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The density of air or atmospheric density, denoted ρ, [1] is the mass per unit volume of Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. It also changes with variations in atmospheric pressure, temperature and humidity.
Different air masses which affect North America as well as other continents, tend to be separated by frontal boundaries. In meteorology, an air mass is a volume of air defined by its temperature and humidity. Air masses cover many hundreds or thousands of square miles, and adapt to the
Air pollution can occur naturally or be caused by human activities. [4] Air pollution causes around 7 or 8 million deaths each year. [5] [6] It is a significant risk factor for a number of pollution-related diseases, including heart disease, stroke, chronic obstructive pulmonary disease (COPD), asthma and lung cancer.
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa ), which is equivalent to 1,013.25 millibars , [ 1 ] 760 mm Hg , 29.9212 inches Hg , or 14.696 psi . [ 2 ]
Dry air (mixture of gases) from Earth's atmosphere contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and traces of hydrogen, helium, and other "noble" gases (by volume), but generally a variable amount of water vapor is also present, on average about 1% at sea level.
If the air is very dry and has few water molecules, the dew point is low and surfaces must be much cooler than the air for condensation to occur. If the air is very humid and contains many water molecules, the dew point is high and condensation can occur on surfaces that are only a few degrees cooler than the air. [8]
Humid air is less dense than dry air because a molecule of water (m ≈ 18 Da) is less massive than either a molecule of nitrogen (m ≈ 28) or a molecule of oxygen (m ≈ 32). About 78% of the molecules in dry air are nitrogen (N 2). Another 21% of the molecules in dry air are oxygen (O 2). The final 1% of dry air is a mixture of other gases.
Diesel exhaust fluid (DEF; also known as AUS 32 and sometimes marketed as AdBlue [3]) is a liquid used to reduce the amount of air pollution created by a diesel engine. Specifically, DEF is an aqueous urea solution made with 32.5% urea and 67.5% deionized water .