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These units express the concentration of air pollution in terms of the mass or volume of the pollutant, and they are commonly used for measurements of both gaseous pollutants, such as nitrogen dioxide, and coarse (PM 10) and fine (PM 2.5) particulates.
The CCME standard for particulate matter 2.5 (PM 2.5) as of 2015 is 28 μg/m 3 (calculated using the 3-year average of the annual 98th percentile of the daily 24-hr average concentrations) and 10 μg/m 3 (3-year average of annual mean). PM 2.5 standards will increase in stringency in 2020. [274]
Particulate matter (PM) is generally classified into two main size categories: PM 10 and PM 2.5. PM 10, also known as coarse particulate matter, consists of particles 10 micrometers (μm) and smaller, while PM 2.5, also called fine particulate matter, consists of particles 2.5 μm and smaller. [29]
Below is a list of 526 cities sorted by their annual mean concentration of PM2.5 (μg/m 3) in 2022. [1] [2] By default the least polluted cities which have fewest particulates in the air come first.
[5] [6] A sub-index value is computed for each pollutant based on the pollutant's ambient air concentration. The highest sub-index value is then taken as the PSI value. In other words, the PSI is determined by the pollutant with the most significant concentration. [7] During haze episodes, PM 2.5 is the most significant pollutant. [8]
The score for each pollutant is non-linear, as is the final AQI score. Thus an AQI of 300 does not mean twice the pollution of AQI at 150, nor does it mean the air is twice as harmful. The concentration of a pollutant when its IAQI is 100 does not equal twice its concentration when its IAQI is 50, nor does it mean the pollutant is twice as harmful.
The Green Book is a direct successor of the Manual of Symbols and Terminology for Physicochemical Quantities and Units, originally prepared for publication on behalf of IUPAC's Physical Chemistry Division by M. L. McGlashen in 1969. A full history of the Green Book's various editions is provided in the historical introduction to the third edition.
PM 2.5 exposure, such as from car exhausts, activates dormant mutations in lung cells, causing them to become cancerous. [206] [205] Unprotected exposure to PM 2.5 air pollution can be equivalent to smoking multiple cigarettes per day, [207] [dead link ] potentially increasing the risk of cancer, which is mainly the result of environmental ...