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Smog calculator

Benzo[a]pyrene is a cancer-causing polycyclic aromatic hydrocarbon produced by burning wood, coal, diesel and tobacco. Enter the concentration outdoors and indoors and the time you spend in each, and the calculator returns the amount you inhale and what it is equivalent to in cigarettes.

The WHO annual guideline is 0.12 ng/m3. A city with wood smoke or heavy traffic can be several times higher in winter.

Indoor air can exceed outdoor air where a wood stove, fireplace or candles are used, or where someone smokes.

About 8.3 litres a minute at rest, and several times more during exercise.

B[a]P inhaled outdoors (ng per day)
0.5
B[a]P inhaled indoors (ng per day)
11.0
Total B[a]P inhaled (ng per day)
11.5
Cigarette equivalent (cigarettes per day)
0.57
Outdoor air as a multiple of the WHO guideline
4.2
What this means
You breathe about 11.95 m3 a day here, taking in 11.5 ng of B[a]P. That is roughly the B[a]P of 0.6 cigarettes. The dose says nothing about your personal risk; it is a way to compare places and habits.

Estimates for information only. Not financial, medical, legal or engineering advice. See the Terms.

Daily dose by place
PlaceHoursAir inhaled (m3)B[a]P (ng)
Outdoors2.0000.9960.498
Indoors22.00010.95610.956

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How this calculator works

Benzo[a]pyrene is one of a large family of polycyclic aromatic hydrocarbons formed whenever organic material burns without enough oxygen. It is used as a marker for the whole family because the mixture tends to occur together and B[a]P has the best exposure data. Concentrations are measured in nanograms per cubic metre. The amount you inhale is the concentration multiplied by the volume of air you breathe, which is the breathing rate times the minutes spent in that place. Resting adults breathe about 8 litres a minute; walking or cycling can double or triple that, and exercise outdoors on a smoggy day can raise the dose sharply. The World Health Organization set an annual guideline of 0.12 ng/m3 for B[a]P in ambient air in its 2000 guidelines for Europe, so a winter city at 0.6 ng/m3 is five times the guideline. The cigarette comparison divides the daily dose by about 20 ng, a common order-of-magnitude figure for the mainstream smoke of one cigarette.

Formula

air inhaled (m3) = hours x 60 x breathing rate in m3 per minute. dose (ng) = air inhaled x concentration in ng/m3. total = outdoor dose + indoor dose. cigarette equivalent = total / 20 ng. Multiple of the guideline = outdoor concentration / 0.12 ng/m3.

Worked example

Two hours outdoors at 0.5 ng/m3 and 22 hours indoors at 1.0 ng/m3 with a resting breathing rate of 0.0083 m3/min. Outdoors you breathe 2 x 60 x 0.0083 = 0.996 m3, for 0.5 ng. Indoors it is 10.96 m3, for 11.0 ng. The total is 11.5 ng a day, about 0.57 cigarettes. The outdoor concentration is 4.2 times the WHO guideline.

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Frequently asked questions

Is this a cancer risk estimate?

No. It compares doses, not probabilities. Turning a dose into a risk needs a unit risk factor from a health agency and assumptions about susceptibility that vary widely. Use the cigarette comparison to judge the size of an exposure, not to predict an outcome.

What raises B[a]P most?

Wood smoke, coal smoke, traffic exhaust and tobacco smoke are the main sources. A wood stove or fireplace can raise indoor concentrations far above outdoor levels, and a single cigarette in a room dominates everything else in this calculator.

Why use B[a]P rather than total PAHs?

B[a]P is measured routinely, it is one of the most potent members of the group, and regulators use it as a marker. Total PAH concentrations are harder to compare between studies because the set of compounds measured differs.

Does a mask help?

A well-fitting N95 respirator filters a large fraction of fine particles, and B[a]P in air is mostly attached to particles, so it reduces the dose. Loose cloth masks do much less. Reducing the source, such as not burning wood indoors, is far more effective.

Sources

Written byAmira MansourCalculator writer. Builds and tests Mathulate calculators against published sources.
Reviewed byMarc LefebvreMathematics teacher. Checks each formula and worked example by hand.

Last updated .

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