The patterns from the 1950's through 1970's sulfur controls are repeating in the ocean shipping world, where sulfur and NOx limits are being tightened. There is a mix of scrubbers and fuel shifts to LNG taking place. Of course the amounts of sulfur and human impact are much smaller. In the 1950's dozens of people died from the toxic sulfur levels in some of London's fogs. Now, the worry is long term subtle damage to the environment. It's still interesting to see steady progress while the patterns repeat.