Smog Calculator

What Is Benzo[a]pyrene and Why Does It Matter?

Benzo[a]pyrene (B[a]P) is a polycyclic aromatic hydrocarbon (PAH) formed when organic matter burns incompletely. It is found in vehicle exhaust, coal smoke, wood burning, and industrial emissions. B[a]P is a known carcinogen and a common marker for overall air pollution from combustion sources. The Smog Calculator estimates how much B[a]P you inhale based on your city's air quality and how much time you spend outdoors.

Because B[a]P exposure is difficult to visualize, researchers often express inhaled doses as cigarette equivalents. One cigarette delivers about 14.86 ng of B[a]P to the smoker. Comparing your daily urban air exposure to that reference makes the health risk easier to understand.

How the Smog Calculator Works

Choose a city with a published B[a]P concentration, or enter a custom value in nanograms per cubic meter (ng/m³). Set how many hours per day you spend outside. The calculator assumes you breathe about 0.83 m³ of air per hour and that indoor B[a]P levels are 90% of outdoor concentrations.

Exposure Formula

The daily inhaled B[a]P dose in nanograms is:

$$\text{daily B[a]P (ng)} = 0.83 \times (\text{hours outdoors} + 0.9 \times \text{hours indoors}) \times \text{concentration (ng/m³)}$$

Where hours indoors equals 24 minus hours outdoors. Yearly exposure multiplies the daily result by 365. Cigarette equivalence divides the B[a]P dose by 14.86 ng per cigarette.

Air Quality Limits

The European Union sets an annual mean limit of 1 ng/m³ for B[a]P in ambient air. The World Health Organization recommends a much stricter guideline of 0.12 ng/m³. Cities like Delhi, Beijing, and Krakow exceed these thresholds. The calculator flags concentrations above EU and WHO limits so you can see when outdoor air quality is concerning.

City Concentrations

Built-in cities include major European, Asian, and North American urban centers with representative B[a]P levels. Krakow and Delhi rank among the highest in the dataset, while Oslo, Copenhagen, and Los Angeles are lower. These values are long-term averages and real conditions change with season, weather, and local traffic.

Example Calculation

Suppose you live in Krakow (6.8 ng/m³) and spend 2 hours per day outside. With 22 hours indoors, the weighted exposure factor is $2 + 0.9 \times 22 = 21.8$ hours equivalent. Daily B[a]P inhaled is $0.83 \times 21.8 \times 6.8 \approx 123$ ng, or about 8.3 cigarettes per day. Over a year that is roughly 3,000 cigarettes worth of B[a]P from ambient air alone.

Reducing outdoor time or improving indoor air filtration can lower exposure, though the most effective public health action is reducing source emissions from traffic and heating.

For related air quality tools, see the Atmospheric Dispersion Calculator for pollutant dispersion modeling, or the Relative Humidity Calculator for atmospheric moisture analysis.