This study examined how relative humidity affects the hourly PM_2.5 readings of two collocated beta attenuation monitors in the field. Relationships between PM_2.5 readings by a stationary beta gauge A and a portable beta gauge B were evaluated at various relative humidity (RH) setpoints and ambient RHs. The PM_2.5 concentrations of two beta attenuation monitors were also compared with those of a collocated manual sampler. This work demonstrated that the mean PM_2.5 concentrations by the beta gauge monitors with RH_A and RH_B (RH setpoint in beta gauge A and B) of 35% result in good agreement with those by the manual sampler. The PM_2.5 readings of RH_B of 35% correlated well with those 35% of RHA , whenever the inlet air of beta gauge B was conditioned with water vapor or the beta gauge was operated normally under ambient conditions. However, the PM_2.5 readings of the beta gauge obtained at RH B=65% exceeded those obtained at RH_A=35%. The mean PM_2.5 readings for RH B65% to RH_A = 35% were 1.91 and 1.26, with (ambient RH = 78.2–93.1%) and without (ambient RH = 61.3–77.1%) added water vapor in the inlet of the beta gauge, respectively. Experimental results demonstrated that the relative humidity markedly affected the beta gauge readings, especially at a high ambient RH. Accordingly, maintaining the RH setpoint of the beta attenuation monitor in an appropriate range for field monitoring is important.

This study compared respirable dust and nanoparticle concentrations measured by different sampling devices at a titanium dioxide pigment factory. Respirable particle mass concentrations, nanoparticle concentrations, particle size distribution and particle metallic content were measured at different sampling locations. The sampling results of the Multi-orifice Uniform Deposit Impactor (MOUDI) showed that the particle size distribution at this titanium dioxide production factory fell in the range of 1–10 μ m. Generally, the higher levels of the respirable particle mass concentrations and nanoparticle number concentrations were near the packing site of the pigment titanium dioxide production factory. Metal analysis results revealed that the titanium dioxide concentrations in respirable dust and nanoparticles were within the limits specified by National Institute for Occupational Safety and Health (NIOSH). During sampling, particle metallic content analysis is essential for identifying the source of particles and for measuring respirable dust and nanoparticle concentrations.

An efficient venturi scrubber system combining a particle growth device and a traditional venturi scrubber was designed and tested in the laboratory. Before the venturi scrubber, saturated steam at 100°C was mixed with normal temperature waste stream to achieve supersaturation conditions allowing submicron particles to grow into micron sizes. Hence the control efficiency of submicron particles was greatly enhanced at a reasonably low pressure drop as compared to that found in the literature. At a flow rate of 250 L∕min and a liquid to gas ratio of 2.5 L∕ m3 , the control efficiency of the present venturi scrubber system for NaCl particles greater than 100 nm is greater than 90%, and pressure drop is only about 44 cm H2 O (4.3 kPa) . In comparison, to remove only 50% of 0.6 μm particles at the same liquid to gas ratio, the pressure drop needed will be greater than 200 cm H2 O (or 19.6 kPa ). Theoretical calculation has also been conducted to simulate particle growth process and the control efficiency of th...