Revised Weighting of CVS/CH Test Results for CO Vehicle Emission Factors

Abstract

APCA NOTE-BOOKat 10 to 15 min after the dust feed system was turned on. Extremely large fluctuations in the screen current are evidence of a high level of back corona activity.The notation Q/m on Figure 2 indicates the interval of time during which a measurement of particle charging effectiveness was made. Particles were collected on a silver mesh filter mounted in a plastic filter holder, fitted with a nozzle for isokinetic sampling. The filter was connected to an electrometer so that the charge accumulation could be monitored during the collection process. A foil shield, grounded through a 10 megohm resistor was wrapped around the body of the filter holder to prevent buildup of charge on the insulating plastic. Upon completion of the sampling period, the total accumulated charge was recorded and the captured dust sample was weighed. These data were then used to calculate the ratio of charge to mass Q/m for the sample.In the experiment associated with Figure 2, the measured value of Q/m was approximately 2.9 fiC/g. Theoretical values of charge for the particle distribution used in this test showed good agreement with the experimental value. Since the theory is based on charging by unipolar ions, it appears that back corona suppression by the action of the screen electrode was successful. Without the screen grid the corona current density at the plate would be limited to the level at which back corona occurs. That value would be of the order of 1% of the corona current used in the experiment above.Experiments with a device similar to the new precharger, but lacking the corona suppression screen, provide for a comparison with the conventional technology.2 Maximum charging levels for low resistivity dusts (<10 10 ohm cm) in the "conventional" device are three to five times greater than those achieved in the high resistivity experiments with the new precharger. But when a high resistivity dust was introduced into the "conventional" device the measured charge to mass ratio dropped to a value less than one tenth of that measured with a similar dust in the new precharger. The new device thus provides a significant advantage where back corona is a problem. SummaryThe aerosol precharger described in the preceding paragraphs can provide a charging environment with relatively high unipolar ion density for particulate matter having high electrical resistivity. The result is a much higher level of charge on the particles than can be achieved by a conventional electrostatic precipitator which is limited by back corona to a low current density.3 Used in conjunction with a downstream collector operated at a low current density and high electric field strength, the precharger may be of significant value in the collection of high resistivity particulate materials. The statutory Federal Vehicle Emission Standard (VES) of 3.4 g/mi for carbon monoxide (CO) is intended to achieve the National Ambient Air Quality Standard (AQS) for CO of 9 ppm, 8 hour average. Analysis of the relationship between vehicle CO emissions and ambient CO c...

Urban-Center CO Air Quality Projections

“…In a previous publication 10 it was suggested that urban center CO air quality after 1974 would improve faster than predictions based on current FTP emission factors because of the introduction of catalyst equipped LDV's. This conclusion was based on an analysis made with GRM which showed that FTP overestimates the contribution of cold start emissions to urban-center CO air quality (8-hr average).…”