in the Environment:
Rivers- Lakes- Ponds- Aquifers- Groundwater.
particles are air pollutants with a diameter
of 2.5 micrometers or less, small enough to invade even the smallest airways.
These particles generally come from activities that burn fossil fuels, such as
traffic, smelting, and metal processing.
PM2.5 particles were measured in micrograms per cubic meter.
For every 10 micrograms per cubic meter increase of PM2.5, CIMT increased by
5.9 percent. After adjusting for various factors, including smoking, the
researchers found that CIMT increased by 3.9 to 4.3 percent for every 10
micrograms per cubic meter increase in PM2.5. There were greater increases in
people over 60, women, and people taking cholesterol-lowering medication. The
greatest increases were seen in women 60 or older: a 15.7 percent rise in CIMT
for every 10 micrograms per cubic meter.
Aerosol radiative effects
The Direct aerosol effect consists of any direct interaction of
radiation with atmospheric aerosol, such as absorption or scattering. It
affects both short and longwave radiation to produce a net negative
radiative forcing. The magnitude of the resultant radiative forcing due to the direct effect of an aerosol is dependent on the albedo
of the underlying surface, as this affects the net amount of radiation
absorbed or scattered to space. e.g. if a highly scattering aerosol is
above a surface of low albedo it has a greater radiative forcing than if
it was above a surface of high albedo. The converse is true of
absorbing aerosol, with the greatest radiative forcing arising from a
highly absorbing aerosol over a surface of high albedo. The Direct aerosol effect is a first order effect and is therefore classified as a radiative forcing by the IPCC. The interaction of an aerosol with radiation is quantified by the Single Scattering Albedo (SSA), the ratio of scattering alone to scattering plus absorption (extinction)
of radiation by a particle. The SSA tends to unity if scattering
dominates, with relatively little absorption, and decreases as
absorption increases, becoming zero for infinite absorption. For
example, sea-salt aerosol has an SSA of 1, as a sea-salt particle only
scatters, whereas soot has an SSA of 0.23, showing that it is a major
atmospheric aerosol absorber.
The Indirect aerosol effect consists of any change to the earth's
radiative budget due to the modification of clouds by atmospheric
aerosols, and consists of several distinct effects. Cloud droplets form
onto pre-existing aerosol particles, known as cloud condensation nuclei (CCN).
For any given meteorological conditions, an increase in CCN leads to
an increase in the number of cloud droplets. This leads to more
scattering of shortwave radiation i.e. an increase in the albedo of the
cloud, known as the Cloud albedo effect, First indirect effect or Twomey effect. Evidence supporting the cloud albedo effect has been observed from the effects of ship exhaust plumes and biomass burning
on cloud albedo compared to ambient clouds. The Cloud albedo aerosol
effect is a first order effect and therefore classified as a radiative
forcing by the IPCC.
An increase in cloud droplet number due to the introduction of
aerosol acts to reduce the cloud droplet size, as the same amount of
water is divided between more droplets. This has the effect of
suppressing precipitation, increasing the cloud lifetime, known as the
cloud lifetime aerosol effect, second indirect effect or Albrecht
effect. This has been observed as the suppression of drizzle in ship exhaust plume compared to ambient clouds, and inhibited precipitation in biomass burning plumes. This cloud lifetime effect is classified as a climate feedback (rather than a radiative forcing) by the IPCC due to the interdependence between it and the hydrological cycle. However, it has previously been classified as a negative radiative forcing.
The Semi-direct effect concerns any radiative effect of caused by
absorbing atmospheric aerosol such as soot, apart from direct scattering
and absorption, which is classified as the direct effect. It
encompasses many individual mechanisms, and in general is more poorly
defined and understood than the direct and indirect aerosol effects. For
instance, if absorbing aerosols are present in a layer aloft in the
atmosphere, they can heat surrounding air which inhibits the
condensation of water vapour, resulting in less cloud formation.
Additionally, heating a layer of the atmosphere relative to the surface
results in a more stable atmosphere due to the inhibition of
atmospheric convection. This inhibits the convective uplift of moisture,
which in turn reduces cloud formation. The heating of the atmosphere
aloft also leads to a cooling of the surface, resulting in less
evaporation of surface water. The effects described here all lead to a
reduction in cloud cover i.e. an increase in planetary albedo. The
semi-direct effect classified as a climate feedback) by the IPCC due to the interdependence between it and the hydrological cycle. However, it has previously been classified as a negative radiative forcing.
Roles of different
Sulfate aerosol has two main effects, direct and indirect. The direct effect, via
albedo, is a cooling effect that slows the overall rate of global warming: the IPCC's best estimate of the radiative forcing is -0.4 watts per square meter with a range of -0.2 to -0.8 W/m² 
but there are substantial uncertainties. The effect varies strongly
geographically, with most cooling believed to be at and downwind of
major industrial centres. Modern climate models addressing the attribution of recent climate change
take into account sulfate forcing, which appears to account (at least
partly) for the slight drop in global temperature in the middle of the
20th century. The indirect effect (via the aerosol acting as cloud
condensation nuclei, CCN, and thereby modifying the cloud properties -albedo and lifetime-) is more uncertain but is believed to be a cooling.
Black carbon (BC), or carbon black, or elemental carbon (EC), often
called soot, is composed of pure carbon clusters, skeleton balls and buckyballs,
and is one of the most important absorbing aerosol species in the
atmosphere. It should be distinguished from organic carbon (OC):
clustered or aggregated organic molecules on their own or permeating an
EC buckyball. BC from fossil fuels is estimated by the IPCC in the
Fourth Assessment Report of the IPCC, 4AR, to contribute a global mean
radiative forcing of +0.2 W/m² (was +0.1 W/m² in the Second Assessment
Report of the IPCC, SAR), with a range +0.1 to +0.4 W/m²
In drinking water
In the atmosphere
In lower atmosphere
In your Body
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