What is the average lifespan of Particulate Matter (PM) in atmosphere? Please include reference with your answer. Thanks!
Current levels of air pollution have reduced life expectancy by an average of 1 year and 8 months worldwide.
Thus, for certain we know that exposure to air pollution reduces life expectancy, but to know the average lifespan of particulate matter itself in the air is presumably difficult in general, at least because air conditions are highly variable, unspecified and in addition, a detailed specification of the nature of the particulate under examination should be provided.
So, the question is not posed very well, because the variability of type, characteristics, concentrations, etc. of particulate matter in the air are closely linked to the general and circumstantial local and environmental conditions. Furthermore, they vary not only according to the type of environment (urban, rural, overpopulated, desert, mountain, hilly, lake, marine, arctic, equatorial, etc. etc.) but also with the altitude (height helps!) and can be influenced by the long-range transport (also cross-border) of air masses coming (in Italy e.g.) for example from the Saharan area (more frequent in the summer months) and from Eastern European or Polar countries (more frequent in the winter months). Furthermore, it is necessary to specify which particulate matter we are referring to, since two main classes of particulate matter can be identified, divided both by size and composition: coarse particulate and fine particulate. Coarse particulate matter consists of particles, including pollen and spores, with a diameter greater than 10 µm (microns). Fine particles, on the other hand, have a diameter of less than 10 µm (microns), e.g. PM1=, PM5, PM2.5 . In any case, from an environmental point of view, the interest and the measurements on the particulate matter suspended in the air are mainly for local purposes, even if cross-border and therefore international surveys cannot be neglected, especially for the radioactive, toxic or particularly polluting contents that can present.
The lifespan of particulate matter (PM) in the atmosphere can vary depending on various factors such as the size of the particles, meteorological conditions, and the chemical composition of the particles. PM is categorized into different size fractions, typically PM10 (particles with a diameter of 10 micrometers or less) and PM2.5 (particles with a diameter of 2.5 micrometers or less).
Generally, larger particles such as PM10 tend to have a shorter lifespan compared to smaller particles like PM2.5. Larger particles are more susceptible to gravitational settling and can be removed from the atmosphere relatively quickly, ranging from a few hours to several days. Wind and rain can also accelerate the removal of larger particles from the air.
On the other hand, smaller particles like PM2.5 can have a longer lifespan in the atmosphere. They are more influenced by atmospheric dynamics and can be transported over longer distances before being removed. The lifespan of PM2.5 can range from a few days to weeks, or even months in some cases.
It's important to note that these estimates are generalizations, and the actual lifespan of PM can vary depending on local conditions and specific particle characteristics. Additionally, certain chemical components of PM, such as sulfate or black carbon, may undergo atmospheric transformations that can affect their lifespan. Therefore, it's challenging to provide a precise average lifespan for all types of particulate matter in the atmosphere.
The residence time of particulate matter in the atmosphere depends on various aspects, mainly on the aerodynamic diameter of PM, density of vegetation and meteorological conditions which are responsible for its dispersion and scavenging (rainfall). However, the average residence time ranges between 9-10 days but may up to few weeks. It the frequency of rainfall is higher the PM may settle down faster.
Hope may be of some help to you.
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