U.S. Air Quality

Good air quality conditions over the cloudy country

Today, the country enjoys good air quality conditions. Air Now, and AQI air quality index reports only moderate conditions specially in California, Arizona and Hawaii (top left), while the rest of the country reached green(good) levels (top right). Due to the clouds in a great portion of the nation, it is difficult to read the color satellite images today. On the other hand, NOAA's Hazard Mapping System reported no significant areas of smoke or dust.

In an effort to make the blog a source of information in atmospheric sciences, today we present a technique used for the measuring of aerosol optical depth and extinction.

Aerosols leave their "signature" in the radiation that comes from the sun and arrives in earth's surface. The study of atmospheric components, not only aerosols but also ozone, water vapor, oxygen, etc., with radiometric techniques is based in comparison between the direct solar radiation spectrum on Earth's surface and extraterrestrial solar spectrum.

Sunphotometers are instruments that allow measuring the atmospheric attenuation of the solar irradiance at different wavelengths. With this attenuation, and the suitable relation between wavelengths, it is possible to characterize aerosols, water vapor, ozone, oxygen, and other gases, in a vertical column through the atmosphere.

The aerosol optical depth (AOD) is the main parameter in the study of the aerosol properties. It is an indicator of the vertical column content of amount of aerosols in the atmosphere, and according to its values and by using Mie theory, it can be used the inversion algorithms methodology to obtain the aerosol size distribution.

The AERONET (AErosol RObotic NETwork) program is a federation of ground-based remote sensing aerosol networks established by NASA and PHOTONS (Univ. of Lille, CNES, and CNRS-INSU) and is greatly expanded by collaborators from national agencies, institutes, universities, individual scientists, and partners. The program provides a long-term, continuous and readily accessible public domain database of aerosol optical, mircrophysical and radiative properties for aerosol research and characterization, validation of satellite retrievals, and synergism with other databases. The network imposes standardization of instruments, calibration, processing and distribution.

AERONET collaboration provides globally distributed observations of spectral aerosol optical depth (AOD), inversion products, and precipitable water in diverse aerosol regimes. Aerosol optical depth data are computed for three data quality levels: Level 1.0 (unscreened), Level 1.5 (cloud-screened), and Level 2.0 (cloud-screened and quality-assured).

The Atmospheric Lidar Group at UMBC has installed a CIMEL sunphotometer (part of a NASA funded project called UMBC Monitoring of Atmospheric Pollution (UMAP) and integrated into AERONET) which is used not only to obtain AOD data, but also to correlate the data with the different Lidars in the group (bottom).

Posted by Daniel Orozco at October 15, 2009 10:36 PM