure 2, FAQ 2.1, IPCC Fourth Assessment Report (2007), Chapter 2)

Could you help me understand the $\ce{O3}$ role in this story?

Thank you!

Answer 1

The contribution of ozone to global warming is complex and there is no strong consensus on its impact

The problem with thinking about ozone as a greenhouse gas (alongside, for example, carbon dioxide and CFCs) is that it isn't something human activity created directly or something where we just need less of it.

First, we want more ozone in the upper atmosphere where it is a barrier to UV reaching the earth's surface (the ozone hole was caused by overuse of CFCs which were banned because they severely reduced the amount in the upper atmosphere). The ozone hole has not yet completely healed despite the ban in the 1980s.

Second, ozone is a short lived component of the atmosphere as it is very reactive, so it is hard to see that it can be a big contributor to warming (and would we choose to minimise it if we could given the problem of its protective value in the upper atmosphere?)

But some researchers have argued it does make a notable contribution in the lower atmosphere, but indirectly. There doesn't appear to be a consensus on how big this effect is (and the Wikipedia reference is old and obsolete). The argument for ozone being a notable contributor is based on the following. Hydrocarbon pollution in the lower atmosphere (often from vehicle emissions) leads to a variety of undesirable reactions some of which lead to the production of ozone (as well as many other irritating components of smog). We really don't want too much smog or ozone in the lower atmosphere because it is bad for health. Some have estimated that it also adds to the warming caused by hydrocarbon emissions (exacerbating the warming potential of methane, for example).

It is hard to judge the estimates of its contribution to warming not least because they rely on models of complex reactions caused indirectly by other pollutants. Also, the big issue with emissions leading to ozone are not its contribution to warming but its contribution to pollution which causes direct harm to people in the short term. In fact regulations around emissions has been striving to reduce those emissions since before we started worrying about global warming. And, many countries have sharply reduced them (this is a major reasons why most western countries insist on catalytic converters in their vehicles). We should reduce ozone pollution by reducing the other emissions that cause it and we have been doing that for decades.

I would argue that ozone is essentially irrelevant to global warming. We should strive to reduce it in the lower atmosphere even if we were not worried by global warming. So even if we can't agree on how big its contribution to warming is (which the literature isn't clear on) we should be reducing it as much as we can for more direct reasons.

And, even if we wanted to report its contribution to warming, the best place to account for it is to add it to the contribution of other emissions (eg methane) rather than to account for it separately as we don't directly emit it from anything.