Standard Real-Time Photoelectric Aerosol Sensor (PAS)

Summary

Since 1991, EcoChem has pioneered the use of the Photoelectric Aerosol Sensor (PAS) for real-time measurement of Carbon aerosols. Previous versions of the PAS monitor (PAS 1000i, 1000e and 1002i ) are widely used by regulatory, research and industrial organizations. Incorporating customer feedback and state-of-the-art advances in measurement techniques, the PAS 2000 features the following technological advances: 
Use of an UV Excimer lamp. This lamp has a higher efficiency than any traditional UV lamp. The Excimer lamp can be rapidly switched on and off without a time delay. The offset produced by pre-charged particles can be eliminated by operating the lamp in a chopped mode. 

• The Excimer lamp produces monochromatic radiation with a half bandwidth of 2% 
• Higher sensitivity instrument with a larger measurement range
• Total microprocessor control with internal data acquisition and storage
• Lighter and more compact design 

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Applications

Ambient Air Version

• Outdoor ambient air quality and monitoring in special settings like parking structures, traffic intersections and motorway tunnels
• Indoor air quality in homes, offices and monitoring indoor sources like kerosene heaters, wood stoves and environmental tobacco smoke 
• Workplace monitoring in industrial environments where PAH are produced 
• Monitoring carbon aerosols during special situations like Forest Fires, Scrap Vehicle Tire Fires and Agricultural Burns 

Source Emission Version 

• Emissions from Combustors, Refinery Heaters, Industrial Boilers and Furnaces 
• Emissions from Municipal, Hazardous and Medical Waste Incinerators 
• Exhausts from Diesel and Gasoline Engines 
• Emissions from Industrial Processes like Coke Ovens, Petroleum Catalytic Cracking, Iron and Steel Foundries, Aluminum and Carbon Black Manufacture 

Features 

• Uses patented Excimer Lamp technology to detect particle-bound PAH continuously in real-time 
• Responds to ultrafine respirable particles which act as carriers of PAH into the body 
• Signal has be correlated to particle-bound PAH, Elemental Carbon (EC) and other soot measurement techniques. These carbon aerosols pose the maximum health risk 
• Sensitive in the nanogm/m3 to microgm/m3 range 
• Simple, reliable, field-rugged and proven technology 
• Automated operation requiring minimum human intervention. Built-in data acquisition for 2500 data points. 
• Proven source monitoring with special dilution sample system.

Measuring Principle 

The PAS 2000 works on the following principles:
• Using an Excimer lamp the aerosol flow is exposed to UV radiation. The Excimer lamp offers a high intensity, narrowband source of UV radiation. The wavelength of the light is chosen such that only the carbon aerosols are ionized, while gas molecules and non-carbon aerosols remain neutral.
• The carbon aerosol particles emit electrons, which are subsequently removed when an electric field is applied.
• The remaining positively charged particles are collected on a filter inside an electrometer, where the charge is measured. The resulting electric current establishes a signal, which is proportional to the concentration of Elemental Carbon and/ or PAH.

Also by operating the Excimer lamp in a chopped mode, the PAS 2000 can eliminate the background signal, which is associated with freshly generated aerosols. The chopped mode also enables a dynamic zero to be generated automatically by the instrument.
 

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Calibration 

Source-specific calibration curves are available or can be generated where the monitor output is compared to an analytically determined EC and PAH concentration. A site-specific calibration curve can provide greater accuracy for the particle size, charge and compound-specific to the source. In addition to the site-specific curves, an approximate universal calibration curve can be used for screening and real-time trending applications. 

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Chassis and Mounting

Housing Options The ambient air PAS 2000 can have the following housing options: 

• Standard desktop unit 
• Rack-mount unit 

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Technical Specifications

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