That's not first and foremost CO2, though. Many other forms of pollution tend to be far worse to local environment. Addressing those might involve things like catalytic converters on ships and the like.
We already know a lot about making megacities smog-free. That's why London and Los Angeles had absolutely dreadful air in the mid-20th century but it's much better now. As for why Delhi hasn't followed the example of richer cities in cleaning up the air, I'd say it is mostly due to lack of funds for infrastructure and enforcement.
The reason that emissions-free energy sources get discussed more than carbon dioxide reduction from the atmosphere is that reducing emissions appears to be significantly less expensive and more scaleable for dealing with the bulk of the problem. Once you bolt on the extras necessary to make coal plants low-CO2, the electricity costs more than if you'd just eliminated coal altogether, so there's no point to it. For an example, see: https://en.wikipedia.org/wiki/Kemper_Project
Mainly because we are talking about NOx and other Health related emmissions that have local effects not CO2 that have global effects. Yes it sucks about the countries where they end up but it's the responability of the local governments to care what level is acceptable and what not. And often governments have to balance the need to stimulate local economy (by affording to buy cheaper used machines) vs the public health concerns.
CO2 isn't the only pollutant I don't want in my lungs. Hydrocarbons, nitrogen oxides, and particulate matter are moved from cities and reduced overall.
> As standards of living raise people find pollution is negatively affecting them and so they solve the problem locally.
This works if the problem is local and bothersome to the locals -- rusting drums leaking poison or heaps of trash. Carbon dioxide and methane are invisible and odorless and instantly become everyone's problem, so we can't expect this mechanism to induce people to solve the problem locally.
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