There are two monitors set up in the Park under the Williamsburg Bridge while painting and other work is being done. There is no signage or other indicators, but we have been told it's Lead that is being monitored. When details are confirmed about the threshold or how the public is alerted, we'll post it.
These are gas-powered and small generators are adding their own tinge to the air here - this one is on the south side of the bridge. See the North side for related links.
There are similar monitors on the Brooklyn side too. We have concerns about dust and pollution from ESCR impacting that side of the East River, too. It's already got enough air quality issued, as you can see from the recent testing and EJ study made there - read about it here