Is it possible the pollen is acidic enough to hurt the early growth of my tomatoes, whose lower leaves turn yellow, almost as if there was a nitrogen deficiency?

No.

The yellow leaves likely are a nutrient deficiency either caused by not enough nutrients or a soggy potting soil that is suffocating the roots. If it is still cold where you are in could be temperature not letting the plants get their nutrients.

It is definitely not pine tree pollen.

We have 7 acres of pine trees between 25 to 30 feet tall standing about 10 feet from the edge of our garden. Where we plant our tomatoes is about 20 feet from the pine trees.

I can agree that the pines lay on the pollen pretty thick. But, I can also say that we've seen absolutely no problems with the tomatoes that could be attributed to the pine pollen.

Thanks...wishful thinking? With your feedback, I'm sure it's not the pollen. Gotta be too wet or temps too low or not enough N or a combo....