With all your rooftop trees in 3-ft square containers, I suspect the problem is environmental and related to water -- too much or too little. Browning is often from too little.

You don't say how long the trees have been in the same container, or the tree size. Nor what they're planted in. It also helps to know about wind , sun & prevailing humidity.

The Pear Tree is in a 25" sq cedar planter. just transplanted last year...plenty of room..doesn't dry out fast at all. The conditions were the same as for the unknown tree...rain for a week about a week ago - sunny and hot this past week...probably over watered a bit...
but this was happening before the rainy week etc...I had already defoliated it and this is the new growth..at first it was okay..but the black started very soon after...
more pictures...here..
www.mihaus.com/trees/PearTree.JPG
www.mihaus.com/trees/PearTreeLeaf.JPG
www.mihaus.com/trees/PearTreeLeaf1.JPG
www.mihaus.com/trees/PearTreeLeaf2.JPG

I'll stay with the environmental here. Think water shortage due to one or more of the following:
1. the soil mix was dry
2. windy
3. low humidity

For # 2 & 3, may need to rig temporary protection now and then.

My reason for suggesting water shortage is that the damage is at the tips, and/or leaf edges, and/or between the veins. In other words, the areas furthest from the water supply.

I don't think so. I think it was the opposite...too much water actually....and also the night watering (watering in the early evening). will see. I'm going to let everything dry out.

Okay, excess water can be another reason for short of water: In other words, some roots die, not enough water gets to the top.

Watch it closely. Rig temporary protection if and when needed, such as from heat/sunlight and/or drying winds

That's hard to do..it's big and the roof is open to the elements...can't really protect it unless I cut it back
and make it smaller. I might give up on it if it doesn't recover. As long as what it has is not contagious to other
trees, I will give it this season to recover...of course now
there's a huge rainstorm, so this will probably make it worse.
BTW the unknown tree...that was id'd as a poplar..has poplar blight...looks just like the pictures...and goes along with the timing...I think I'll get rid of it because this will happen every year until it's over a certain height-once they have it they always get it. I looked at it this morning at every leaf is turning black.
too much trouble.