Reading EPA air quality data

An air-quality line in a ZIP report describes the nearest relevant monitor, how far it is, and what that monitor has been measuring. It does not describe the air on a porch.

What a monitor measures

EPA’s Air Quality System stores measurements from outdoor monitors run by state, local, tribal, and federal agencies. Common pollutants include ozone, fine particles (PM2.5), and sometimes nitrogen dioxide, sulfur dioxide, carbon monoxide, or lead. Not every monitor measures every pollutant. A site can be excellent for ozone and silent on particles, or the other way around.

Monitors are placed to represent an area and to track standards. They are not placed on every block. A reading is the air at that instrument for that hour or day, after the agency’s own quality checks. It is not a personal exposure monitor.

What the comparison shows

Consilium Compare names the nearest useful monitor, the distance from the ZIP, and a short reading of the pollutant context in the current file. Distance matters. A monitor two miles away in the same basin is more informative than a monitor fifteen miles away across a ridge, a port, or a prevailing wind. The report keeps that distance visible so the number is not treated as if it were taken at the ZIP centroid’s front door.

Air context is separate from the industrial-release section. A TRI facility reports pounds released over a year. A monitor reports concentrations in the air at a site. Either one can be present without the other. Neither one, alone, tells you whether a specific house has an indoor air problem.

What it does not prove

A monitor summary is not a medical statement and not a claim that one ZIP is healthy. Outdoor air changes with season, wildfire smoke, traffic, and weather. Indoor air depends on the building. A ZIP with a “better” nearby monitor can still have a busy arterial, a warehouse dock, or a smoky month that the annual summary smooths over.

Updated September 29, 2026

Use the comparison to see whether the two ZIPs are being described by similar monitors at similar distances, and whether one side’s monitor record is thin. For a property, look at the current EPA outdoor air quality data for that area, and treat the house itself as a separate question.

The report does not rank the ZIPs from this section. See the layout in the sample report, and the related notes on TRI facilities and flood zones.