Explain units of measure for PM2.5 somewhere on site

[theecrit]

Description

When we adjusted the way PM2.5 readings are displayed in the data point pop-up, we removed the microgram unit symbol. We want to make sure visitors have a clear understanding of what they're actually looking at and what the readings really mean. Our initial lean approach was going to simply add a line underneath the map that all units displayed are in micrograms, but that's a stopgap approach (per #464).

User requirements

• I have a way to dig into the meaning of particulate measures that's accessible from the map page. This might be simply be a link to a new page that describes how particulates are measured for different pollutants. This info page could be part of a larger educational section about AQ in general, so that if people enter that page through a different doorway (eg from the "West Oakland's Air" page, for example), it still makes sense to them.