It's only fine until those sulfates react with water vapor in the atmosphere to form sulphuric acid. That stuff rains back down and contributes to ocean acidification which is causing serious harm to all sorts of marine ecosystems.

Good thing humans are the only life on earth.

This is wrong in some many ways. To add to the already mentioned. Ocean water is the largest carbon dioxide buffer by absorbing CO2 to become carbonic acid. As the sulfur acidifies the Ocean, this "competes" with the carbonic acid, increasing the CO2 emissions from the Ocean.

In other words, all geoengineering tropes end up being horseshit.

Also, the cooling effect sulphate aerosols can cause only really happens at high altitudes. At low altitudes the reflected light is less likely to escape to space, and the aerosols fall out of the air faster.

Even if they reached high altitudes, one of the effects of being in the atmosphere is moving with the wind, across entire hemispheres. And at tropospheric heights, sulphates, their products, and other byproducts of combustion may destroy ozone at significant levels.

There may come a day where aerosol-based geo-engineering becomes a part of climate management, but it's definitely not with bunker fumes.