Alcohol concentration as measured by a breath sample is expressed in which unit?

Alcohol concentration as measured by a breath sample is expressed in which unit?

• A. Parts per million of breath
• B. Grams per 210 liters of breath
• C. Percent blood alcohol
• D. Milligrams per liter

Answer: (A)

Breath alcohol concentration is reported as parts per million of alcohol in breath. The breath sample is a gas, so the instrument expresses ethanol levels as a very small fraction of ethanol molecules per unit of breath, which is naturally described in ppm. This unit is what the device directly displays and is then used internally (via a standard ratio) to relate the breath result to blood alcohol if needed. Other options describe different contexts—grams per 210 liters of breath is an older forensic reference, percent BAC refers to blood rather than breath, and milligrams per liter is not the unit this device uses.

Breath alcohol concentration is reported as parts per million of alcohol in breath. The breath sample is a gas, so the instrument expresses ethanol levels as a very small fraction of ethanol molecules per unit of breath, which is naturally described in ppm. This unit is what the device directly displays and is then used internally (via a standard ratio) to relate the breath result to blood alcohol if needed. Other options describe different contexts—grams per 210 liters of breath is an older forensic reference, percent BAC refers to blood rather than breath, and milligrams per liter is not the unit this device uses.