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Atmospheric pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m 3, μg/m 3, etc.) at sea level will decrease with increasing altitude because the atmospheric pressure decreases with increasing altitude.
For example, the conversion factor between a mass fraction of 1 ppb and a mole fraction of 1 ppb is about 4.7 for the greenhouse gas CFC-11 in air (Molar mass of CFC-11 / Mean molar mass of air = 137.368 / 28.97 = 4.74). For volume fraction, the suffix "V" or "v" is sometimes appended to the parts-per notation (e.g. ppmV, ppbv, pptv).
This article presents methods for converting concentrations from ppmv to mg/m 3 (and vice versa) and for correcting the concentrations to the required reference conditions. All of the concentrations and concentration corrections in this article apply only to air and other gases. They are not applicable for liquids.
The EPA reviewed this NAAQS in 1985 and 1996, and in both cases concluded that the existing standard was sufficient. The most recent review by the EPA occurred in 2010, resulting in a new 1-hour NO 2 primary standard set at 100 ppb; the annual average of 0.053 ppm remained the same. Also considered was a new 1-hour secondary standard of 100 ppb.
A median concentration of 0.62 parts per billion (ppb) was found in urban air in 1999. [9] A study conducted in 2012 found that in country air the median concentration was found to be 0.01 ppb and indoors the median concentration was 1.0 ppb. It can also be released into the air through the burning of coal, gas, and oil. The use of ethylbenzene ...
Scientists at San Jose State University say that a large fire that burned at a battery plant in Monterrey County, California earlier this month has left heightened levels of heavy metals in a ...
The International Committee for Weights and Measures (CIPM) approved a redefinition of the SI base units in November 2018 that defines the kilogram by defining the Planck constant to be exactly 6.626 070 15 × 10 −34 kg⋅m 2 ⋅s −1. This approach effectively defines the kilogram in terms of the second and the metre, and took effect on 20 ...
The factor–label method can convert only unit quantities for which the units are in a linear relationship intersecting at 0 (ratio scale in Stevens's typology). Most conversions fit this paradigm. An example for which it cannot be used is the conversion between the Celsius scale and the Kelvin scale (or the Fahrenheit scale). Between degrees ...