I'm struggling to explain the most important aspects of air pollution in a concise way. I understand CO2 is the biggest issue and long-term driver of global warming, but beyond that I'm lost. News articles about air pollution sometimes mention particle pollution, methane, sulfur dioxide, aerosols, carbon monoxide, nitrous oxide, and others, but I have no idea about their relative importance in regard to the impact on human life and earth ecosystems.

I understand from Wikipedia that carbon dioxide equivalent (CO2e) is used as a way to simplify all of the above into a single number expressing the global warming impact of a collection of air pollutants, usually computed based on the global warming impact over 100 years.

Simplifying everything down to 1 number is appealing, but seems like it also loses a lot of information. On the other hand, enumerating every single pollutant seems to just make everything confusing unless you're already an expert. What I'm imagining is a compromise where we could express air pollution in CO2e plus a couple other numbers that capture some of the most important details that CO2e doesn't address.

My question: What are the most important pieces of information that get lost by converting all air pollution into CO2e?

  • Great question! Looks like this article might provide some clues or references, but I don't have time now to dig into it: "Alternatives to the global warming potential for comparing climate impacts of emissions of greenhouse gases"
    – LShaver
    Commented May 24, 2019 at 13:35
  • 3
    Nobody converts all air pollution into CO2e - they do it only for those substances that have a warming effect and then only to calculate the warming effect, not any others (but that's what you're asking for). This makes your question very broad. I suggest you limit it to substances having a warming effect and ask for those by name specifically (it's not hard to find them since you know what CO2 equivalents are).
    – user2451
    Commented May 24, 2019 at 15:04

1 Answer 1


Time span.

Most of the others are short term. CO2 ultimately depends on the rate biomass increases, and the speed it mixes into the deep ocean. Processes that take very long periods (thousands of years)

Methane and NOx both have half lives in the decades range. So you see CO2e of 20 on a short period (couple of decades) down to 7 over a longer period (century)

Dust falls out of the atmosphere faster. Events that put large quantities of particles into the upper atmosphere (Pinatubo being the most recent big one) have an effect that lasts about 2 years.


Consider Fictide (A fictitious compound) Say it is 1000 CO2e, but it's present only a one part per billion.

So we have 1 part/billion * 1000 = equivalent to 1/million CO2 Since CO2 is currently 415 ppm, the effect of fictide is a drop in the bucket.

Overall the other gasses are a distraction. Most of them are either natural sourced (CH4) or are side effects of combustion (NOx)

(Yes cows produce methane. So do termites. Remove cows, you replace them with something that eats cellulose. You can't)

There are various proposals to get rid of human caused methane. Far better to spend that effort and resources to get rid of human caused CO2.

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