It is an area weighted mean radius of the aerosol particles.
Aerosol effective radius (microns) is defined as:
r = particle radius
n(r) = particle size distribution (number of particles per cm
2 with
radius in the range r and r+dr microns)
To characterize the size of atmospheric particles, aerosols are usually divided
into three modes: the Aitken mode (diameter less than 0.5 μm),
the accumulation mode (0.5 to 2.5 μm), and the coarse
mode (greater than 2.5 μm). The Aitken and accumulation modes are collectively
referred to as fine particles. Human produced emissions (e.g biomass burning in
southern Africa and South America and Industrial pollutions) are examples of
small mode aerosols. Example of the coarse mode particles are the large Africa's
Sahara Desert dust particles that cross Atlantic ocean and reach America
In air pollution studies PM-2.5 aerosols are referred to particulate
matter smaller than 2.5 μm that is suspended in the air.
In general, submicron aerosols (particles smaller than 1 micron in diameter)
affect human health by penetrating to the deepest part of human lungs.
Atmos Composition
