Each row is a cancer risk pollutant, with its health effect listed beside it. Each column is a period of time — the calendar years, the year so far (YTD), the most recent 365 days, and the most recent complete quarter. The bottom row, Total (Combined), adds the pollutants together for that period.

The number in each square is the measured level divided by the Screening Level, written as a multiple with an “x.” An asterisk after a number means that period had between 60% and 75% of its scheduled samples, so the average rests on thinner data; periods below 60% are left blank. A double asterisk (**) before a number means most of the samples behind it were below the laboratory’s detection limit; those samples are counted at half the detection limit, so the number is set by the laboratory’s detection limit rather than by the air. It is not an upper bound — the true level could be anything from near zero up to the detection limit, so read the value as uncertain in either direction.

On the Kenner card, find the row for Acrylonitrile and the column for 2024. The square reads 6.14x. Breathing acrylonitrile increases the risk of cancer. That number means the average level of acrylonitrile in 2024 was about six times the screening level; on the color scale at the right, the square falls in the band covering five to ten times the screening level.

In the same column, Benzene reads 0.91x: the average benzene level was just under its screening level, in the palest band. And Kenner’s Total (Combined) for 2024 is 11.91x: adding all nine cancer pollutants together, the combined level was about twelve times the screening level; most of that total is acrylonitrile.

Two rows to read with care. Vinyl chloride reads about **1.2x in every period at every site. Almost every vinyl chloride sample is below the laboratory’s detection limit, and half of that detection limit is itself above the screening level, so the number is set by the laboratory rather than by the air — the ** says the true level is unknown, somewhere below the detection limit, not that it is at most 1.2x. The same applies to 1,2-dichloroethane, and to 1,3-butadiene before 2023. Carbon tetrachloride and chloroform read close to 1.0x at every site, including Madisonville on the north shore: these two are found at that level across the country and the region, not from a local source.

For a general explanation of heat maps, see the Frequently Asked Questions.