Air Day

What the day is

Air Day is observed on November 11. It marks the atmosphere generally: what it is made of, where it came from, and what is in it that should not be.

Origin and background

The origin of the observance is not documented.

Air is roughly 78 percent nitrogen and 21 percent oxygen, with argon making up most of the remainder and carbon dioxide a small fraction that matters enormously. The oxygen is not original. Earth's early atmosphere had almost none, and it accumulated because cyanobacteria began producing it as a waste product, in what is usually called the Great Oxidation Event. That waste was toxic to most life existing at the time, and the atmosphere we depend on is the residue of an ancient mass extinction.

The practical concern now is what has been added. Air pollution, particularly fine particulate matter small enough to reach deep into the lungs and cross into the bloodstream, is associated with millions of premature deaths annually worldwide. It contributes to heart disease, stroke, respiratory illness and, increasingly clearly, to cognitive decline.

A substantial share of that exposure is indoor. Cooking, heating, cleaning products and poor ventilation produce concentrations that often exceed outdoor levels, and household air pollution from solid cooking fuels remains a major cause of death in lower-income countries.

The encouraging part is that air quality responds quickly to policy. Cities that have restricted traffic or fuel types have recorded measurable improvements within years, not decades.

How to take part

• Use the extractor fan whenever you cook, and open a window afterward. Frying is a significant indoor particulate source.
• Check your local air quality index for a week and notice how it varies with traffic and weather.
• Change filters in heating and ventilation systems, which most households neglect.
• Do not idle a car outside a school. The exposure falls on children at exactly head height.
• Test for radon if you live somewhere it occurs. It is invisible, common in some regions, and a leading cause of lung cancer in non-smokers.