Aerosols and Air Pollution
• Solid or liquid particles (in range of 0.002µm to 100µm) suspended in the
air, both natural & anthropogenic are known as aerosols
• Aerosol particles vary greatly in size, source, chemical composition,
amount and distribution in space and time
• AOD is the degree to which aerosol prevents transmission of
light to earth by means of scattering & absorbing sunlight
• An AOD of less than 0.1 indicates clear sky with maximum
visibility; whereas AOD value more than 1 indicates presence
of aerosol & extinct solar radiation reaching ground surface
by absorbing or scattering
• Depending upon their size, type, location & source of
emission, aerosols can either cool the surface (Sulfates
& Nitrates), or warm it (Black Carbon)
Aerosol Optical Depth Data
Aerosol Optical Depth Data
Retrieval of Aerosol Optical Depth Data
• AOD data can be retrieved by following means:
i. Ground based measurement
ii. Satellite data & imagery
• Ground based measurements can be carried out with:i.
Hand-held sunphotometers which measures AOD
at 5 wavelengths (380,440,500,675 & 870 nm)
ii. Sunphotometers installed by AERONET-NASA at
selected sites
iii. CIMEL Sun-sky Radiometers
Satellite data can be retrieved from the sensors on-board to
various satellites launched by NASA, which are named below:
Sensor/Platform Parameter Spatial Coverage
AVHRR/NOAA-series • Optical Depth,
• Angstrom exponent
Daily coverage of global
ocean
TOMS/Nimbus, ADEOSI,EP • Optical Depth Daily coverage of Global
land & oceanPOLDER,-1,-2 PARASOL • Optical Depth,
fine mode fraction,
• Angstrom Exponent,
• Non-spherical fraction
MODIS/Terra,Aqua • Optical Depth
• Fine-mode fraction
• Angstrom exponent
• Effective radius
MISR/Terra • Optical depth
• Angstrom Exponent
• Small-medium-large
fraction
• Non-spherical fraction
Weekly coverage of global
land & ocean, including
bright desert
https://worldview.earthdata.nasa.gov/
Aerosol Direct Radiative forcing
• The AODs and associated aerosol optical and microphysical parameters,
obtained from the Sun–sky radiometer observations during the study
period, along with other radiation and chemical parameters of aerosols
prevailing over the experimental site in the Optical Properties of Aerosols
and Clouds(OPAC) model have been used as input information to the
SantaBarbara DISORT Atmospheric Radiative Transfer (SBDART)model to
derive the aerosol direct radiative forcing (ADRF in W/m2) at the:
i. Bottom of the atmosphere (BOA)
ii. In the atmosphere (ATM)
iii. At top of the atmosphere (TOA)
Spectral-Temporal variation & Influence of Meteorological parameter
Long range transport & satellite images of fire/smoke aerosols