Measurement of ultrafine particles: A comparison of two handheld condensation particle counters

The objective of this study was to compare two real-time condensation particle counters for measurement of number concentrations of ultrafine particles (UFPs). The comparison is based on the data from side-by-side measurements conducted in several locations, both indoors and outdoors. CPC 3007 and P-Trak(TM) 8525 manufactured by TSI (instruments A and B, respectively) were used simultaneously. They measure particles in sizes from 0.01 to greater than 1 mum and 0.02 to greater than 1 mum, respectively. The results reveal a good correlation between the two instruments. The ratios of measured aerosol concentrations varied from 0.81 to 1.17, which implies that in all data sets the difference between the two instruments was less than +/-20%. About 63% of the results were in the range of +/-10%, and about 44% showed differences less than +/-5%. The maximum particle concentration detected by instrument A was approximately 105,000 particles cm(-3) and the minimum was about 230 particles cm(-3) . Because of the lower particle size threshold for instrument A, it was expected that this instrument should never show concentrations lower than those detected by instrument B. This was the case in most of the measurement series. The results revealed that the concentration of UFPs changes rapidly, especially in the presence of a local UFP source. A sampling interval of 1 min is sufficient to provide substantial information about the change in concentration level.