How Detrimental is Working Polluted Squares Really?

Following some advice from tootall in regards to my Korean War scenario, I'm using pollution to delineate the Chinese Border (which remain after the Chinese Border and it's Border Barrier that ring said barrier to keep the Chinese on one side and the UN and North Koreans on the other before the Chinese intervention is triggered and said border civ and barriers are event-trigger destroyed) and mark the area outside the UN (Human player) designated area of operations that they can't operate in by their mandate by house rule. However, these pollution tiles have been thus placed that a number of them occupy spaces being worked by default and improved by road and irrigation/farmland or mining by coastal or border Chinese cities. Will this greatly detriment these cities to the point of constant starvation or inability to support a simple garrison to stop civil disorder, especially as the Chinese civ cannot build settler/engineer-type units to improve new land, as I don't want them building new cities as the AI is wont to do?

Polluted squares produce half of what they usually would, rounded up. The AI would consider cleaning pollution the highest priority as far as I know, but you've disabled engineers anyway.

You could delineate the border with a railroad, or with farmland instead. The current border seems to be defined by the Yalu and Tumen rivers, so, unless there was a big difference in the 1950's, you could just include those rivers on the map and point them out in the house rules and maybe with a few pollution spots as a reminder.

Or, give China a set of border barrier units right beside the border, to halt the UN.

Since it is a house rule anyway, is there any particular reason why you can't just use Chinese city radii as an approximation of the border?

Alternatively, maybe you can be evil and include events that spawn overwhelming numbers of Chinese units every turn the UN is too close to the border, so that the player will never reach the border if they try.

I think maybe, now that I know how production is affected, I'll maybe see if I can get the AI working spaces outside the AoO Boundary terrain markers (pollution) on their side of the border by changing where the land begins improved. Thank-you for this information on pollution, Prof. Garfield.