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  • Nitrous oxide ($N_2O$) - primary greenhouse gas
  • Carbon dioxide ($CO_2$) - primary greenhouse gas
  • Methane ($CH_4$) - primary greenhouse gas, explosive
  • Nitrogen monoxide ($NO$) - secondary greenhouse gas, toxic
  • Nitrogen dioxide ($NO_2$) - secondary greenhouse gas, toxic
  • Sulfur dioxide ($SO_2$) - secondary greenhouse gas, toxic
  • Carbon monoxide ($CO$) - secondary greenhouse gas, toxic

So, why is Carbon Dioxide pollution given more importance in "pollution measurement"(Carbon-Footprints), when Sulfur Dioxide and Nitrogen Dioxide are much more dangerous to Land dwellers, including Humans ?

At this rate, the Oceans will die from Nitrogen pollution or acidify from Plastic pollution; before the ocean level can even threaten us. So, why are we focusing on Carbon dioxide at the cost of the toxic compounds ?

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    $\begingroup$ $CO_2$ is a greenhouse gas. It does not have a toxic effect (at least if the concentrations are not far too high). I wouldn't consider $CO_2$ as an air pollutant. $NO_2$ and $SO_2$ are air pollutants. If you inhale them, they harm your respiratory system. $CO_2$ has a global long term effect on the climate. $NO_2$ and $SO_2$ have a regional impact on air quality. They can also lead to acid rain - but this is also more a short term effect. $\endgroup$ – daniel.neumann Dec 14 '17 at 11:56
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    $\begingroup$ Oxides of nitrogen: You mean $N_2O$? Important for the impact on climate are three factors: (a) how strong and which wave lengths does a molecule absorb? (b) how long is the life time of the molecule in the atmosphere? (c) where in the atmosphere do we find the relevant molecules? $\endgroup$ – daniel.neumann Dec 14 '17 at 12:00
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    $\begingroup$ Carbon dioxide is also acidifying the oceans - globally. $\endgroup$ – Communisty Dec 14 '17 at 14:35
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    $\begingroup$ Water vapor is a strong greenhouse gas, but I guess it is politically correct. $\endgroup$ – blacksmith37 Dec 14 '17 at 20:09
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    $\begingroup$ @Neel There is clear scientific evidence that CO2 is acidifying oceans. See for example Caldeira & Wickett (2003). You might also search for "co2 acidification coral reefs". You are welcome to ask another question on this topic. $\endgroup$ – daniel.neumann Dec 14 '17 at 22:04
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greenhouse gases other than CO2

The gases N2O and CH4 are relevant greenhouse gases besides CO2. They even have a stronger warming impact per molecule. A brief summary for N2O is provided in its Wikipedia article.

Edited later on (thanks to Communisty for the comment): The global warming impact of these greenhouse gases other than CO2 is measured/presented in CO2-equivalents: i.e. the warming potential of N2O equals 298 CO2-equivalents, which means that one N2O molecule is 298 times worse than a CO2 with respect to its warming potential. Therefore, CO2 is more visible in the media.

Why focus more on CO2?

contribution to global warming

Although N2O and CH4 have a stronger greenhouse impact than CO2 per molecule, the concentrations of them are considerably lower. Therefore, in sum (heat trapping potential x number) CO2 has a stronger impact on climate change. The figure below visualizes it nicely (please find the reference below):

enter image description here

Figure TS.6 on page 53 of the 5th IPCC Assessment on the Physical Science Basis (www.ipcc.ch/report/ar5/wg1/).

practical aspects

There are also practical aspects why a focus is put on CO2: many CO2 emission sources are know and clearly to identify (combustion processes). Moreover, many of the CO2 sources are point sources. Some of them are many and small (cars) but nonetheless: we know them and know to locate them.

In contrast, N2O and CH4 emissions sources are often diffusive sources (or area sources) such as natural and agricultural soils and cattle (and other) life stock. Here you find a text and a nice figure on this topic: www.soest.hawaii.edu/mguidry/Unnamed_Site_2/Chapter%202/Chapter2C3.html

Thus, it is easier to reduce CO2 emission by specific measures: don't combust so much fuel/combustion-material.

greenhouse gases vs. air pollution

As stated above, CO2 (in sum) has a higher global warming impact (in the moment). And large parts of its emissions are easier to manage. Therefore, the focus is on CO2.

Moreover, greenhouse gas emissions have a global impact: the greenhouse gases alter the global climate. In contrast, air pollutants have a local or regional impact. Also their life time or/and residence time in the lower troposphere is shorter than the residence time of greenhouse gases in the atmosphere. Therefore, the temporal and spatial extend of greenhouse gases is larger/longer than that of air pollutants. Thus, one focuses more on the longer lasting global problem: greenhouse gases.

regional vs. global

Because greenhouse gas emissions cause global problems they are tackled on a global level -- IPCC, United Nations Climate Change Conferences, etc.

Although air pollution is also a topic dealt with on global or continental level (e.g. hemispheric transport of air pollutants (HTAP), European Monitoring and Evaluation Programme (EMEP)), it is mainly a regional or local problem.

In Europe many municipalities have recognized the problem of air pollution in cities and try to deal with it (actually, they are forced by the EU). Also in Chinese cities municipalities start working on this topic.

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    $\begingroup$ To add: we might hear more of carbon dioxide as the potential of other greenhouse gases is often quantified as carbon dioxide equivalent i.e. all other greenhouse gases are compared to the main one we can affect on. $\endgroup$ – Communisty Dec 14 '17 at 14:38
  • $\begingroup$ @Communisty thanks for the remark. I added it as second paragraph. $\endgroup$ – daniel.neumann Dec 14 '17 at 15:18
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    $\begingroup$ Another point here is that cars, power plants, and such like don't run on N20 or S02. Their release is usually an accidental byproduct of CO2 release, and can be mitigated or eliminated without abandoning the technology, e.g. SO2 scrubbers at coal-fired power plants, emissions controls on cars, and so on. $\endgroup$ – jamesqf Dec 14 '17 at 19:59

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