Abbreviations

Updated Thursday, September 28, 2017

ppb: parts per billion

ppm: parts per million

μm: micrometre (International spelling as used by the International Bureau of Weights and Measures;^[1] SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is an SI derived unit of length equaling 1×10⁻⁶ of a metre (SI standard prefix "micro-" = 10⁻⁶); that is, one millionth of a metre (or one thousandth of a millimetre, 0.001 mm, or about 0.000039 inch).^[1]

The micrometre is a common unit of measurement for wavelengths of infrared radiation as well as sizes of biological cells and bacteria,^[1] and for grading wool by the diameter of the fibres.^[2] The width of a single human hair ranges from approximately 10 to 200 μm. The first and longest human chromosome is approximately 10μm in length.

µg/m³: micrograms per cubic metre

PM2.5: fine particles with a diameter of 2.5 micrometers (μm) or less^[5] (PM_2.5),^[6] ultrafine particles, and soot.

(from Wikipedia):  Atmospheric particulate matter, also known as particulate matter (PM) or particulates, or suspended particulate matter (SPM) are microscopic solid or liquid matter suspended in Earth's atmosphere. The term aerosol commonly refers to the particulate/air mixture, as opposed to the particulate matter alone.^[3] Sources of particulate matter can be natural or anthropogenic. They have impacts on climate and precipitation that adversely affect human health.

Subtypes of atmospheric particulate matter include suspended particulate matter (SPM), thoracic and respirable particles,^[4] inhalable coarse particles, which are [coarse] particles with a diameter between 2.5 and 10 micrometers (μm) (PM₁₀),^[5] fine particles with a diameter of 2.5 μm or less^[5] (PM_2.5),^[6] ultrafine particles, and soot.

The IARC and WHO designate airborne particulates a Group 1 carcinogen.^[7] Particulates are the deadliest form of air pollution^{[citation needed]} due to their ability to penetrate deep into the lungs and blood streams unfiltered, causing permanent DNA mutations, heart attacks, and premature death.^[8] In 2013, a study involving 312,944 people in nine European countries revealed that there was no safe level of particulates and that for every increase of 10 μg/m³ in PM₁₀, the lung cancer rate rose 22%. The smaller PM_2.5 were particularly deadly, with a 36% increase in lung cancer per 10 μg/m³ as it can penetrate deeper into the lungs.^[9]