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Radon in Boston, Massachusetts

EPA puts Suffolk County, where Boston is, in Zone 3, its lowest radon zone, and most reported tests there come back low, though 10.4% of 8,525 (2008 to 2017, laboratory totals) reached 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

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  • Share at 4+ pCi/L

    10.4%

    13.4 pts below MA

    Suffolk
    10.4%
    MA
    23.8%

    Suffolk, 13th of 14 in MA, 2008 to 2017

  • Median result

    1.3pCi/L

    Below action level

    Suffolk
    1.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of Suffolk's tests, 2008 to 2017

  • Nearest county

    21.2%

    Norfolk, 13 miles

    Norfolk
    21.2%
    Suffolk
    10.4%

    39,205 tests, 2008 to 2017

  • EPA radon zone

    Zone 3

    Low potential

    1. 1
    2. 2
    3. Zone 3

    1 highest, 3 lowest

    Suffolk, where Boston is

  • Tests reported

    8,525

    In Suffolk

    Suffolk
    8,525
    Norfolk
    39,205

    Reported to CDC before any fix, 2008 to 2017

Read a result for Boston

Starts at Suffolk County's median, 1.3 pCi/L

1.3pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 1.3 pCi/L

Below 2 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 4 and aboveEPA says fix it

This result is below 2 pCi/L, the level at which EPA says a fix should be considered. Suffolk County's median reported result, 2008 to 2017.

Interpret this reading

The data

Boston, What is published

What is published for Boston

Information:

Every figure for Boston is a county's

Radon data is published by county, not by city, so for Boston it is Suffolk County's: its EPA zone (Zone 3) and the 8,525 tests reported to CDC for 2008 to 2017, laboratory. Only a test tells you about one home.

Boston covers 48.3 square miles of land, all of it in Suffolk County. Its 672,973 residents live 13,921 to the square mile.

Boston, Counties

The county Boston lies in

Measured

Suffolk County's EPA zone and the figures CDC publishes for it, 2008 to 2017, laboratory.

Suffolk CountyZone 3Lower predicted potential

10.4%
Reported tests at or above 4 pCi/L
1.3 pCi/L
Median reported result
8,525 tests
Tests reported to CDC
None
Yearly figures on file

Suffolk County ranks 13th of 14 Massachusetts counties with 30 or more tests for that period, 13.4 points below the 23.8% pooled across Massachusetts's counties, 25.3 points below the national pool of 35.7%.

The counties nearest Boston with a CDC figure for 2008 to 2017, laboratory, measured from the middle of the city: Norfolk County (13 miles, 21.2% of 39,205 tests), Middlesex County (19 miles, 22.0% of 75,220 tests) and Essex County (26 miles, 28.7% of 20,398 tests). Across the 8 nearest, the share at or above 4 pCi/L runs from 17.0% to 33.5%; the farthest of them, Dukes County, is 67 miles away at 17.4%.

No business in the directory gives Boston as its address; the Massachusetts list covers it.

The counties around Boston

By distance from the middle of Boston; counties with 30 or more tests.

Nearest counties to Boston with 30 or more tests
CountyDistanceTestsAt or above 4 pCi/LMedian
Norfolk County13 mi39,20521.2%1.8 pCi/L
Middlesex County19 mi75,22022.0%1.9 pCi/L
Essex County26 mi20,39828.7%2.2 pCi/L
Plymouth County29 mi16,32017.0%1.7 pCi/L
Bristol County36 mi13,35823.2%2.0 pCi/L
Worcester County42 mi46,44033.5%2.6 pCi/L
Barnstable County58 mi6,52120.6%2.0 pCi/L
Dukes County67 mi31717.4%1.7 pCi/L

Predicted: EPA Map of Radon Zones, by county. Measured: CDC tracking data, by county, 2008 to 2017, laboratory.

Boston, Geology

The ground under Boston

Predicted

Most of the ground under Boston is one class on USGS's geologic map: 89.2% of its land is low radon potential, with 5.3% moderate. The map puts 89.2% of Boston in the area it calls Boston Basin and 5.3% in Esmond-Dedham terrane. USGS gives the first a radon index of 8, in the low band (5 to 8), and the second 11, in the moderate band (9 to 11).

USGS's geologic areas under Boston
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Boston BasinProterozoic to Pennsylvanian sedimentary rocks.Low889.2%
Esmond-Dedham terraneGranite plutons, mafic metasedimentary and metavolcanic rocks.Moderate115.3%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Boston beside its county and Massachusetts

Suffolk County as a whole has 0.5% of its land rated high; none of that ground lies under Boston. Across Massachusetts 31.9% of the land is rated high; none of Boston's is.

Share of land by USGS radon potential: Boston, the county it lies in and Massachusetts
AreaEPA zoneLow potentialModerate potentialHigh potential
BostonBy county89.2%5.3%None
Suffolk CountyZone 387.0%4.2%0.5%
Massachusetts14 counties, pooled by land areaVaries8.7%57.9%31.9%

The map rates the ground, not the air in any home.

Boston, Homes

Homes in Boston

Boston has 307,840 homes, and many share a building: 46% are in buildings of five or more, 12% are detached houses, against 14% across Suffolk County. Half of its homes were built before 1947, close to Suffolk County's 1948: 59% date from before 1960 and 17% from 2000 or later. Most occupied homes here are rented: owners live in 35% (Suffolk County: 37%). A tenant can run a test; a fix is the landlord's to make.

Homes in Boston, Suffolk County, Massachusetts, 2019 to 2023
HomesBostonSuffolk CountyMassachusetts
Housing units307,840353,9303,014,657
Detached houses12%14%51%
In buildings of 5 or more46%44%22%
Mobile homesunder 1%under 1%1%
Built before 196059%58%47%
Built since 200017%16%14%
Middle year built194719481963
Owner-occupied35%37%63%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.

Local help

Boston, Local resources

Local resources for Boston

Who to ask in Massachusetts: its radon program, test kits and professionals.

The program's own words on licensing are on the Massachusetts page.

What it means

Boston, Questions

Questions about radon in Boston

What radon zone is Boston in?

Boston takes its zone from Suffolk County, which EPA puts in Zone 3, the map's lowest class: a predicted county average under 2 pCi/L. A low zone does not clear a house: homes over the action level are found in all three.

What are radon levels in Boston?

Suffolk County's 8,525 tests for 2008 to 2017 (laboratory totals) put 10.4% at or above 4 pCi/L: most tests near Boston come back under EPA's action level, but not all. The median reported result was 1.3 pCi/L.

Should I test my home in Boston?

Yes. Roughly one reported test in 10 in Suffolk County reached 4 pCi/L. That is below Massachusetts' pooled 23.8%, and still not a reason to skip it, and ranks Suffolk County 13th of the 14 Massachusetts counties with 30 or more tests. Only a test puts a number on one house. How to test a home.

What ground is Boston built on, as far as radon goes?

89.2% of Boston sits on what USGS's map calls "Boston Basin", rated low for radon potential, radon index 8; another 5.3% is "Esmond-Dedham terrane", rated moderate for radon potential, radon index 11. So the ground changes within Boston itself.

Is radon higher in the counties around Boston?

Yes, in every direction measured. Each of the 8 nearest counties with a figure reports a larger share of high tests than Suffolk County's 10.4%; the highest is Worcester County (33.5%, 42 miles off).

The answers use the published figures of Suffolk County, the county Boston lies in.

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