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Instrument: PAS : Photoelectric Aerosol Sensor
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Description
The EcoChem Photoelectric Aerosol Sensor (PAS 2000) uses the principle of photoionization to measure particle-bound polycyclic aromatic compounds/hydrocarbons (PAH). The sampled air stream and particles are exposed to radiation at 220 nm from a pulsed excimer lamp. Radiation at this wavelength ionizes PAH-coated aerosols but not gas molecules or non-carbon aerosols. The resulting free electrons are removed from the air stream and the positively charged particles are collected on a filter inside an electrometer where the charge is measured. The resulting electric current is proportional to the concentration of the total particle-bound PAH in the sample with no specification of which PAHs are present. The low volatility of the various PAHs reduces the amount of gaseous PAH in the sample and ensures that the sample is particle-bound PAH. The sample flow rate is measured with a mass flow meter and is controlled by a variable speed motor that maintains a constant mass flow of 2.0 l/min referenced to standard temperature and pressure conditions of 0 °C and 1 atm. Data units for the PAC are currently reported in femptoAmps, as a reliable conversion has not yet been established.

Information obtained from http://eosweb.larc.nasa.gov/GUIDE/dataset_documents/narsto_epa_ss_f...

Online Resources
http://eosweb.larc.nasa.gov/GUIDE/dataset_documents/narsto_epa_ss_fresno_particle_pac_data.html