Direct field observation of the relative humidity effect on the β-gauge readings

Chuen-Tinn Tsai*, Chung Tso Chan, Cheng Hsiung Huang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


The effect of ambient relative humidity (RH) on hourly particulate matter (PM10) readings of β-gauge monitors has been studied using two collocated monitors in the field. The inlet air of monitor 1 was conditioned with water vapor to increase its RH, whereas monitor 2 operated normally in ambient conditions. Experimental data showed that PM10readings of monitor 1 were nearly the same as monitor 2, as long as the RH of its conditioned incoming air did not exceed -80–85%. However, when the RH exceeded -80–85%, PM10readings of monitor 1 became higher than monitor 2, and the difference increased with increasing RH. The measurement of pressure drop across the filter was also conducted, and the data revealed that the increase of pressure drop per unit of PM10concentration decreased when RH was higher than -80–85%, as compared with the case when RH was lower than 80–85%. This is perhaps because of more porous structure of deposited particles in the β-gauge monitor when RH is greater than -80–85%. The theoretical calculation using an evaporation model and a thermodynamic model has been conducted to simulate the β-gauge readings. The results show that the theoretical PM10concentrations using the evaporation model are in better agreement with the actual β-gauge readings than those using the thermodynamic equilibrium model.

Original languageEnglish
Pages (from-to)834-840
Number of pages7
JournalJournal of the Air and Waste Management Association
Issue number6
StatePublished - 1 Jan 2006

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