Date ( Publication )

2011-04-01T19:01:00

Purpose

Aerosol light scattering coefficient is measured with an integratingnephelometer [see e.g, Heintzenberg and Charlson, 1996]. Integrating nephelometers have been operated at baseline monitoring stations since the deployment of a four-wavelength instrument at NOAA's Mauna Loa Observatory in 1974. At present, there are about a dozen sites monitoring Aerosol light scattering coefficient routinely around the globe, many of them part of the GAW global network. This instrument operates at wavelengths of 450, 550, and 700 nm, and has the added feature of being able to measure Aerosol light scattering coefficient over two angular ranges: total scattering (7-170° degrees) and hemispheric backscattering (90-170°).

Status

Completed

Maintenance and update frequency

As needed

Keywords

• SHARE , Network , Station , High Altitude

Keywords

• GAWSIS

Keywords

• WMO-GAW

Keywords

• CEOP

Keywords ( Place )

• Nepal

Keywords ( Theme )

• aerosol , aerosol Back Scattering Coefficient

Keywords ( Theme )

• air , research , pollution , ecosystems , landscape , natural areas , climate

Use limitation

No conditions apply

Access constraints

Copyright

Other constraints

Character set

UTF8

Topic category

• Climatology, meteorology, atmosphere
• Environment
• Geoscientific information

Supplemental Information

Reference system identifier

EPSG / WGS 1984 / 7.4

Topology level

Geometry only

Geometric object type

Point

Geometric object count

1

OnLine resource

SHARE Geonetwork portal  

SHARE Geonetwork portal

OnLine resource

ISAC EVK2-Nepal Climate Observatory - Pyramid website  

ISAC EVK2-Nepal Climate Observatory - Pyramid website

OnLine resource

GAWSIS (Global Atmosphere Watch Station Information System) report about Nepal Climate Observatory - Pyramid  

GAWSIS (Global Atmosphere Watch Station Information System) report about Nepal Climate Observatory - Pyramid

OnLine resource

Official website of CEOP-HE (Coordinated Energy and water cycle Observation Project - High Elevation)  

Official website of CEOP-HE (Coordinated Energy and water cycle Observation Project - High Elevation)

OnLine resource

3563.pdf  

Product Information-Model 3563 Integrating

Nephelometer

Hierarchy level

Series

Other

data:aerosol back scattering coefficient

Statement

TSI Integrating Nephelometers are designed specifically for studies of direct radiative forcing of the Earth’s climate by aerosol particles, or studies of ground-based or airborne atmospheric visual air quality in clean areas. They may also be used as an analytical detector for aerosol particles whenever the parameter of interest is the light-scattering coefficient of the particles after a pretreatment step, such as heating, humidification, or segregation by size. The light-scattering coefficient is a highly variable aerosol property. Integrating Nephelometers measure the angular integral of light scattering that yields the quantity called the scattering coefficient, which is used in the Beer-Lambert Law to calculate total light extinction. Model 3563 includes three-wavelength and backscatter features. During operation, a small, turbine blower draws an aerosol sample through the large diameter inlet port into the measurement volume. There, the sample is illuminated over an angle of 7 to 170 degrees by a halogen light source that has been directed through an optical pipe and opal glass diffuser. The sample volume is viewed by three photomultiplier tubes (PMTs) through a series of apertures set along the axis of the main instrument body. Aerosol scattering is viewed against the dark backdrop of a very efficient light trap. The light trap, apertures, and a highly light-absorbing coating on all internal surfaces combine to give a very low scattering signal from the walls of the instrument. The light scattered by the aerosol is split into three colors using high-pass and band-pass color filters in front of the PMT detectors. A constantly rotating reference chopper provides three modes of signal detection. The first mode, described above, is a measure of the aerosol light-scattering signal allowed by an opening in the rotating shutter. The second mode blocks all light from detection and gives a measurement of the PMT dark current, which is subtracted from the measured signal. The third mode inserts a translucent portion of the shutter into the direct path of the light to provide a measure of the light-source signal. In this way, the instrument compensates for changes in the light source. In backscatter mode, the backscatter shutter rotates in front of the light source to block light in the 7- to 90-degree range. When this portion of light is blocked, only light scattered in the backward direction is transmitted to the PMT detectors. The backscatter signal can be subtracted from the total signal to calculate forward-scattering data. When this measurement is not of interest, the backscatter shutter can be “parked” in the total-scatter position. Periodically, an automated ball-valve built into the inlet can be activated to divert all of the aerosol sample through a high-efficiency filter. This gives a measure of the clean-air signal for the local environment. This signal is subtracted, along with the PMT dark-current signal, from the aerosol-scatter signal to give only that portion of the scatter signal provided by the sample aerosol. Particle-scattering parameters for all three wavelengths of total and backscatter signal are continuously averaged and passed to a computer or data logger for permanent storage. A built-in sample heater minimizes condensation on the instrument walls caused by humid aerosols. At high humidities, atmospheric particles such as sulfates and sodium chloride adsorb water and can therefore undergo phase transitions. The result would be changes in particle size, shape, and refractive index. Operating aerosol instruments in an air-conditioned laboratory often results in sample flows with greater than 100-percent relative humidity. The heater protects against this problem by warming the walls of the sample chamber to match the temperature of the inlet air sample. The heater can be switched on or off as needed.

gmd:MD_Metadata

File identifier

bdee2e42-232d-4add-99f0-ec7687f2203d   XML

Metadata language

eng

Character set

UTF8

Parent identifier

d83f95af-91e7-443e-974f-c7e1f0be700d

Hierarchy level

Series

Date stamp

2011-09-21T10:06:24

Metadata standard name

ISO 19115:2003/19139

Metadata standard version

1.0