The volume of flame, however, is increased by inert gas, and there is a proportionate diminution of the heating effect. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 Various. Nitrogen by itself is an inert gas, colorless and uninflammable. Scientific American Supplement No. 819 Various.
There are two primary fungus diseases that can produce black spots on tomato plant leaves: Septoria leaf spot and Alternaria leaf spot, also known as early blight. Septoria and Alternaria differ slightly in appearance and prefer slightly different weather climates.
The most likely culprit, I think, is going to be item (3) above. At least, that is what the problem is in my large tomato garden 95% of the time when leaves begin yellowing and/or curling. If you have bacterical speck, you will notice tiny specks of brown to black to almost purple on the leave surfaces.